Recent Advances of Avian Endocrinology: Satellite Symposium of the 28th International Congress of Physiological Sciences, Székesfehérvár, Hungary, 1980

Advances in Physiological Sciences, Volume 33: Recent Advances of Avian Endocrinology covers the proceedings of the satellite symposium on the Recent Advances in Avian Endocrinology that is held in conjunction with the 28th International Congress of Physiological Sciences. The text contains 53 chapters in which the chapters except Chapter 1 are organized into five parts according to the issues they tackle. The opening chapter discusses some effects of environmental pollutants on endocrine regulatory mechanisms. The next eight chapters cover topics of neuroendocrinology, while the next chapter discusses female and male reproduction. Part 3 explains prostaglandins and Part 4 tackles thyroid function. The final part discusses hormonal control of metabolism. Veterinarians, biologists, ornithologists, and other professionals interested in avian endocrinology will find this book a great reference material, especially on the nature of the avian endocrine system.

• Language: English
• Publisher: Elsevier Science
• Release date: Oct 22, 2013
• ISBN: 9781483148335

Book preview

PREFACE

Research in Animal Sciences was initiated at the Veterinary School of Budapest some 150 years ago. Earlier research was focused mainly on diagnosis, treatment and defence of contagious diseases of bacterial, viral and parasitological origin. However, in the 1930s, a substantial analysis of mineral imbalances was made, and it could be said that following World War II, animal physiology separated from the human physiology oriented approach.

The University of Veterinary Science as well as the newly formed agricultural research and university departments always were responsive to modern problems as is reflected by the fact that the radioisotope technique was introduced already 10 years after the war at the University of Veterinary Sciences, Budapest and there was another breakthrough when the in vitro methods became available, which eventuated in the recently used RIA techniques.

The challenge created by the industrialization of animal husbandry was met, amongst other disciplines, by animal physiology and especially in the endocrinology of reproduction and metabolism.

When the possibility of having a Satellite Symposium was raised, we remembered the first step in animal physiology, a Satellite Symposium on Perinatal Homeostasis, organized in Lyon in 1967, by Professor J. Bost.

Unanimous votes were given for topics on avian physiology, and as this has been emphasized within Section 14 of the 28th IUPS Congress later we turned to a more specified field, i.e. avian endocrinology, and this was announced in 1978.

The number of participants was restricted to 40–60 in order to keep the size of the meeting and its working potential on a fairly efficient level.

However, there were 72 participants who actually registered, representing most parts of the world.

This volume is devoted to all those participating in the Symposium for them to recall and reflect on the points of interest and on the high level critical remarks and to enhance the personal contacts born there. We hope, however, that all those avian endocrinologists who could not participate, will get new information on data presented here.

The organizers overcoming difficulties entailing lack of funds and administrative help, most gratefully acknowledge the earnest work of members of the Department of Physiology, University of Veterinary Science, Budapest, as well as that of volunteer students.

The Editors

SOME EFFECTS OF ENVIRONMENTAL POLLUTANTS ON ENDOCRINE REGULATORY MECHANISMS

W.N. Holmes, J. Gorsline and K.P. Cavanaugh,     Biological Sciences, University of California, Santa Barbara, USA

Publisher Summary

This chapter describes the effects of environmental pollutants on endocrine regulatory mechanisms. The most common cytotoxic effects of chlorinated hydrocarbon insecticides on mammalian adrenocortical tissues involve the structural changes in the mitochondria of zona fasciculata cells. The structural disintegration is associated with a loss of responsiveness to corticotropin, and the activities of some of the mitochondrial enzyme systems involved in steroidogenesis are severely disrupted. In particular, the steps involving the conversion of cholesterol to pregnenolone and the 11β-hydroxylation of cortisol and corticosterone precursors are affected most seriously. Compounds such as organophosphate, phosphothioate and carbamate pesticides, polychlorinated biphenyls, aromatic amines, and anatoxins also seem to directly impair the synthesis of adrenal steroid hormones. Although some of these compounds may affect different stages in the steroidogenic pathway, the overall pattern of response involves a severe reduction in corticotropin responsiveness. The primary site of action of these compounds also seems to be the cells of the zona fasciculata, leading to a decrease in the production of glucocorticoids. Results from some recent studies have suggested that the inhibitory effects of the compounds derived from the ingested crude oils reflect a failure of the adrenal cortex to respond adequately to corticotropic stimulation.

INTRODUCTION

Our present awareness of the threat posed by some environmental pollutants to the survival of many species is due largely to the concern expressed by the late Dr. Rachel Carson (1962). Some 14 years earlier, however, mammalian physiologists had described the cytotoxic effects of chlorinated hydrocarbons on adrenocortical tissues (Nelson & Woodward, 1949). This early observation and, later, studies on the associated changes that occur in adrenocortical function ultimately led to the use of these compounds as chemotherapeutic agents in patients suffering adrenocortical carcinoma (Vilar & Tullner, 1959; Nichols & Richardson, 1960; Nichols, 1961; Cazorla & Moncloa, 1962; Hoffman & Mattox, 1972; Hart et al. 1973; Hajjar et al. 1975).

Studies on the effects of pollutants on adrenocortical and gonadal steroid hormone regulators have been conducted mostly on mammals and, as is so often the case, they have preceded similar studies on lower vertebrates. In order to establish a basis for comparison, therefore, we must briefly review the areas in which there has been substantial progress toward identifying these effects in laboratory mammals.

The most common cytotoxic effects of chlorinated hydrocarbon insecticides on mammalian adrenocortical tissues involve structural changes in the mitochondria of zona fasciculata cells. These changes, which may occur in the dog as soon as 2 hours after a single i.v. dose of m,p’DDD, are first seen as a swelling, followed later by dissolution of the cristae and finally by complete collapse of all internal organization (Hart et al. 1973). This structural disintegration is associated with a loss of responsiveness to corticotropin and the activities of some of the mitochondrial enzyme systems involved in steroidogenesis are severely disrupted. In particular, the steps involving the conversion of cholesterol to pregnenolone and the 11β-hydroxylation of cortisol and corticosterone precursors are affected most seriously (Hart et al. 1971, 1973; Hart & Straw, 1971a, b, c).

Compounds such as organophosphate, phosphothioate and carbamate pesticides, polychlorinated biphenyls, aromatic amines and aflatoxins also seem to impair directly the synthesis of adrenal steroid hormones. Although some of these compounds may affect different stages in the steroidogenic pathway, the overall pattern of response involves a severe reduction in corticotropin responsiveness (Toth et al. 1971; Bruckner et al. 1974; Civen & Brown, 1974; Sanders & Kirkpatrick, 1975, 1977; Singh & Venkitasubramanian, 1975; Civen et al. 1977a, b). The primary site of action of these compounds also seems to be the cells of the zona fasciculata, leading to a decrease in the production of glucocorticoids (Kovacs et al. 1970; Horvath et al. 1971). There appears to be no substantial evidence to suggest that either these compounds or those of the chlorinated hydrocarbon series interfere with mineralocorticoid synthesis by cells of the zona glomerulosa (Nelson & Woodward, 1949; Nichols, 1961; Kaminsky et al. 1962).

Many pesticides and pollutants that affect adrenocortical function have also been shown to impair reproduction in both male and female mammals. Again much of this information has been derived from studies on the effects of chlorinated hydrocarbons (see reviews, Mori arty, 1975; Thomas, 1975). These compounds seem to have two distinct, but related, types of effect in mammals. Forst of all, there is evidence that some chlorinated hydrocarbons may impair reproductive cyclicity by causing reductions in plasma estrogen, progesterone and androgen concentrations; this effect, however, may not necessarily reflect a direct interference with gonadal steroidogenesis (Peakall, 1976). We are unaware of any direct evidence that chlorinated hydrocarbons suppress normal gonadal steroid hormone synthesis. For example, the episodic patterns of changing plasma estrogen and progesterone concentrations have not been measured throughout the ovarian cycles of mammals exposed to chlorinated hydrocarbon insecticides. Other changes that occur in organisms exposed to chlorinated hydrocarbons, however, suggest indirectly that the secretion of gonadal steroid hormones has been seriously affected: these changes include attenuation of ovarian cyclicity, lowered incidences of male fertility and fertilization of the female, and high frequencies of prenatal mortality. The second type of effect that the chlorinated hydrocarbon insecticides have on reproductive processes involves their competition with endogenous gonadal steroid hormones for receptor-binding sites in target tissues (Bitman et al. 1968; Levin et al. 1968; Welch et al. 1969; Bitman & Cecil, 1970; Hammond et al. 1979). These effects have been described as the uterotropic and the estrogenic actions of the chlorinated hydrocarbon insecticides, but there is also evidence that they compete with endogenous androgens for receptor-binding sites in target tissues in the male (Blend & Schmidt, 1971; Smith et al. 1972; Wakeling & Visek, 1973; Wakeling et al. 1973). However, although some chlorinated hydrocarbons are able to mimic some estrogenic responses, there is no reason to believe that they can replace endogenous ovarian steroid hormones and effectively support a successful reproductive cycle. Indeed, many of the adverse effects on reproduction that are attributed to these compounds may reflect their inabilities to mimic the full spectrum of physiological effects produced by the endogenous gonadal steroid hormones.

Other pollutants that have been shown to impair reproduction in mammals include the carbamate and organophosphate insecticides, aniline and some polycyclic hydrocarbons (Collins et al. 1971; Hatakeyama et al. 1971; Weil et al. 1973; Cambon et al. 1979; Mattison, 1980). There is evidence that some of these pollutants may directly suppress gonadal steroidogenesis, although there have been no studies comparing the gonadotropic responses of ovarian and testicular tissues from contaminated organisms; there have also been no reports of ultrastructural change to substantiate this belief.

All of the contaminants we have considered share the common characteristic of being particularly fat-soluble and this property predisposes them to accumulate in the lipid-rich endocrine tissues of the body. The generally consistent pattern of their effects on physiological mechanisms regulated by the hormones produced by these tissues, therefore, may not be entirely important if adrenocortical and gonadal dysfunction is to be minimized. To this end, contaminated organisms respod by increasing the rate of hepatic clearance and the subsequent rate of metabolism of these circulating xenobiotic compounds. This is accomplished through the action of a substrate-inducible mixed function oxidase (MFO) system located in the endoplasmic reticulum of the hepatocytes. The contaminants are in this way rendered more water-soluble and thus more amenable to excretion. Although induced increases in hepatic MFO activity are directed primarily toward the metabolism of the xenobiotics, there is a mounting body of evidence to suggest that this enzyme system may also accelerate the metabolism and turnover of some endogenous substrates, in particular the steroid hormones. Thus, the trends toward hypoadrenocorticalism and impaired reproduction in some contaminated organisms may be exacerbated by the very mechanism intended to rid their tissues of the contaminant.

The evidence that increases in hepatic MFO activity are associated with an overall increase in gonadal and adrenocortical steroid hormone metabolism is somewhat fragmentary. Increases in MFO activity have been implicated as major factors responsible for the frequent high levels of gonadal steroid hydroxylation in mammals exposed to some pollutants. Under these circumstances, androgens may be rapidly converted to several polar metabolites, some of which are known to be hydroxylated at the 2β-, 6β-, 7α- and 16α-positions (Conney & Klutch, 1963; Kuntzman et al. 1964; Jacobson et al. 1969; Conney et al. 1973). Similarly, the metabolism of estrogens and progesterone to polar derivatives may also increase following the induction of high levels of hepatic MFO activity (Kuntzman et al. 1966; Levin et al. 1968; Welch et al. 1971; Nowicki & Norman, 1972). The metabolism of the adrenocortical steroids has been less extensively studied, overall increases in metabolism to form polar derivatives of Cortisol and corticosterone hydroxylated at the 2α- and 6β-carbon positions have been reported in mammals exposed to chlorinated hydrocarbons (Herken & Seeber, 1963; Bledsoe et al. 1964; Kuntzman et al. 1964; Kupfer et al. 1964; Balazs & Kupfer, 1966; Kupfer & Peets, 1966). There is evidence, however, that the formation of polar derivatives via this pathway may in some cases reflect only a shift away from reductive metabolism (Bradlow et al. 1973).

There is clear and substantial evidence that mammals exposed to certain pollutants may develop symptoms of hypoadrenocorticalism and impaired reproduction. Reports of similar effects in lower vertebrates are infrequent and they are mostly limited to observations on a few species of teleost fishes and birds. There have been several reports, however, that petroleum hydrocarbons may also affect these mechanisms in some lower vertebrates. In our attempt to review the effects of pollutants in birds, therefore, we have not only considered the effects of those pesticides and contaminants known to affect adrenocortical and reproductive function in mammals but we have also considered the effects that petroleum hydrocarbons may have on these processes.

EFFECTS ON ADRENOCORTICAL FUNCTION IN BIRDS

Pesticides and other contaminants

Chickens chronically exposed to food containing DDT show symptoms very similar to those seen in mammals. In one study, a significant decrease was observed in the adrenal corticosterone content of birds consuming food contaminated with technical grade DDT; judged by the concomitant decrease that occurred in liver glycogen concentrations, this decline probably reflected lower levels of adrenocortical activity (Srebocan et al. 1971). A more definitive assessment of changes in adrenocortical activity was made in another study where chickens were chronically exposed to o,p’DDD (Komisarenko et al. 1971). These investigators found significant decreases in plasma corticosterone concentration that were accompanied by enhanced hepatic clearances of corticosterone. Furthermore, contaminated birds with suppressed plasma corticosterone concentrations were refractory to treatment with ACTH. These investigators also found degenerative changes in the adrenocortical tissue but they reported no details that might indicate whether these changes were similar to those seen in mammals exposed to DDD (cf. Komisarenko et al. 1971; Hart et al. 1973).

Although aflatoxin is not an environmental pollutant, it is a common dietary contaminant and birds appear to be extremely sensitive to its presence in their food. This sensitivity has led to the use of birds as test animals for screening foodstuffs suspected of being contaminated with aflatoxin. Chickens fed small amounts of aflatoxin show highly significant dose-related reductions in adrenal cholesterol and adrenal corticosterone content (Thaxton et al. 1972). Since no measurements of plasma corticosterone concentrations were made in chickens consuming aflatoxin-contaminated food, we have no direct evidence that these changes reflect reduced adrenocortical activity. However, this compound does cause a severe decline in adrenocortical activity in mammals and the reduced adrenal steroid contents found in contaminated chickens probably reflected a similar decrease in activity (cf. Singh & Venkitasubramanian, 1975).

There have also been no measurements of plasma corticosterone concentrations in birds exposed to organophosphate pesticides. The results of some experiments on ducklings maintained on high salt intakes, however, suggest that ingested organophosphate pesticides reduced their adrenocortical activity and that some corticosterone-dependent mechanisms may, as a result, have been seriously impaired (Friend & Abel, 1976; Herin et al. 1978). Both groups of investigators found that nasal salt gland secretion was diminished significantly when the ducklings were given food contaminated with either Parathion or Chlorpyfros. The apparent cause of death in many of these ducklings, however, may not have been due solely to an acute dysfunction of nasal salt gland activity. When birds such as mallard ducklings are exposed to seawater or hypertonic saline drinking water, high rates of solute-linked water uptake develop in the mucosal cells of the small intestine (Crocker & Holmes, 1971). To maintain their osmotic balance, without incurring a water deficit, the birds must then excrete the excess electrolyte via the nasal glands. The initiation and continuation of both of these homeostatic mechanisms are at least partially regulated by corticosterone (see review, Holmes, 1978). In view of the suppressed adrenocortical function that occurs in mammals exposed to these pesticides, the effects observed in the ducklings may well have been caused by a reduction in adrenocortical activity as well as the anticholinergic action attributed to these pesticides. As a result of these effects the development of the corticosterone-dependent increases in mucosal water transfer were probably impaired and when the ducklings were challenged with an intraperitoneal load of hypertonic saline, the nasal glands were also unable to respond adequately.

Petroleum hydrocarbons

In recent years, hydrocarbons derived from petroleum have become a common source of environmental pollution, and when these compounds enter the food web they may cause serious injuries to some seabird populations. Crude oil, of course, is a complex mixture of a large number of hydrocarbon compounds, many of which are known to be toxic. Nevertheless, until a few years ago, little attention was paid to defining their pathological effects in organisms consuming petroleum-contaminated food and water.

Our own interest in this subject was aroused by the realization that petroleum hydrocarbons might interfere with adrenocortical function in birds in much the same manner as had been described for some pesticides. We were especially intrigued by the observation that when ducklings exposed to hypertonic saline drinking water were given a small single oral dose of crude oil, they failed to develop increases in solute-linked mucosal water transfer rates that were sufficient to ensure their survival (Crocker et al. 1974). The effects of ingesting a small quantity of crude oil were quite similar to those we had previously observed in seawater-adapted birds given spironolactone, a physiologically inert compound that competes with corticosterone for binding sites in target tissues such as the intestinal mucosa (Crocker & Holmes, 1971a,b). Several chemically distinct crude oils collected from a wide range of geographic locations were each found to be qualitatively similar in their inhibitory effects on the development of mucosal transfer rates of ducklings either adapting to or living in simulated marine environments (Crocker et al. 1975). Few general statements can be made regarding which component of the crude oil is responsible for their inhibition. Comparisons of the inhibitory potencies of distillation fractions derived from crude oils with different chemical compositions has revealed the presence of inhibitory compounds in fractions representing all molecular weight ranges (Crocker et al. 1975). For example, in some crude oils the greatest inhibitory activity is associated with a low-boiling-point fraction of relatively sparse abundance, whereas in others, high-boiling-point fractions may cause the greatest inhibition (Crocker et al. 1975).

Results from some of our more recent studies have suggested that the inhibitory effects of compounds derived from the ingested crude oils reflect a failure of the adrenal cortex to respond adequately to corticotropic stimulation (Holmes & Gorsline, 1980). Although our evidence to support this hypothesis is indirect, it is interesting to note that increases in mucosal transfer, similar to those seen in seawater-adapted birds, can be induced by injecting freshwater-maintained ducklings with corticosterone. On the other hand, the inhibitory effects of ingested crude oil in seawater-adapted ducklings can be prevented by treating the birds with corticosterone prior to giving them an oral dose of crude oil (Crocker & Holmes, 1976).

Freshwater mallard ducks, particularly the adults, seem to be remarkably tolerant of petroleum-contaminated food and, during prolonged exposure, the incidence of mortality may be no higher than it is among birds consuming uncontaminated food (Holmes et al. 1979). But, although these birds may show no obvious symptoms of distress, the ingested petroleum seems in some way to restrict their abilities to respond to environmental stressors, especially those that stimulate the increases in adrenocortical activity. This could explain why contaminated birds adapted to seawater are more sensitive to stressors than similarly contaminated freshwater birds (Holmes et al. 1978, 1979). As we have indicated above, the seawater-adapted birds must develop sustained high levels of adrenocortical activity in order to stimulate increases in mucosal water transfer and to initiate the extrarenal excretion of electrolytes via nasal salt glands. The imposition of additional stressors under these circumstances may exceed the capacity of the adrenal cortex to respond to more corticotropic stimulation.

To test this hypothesis we have attempted to identify the effects of ingested petroleum on adrenocortical activity in otherwise unstressed birds maintained on freshwater. Under conditions of a constant daily photoperiod, these birds show diurnal changes in plasma corticosterone concentration that include two daily maxima; one peak starting before dawn and continuing through the early hours of the light phase, and a second lesser peak starting before the onset of darkness and reaching a maximum early in the night. During their first week of exposure to food contaminated with 3% (v/w) South Louisiana crude oil, similarly unstressed birds appear to show striking declines in adrenocortical activity and the characteristic pattern of diurnal change in plasma corticosterone concentration is almost completely obliterated. Similar abrupt declines in plasma corticosterone concentrations also occur during the first week that unstressed mallard ducks are exposed to food containing lower concentrations (0.5% and 1%) of this crude oil. The lower-than-normal plasma corticosterone concentrations persist for several weeks of continuous exposure at each level of contamination.

Corticosterone is synthesized primarily by adrenocortical cells located in the inner zone of the duck adrenal gland (Klingbeil et al. 1979). An examination of these adrenocortical cells in birds that have been consuming food contaminated with South Louisiana crude oil for seven days revealed extensive degeneration of the mitochondrial cristae similar to that seen in zona fasciculata cells from mammals exposed to DDD. The few intact cristae remaining in these affected cells, however, were in the very labile tubulo-vesicular conformation which only occurs in cells exposed to corticotropic stimulation (Pearce et al. 1979, 1980). Thus, although some cellular degeneration may have occurred in the adrenocortical tissue, the conformation of the remaining mitochondrial cristae suggests that cells in the inner zone were subject to corticotropic stimulation immediately prior to fixation.

The decline in plasma corticosterone concentration that occurs in mallard ducks during their first week of exposure to petroleum-contaminated food is accompanied by an equally rapid increase in hepatic MFO activity and the extent of this increase is proportionate to the amount of crude oil consumed. Less rapid but similarly proportionate increases in enzyme activity occur during the next few weeks and they ultimately stabilize at levels ranging from 3 to 5 times those found in birds consuming uncontaminated food (see Holmes & Gorsline, 1980). Although plasma corticosterone concentrations and hepatic MFO activities are inversely related during the first few weeks that the birds are exposed to contaminated food, we have no evidence at this time to indicate whether high levels of endogenous hormone metabolism contribute to their hypoadrenocortical state.

Based on these limited data we have constructed a tentative schema suggesting the pathways whereby hypoadrenocorticalism may develop in mallard ducks exposed to petroleum hydrocarbons (Fig. 1). In many respects, however, the pattern of change outlined in this summary may also apply to other species exposed to other environmental pollutants known to affect adrenocortical activity.

Fig. 1 The pathways whereby petroleum hydrocarbon pollutants may affect adrenocortical function in birds.

EFFECTS ON REPRODUCTION IN BIRDS

Pesticides and other contaminants

Several developmental and behavioral aspects of reproduction in birds are affected by chlorinated hydrocarbon pesticides. In females, these include changes in the rates of ovarian follicular differentiation, delayed oviposition, decreased fertilization, lowered rates of hatchability, thinning of eggshells, prolonged incubation, increased aggression, and destruction of eggs (see reviews, Mori arty, 1975; Thomas, 1975). In males, these compounds cause abnormal testicular development characterized by reduced thickness of the germinal epithelium, accumulation of fluid in the seminiferous tubules, malformation of spermatozoa, and impaired development of some secondary sexual characteristics (Burlington & Lindeman, 1950; Albert, 1962; DeWitt et al, 1963; Eroschenko and Wilson, 1974; Eroschenko, 1978).

The chlorinated hydrocarbons known to exert some of these effects include DDT, DDE, Dieldrin, Kepone (Chlordecone), polychlorinated biphenyl (PCB) and pentachloronitrobenzene (PCNB). In some instances, these contaminants may interact directly with the target tissues of ovarian steroid hormones. Studies on the quail and the chicken have shown that DDT isomers compete effectively with endogenous estrogens for nuclear receptor sites in the oviduct and that this interaction elicits several changes similar to those seen following treatment with natural estrogens (Bitman et al, 1968; Turner & Eliel, 1978). Exposure of chickens and Japanese quail to Kepone may also induce differentiation of the oviduct. These changes include increases in weight, cellular differentiation, the generation of cilia, the formation of the tubular glands and the synthesis of the specific mRNA necessary for ovalbumin and conalbumin synthesis (Eroschenko & Wilson, 1975; Palmiter & Mulvihill, 1978). Also, a series of studies on the duck, the Japanese quail and the ringdove have shown that exposure to DDT causes abnormal development of the shell gland; this is sometimes accompanied by decreases in carbonic anhydrase and calcium-dependent ATPase activities (Bitman et al, 1970; Peakall, 1970; Kolaja & Hinton, 1976, 1977a,b). Clearly, many of these pesticides are able to mimic some, but not all, of the functional changes exerted by endogenous estrogens (Cooke, 1970). There are no reports of interactions between chlorinated hydrocarbon pesticides and androgen receptors in male birds.

There is little direct evidence to suggest that chlorinated hydrocarbon pesticides exert inhibitory effects on gonadal steroid hormone synthesis. In only one study involving ringdoves exposed to p,p’DDT have significant declines in plasma estradiol concentrations been recorded (Peakall, 1970). Nevertheless, the frequent impairment of normal reproduction following exposure of birds to these pesticides strongly suggests that low plasma concentrations of these hormones may occur in many contaminated birds. Many of the pesticides, however, are potent inducers of hepatic MFO activity and so the possibility must also be considered that these substances may indirectly cause enhanced hormone metabolism in some contaminated birds.

Petroleum hydrocarbons

The continuous spillage of petroleum and the resulting development of persistent, low level contamination in many regions may well be a major factor contributing to the demise of some seabird colonies. The first experimental evidence supporting this belief showed quite clearly that ingested petroleum hydrocarbons were capable of adversely affecting reproduction in birds (Grau et al, 1977). In this study on Japanese quail, a single oral dose of Bunker C fuel oil was found to reduce laying for several days and the eggs laid during this period showed higher than normal incidences of embryo mortality. Later, oviposition was shown to be slowed most effectively by an ether extract of the fuel oil whereas a chloroform extract contained more of the material affecting hatchability (Wootton et al, 1979).

Our own studies on the effects of ingested petroleum in mallard ducks have confirmed and extended these observations on quail (Holmes et al, 1978). Using uniformly composed groups of mated females exposed to a long photoperiod, we have found that food contaminated with either Kuwait or South Louisiana crude oil causes a delay in the onset of laying fertilized eggs. During the next few weeks the mean daily rate of oviposition and the hatchability of the eggs are consistently lower than those in birds consuming uncontaminated food. Also, the shells of eggs laid by birds consuming food contaminated with South Louisiana, but not Kuwait, crude oil are significantly thinner than the shells of eggs laid by control birds. At autopsy, we have found contaminated birds to have abnormally small oviducts and ovaries containing a large number of atretic follicles with few follicles in the later stages of differentiation.

In an attempt to define these effects more rigorously we have extended the study to monogamous pairs of birds given food contaminated with South Louisiana crude oil. Again, mated females show significant delays in the onset of oviposition, erratic patterns of laying with frequent anovulatory periods that sometimes last up to two weeks, and low incidences of fertilization. In contrast, birds receiving uncontaminated food rarely pause more than two or three consecutive days without laying. However, not only is the regularity of follicular development impaired by petroleum but the mechanism controlling the daily synchrony of ovulation and oviposition also seems to be disturbed. For example, control females lay most of their eggs between the second and fifth hour of the light phase whereas those consuming contaminated food lay their eggs during a much longer interval of the light phase.

Each of these abnormalities tends to reinforce the notion that ingested petroleum hydrocarbons interfere with ovarian steroidogenesis. In support of this hypothesis we have found that the pronounced and short-lived maximum in plasma estradiol concentration that occurs 4 hours prior to ovulation is significantly depressed and attenuated in birds consuming the contaminated food. Similarly, the less pronounced peak that occurs 16 to 20 hours before ovulation is also suppressed and flattened. During the diurnal cycle preceding ovulation there is only one daily peak in plasma progesterone concentration and this coincides with the major peak in estradiol; this peak is also suppressed slightly in birds consuming contaminated food. The dampening and attenuation of these peaks in ovarian steroid hormone concentrations are strikingly reminiscent of the dampening of cyclical change in plasma corticosterone concentrations we have described in birds consuming this crude