Sexual differences in the Japanese quail: behavior, morphology, and intracellular metabolism of testosterone

Three experiments were carried out to study whether differences in the intracellular metabolism of testosterone (T) can explain sexually differential responses to T in Japanese quail. In the first experiment, a series of dose-response curves in which length of Silastic testosterone implants was related to effects on several behavioral and physiological variables was established. In Experiment 2, adult males and females were assigned to six experimental groups: intact males and females (I-males and I-females), castrated males and females implanted subcutaneously with 40-mm Silastic implants of T (T-males and T-females), and castrated males and females without hormone treatment (CX-males and CX-females). No CX-bird (male or female) and no I-female exhibited male sexual behavior. However, I-males and T-males regularly copulated during the behavioral tests. No crowing was ever heard in CX-animals and I-females. T-females crowed less than T-males and their crowing sounded weaker than those of males. The cloacal glands of T-females were less developed than those of males. Radioimmunoassay of T and 5 alpha-DHT showed that T-males and T-females have similar plasma levels of androgens. No striking differences were observed in the way testosterone is metabolized by the pituitary gland and central nervous tissues of males and females. By contrast, the production of 5 alpha-dihydrotestosterone (5 alpha-DHT) and 5 alpha-androstane-3 alpha, 17 beta-diol (5 alpha, 3 alpha-diol) was higher in the cloacal glands of males than in those of females. These sex differences were not detected between T-males and T-females. In experiment 3, the cloacal gland of males produced more 5 alpha-reduced metabolites than those of females. The pituitary gland of females also produced more 5 beta-androstane-3 alpha, 17 beta-diol (5 beta, 3 alpha-diol). In syringeal muscles, the production of 5 beta-dihydrotestosterone (5 beta-DHT) and 5 beta, 3 alpha-diol was higher in females compared to males.     

Androgen feedback-dependent and -independent control of photoinduced LH secretion in male tree sparrows (Spizella arborea)

Photoperiodic control of gonadotrophin secretion in male tree sparrows was studied by examining changes in plasma LH in castrated birds retained on short daylengths and in castrated birds transferred to long daylengths. Plasma LH concentrations were markedly higher in photostimulated birds than in non-photostimulated birds throughout the 25-day experiment, and implantation of the antiandrogen cyproterone (free alcohol), which should have blocked the action of castration-resistant androgens, did not increase plasma LH in either group. Such results, obtained from birds in which testosterone feedback was inoperative, indicate that the gonadostimulatory effect of long daylengths in intact males must be mediated, at least in part, by an androgen feedback-independent mechanism. To determine whether changes in testosterone feedback facilitate gonadotrophin secretion during photostimulation, two feedback performance characteristics (i.e. set point (minimum concentration of testosterone that suppresses plasma LH) and sensitivity (change in plasma LH per unit change in testosterone)) were quantified by evaluating plasma LH responses of non-photostimulated castrated birds and of photostimulated castrated birds to replacement testosterone (0-4.16 mumol). The data indicate that, in addition to stimulating LH secretion by an androgen feedback-independent mechanism, long daylengths reduce feedback inhibition of LH secretion by increasing the putative set point and decreasing the sensitivity of the testosterone feedback mechanism. The feedback-independent effect is the predominant effect of photostimulation on LH secretion in male tree sparrows.     

Androgen induction of a specific uterine protein.

Studies were conducted to determine the ability of androgens in vitro to elicit the induction of a specific uterine protein (IP) normally attributed to estrogens. Both 5alpha-dihydrotestosterone (5alpha-DHT) and testosterone were effective in stimulating IP synthesis in rat uterine tissue in a concentration dependent manner (0.1 muM to 50 muM). 5alpha-DHT was more effective than testosterone and reached approximately 85% of the estradiol stimulated IP response at 10 muM and 50 muM; whereas testosterone was only able to achieve about a 70% IP response at 50 muM. This androgen stimulated IP synthesis was stereospecific since cis-testosterone and 5beta-DHT, inactive androgen isomers, were unable to evoke a detectable IP response at any concentration studied. Antiandrogens were unable to inhibit the 5alpha-DHT stimulated IP synthesis but antiestrogens were able to greatly inhibit the 5alpha-DHT and testosterone stimulated IP responses in a concentration dependent manner. The anti-estrogens, themselves, were very weak inducers of the IP response. The nuclear accumulation of the estrogen receptor by various androgens and inactive androgen isomers was also determined. Approximately 100% nuclear accumulation of receptor was attained with 1 muM 5alpha-DHT, whereas 50 muM testosterone was needed for 100% uptake. 5beta-DHT was unable to translocate the receptor at the lower concentrations tested, but caused a significant nuclear accumulation of 50 muM. Cis-testosterone was unable to cause the nuclear accumulation of the estrogen receptor at all concentrations studied. These studies suggest that some of the estrogen receptors accumulated in the nuclei by androgens, inactive androgen isomers, or antiestrogens may not be capable of eliciting a biological response.     

Steroids modulate the release of luteinizing hormone from quail pituitary cells

An enzymatically dispersed pituitary preparation from male Japanese quail (Coturnix coturnix) was used to study the effects of gonadal and adrenal steroids on gonadotropin release. Cells were preincubated for 18 hr with or without steroids and then challenged with chicken luteinizing hormone-releasing hormone (cLH-RH I; Gln8-LH-RH). Preincubation with testosterone (T; 10 nM) significantly suppressed (P less than 0.05) luteinizing hormone release in response to cLH-RH I (10 ng/ml). Preincubation with 5 alpha-dihydrotestosterone (5 alpha-DHT) (10 nM) caused even further suppression of LH-RH-stimulated LH release while the same concentration of 5 beta-dihydrotestosterone and estradiol-17 beta had no effect. In addition, preincubation with corticosterone (10 nM) significantly (P less than 0.01) suppressed the amount of LH released in response to cLH-RH I. Pituitary cells from immature males, when stimulated with cLH-RH I, released LH in a dose-related manner. Neither T nor 5 alpha-DHT (10 nM) altered the effect of LH-RH. These data suggest that T and 5 alpha-DHT play a role in mediating LH release in the avian pituitary while 5 beta-reduced androgens have no effect. There appears to be no androgen effect in the immature quail. In addition, corticosterone seems to be a factor in controlling gonadotropin secretion in the quail.     

Ontogenetic steroidogenesis by testes, ovary, and adrenals of embryonic and postembryonic chickens (Gallus domesticus)

To elucidate the relationship between steroidogenesis and sex differentiation in the chicken, pituitary and plasma LH, plasma, testicular, ovarian, and adrenal testosterone, estradiol-17 beta, estrone, and progesterone; and plasma and adrenal corticosterone and cortisol concentrations from 8-, 10-, 12-, 14-, 16-, 18-, and 20-day-old embryonic and 1-, 3-, 7-, and 14-day-old chicks were determined by radioimmunoassay. The plasma LH level was high in 10- to 12-day-old embryos and decreased with advancing age. No sex difference was observed in plasma, testicular, and ovarian testosterone concentrations at embryonic ages. After hatching, a higher testosterone level was observed in the testes than in the ovary, while a similar testosterone level was observed in the plasma of both sexes. Both plasma estradiol-17 beta and estrone concentrations were significantly higher in the female embryo than in the male embryo. Higher values of the two estrogens were observed in the left ovary of the female embryo than in the testes of the male embryo, and the estradiol concentration in the female embryonic ovary was much higher than the testosterone concentration in the male embryonic testes. No sex difference was observed in plasma progesterone, corticosterone, or cortisol. Both plasma and adrenal corticosterone concentrations reached peaks at hatching time. These results indicate that the chicken embryonic ovary is much more active in production and secretion of sex hormones with special reference to estrogenic hormones than are the embryonic testes. It is strongly suggested that the sex of the avian species is basically male, having homozygosity of sex chromosomes (ZZ), and that the estrogens secreted by the embryonic ovary have important roles in female sex differentiation.     

Studies on the feedback regulation of gonadotropin concentrations in male rats (I). The effects of hypothalamic implantation of testosterone and its metabolites on gonadotropin release in castrated male rats (author's transl)

Testosterone (T), 5 alpha-dihydrotestosterone (5 alpha-DHT), 5 alpha-androstane-3 alpha, 17 beta-diol (3 alpha-diol) and estradiol-17 beta (E) or cholesterol (control) were implanted into the hypothalamic median eminence--arcuate nucleus (ME-ARC) region of long-term castrated male rats. Serum LH and FSH levels were measured before and after the implantation. T or E implantation resulted in a 65.5% (P less than 0.01) or 80.2% (P less than 0.01) decrease in serum LH levels respectively, within 7 days after the intrahypothalamic application. 5 alpha-DHT or 3 alpha-diol implantation in the ME-ARC region also resulted in a significant lowering of serum LH levels, although their inhibitory action was less effective than that of T or E. There were no significant differences in serum LH levels 20 min after the intraperitoneal injection of 2 micrograms/kg of LH-RH between the control group and the T, 5 alpha-DHT, 3 alpha-diol or E group. E implantation also resulted in a 34.7% (P less than 0.01) decrease in serum FSH levels at the 7th day, but other steroids failed to reduce serum FSH levels after the intrahypothalamic application. These studies suggest that aromatization of T to E is not indispensable to the negative feedback effect of androgen on the hypothalamic LH-RH release. It might also be supposed that E is one of the factors regulating the serum FSH level.     

Inhibitory effect of the ovaries on neonatal androgen imprinting of growth hormone secretion in female rats

The effect of neonatal androgen treatment on the GH secretory pattern was examined in intact and ovariectomized adult female rats. Neonatal ovariectomy or sham operation was performed at 1-2 days of age; thereafter, the animals were immediately given testosterone propionate (250 micrograms) or vehicle. Other rats, also treated neonatally with testosterone, were ovariectomized 15-22 days before blood sampling. Plasma GH was measured in blood samples obtained from indwelling intraatrial cannulae every 20 min for 8 h when the animals were 100-140 days old. Plasma GH secretory patterns were analyzed by a pulse analysis computer program (PULSAR). Neonatal testosterone treatment did not affect the GH secretory pattern of female rats with intact ovaries. In contrast, neonatal androgen treatment enhanced GH pulse height as well as mean GH concentration in neonatally ovariectomized female rats to levels comparable to those in intact male rats. Neonatal testosterone administration also significantly increased GH pulse height and mean plasma GH concentration in female rats that were ovariectomized during adulthood. However, the GH secretory pattern of ovariectomized female rats given testosterone neonatally still differed markedly from that of normal males, in that GH pulses occurred less regularly and baseline levels were higher. Pituitary GH content and concentration in neonatally ovariectomized female rats were increased to levels indistinguishable from those in male rats by neonatal testosterone treatment. No significant effect of neonatal testosterone was observed in sham-operated females. Neonatal ovariectomy decreased basal plasma GH levels, but did not affect plasma GH pulse height or pituitary GH levels. The serum estradiol concentration was markedly decreased in ovariectomized female rats, but was unchanged in sham-operated rats given neonatal testosterone, raising the possibility that serum estradiol secretion mediated the antagonistic effect of the ovaries on neonatal androgen imprinting. These results indicate that the presence of ovaries can prevent the stimulatory effect of neonatal androgen exposure on GH storage and secretion in adult female rats.     

Inhibition of ovarian estradiol-17beta secretion by luteinizing hormone in prepubertal, pregnant mare serum-treated rats.

Serum estradiol-17beta levels, elevated prior to the luteinizing hormone (LH) surge, decline abruptly following the release of endogenous LH or the injection of exogenous LH. To investigate the mechanism of this decline, bovine LH (NIH-LH-B8) was administered to immature rats, in which follicular maturation and estrogen biosynthesis were induced by a non-ovulating dose of pregnant mare serum gonadotropin (PMS). Serum and ovarian estradiol-17beta concentrations fell detectably by 4h, and reached levels around 20% of the controls by 8h after iv injection of 10 mug LH. Concomitant decreases occurred in ovarian androgen concentrations, following an initial rise, and in the in vitro ovarian testosterone aromatizing enzyme activity. The LH-induced inhibition of the aromatase activity was found to be of a non-competitive type. It is proposed that two enzyme systems are inhibited as a result of the LH treatment: the C17,20-lyase and the C19 androgen aromatase, thereby leading to decreased concentrations of estrogens in the ovaries and blood.     

Rat adrenal 5 alpha-reductase mRNA content and enzyme activity are sex hormone dependent

To investigate the effects of sex hormones on 5 alpha-reductase, we examined 5 alpha-reductase mRNA content and enzyme activity in the adrenal cortex of peripubertal male and female rats. In male rats, the influence of castration or hormone-replacement treatment with dihydrotestosterone (5 alpha-DHT) on 5 alpha-reductase was assessed. To stimulate ovarian sex hormone production in immature female rats, the effect of a single injection of 5 IU pregnant mare serum gonadotrophin (PMSG) on 5 alpha-reductase was examined. The efficacy of the treatments was demonstrated by measuring serum LH and ventral prostate weight in male rats, and serum oestradiol and ovarian weight in female rats. Growth hormone was also measured across all treatments in male and female rats. Adrenal 5 alpha-reductase mRNA levels were determined by RNA blot analysis utilizing a rat 5 alpha-reductase cDNA as probe. 5 alpha-Reductase enzyme activity was estimated by isolating [3H]5 alpha-DHT by thin-layer chromatography after incubation with [3H]testosterone. The identity of the [3H]5 alpha-DHT formed was demonstrated by recrystallization of the derivatized DHT to constant specific activity. In controls, adrenal cortical 5 alpha-reductase mRNA content was nearly four times higher in immature female rats compared with intact peripubertal males. Castration resulted in a sevenfold increase in adrenal 5 alpha-reductase mRNA content compared with that in intact controls, while in DHT-injected castrated animals the mRNA level was nearly undetectable. The content of adrenal 5 alpha-reductase mRNA in anoestrous rats was nearly four times higher than in PMSG-treated animals.(ABSTRACT TRUNCATED AT 250 WORDS)     

In vivo regulation of steroidogenesis by ovine gonadotropins in male and female mudpuppies,Necturus maculosus Rafinesque

Using steroid radioimmunoassay the in vivo steroidogenic responses of male and female mudpuppies (Necturus maculosus) to single injections of ovine FSH and LH were investigated. In males, the major effect of LH was to stimulate testosterone and 5α-dihydrotestosterone secretion within 2 hr of injection, with a lesser effect on estrogen (estrone and estradiol-17β) secretion. In contrast, FSH primarily stimulated secretion of estrogens. The effects of both FSH and LH on steroid secretion in males were dose related. Castration of males reduced plasma androgen, and estrogen to very low or nondetectable levels and abolished the steroidogenic response to LH. Interrenalectomy prevented a postcastration rise in the progesterone level. In females, FSH did not stimulate steroid secretion but LH increased plasma androgens. Homologous pituitary extracts also stimulated plasma levels of all gonadal steroids measured.     

The endocrine control by luteinizing hormone of testosterone secretion from the testis of the Japanese quail

Injections of chicken or ovine luteinizing hormone (LH) into sexually mature male Japanese quail greatly increased plasma levels of testosterone. Maximal responses were obtained within 15 min of an iv injection and between 1 and 2 hr following sc or im injections. Saline treatment had no effect on plasma testosterone. In chronically castrated quail LH was not effective in altering androgen levels. The responses to LH were dose related, significant increases being obtained following sc injections of 5 μg of chicken LH (fraction AE1) or 10 μg of ovine LH (NIH-LH-S19). Chicken LH (AE1) was appropriately 1.8 times as potent as NIH-LH-S19. Ovine FSH (NIH-FSH-S10) stimulated testosterone release in very large doses (1 mg) but was at least 100 times less active than LH-S19. An iv injection of an antiserum raised against chicken LH into mature male quail caused a rapid decrease in plasma testosterone levels. Treatment with FSH-S-10 for up to 1 week failed to facilitate the subsequent response to an injection of LH. The responsiveness of the testis to exogenous LH was tested at various times during a photoinduced gonadal growth cycle. Sexually immature quail showed only a marginal response to an sc injection of 20 μg of NIH-LH-S19. A marked increase in responsiveness occurred after 6 long days. This coincides with the time when plasma testosterone levels increase naturally after transfer to long daylengths and with the period when Leydig cell maturation becomes complete. These in vivo results add further weight to the belief that, in birds, or at least in the quail, peripheral androgens are controlled by pituitary LH and that FSH plays no significant role in the acute release of testosterone from the mature testis.     

Relation of gonadal hormones to differential LH response to naloxone in prepubertal male and female rats

Naloxone (NAL) has been shown to induce LH release in female but not in male rats 10-25 days of age. The purpose of this study was to examine the role of neonatal gonadal hormones on NAL-induced LH release in male and female rats 15, 25, and 35 days of age. On each of these days rats received a s.c. injection of either NAL (5 mg/kg) or physiological saline, and blood was collected 30 min later by decapitation. At 15 days of age, NAL induced LH release in intact and ovariectomized (OVX) female rats, and in male rats castrated (CAST) on the 1st day of life (neonate CAST males). Injection of 10 micrograms estradiol benzoate (EB) 24 h prior to NAL administration blocked NAL-induced LH release in these rats. NAL had no effect on LH release in 15- or 25-day-old intact and CAST male rats or in female rats given 2 mg testosterone propionate at 3 days of age (androgenized female rats). At 35 days of age, NAL induced LH release in intact, OVX, and OVX-EB treated female rats, and in neonate CAST and neonate CAST-EB treated male rats. NAL had no effect on serum LH levels in androgenized female rats. NAL induced LH release in intact and CAST 35-day-old male rats, but pretreatment with estrogen prevented NAL from eliciting LH release. These results indicate that neonatal exposure to androgen is responsible for the sex difference in the LH response to NAL observed in prepubertal male and female rats before 30 days of age.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of oestradiol on gonadotrophin levels in normal and castrated men

Context  Testosterone inhibits gonadotrophin release in men either directly or after aromatization to oestradiol. We hypothesized that in males the androgen receptor-mediated effect of testosterone on LH release is negligible relative to that of oestradiol.
Objective  To compare the effect of experimentally induced variations of plasma oestradiol levels on LH levels in normal (physiological testosterone levels) and castrated men (very low testosterone levels).
Design  Prospective, open label, intervention.
Subjects and interventions  We suppressed endogenous oestradiol in 10 young men with letrozole 2·5 mg once daily. In these men and in 10 young healthy castrated men, we restored plasma oestradiol levels with oestradiol patches (first week 100 μg/day, second week 50 μg/day, third week 25 μg/day and fourth week no oestradiol patch).
Measurements  The effect of the intervention on plasma levels of LH were monitored and compared between the groups.
Results  With the intervention, the mean plasma oestradiol level in the two groups varied from supraphysiological to below the lower reference range. Levels of LH mirrored plasma oestradiol levels in both the groups, as did testosterone in the intact group. Despite similar oestradiol levels, mean levels of LH were significantly higher in the castrated group compared to the intact group for all doses of oestradiol, and supraphysiological levels of oestradiol were unable to suppress LH into the physiological range in the castrated group.
Conclusions  Physiological plasma oestradiol levels have a substantial suppressive effect on LH in men. However, low-normal testosterone levels are a prerequisite for suppression of LH into the normal range.     

Effects of sex steroids on aggressive behavior of adult male Japanese quail

We found that the order of aggressiveness of adult male Japanese quail determined by paired fighting was not correlated with plasma testosterone level, plasma LH level, size of cloacal protrusion, testicular weight, nor body weight. Injections of testosterone into lower-ranked individuals did not elevate their ranks of aggressiveness. Aggressive behavior was lost after castration. Injections of testosterone, androstenedione, and estradiol-17β restored aggressive behavior in castrated males. The order of aggressiveness of these hormone-injected castrated birds was identical to the order observed before castration. Administration of individually different doses of testosterone did not change the order. Injections with 5α- and 5β-dihydrotestosterone did not restore aggressive behavior in castrated males. These results are consistent with the hypothesis that aggressive behavior in adult male Japanese quail, as well as their sexual behavior, is induced by estradiol-17β converted by aromatase in the brain from testosterone. However, no correlation seems to exist between the endogenous or exogenous testosterone level and the order of aggressiveness.     

Growth hormone-releasing hormone messenger ribonucleic acid in the hypothalamus of the adult male rat is increased by testosterone

Since intact adult male rats have higher GH pulse amplitude than do castrated animals and since GH-releasing hormone (GHRH) secretion is predominantly responsible for the production of these GH pulses, we hypothesized that testosterone stimulates GHRH synthesis in neurons of the hypothalamus. To test this hypothesis, we compared GHRH mRNA content in individual neurons of the arcuate (ARC) and ventromedial (VMH) nuclei among groups of intact (n = 3), castrated (n = 5), and castrated testosterone-replaced (n = 5) adult male rats. Cellular GHRH mRNA content was measured by using semiquantitative in situ hybridization with an 35S-labeled cRNA probe complementary to the coding sequence of rat GHRH mRNA. Castration resulted in an approximately 35% decline in GHRH mRNA signal relative to that in intact animals in both the ARC (P less than 0.005) and VMH (P less than 0.005). Replacement with testosterone at the time of castration completely prevented the decline in both areas. Testosterone can exert effects either through activation of the androgen receptor directly or through aromatization to estradiol; therefore, we also examined the effects on GHRH mRNA of replacement with 17 beta-estradiol (n = 5) or dihydrotestosterone (DHT), a nonaromatizable androgen (n = 4). Estradiol had no effect on the castration-induced decline in GHRH mRNA in either the ARC or VMH. In contrast, DHT partially prevented the postcastration decline in GHRH in the ARC (P less than 0.005), while having no statistically significant effect on GHRH mRNA in the VMH. These results clearly indicate that testosterone stimulates expression of GHRH mRNA in neurons of the hypothalamus. Furthermore, the failure of estradiol to substitute for testosterone and the ability of DHT to substantially support GHRH mRNA suggest that testosterone exerts its effects on GHRH gene expression predominantly through direct activation of the androgen receptor.     

Extragonadal effects of luteinizing hormone in mice

LH is composed of isoforms which exhibit microheterogeneity. We recently demonstrated that a particular ovine or porcine LH preparation (G100-fr.3) stimulates kidney growth. This study was conducted to clarify the physiological role of this renotropic activity and other extragonadal effects of the ovine LH preparation in CD-1 mice. Hypophysectomy caused a significantly greater reduction in relative dry kidney weight (i.e. g/100 g body weight) when compared to adrenalectomy, castration, thyroidectomy, and castration plus thyroidectomy. Supplementation with G100-fr.3 in these animals partially restored not only kidney size but also DNA, RNA and protein content. Treatment with standard LH preparations (NIDDKoLH24 and G3-268DA), as well as PRL, GH, FSH and TSH, failed to reverse the renal atrophy induced by hypophysectomy and castration. Administration of testosterone to castrated hypophysectomized mice increased kidney weight and RNA content, but not renal DNA. The relative dry kidney weight increased significantly at the onset of puberty in intact male mice, but not in castrated males or intact female mice. In addition, human CG increased kidney size in hypophysectomized male mice, but not in castrated hypophysectomized animals. These findings indicate that LH isoforms may regulate kidney growth in the male mouse both directly as a renotropin stimulating hyperplasia and indirectly as a gonadotropin via testicular androgen, producing cellular hypertrophy. It was also noted that G100-fr.3 decreased hepatic weight, DNA, RNA and protein, but produced no significant change in the spleen, heart or adrenal glands in castrated-hypophysectomized mice. Such extragonadal effects of G100-fr.3 were also observed in intact female mice. These results suggest that certain LH isoforms may have extragonadal actions involving the kidney and liver.     

Differential effects of testosterone, 5 alpha-dihydrotestosterone and oestradiol-17 beta on plasma concentrations of LH in castrated ferrets

The biological activity of testosterone often depends on the conversion of testosterone within the target cell to an androgenic or oestrogenic metabolite. The purpose of this study was to compare the relative ability of testosterone and two of its metabolites, dihydrotestosterone (DHT) and oestradiol, to suppress LH secretion in castrated male ferrets. Castrated ferrets were treated with five different doses of steroid by implanting various numbers of s.c. silicone elastomer capsules packed with either testosterone, DHT or oestradiol. The lowest dose of oestradiol (0.1 mm capsule length/100 g body weight, mean estimated total release rate of 25 ng/day) significantly suppressed plasma concentrations of LH in castrated ferrets. Higher amounts of DHT (2.5 mm capsule length/100 g body weight, mean estimated total release rate of 88 ng/day) were required for a significant reduction in plasma concentrations of LH. Concentrations of LH were also significantly lowered by testosterone when administered at a 2.5 mm capsule length/100 g body weight; however, estimated total release rate was 312 ng/day from these capsules. The fact that oestradiol was more effective than DHT, and that DHT was more effective than testosterone in inhibiting LH secretion in castrated ferrets, suggests that in gonadally intact ferrets, testosterone may be converted to DHT or oestradiol within target cells that mediate steroid negative feedback on LH secretion.     

Effects of testosterone propionate or dihydrotestosterone propionate on plasma FSH and LH levels in neonatal rats and on sexual differentiation of the brain.

The present study tests the hypothesis that the effects of perinatal androgen administration on the development of the brain are brought about indirectly by a suppression of plasma gonadotropin (GTH) titers. Both castrated male and intact female rats were treated neonatally with 5 alpha-dihydrotestosterone propionate (DHTP) or testosterone propionate (TP) throughout the first ten postnatal days of life and the corresponding effects on neonatal plasma FSH and LH levels and the subsequent ability of the adult to exhibit cyclic GTH release and female sex behavior (lordosis) were determined. In males castrated within 24 h of birth, subcutaneous injections of DHTP (60 or 180 mug per 100 g average body weight) or TP (60 mug/100 g) given on day 2, 4, 6, 8 and 10 reduced plasma levels of FSH and LH as determined by radioimmunoassay 48 h following the first and last injections. However, TP but not DHTP masculinized the development of the regulation of GTH release as mesured by luteinization of subcutaneous ovarian grafts, and also suppressed the ability of adult neonatally castrated male primed with estradiol benzoate and progesterone to display lordosis behavior. In intact females, the same neonatal DHTP and TP injection regime lowered FSH and LH plasma levels following the last injection (day 12), while DHTP lowered LH, but not FSH, following the first injection (day 4). All TP treated females had ovaries devoid of CL by 45 days of age and showed prolonged vaginal cornification. However, DHTP failed to masculinize the pattern of GTH release in females since DHTP-treated females, like oil-treated females, possessed CL(days 45 and 100) and exhibited vaginal cycles (days 80-100). Lordosis quotients of females treated neonatally with DHTP were as high as those of oil-treated females and significantly higher than those of TP-treated females. These results demonstrate that the ability of TP to induce maculine differentiation of the neural regulation of GTH release and female sex behavior does not depend on its ability to depress circulating LH and FSH levels in the neonatal male, or LH levels in the neonatal female rat.     

Sexual differentiation of positive feedback: effect of hour of castration at birth on estradiol-induced luteinizing hormone secretion in immature male rats

In the male rat, a dramatic increase in hypothalamic testosterone and estradiol concentrations occurs during the first few hours of postnatal life. These experiments sought to determine whether such increases participate in the defeminization of positive estrogen feedback effects on LH secretion. Newborn male rats were castrated either in utero (0 h males), or 10 or 24 h after birth. Some males were castrated at 0 h in utero and injected at the time of surgery with 1,2.5, or 5 micrograms testosterone propionate. A group of females was ovariectomized at 0 h in utero (0 h females). The control group consisted of male and female rats sham gonadectomized at 0 h in utero which were either gonadectomized at 21 days of age or left intact. The experimental groups were challenged before puberty to determine if estrogen induced a release of LH using two different types of estrogen treatment. The first treatment consisted of an injection of 0.2 microgram estradiol benzoate (EB) on day 28 followed by a second 10 micrograms injection of EB on day 29. This treatment resulted on the afternoon of day 30 in a surge of LH in intact females. Normal males, 0 h males, or females castrated at 21 days did not have a significant LH surge. The second test consisted of the daily injection of 0.05 microgram EB on days 23-27; on day 28 the rats were injected with 2.5 micrograms EB. Zero hour male and female rats showed a large LH surge on the afternoon of day 29; sham castrated males never responded to this treatment. No sex difference was observed in the mean size of the LH surge providing the males were castrated at 0 h in utero. The effect of the hour of castration on the day of birth also was studied. Males castrated at 10 or 24 h after birth showed either no LH surge or the magnitude of the surge was greatly reduced compared to that obtained in the 0 h males (P less than 0.001). The fact that 0 h males injected with 1 microgram testosterone propionate never showed an LH surge after prepuberal treatment with estrogen suggests that 0 h is a time during which the newborn is sensitive to the defeminizing effect of androgens. These results are consistent with the idea that the testicular hyperactivity which occurs at the time of birth could influence the defeminization of the LH surge mechanisms.     

Effect of the antiandrogen flutamide on pituitary LH content and release

Flutamide is a nonsteroidal antiandrogen that blocks androgen receptors, with a consequent increase in serum immunoreactive LH (I-LH) in the presence of high testosterone concentrations. Several studies suggested that the gonadal steroids also play an important role in the regulation of LH bioactivity (B-LH). Therefore, it seems difficult to understand how the blockade of pituitary androgen receptors leads to the increase in testosterone levels. The present study was designed to elucidate the effect of flutamide on serum I-LH, B-LH and testosterone, as well as on in vitro stimulation of pituitaries by gonadotropin-releasing hormone (GnRH), in intact and androgen-treated castrated rats. In intact animals, a dose of flutamide as low as 0.5 mg/day provoked a 7- to 8-fold increase in serum I-LH levels over the vehicle-injected controls, whereas B-LH and testosterone were unaffected. However, higher doses significantly increased serum B-LH to values similar to those obtained in vehicle-injected castrated animals, resulting in high testosterone levels. Flutamide treatment provoked a decrease in I-LH and B-LH pituitary content; this effect was significantly higher under in vitro GnRH stimulation. The releasable I-LH under GnRH stimulation was not affected by flutamide treatment; however, a marked decrease was observed in B-LH.(ABSTRACT TRUNCATED AT 250 WORDS)