The effect of prenatal stress on steroidogenesis in the gonads of Arctic foxes (Alopex lagopus)

Handling is a source of stress for farm-bred blue foxes. The influence of handling during the late gestational period was investigated in 10-day old male and female blue foxes. Testosterone and estradiol were measured by RIA in the plasma, gonadal homogenates and in vitro incubates from blue foxes of both sexes. The gonads were incubated in vitro without or with human chorionic gonadotropin. In cubs of both sexes, the gonad weights and ovarian estradiol production were decreased by stress. The testicular testosterone and ovarian estradiol contents were increased in prenatally stressed cubs as compared to the controls. The testicular content and baseline in vitro production of testosterone were not affected by prenatal stress, but the testicular response to human chorionic gonadotropin was higher in the stressed group. This study suggests that prenatal stress induced by handling pregnant vixens may influence gonadal steroidogenesis and this effect was more pronounced in female cubs.     

Influence of prenatal stress on steroidogenesis in gonads of blue foxes

Handling is a source of stress for farm bred blue foxes. The influence of handling during the late gestational period was investigated in 10-day-old male and female blue foxes. Testosterone and estradiol were measured by RIA in the plasma, gonadal homogenates andin vitro incubates, from blue foxes of both sexes. The gonads were incubatedin vitro without or with human chorionic gonadotropin. In cubs of both sexes, the gonad weights and ovarian estradiol production were decreased by stress. The testicular testosterone and ovarian estradiol contents were increased in prenatally stressed cubs as compared to the controls. The testicular content and baselinein vitro production of testosterone were not affected by prenatal stress, but the testicular response to human chorionic gonadotropin was higher in the stressed group. This study suggests that prenatal stress induced by handling pregnant vixens may influence gonadal steroidogenesis and that this effect was more pronounced in female cubs.     

The effects of pinealectomy on pituitary and plasma gonadotropin levels in Carassius auratus exposed to various photoperiod–temperature regimes

The effects of pinealectomy on pituitary and plasma gonadotropin levels and gonadal development in female goldfish exposed to various photoperiod-temperature regimes during different seasons were examined. Pinealectomy during autumn had no effect on either pituitary or plasma hormone levels or gonadal development. When goldfish are pinealectomized in spring and exposed to long photoperiod conditions, the ovaries regress and plasma gonadotropin levels are significantly depressed compared to sham operated animals. Sham operated goldfish exposed to short photoperiod conditions in spring had regressing ovaries whereas pinealectomized animals under this regime either spawned or had ovaries in the late vitellogenic phase. Plasma gonadotropin titres in the pinealectomized group were significantly lower than those of sham operated animals. The pineal can be either stimulatory or inhibitory to gonadal development depending on the photoperiod regime to which the animals are exposed. The pineal apparently influences gonadal activity by modulating gonadotropin secretion. A diurnal variation in plasma gonadotropin levels was also observed in both sham operated and pinealectomized goldfish exposed to a long photoperiod warm-temperature regime in spring.     

Diurnal variations in pituitary gonadotropin content and in gonadal response to exogenous gonadotropin and prolactin in Notemigonus crysoleucas

Diurnal variations in pituitary gonadotropin content were determined in the golden shiner, Notemigonus crysoleucas. In fish maintained on a 15-5L/8-5D–15°C regime, a pronounced circadian variation in pituitary gonadotropin potency was observed, the gonadotropin content being minimal early and maximal late during the light phase. Little temporal variation was seen in fish exposed to a 9L/15D–15°C regime. The effects of gonadotropin and prolactin treatment on gonadal activity in N. crysoleucas were also investigated. Salmon gonadotropin was effective in stimulating an increased rate of gonadal development when given early during the light phase in fish maintained on a 15.5L/8-5D–15°C regime; injections of gonadotropin given late in the light phase failed to accelerate gonadal growth. Regardless of time of injection, ovine luteinizing hormone accelerated gonadal growth in fish maintained on a 9L/15D–15°C regime. Ovine prolactin retarded gonadal development in fish exposed to a 15.5L/8-5D–24°C regime, independent of injection time. In fish maintained on a 15.5L/8-5D–15°C regime, injections of prolactin given early, but not late, during the light phase repressed gonadal maturation. These data show that under certain photoperiod-temperature conditions there is a temporal aspect to responsiveness to exogenous hormone treatment.     

Restoration of normal gonadotropin responses to naloxone by chronic bromocriptine treatment in elderly men.

Naloxone is unable to stimulate FSH and LH secretion in elderly men, suggesting a reduced endogenous opioid control of gonadotropin secretion in senescence. In the present study, we examined whether in elderly men a chronic dopaminergic stimulation with bromocriptine (5 mg/day for 7 days) modifies the gonadotropin response to naloxone (4 mg as an i.v. bolus plus 10 mg infused in 2 h). Eleven younger men (group 1, 22-40 years old) participated as controls. Twenty-two elderly men were selected from a larger population and were divided into two groups: subjects with compensated gonadal failure (normal blood testosterone and elevated gonadotropin concentrations; group 2, n = 11; 62-80 years old) and men with normal gonadal function (normal blood testosterone and gonadotropin levels; group 3, n = 11; 61-82 years old). Naloxone induced a striking LH and a slight but significant FSH increase in group 1, but was unable to change serum gonadotropin concentrations in elderly subjects of both groups 2 and 3. When experiments were repeated after bromocriptine treatment, no significant differences in LH and FSH responses to naloxone were observed in the younger subjects. On the other hand, bromocriptine restored significant gonadotropin responses to naloxone in elderly men. In fact, after bromocriptine, naloxone-induced FSH and LH increments in groups 2 and 3 were indistinguishable from those observed in group 1. These data suggest that in men age-related dopaminergic alterations may underlie the defective endogenous opioid control of gonadotropin secretion.     

Effects of drug administration on gonadotropins, sex steroid hormones and binding proteins in humans

The possible mechanisms by which the administration of drugs may alter the gonadal function in humans are considered in this review. Based on personal data, and on data published in the literature, the following events may occur: (1) blockade of gonadal steroidogenesis; (2) interaction of drug(s) with the steroid-binding protein system in plasma, and (3) interference of drug(s) at the level of the feedback control of gonadotropin secretion. Representative examples of the above mechanisms are as following: (1) Ketoconazole possesses inhibitory effects in vitro on cytochrome P-450. When given in adult males, it decreased the plasma concentrations of testosterone (T) and androstenedione and increased 17 alpha-hydroxyprogesterone levels, suggesting that this drug acts in vivo on gonadal steroidogenesis by blocking the 17,20-lyase. (2) Danazol is a progestagen with high affinity for sex steroid-binding protein (SBP); when given in high dosages in normal males, it increased rapidly the dialyzable fraction (percent protein unbound or free fraction) of T. This suggests that by interacting with the binding sites of SBP, danazol and/or its metabolites displace the fraction of T bound to SBP. However, in males as well as in females, the long-term administration of danazol decreased also the binding capacity of SBP, and consequently increased the free fraction of sex steroid hormones. (3) Dihydrotestosterone (DHT), the most active androgen in many target cells, given at therapeutic dosages to adult males, resulted in a decrease in plasma concentrations of luteinizing hormone (LH) and T, without any significant change in the percent of free T, even though the affinity of DHT for SBP is higher than that of T. This suggests that the main effect of DHT is to inhibit gonadotropin secretion at the central level. (4) Flutamide, a nonsteroidal antiandrogen, increased both LH and T levels, demonstrating its pure antiandrogenic activity on gonadotropin secretion. The consequence(s) of the effects of such drugs on the production, the metabolic clearance rate and the bioavailability of sex steroid hormones are discussed.     

The tubero-infundibular neuron system: a component of the photoperiodic control mechanism of the white-crowned sparrow,Zonotrichia leucophrys gambelii

Summary To assess the roles of the hypothalamic neurosecretory and tubero-infundibular neuron systems in the mechanism of photoperiodic control of testicular growth in Zonotrichia leucophrys gambelii, midline electrolytic lesions were created in the median eminence, in its individual divisions, and in the region of the infundibular nucleus. Radiography was employed to facilitate the stereotaxic placement of lesions. Extensive damage to the neurosecretion-rich anterior division of the median eminence neither prevented the initiation of testicular growth in photosensitive, photostimulated birds nor induced gonadal regression in birds in which gonadal growth had previously been initiated by natural photoperiodic stimulation. Likewise, there was no impairment of the gonadotropin release mechanism when damage was restricted primarily to the neurosecretion-deficient posterior division of the median eminence. However, in birds in which the zone of damage included both divisions of the median eminence, the photoperiodic testicular response was abolished or markedly suppressed; if testicular growth had been initiated prior to electrocoagulation of the median eminence, testicular regression was induced. Gonadotropic insufficiency comparable to that induced by lesions in the median eminence was caused also by large lesions in the region of the infundibular nucleus or by smaller ones restricted primarily to its median, basal portion. Zones of damage that impair gonadotropic function thus correspond to (a) the chief nucleus of origin of the tubero-infundibular tract, (b) the principal route of entry of tubero-infundibular fibers into the anterior and posterior divisions of the median eminence, and (c) the terminal distribution of tubero-infundibular fibers in the eminential zones of neurovascular contact. These observations suggest that the tubero-infundibular neuron system is an essential component of the photoperiodic control mechanism of Z. leucophrys gambelii and are consistent with an hypothesis that assigns to this parvicellular neuron system the production of a neurohormone that regulates the release of a growth-stimulating gonadotropin from the pars distalis. The failure of anterior median eminence lesions to eliminate gonadotropin release is inconsistent with the hypothesis that the eminential component of the hypothalamic neurosecretory system is an essential element of the mechanism that controls photoperiodic testicular growth.This investigation was supported by a research grant (NB 01353) to Professor Donald S. Farner from the National Institutes of Health. A portion of the research was conducted while the author held the William T. Porter Fellowship of The American Physiological Society. I am grateful to Professor Farner for his suggestions and criticisms.This paper is based on a thesis submitted in partial fulfillment of the requirements for the Ph. D. in Zoophysiology at Washington State University. Portions of this study have been published previously in abstract form (F. E. Wilson and Farner, 1965).     

From contraception to cancer: a review of the therapeutic applications of LHRH analogues as antitumor agents.

LHRH and its analogues produce profound antireproductive effects in both sexes of a variety of animal species. Although the LHRH agonists induce gonadotropin release, gonadal steroid secretion, ovulation, and spermatogenesis as an expression of their traditional profertility pharmacologic profile, they paradoxically and characteristically cause predominant antifertility effects which have been extensively evaluated for potential contraceptive purposes. These agonists produce their antireproductive effects in both males and females by common mechanisms, ultimately resulting in disruption of pituitary-gonadal function, depression of steroidogenesis, and inhibition of target organs dependent on such gonadal support. Similar antireproductive effects have been observed with the LHRH antagonists which competitively inhibit LHRH-induced gonadotropin secretion resulting in reduced blood gonadal steroid levels. Use of the inhibitory properties has been extended to cancer therapy based on the ability of the LHRH analogues (particularly the agonists) to inhibit the growth of steroid-dependent (responsive) tumors (e.g., mammary, prostate) similar to that produced by gonadectomy and antisteroid treatments. The use of these peptides for selected hormone-sensitive tumors presents a novel pharmacotherapeutic application for this class of drug.     

In vitro production of ovarian steroids in yellow perch (Perca flavescens): effects of photothermal manipulation, gonadotropin and phorbol ester

We investigated the capacity of ovaries of yellow perch to produce steroid hormones in vitro and the ovarian response to gonadotropin and phorbol ester during the annual reproductive cycle. The effects of photothermal manipulation on perch gonadal steroidogenesis and its regulation have also been examined. Initially, all females kept indoors were exposed to the same water temperature and photoperiod. By the end of August, following the first sampling, fish were submitted to different photothermal regimes. Group A was maintained under photothermal conditions characteristic for southern Ohio. Group B was submitted to a condensed light/temperature regime designed to accelerate physiological changes that depend on photothermal stimuli. In group A, basal in vitro production of ovarian estradiol (E2) was the highest in October and November, and hCG significantly stimulated E2 secretion during the entire period of vitellogenesis (October-January). In this group, the highest production of basal testosterone (T) was observed before spawning. hCG-stimulated production of T was highest at the beginning of vitellogenesis. Gonadotropin stimulated T production before spawning, a time when gonadotropin was unable to stimulate E2 production. Phorbol ester (PDBu) stimulated E2 and T production during vitellogenesis at the same time points as hCG did (E2: December, January; T: December). hCG-stimulated T production was not mimicked by PDBu in April. Condensing of the photothermal cycle resulted in diminished ovarian production of E2 during vitellogenesis. Moreover, the fish submitted to a condensed photothermal cycle demonstrated augmented T production during the postvitellogenic stage of ovarian development. Ovaries of group B did not respond to PDBu. Generally, the seasonal fluctuations in ovarian capacity to produce E2 and T as well as in gonadal responsiveness to gonadotropin observed in female yellow perch illustrate the dynamic nature of ovarian endocrine function. The lack of response to gonadotropin with regard to E2 production prior to spawning is not due to insensitivity to gonadotropin, but rather due to some deficiency in steroidogenesis (e.g. reduced aromatase activity). It appears also that ovarian steroidogenesis and its regulation are dependent on annual changes of photothermal conditions.     

Oocyte maturation in white sturgeon,Acipenser transmontanus: some mechanisms and applications

Synopsis The ovaries of four pre-spawning white sturgeon females were sampled and their oocytes incubated in the presence of eight gonadotropin preparations, 21 steroids, a prostaglandin and a catacholamine. Among the gonadotropin preparations, acetone dried pituitary gland powder from white sturgeon, common carp and chum salmon (in decreasing order of potency) were capable of inducing oocyte maturation (germinal vesicle breakdown — GVBD), while human chorionic gonadotropin, pregnant mare's serum gonadotropin, equine luteinizing hormone, bullfrog gonadotropin, and a stellate sturgeon pituitary chromatographic fraction capable of inducing testosterone production in white sturgeon testicular tissue failed to elicit any oocyte maturation response. The progesterone derivatives were the most potent steroid inducers of GVBD, followed closely by several corticosteroids. In vitro incubation of white sturgeon oocytes, in the presence of a suitable steroid (progesterone), can be used as a diagnostic tool in screening out unresponsive females for induced spawning work. The two remaining compounds, prostaglandin F_2a and epinephrine, failed to cause ovulation in progesterone-matured white sturgeon oocytes.     

Induced ovulation in Atlantic croaker (Sciaenidae) using hCG and an LHRH analog: A preliminary study

A single dose of LHRHa (D-Ala(6), des Gly(10)- LHRH-ethylamide; 100 mug/kg body weight); administered by intramuscular injection, effectively induced ovulation in the Atlantic croaker (Micropogonias undulatus ); 37 of 40 (92%) females were successfully hand-stripped and there was no mortality. A single dose of human chorionic gonadotropin (hCG; 500 IU/kg body weight) was successful in inducing oocyte hydration. However, only 16 of 30 (53%) females ovulated successfully and could be hand-stripped. Another 8 females became extremely bloated and died. Thus LHRHa was shown to be the more reliable method of inducing ovulation in the Atlantic croaker. The response interval between hormone treatment and ovulation at different water temperatures was also determined.     

The hypothalamic-pituitary axis in diabetes mellitus

The hormonal response to LHRH and TRH was evaluated in three groups of male diaetics. Five patients were receiving therapy with the hypoglycemic agent glibenclamide, five were on NPH insulin and five were on dietary therapy alone. When compared to controls, the latter two groups had intact gonadotropin responses to LHRH. Despite normal basal gonadotropin levels, however, the group receiving glibenclamide therapy showed significantly exaggerated LH and FSH responses to LHRH. Both basal PRL and TSH levels, as well as the responses to TRH were normal in all three groups. These results indicate that LH, FSH, TSH and PRL secretion is intact in uncomplicated diabetes mellitus. The exaggerated LH and FSH responses to LHRH in the glibenclamide treated subjects are probably related to primary gonadal involvement; alternatively, there may be augmented pituitary gonadotropin secretion in this group.     

Effects of castration of immature rats on serum FSH and LH, and of various steroid treatments after castration

The intricate relationship between the gonads and pituitary gonadotropin secretion has been studied in the immature, 26-day-old rat. In male rats or chidectomized at this age, serum LH and FSH rose to significantly higher levels at 8 hours postcastration. A much later response was seen in ovariectomized females: at 24 hours and 48 hours for FSH and LH respectively. When groups of rats castrated at 26 days of age were treated with pharmacologic dosages of various steroids for 6 and 15 days postoperative, it was found that testosterone, 5alpha-dihydrotestosterone, and estradiol prevented the rise of both FSH and LH, in both sexes. A steroid-derived drug, 17alpha-ethinyl-testosterone-2, 3-isoxazol, was also effective, while progesterone alone was unable to suppress gonadotropins in either sex. Results reaffirm that the gonadal-hypophyseal relationhsip is sensitive before puberty. The marked sex difference in the response to castration is undoubtedly due to different gonadal hormones (androgen or estrogen) present at the time of castration, and their contributions to this feedback process. However it appears that hormones of either type can suppress both gonadotropins in both sexes. Results with 17alpha-ethinyl-testosterone-2, 3-isoxazol were particularly encouraging with respect to its clinical usefulness as a gonadotropin inhibitor with little or no biologic activity as a sex steroid.     

Plasma estradiol concentrations and effect of HCG on plasma estradiol and testosterone in normal subjects and patients with endocrine disorders.

Plasma estradiol concentrations were determined by radioimmunoassay in various endocrine disorders using antiserum to estradiol-17beta succinyl bovine serum albumin. Clinical significance and diagnostic value of plasma estradiol were assessed in hypothalamic-pituitary, adrenal and gonadal disorders. In general, estradiol concentration was correlated well with the degree of sexual maturity and was of great diagnostic use. Plasma estradiol in females mainly originated from the ovary, while the testis is the principal source of estradiol in males. The adrenal gland seemed to play a minor role as a source of estradiol at least in normal males and females. The role of estradiol in gynecomastia and in liver disease was also investigated. More than a half of the cases with gynecomastia had elevated concentrations of plasma estradiol, which probably explains the pathogenesis of this manifestation. Cirrhotic patients showed frequently hyperestrogenemia probably due to delayed disappearance of estradiol. In the study of stimulation with human chorionic gonadotropin (HCG), 3,000 IU daily for three days in ten normal men, the peripheral concentrations of esradiol showed maximum and fourfold increases 24 hours after the 1st injection of HCG. The testosterone levels, on the other hand, increased stepwise and reached a maximum of about two times preinjection levels 24 hours after the 3rd injection. In gonadal disorders, HCG produced various patterns of plasma estradiol and testosterone in accordance with the gonadal conditions and dissociated response patterns of both sex hormones were frequently found. The determination of plasma estradiol was useful in the study of the function of not only the ovary, but also the testis and the simultaneous measurement of plasma estradiol and testosterone after HCG administration presented interesting informations about pathophysiology of gonadal disorders.     

Final oocyte maturation in vivo and in vitro in marine fishes with pelagic eggs; yolk protein hydrolysis and free amino acid content

The role of free amino acids (FAA) in oocyte hydration during final maturation has been studied in plaice Pleuronectes platessa and lemon sole Microstomus kitt by in vivo and in vitro measurements. In vitro final maturation was initiated by the administration of human chorionic gonadotropin on large vitellogenic oocytes. The eggs produced in vitro had the same fraction of their total amino acid pool present in the free form as the in vivo hydrated eggs, regardless of whether FAA had been present in the incubation medium or not. The FAA pool in the mature egg was increased 10–15 times that of the oocyte, and the two FAA pool profiles differed strongly. The FAA profiles of the egg groups (intra- as well as interspecific) were almost identical except that the taurine content was lower in eggs in vitro . A major protein band of about 100 kDa was present on SDS electrophoretic gels of oocytes but missing on gels of hydrated eggs. This protein, presumably a lipovitellin, is the most likely origin of the egg FAA pool. We suggest that marine fishes with pelagic eggs share a common mechanism for oocyte hydration whereby partial hydrolysis of specific yolk proteins to FAA creates a major part of the osmotic potential needed for the water influx.     

Induction of oocyte maturation in the white croaker Micropogonias furnieri (Pisces: Sciaenidae) by human chorionic gonadotropin.

The present work aimed to identify the best doses of human chorionic gonadotropin (hCG) needed to induce oocyte maturation of Micropogonias furnieri and to characterize ovarian dynamics during the periovulatory period. Adult M. furnieri females with fully developed ovaries were injected intraperitoneally with four different doses of hCG. The gonadotropin response was succeeded by analyzing morphologically gonadal biopsies and following the postinjection changes in follicle diameter. Oocyte maturation was induced by three doses used: 100, 300, and 500 IU of hCG kg bw-1, and was reached 48 h after treatment with 300 and 500 IU of hCG kg bw-1, and 72 h after treatment with 100 IU of hCG kg bw-1. Concerning ovarian dynamics, only 100 and 300 IU of hCG kg bw-1 mimicked the natural ones which have a synchronic group maturation. In conclusion, the dose mimicking natural ovarian dynamics and inducing oocyte maturation more quickly is 300 IU of hCG kg bw-1.     

Effect of melatonin on GnIH precursor gene expression in Nile tilapia,Oreochromis niloticus

Sexual maturation and gonadal development of fish is greatly influenced by photic information, an external environmental factor, and melatonin mediates this information to regulate gonadotropin (GTH) secretion and gonadal activation. The relationship between gonadotropin inhibiting hormone (GnIH) and melatonin in fish, however, has not been studied to date. Here, the GnIH expression pattern and daily change of melatonin levels were compared to each other in mature tilapia (body length 16.1 ± 0.2 cm, body weight 77.7 ± 3.43 g), and the effect of melatonin injection on GnIH gene expression was investigated. GnIH gene expression increased at night when the secretion of melatonin increased, whereas gene expression decreased during the day when melatonin secretion decreased. Injecting tilapia intraperitoneally with melatonin increased GnIH gene expression and decreased the expression of gonadotropin releasing hormone (GnRH) and GTH. Furthermore, the injection decreased the 11-KT concentration in male tilapia. These results indicate that melatonin is likely to suppress the hypothalamus-pituitary-gonad (HPG) axis via the action of GnIH in this species.     

Hormone responses to clomiphene citrate in young chimpanzees

The responses of gonadotropin and gonadal steroids to the administration of clomiphene citrate were studied in male and female chimpanzees, aged 3.6 to 9.9 years. Follicle-stimulating hormone (FSH) was significantly reduced after treatment in the prepubertal females (n = 4) and in early pubertal males (n = 2) but not in prepubertal males (n = 5). FSH was unchanged or increased in early pubertal females (n = 2) and late pubertal males (n = 2). There was no consistent response to treatment with clomiphene citrate by luteinizing hormone (LH) in either males or females, nor by 17 beta-estradiol in the females. Testosterone levels were reduced in the early pubertal males only. These results support the hypothesis that negative feedback by gonadal steroids is operative in prepubertal chimpanzees and that puberty is accompanied by a reduction in the sensitivity to such feedback.     

Regulation of testicular differentiation and testosterone production in the fetal mouse gonad in vitro

The objective of the present study was to develop a chemically-defined medium in which early stages of testicular differentiation can be investigated in an organ culture system. Mouse gonadal primordia were explanted before and after initiation of morphological sex differentiation, i.e. 11 and 12 day of gestation (d.g.), respectively. We found that a combination of human albumin fraction, insulin (or IGF-I), and sodium pyruvate promoted testicular organization of gonadal explants of 11 d.g., but not those of 12 d.g. Insulin also increased the production of testosterone from testicular explants of 11 d.g., but not those of 12 d.g. For the younger explants, progesterone was more efficient than pregnenolone as a steroid precursor during the first day of culture, but the maximum effect of pregnenolone was much higher than that of progesterone in later stages. The responsiveness to human chorionic gonadotropin increased gradually along with testicular organization. The addition of either serum or pregnenolone prominently increased the activity of delta 5-3 beta hydroxysteroid dehydrogenase in testicular explants of 11 d.g., but not the number of positive cells as demonstrated by histochemical staining. These results suggest that insulin (or IGF-I) is required during the initial phase of testicular organization, which is reflected by an increase in testosterone production and sensitivity to gonadotropins.