Luteinizing hormone-dependent activity and luteinizing hormone-independent differentiation of rat fetal Leydig cells

Addition of 5x10(-2) U/ml recombinant luteinizing hormone (LH) to testes from fetuses at 16.5 day post conception (dpc) cultured for 5 days increased the number of Leydig cells by 34% and the acute LH-stimulated testosterone production by 600%. To determine whether these positive effects of LH in vitro are physiologically relevant in vivo, fetuses were decapitated on days 16.5 pc (before the onset of LH expression in the hypophysis) or 18.5 pc (before the surge of LH in the fetal plasma) and removed at 21.5 dpc. The number of fetal Leydig cells per testis and the acute LH-stimulated testosterone production by the testes ex vivo were unaltered by decapitation. Since, in all groups, the number of Leydig cells doubled between 16.5 and 18.5 dpc and between 18.5 and 21.5 dpc, these results suggest that neither the appearance of new fully differentiated fetal Leydig cells nor the maintenance of differentiated functions in existing fetal Leydig cells depend on LH during late fetal life, although this hormone is present in the plasma. Decapitation reduced the testosterone concentrations in the plasma (-56%) and in the testis in vivo (-67%) and the basal testosterone secretion of the testis ex vivo (-70%). This suggests that LH is required to maintain the physiological activity of the Leydig cell during late fetal life. However, the decrease of the in vivo testosterone production after decapitation was not sufficient to impair the growth of the Wolffian ducts and the lengthening of the anogenital distance. In conclusion, during late fetal life in the rat, Leydig cells are LH-independent for their functional differentiation and LH-dependent for their activity.     

Prenatal testosterone and luteinizing hormone levels in male rats exposed during pregnancy to 2,3,7,8-tetrachlorodibenzo-p-dioxin and diethylstilbestrol

Changes in the perinatal testosterone surge have been related to demasculinization of the central nervous system and androgen-dependent growth of the reproductive organs in male mammals. Earlier reports suggest that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) interferes with androgen production, but the perinatal effects have remained elusive. In the present study we explored in utero-effects of TCDD (0.05, 0.1, 0.5, and 1.0 microg/kg), introduced on day 13.5 of pregnancy, on prenatal (day 19.5 post-conception [p.c.]) testosterone (T) surge and pituitary luteinizing hormone (LH) production in TCDD-resistant Han/Wistar (H/W) and TCDD-sensitive Long-Evans (L-E) rats. To elucidate estrogenic effects on T and LH production, Sprague-Dawley (S-D) fetuses with previously known DES-sensitivity were exposed in utero to diethylstilbestrol (DES, 100-300 microg/kg) on days 13.5, 15.5, and 17.5 p.c. For comparison, H/W fetuses that responded to TCDD treatments were exposed to DES at concentration of 100 microg/kg. It was found that TCDD has a stimulatory effect on testicular T synthesis in the H/W fetuses and that their circulating T concentrations increased significantly. The effect was not seen in the inbred L-E fetuses, which throughout the study showed considerably low testicular T levels. Pituitary LH concentrations also increased in the H/W fetuses exposed to TCDD. Effects of TCDD (1.0 microg/kg) in the H/W fetuses could be confirmed in vitro by human chorionic gonadotropin (hCG) stimulation assay showing the highest response rate in the TCDD exposed testes. Stimulation of cyclic AMP (adenosine-3', 5'-cyclic monophosphate[cAMP]) production was not considerably altered by in utero TCDD exposure. A significant depression in testicular and plasma T content was seen in the DES-exposed S-D and H/W fetuses, but pituitary LH levels did not alter considerably. In the presence of hCG, DES-exposed testes showed lower in vitro T and cAMP production rates compared to the untreated testes. TCDD (1.0 microg/kg) increased and DES decreased the male body weight gain, but the changes were not sex-dependent. It is concluded that TCDD may increase the amplitude of the prenatal testosterone surge in male rats by stimulating pituitary LH production and enhancing the sensitivity of the fetal testis to LH. DES, on the contrary, apparently impairs testicular steroidogenesis and pituitary function.     

Effect of stress administered during pregnancy on the development of fetal testes and their subsequent function in the adult rat

When maternal stress, containing a large anxiety component, was administered during pregnancy there was a significant decrease in 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) activity in the fetal testis from days 16 to 20 of gestation, but not at birth nor in the first week after birth. However, persistent effects were found in adult males of 90 days of age. Basal testosterone concentrations in both plasma and testes and testicular 3 beta-HSD activity were significantly lower whilst basal plasma progesterone concentrations were significantly higher in the stressed group. When the stressed offspring were subjected to short-term stress (one session), their plasma testosterone concentration was significantly below that of the controls. It is suggested that suppressed gonadotrophin secretion during critical periods of development alters fetal testicular function, and that raised circulating levels of stress-induced hormones such as beta-endorphin may be responsible for changes in gonadotrophin secretion.     

Ontogenesis of the in vitro response of rat testis to gonadotropin-releasing hormone.

The age-related evolution of the in vitro effects of a gonadotropin releasing hormone agonist ([D-Trp6]-GnRH) on the secretion of testosterone by the testis, cultured during 3 days on a Millipore filter floating on M199 medium, was studied during the perinatal period in the rat. The basal and luteinizing hormone (LH)-stimulated secretions by testes explanted on fetal day 14.5 were unaffected by the agonist. With fetal testes explanted on days 16.5 and 18.5 post-conception, the agonist inhibited, in a concentration-dependent manner, both basal and LH-stimulated secretions from the second or the third day of treatment onwards. With fetal and neonatal testes explanted on days 20.5, 21.5 and 31.5 post-conception, the GnRH agonist also had a long-term inhibitory effect on LH-stimulated secretion, but increased basal secretion. This stimulatory effect was already observed after 4 h of culture, and was maintained for 3 days. These results suggest that, during fetal development, the cellular mechanisms involved in the negative testicular response to GnRH are differentiated 3-5 days before those involved in the positive response. Lastly, after 3 days of preculture in hormone-free medium, fetal testes explanted on day 14.5 displayed long-term GnRH agonist inhibition of in vitro basal secretion of testosterone. This observation points out a spontaneous differentiation of the negative responsiveness to GnRH in the cultured fetal testis.     

Reduction in testicular function in rats. I. Reduction by a specific gonadotropin-releasing hormone antagonist in fetal rats

A gonadotropin-releasing hormone (GnRH) antagonist, when injected 24 h before sacrifice to rat fetuses, did not modify plasma testosterone concentrations in males on day 18 of gestation but it did on days 19, 20 and 21. This GnRH antagonist reduced plasma luteinizing hormone (LH) levels and increased pituitary LH content in both male and female 19-day-old fetuses from mothers adrenalectomized on day 14 of gestation. An inverse relationship between plasma testosterone and LH levels was noted in males and females, on days 19 and 21. These data suggest that the hypothalamic control of gonadotropic function is operating by day 19 of fetal life and that a negative feedback of testosterone on LH and probably GnRH release is also operating in rat fetuses on days 19 and 21 of gestation.     

Daily hormonal changes in the maternal, fetal, and amniotic fluid compartments before parturition in a primate species

The daily hormonal fluctuations that occur simultaneously in the fetus, mother, and amniotic fluid during late gestation and before preterm parturition were studied in long term catheterized rhesus macaques. Blood and amniotic fluid samples were collected twice daily and analyzed by RIA for estrone, estradiol, dehydroepiandrosterone sulfate (DHEAS), progesterone, cortisol, and prostaglandin F2 alpha metabolite (PGFM). Vaginal delivery in monkeys with live fetuses was preceded by rising concentrations of DHEAS in fetal, but not maternal, blood. Parallel increases in fetal plasma estrone, maternal plasma estrone and estradiol, and amniotic fluid estrone preceded the rise in amniotic fluid PGFM (P less than 0.005, by analysis of variance). Cortisol levels remained stable in maternal blood and amniotic fluid, but increased before delivery in fetal blood. Nocturnal progesterone peaks in both fetal and maternal blood increased progressively in magnitude in fetuses before parturition. Rising concentrations of fetal DHEAS, estrone, and progesterone indicated an increase in adrenal activity before parturition in the rhesus fetus. PG production, reflected in amniotic fluid PGFM concentrations, was temporally related to increasing amniotic fluid concentrations of estrone. Although progesterone withdrawal may occur at a local tissue level, parturition occurred without an apparent decrease in circulating maternal, circulating fetal, or amniotic fluid progesterone concentrations.     

Maternal and fetal production rates of progesterone in rhesus macaques: placental transfer and conversion to cortisol

Maternal and fetal progesterone (P4) metabolism and placental transfer were examined in vivo. Via a femoral vein, 3.2 microCi[14C]P4 were infused at a constant rate for 2 h into five rhesus macaques on days 131-137 of gestation. Simultaneously, 12 microCi[3H]P4 were infused into the fetuses via a placental bridging vein. Measurement of steady state concentrations of [14C]- and [3H]P4 in the maternal and fetal circulations permitted calculation of the MCRs, production rates (PRs), and transfer rates (Vs) of P4. The maternal MCR (533 liters/day) was higher than the fetal MCR (93 liters/day), whereas the maternal PR did not differ significantly from the fetal PR (2.3 and 1.0 mg/day, respectively). Placental transfer of P4 from the fetal to maternal circulation (VFM) was greater than that from the maternal to fetal circulation (VMF). Values were 0.23 and 0.07 mg/day, respectively. The utilization of circulating P4 as a substrate for fetal cortisol (F) production was examined in three additional monkeys for whom the amount of isotopically labeled P4 infusate was increased 5-fold. By determining the ratio of specific activities of [3H]F and [3H]P4 in the fetal circulation, we found the maximum contribution of circulating fetal P4 as a precursor of fetal F to be less than 1%. Our results indicate that: 1) higher fetal than maternal plasma P4 concentrations (11.3 and 4.3 ng/ml, respectively) are most likely the result of 5-fold lower fetal MCR, since the PRs are similar in the fetal and maternal compartments, and the VFM is greater than the VMF; and 2) fetal F production using circulating P4 as a substrate is minimal.     

Developmental patterns of the testicular response to experimental modifications of circulating androgen levels in the fetal rabbit.

The circulating level of free androgens in fetal and newborn rabbits was reduced by active immunization of mothers against testosterone (T) or was increased by injecting dihydrotestosterone (DHT) into the mothers. After immunization, about 100% of the circulating T and DHT in fetuses was bound. After maternal injection of DHT, the circulating level of this hormone in fetuses was increased 2- to 120-fold. The effects of these treatments were evaluated by determining testicular levels of T, a physiological index of circulating gonadotropin. From 20--23 days of gestation, testicular T content was modified neither by circulating antibodies nor by an increase of blood DHT. The same overloads of circulating DHT, which were ineffective between 20--23 days, significantly reduced testicular T content between 25--29 days. Testicular T content was significantly increased in newborns from immunized mothers. These results suggest that the appearance of the negative feedback action of circulating androgens takes place relatively late, at 24 or 25 days, after differentiation of the genital tract.     

Catecholamines stimulate testicular testosterone release of the immature golden hamster via interaction with alpha- and beta-adrenergic receptors.

Several lines of evidence suggest that catecholamines are involved in the regulation of the development of the testis. We have therefore investigated the ability of testicular parenchyma (decapsulated pieces of testes) from 18 to 20-day-old golden hamsters to respond to catecholaminergic stimuli in vitro. Norepinephrine and epinephrine, as well as the beta-receptor agonist isoproterenol and the alpha-adrenoreceptor agonist phenylephrine were able to significantly stimulate testicular testosterone production. Dopamine and serotonin were not effective. The stimulatory action of norepinephrine on testosterone production was dependent on the concentration. In incubations of testes with human chorionic gonadotropin (hCG) and norepinephrine, no synergistic effects on testosterone release were observed. The stimulatory effect of norepinephrine could be partially blocked by incubation with beta-receptor antagonist propranolol, or with alpha-receptor antagonist prazosin, while a combination of propranolol and prazosin completely inhibited the norepinephrine-induced testosterone production. Moreover, isoproterenol and phenylephrine in combination stimulated testosterone more than either drug did alone. Measurements of concentrations of norepinephrine and epinephrine in testicular homogenates revealed higher values for these catecholamines than in the plasma, implying that catecholamine levels in the interstitial spaces of the testis might be in the range of concentrations effectively stimulating testosterone production in vitro. This suggests that in the immature testis of the golden hamster, catecholamines acting through both alpha- and beta-adrenergic receptors may be potent physiological stimulators of testosterone production.     

Handling during pregnancy in the blue fox (Alopex lagopus): the influence on the fetal gonadal function

In previous studies it has been shown that handling produced stress in pregnant blue fox vixens increasing plasma level and adrenal in vitro production of cortisol. Moreover, this treatment increased plasma cortisol levels in the fetuses. The present study was designed to examine effects of a 1-min daily handling stress applied to pregnant blue fox vixens on fetal gonadal steroidogenesis. Plasma concentrations of oestradiol and testosterone, gonadal content and gonadal in vitro production of these steroids, and response to exogenous hCG as well as gonadal weights, and anogenital distances were measured in control (C, n=69) and stressed (S, n=54) fetuses on 47-48 days of pregnancy. Maternal stress induced a suppression of gonadal steroidogenesis in the fetuses. The decreased testosterone content in the testes and oestradiol content in the ovaries were demonstrated in stressed fetuses compared with control (testosterone: 4.91+/-0.46 vs. 7.35+/-0.87 ng/both testes, P<0.05; oestradiol: 29.1+/-3.4 vs. 46.5+/-4.9 ng/both ovaries, P<0.05). The ovarian oestradiol in vitro production in female fetuses from stressed mothers was decreased in comparison with control (3.69+/-0.39 vs. 7.52+/-1.51 pg/ovary/h, P<0.05). The same difference was observed between stressed and control male fetuses in the testosterone testicular response to hCG (5.34+/-0.64 vs. 8.73+/-0.40 ng/testis/h, P<0.05). The ovarian weight from stressed fetuses was lower in comparison with control (12.9+/-0.7 vs. 16.8+/-0.6 mg, P<0.05). The anogenital distance in female fetuses from stressed vixens was also reduced (0.6+/-0.03 vs. 0.8+/-0.02 cm, P<0.01). These results indicate that prenatal stress resulted in a significant reduction of hormonal and morphometric measures of the reproductive system in blue fox fetuses with more drastic effects in female fetuses.     

Hormonal regulation of androgen-binding protein in the rat

Effects of gonadotropins and gonadal steroids on androgen-binding protein (ABP) production by the testis and its secretion into the blood and transport into the epididymis were studied in 20- and 30-day-old rats. These animals had been treated with hCG, FSH, the Nal-Glu GnRH antagonist [Ac-D2Nal1,D4ClDPhe2,D3Pal3,Arg5,DGlu6(AA) ,DAla10]LHRH (antagonist), testosterone propionate, or estradiol benzoate, alone or in combination, for 10 days before assessment of ABP. Antagonist administration suppressed the testicular content (nanograms per organ) of ABP to below control (untreated) levels in both age groups. When hCG or testosterone was given along with the antagonist, they overcame the effect of the antagonist, and the resultant ABP values exceeded untreated control levels in both the 20- and 30-day-old rats. Treatment of rats with these hormones in the absence of the GnRH antagonist also elevated the ABP content of the testis above that of untreated controls. FSH administered with antagonist was able to prevent the antagonist-induced suppression of testicular ABP content. When rats were treated with FSH alone, the content of ABP in the testis was increased above untreated control levels in the 30-day-old group, but not in the 20-day-old group. The simultaneous administration of FSH and hCG did not result in an increase in testicular ABP content above that caused by hCG or testosterone alone. The increase in the ABP content of the testis caused by FSH administration was only about one sixth that caused by hCG or testosterone. Since testosterone or hCG, even in the presence of antagonist, was able to maximally stimulate ABP production by the testis of both age groups, we conclude that testosterone is the major in vivo regulator of its synthesis. Only combined treatment with hCG and FSH was able to increase transport of ABP into the epididymis of 20-day-old rats. All treatments that increased the testicular content of ABP in the 30-day-old rats also increased its transport into the epididymis. Treatments that drastically reduced the content of ABP in the testis of 20-day-old rats (antagonist, estradiol, estradiol plus antagonist) also reduced ABP secretion into the serum. Only treatment with estradiol reduced the secretion of ABP into the serum of 30-day-old rats. None of the treatments increased the ABP secretion into the bloodstream above untreated control levels.     

Reduction in testicular function in rats. II. Reduction by dexamethasone in fetal and neonatal rats

Chronic administration of dexamethasone in drinking water to maternal rats from days 15 to 21 of gestation (1) reduced plasma testosterone concentrations in male fetuses between days 19 and 21 but not earlier on day 18 and abolished the prenatal peak of plasma testosterone which normally occurs on day 19 of gestation, and (2) suppressed the postnatal surge of plasma testosterone in male newborns 1.5 and 2 h after delivery at term by cesarean section. The administration of dexamethasone to male fetuses at birth induced 1 h later a slight but not significant increase in hypothalamic gonadotropin-releasing hormone (GnRH) and pituitary luteinizing hormone (LH) contents, reduced drastically plasma LH levels and completely prevented the postnatal surge of plasma testosterone which occurred normally in littermate controls. A rise in pituitary LH content, and a sharp reduction in plasma LH and testosterone concentrations were noted in 19-day-old male fetuses whose mothers were acutely treated with dexamethasone on day 18 of gestation. Similar evolutions for LH were observed in littermate females. These results suggest that the inhibitory effects of exogenous glucocorticoids on testosterone secretion could be mediated in both fetuses and newborns at least partially through suppression of the hypothalamic and pituitary secretion of GnRH and LH, respectively, and provide insight how stress or hormone imbalance may affect the development of this neuroendocrine system.     

Stimulation of testosterone production in vivo and in vitro in the male rhesus monkey fetus in late gestation.

To assess intrauterine fetal testicular function, the carotid or femoral vessels of rhesus monkey fetuses, 129-145 days gestational age, were catheterized following hysterotomy of the mother. The fetus was returned to the uterus, the catheters were exteriorized through the mother's vagina and the pregnancy was allowed to continue. In this chronic preparation, basal levels of testosterone (measured with an RIA with 65% cross-reactivity with 5 alpha-dihydrotestosterone) in male fetal serum were 0.85 +/- 0.29 (SD) ng/ml. Administration of a 10 or 100 IU intra-arterial bolus of hCG into the fetal circulation stimulated in increase in fetal serum testosterone levels of 70 and 630%, respectively. Other fetuses were challenged with bolus infusions of 10 and 50 micrograms of synthetic gonadotropin releasing hormone (GnRH). The lower dose caused an increase in serum testosterone concentrations in only one of four fetuses, while the higher dose resulted in a positive response in all three experiments performed. With this dose, the mean increase in circulating testosterone concentration after 1 h was 105%. In vitro, specific binding of iodinated hCG was demonstrated in testicular homogenates from rhesus fetuses near term and hCG stimulated testosterone biosynthesis in testicular minces. Maximal stimulation was achieved at hCG concentrations between 5 and 50 ng/ml. The data indicate that the testes of fetal rhesus monkeys during late gestation are capable of androgen biosynthesis and can bind and respond to gonadotropin stimulation. Furthermore, the pituitary-gonadal axis in the fetal male monkey is capable of responding to GnRH stimulation at this stage of gestation.     

Induction and maintenance of gonadotropin and lactogen receptors in hypoprolactinemic rats

The effect of 2-bromo-alpha-ergocriptine (BR)-induced hypoprolactinemia on the induction and maintenance of testicular gonadotropin and lactogen receptors was studied in 60-day-old rats after receptor regulation by a gonadotropin-releasing hormone agonist analog [[D-Ser-(tBu)6]des-Gly10-GnRH N-ethylamide (GnRH-A)] and in young animals during sexual maturation. In adult animals, BR treatment delayed the reappearance of LH binding in the testis after GnRH-A injection, but had no effect on the recovery of lactogen binding. BR treatment also inhibited the increase of LH binding that occurred in control animals during the experimental period, but did not affect lactogen binding. Furthermore, BR potentiated the effect of GnRH-A on the decrease of Leydig cell testosterone synthesis observed 2 days later in vitro. Eight days after GnRH-A injection, concomitant BR treatment significantly inhibited the recovery of Leydig cell cAMP production. In peripubertal (25- to 46-day-old) animals, BR diminished the normal rise in testicular LH receptors, but did not affect the increase in lactogen receptors. Serum testosterone levels and other features of pubertal development, such as balano-preputial separation and spermatogenesis, were unaffected by hypoprolactinemia. In neonatal female animals, significant lactogen binding was detected at 3 days of age, whereas hCG binding was not demonstrable until 9 days after birth. These findings indicate that the expression of lactogen receptors precedes that of LH receptors in the developing gonad, and that the increase of LH binding in the testis during pubertal development requires normal circulating PRL levels. In adult animals, hypoprolactinemia potentiates GnRH-A-induced desensitization of steroidogenesis and cAMP formation, as well as LH receptor down-regulation, delaying the recovery of these phenomena. Although decreased serum PRL levels were associated with a marked reduction in testicular LH receptors both during development and in adult life, the absence of changes in lactogen receptors indicates that the latter sites are largely independent of the circulating PRL concentration.     

Pituitary and plasma levels of luteinizing hormone and follicle-stimulating hormone in male and female rabbit fetuses

To study the ontogenesis of fetal pituitary gonadotrophin synthesis and release, LH and FSH were measured by radioimmunoassay in fetal rabbit pituitary glands and blood of both sexes from day 18 of gestation until birth. Results on levels of testicular and plasma testosterone were also included. Immunoreactive LH was first detected on day 19 in the pituitary gland and on day 20 in the plasma of fetuses of both sexes. Pituitary FSH was first measurable in both male and female fetuses at 24 days of gestation. Levels of FSH could not be detected in the blood of male fetuses at any time during gestation. In females, FSH could be measured in the circulation from day 27 of gestation until birth. These results show that (1) the ontogeny of pituitary LH and the onset of testosterone secretion are closely correlated and take place between 18 and 20 days of gestation just before the beginning of differentiation of the male genital tract, and (2) the highest concentrations of pituitary LH and FSH are observed, in both sexes, in late gestation after days 24-25.     

Direct inhibitory effect of glucocorticoids upon testicular luteinizing hormone receptor and steroidogenesis in vivo and in vitro

The direct effects of glucocorticoids on testicular LH receptor content and steroidogenesis were studied in vivo and in vitro. Immature hypophysectomized rats were treated with varying doses of dexamethasone, corticosterone, or a synthetic progestin, 17,21-dimethyl-19-nor-pregna-4,9-diene-3,20-dione (R5020). Some animals were also treated concomitantly with FSH to prevent the hypophysectomy-induced decrease in testis functions. At the end of 5 days of treatment, testicular LH/hCG receptor content was measured by [125I]hCG binding assay while steroidogenic responsiveness was measured by in vitro incubation of testes. Dexamethasone decreased testicular LH receptor in control and FSH-treated hypophysectomized rats in doses as low as 10 microgram/day, whereas corticosterone (10 microgram/day) decreased testicular LH receptor in the FSH-treated rats but had no effect in rats not treated with FSH. In contrast, R5020 had no effect on testicular LH receptor content. In vivo treatment of hypophysectomized rats with FSH increased both basal and hCG-stimulated production of androstanediol in vitro. In contrast, concomitant treatment with dexamethasone, but not R5020, decreased both basal and hCG-stimulated testicular androstanediol production. The direct effect of glucocorticoids on testicular steroidogenic potentials was also studied in primary culture of testicular cells obtained from adult hypophysectomized rats. Treatment of cultured testicular cells wtih hCG increased testosterone production. The addition of various natural and synthetic glucocorticoids, but not R5020, to hCG-treated cells decreased testosterone production in a dose- and time-related manner (triamcinolone greater than or equal to dexamethasone greater than cortisol greater than or equal to corticosterone). A 40% decrease in testosterone production was apparent at 6 h after addition of 10(-7) M dexamethasone to hCG-treated cells. These results demonstrate the direct inhibitory effect of glucocorticoids on testicular LH receptor content and steroidogenesis, suggesting the adrenal glucocorticoids may regulate testis functions.     

Changes in follicle-stimulating hormone secretion in spontaneously hypertensive rats.

FSH and testosterone plasma levels, pituitary FSH content and concentration and the weight of testis, seminal vesicles and ventral prostate have been studied at the ages of 30, 60 and 90 days in spontaneously hypertensive rats (SHR) and normotensive control (WKY) rats. In vitro FSH secretion by pituitaries, and the response to orchidectomy and to exogenous administration of either LHRH (1 microgram) or LHRH agonist (0.05, 0.1, 1, and 5 micrograms/kg) were analyzed in 90-day-old SHR and WKY male rats. Ventral prostate weight and FSH plasma levels were determined in other groups of adult male rats castrated and castrated and implanted for 15 days with silastic capsules containing testosterone, dihydrotestosterone or estradiol. Also FSH plasma levels and pituitary FSH concentration were determined at the ages of 30, 60 and 90 days in SHR and WKY female rats. Male SHR showed increased plasma FSH levels and high testicular weight in all the cases, and enhanced testosterone levels in plasma and pituitary FSH content on days 60 and 90. Weight of seminal vesicles and ventral prostate was normal or reduced, depending on the animal age. Adult SHR had increased FSH secretion in vitro, normal response to orchidectomy and did not exhibit FSH increases after LHRH administration. The efficiency of testosterone to stimulate ventral prostate growth and the ability of estradiol to reduce FSH plasma levels were decreased in SHR. Female SHR showed a significant increase in the pituitary content of FSH on day 30 and on proestrus at the ages of days 60 and 90.(ABSTRACT TRUNCATED AT 250 WORDS)     

Transient neonatal hypothyroidism alters plasma and testicular sex steroid concentration in puberal rats

The stimulatory and inhibitory effects on testicular steroidogenesis of transient neonatal hypothyroidism from day 1 postpartum through different postnatal developmental events on testis at puberal age (60 days old) were studied in vivo. Hypothyroidism was induced in neonates by feeding the lactating mother or directly with 0.05% methimazole (MMI) through drinking water from the day of parturition to 10, 15, 30, 40 and 60 days, and were killed at day 60 postpartum. Plasma and testicular interstitial fluid (TIF) progesterone, testosterone, dihydrotestosterone (DHT) and estradiol concentrations were assessed. Testis weight and volume significantly increased in rats subjected to 10 and 15 days of hypothyroidism, decreased in rats subjected to 30, 40 and 60 days of hypothyroidism. A consistent increase in Leydig cell number was seen in puberal rats subjected to transient neonatal hypothyroidism but decreased in 60 days hypothyroid rats. Peritubular myoid cell number was consistently decreased in all experimental rats. Leydig cell diameter decreased consistently in all experimental groups. Persistent hypothyroidism (60 days hypothyroid) consistently decreased both plasma and TIF sex steroids. In transient hypothyroid rats, progesterone concentration decreased in both plasma and TIF. Transient hypothyroidism from birth to day 10 postnatal age maintained normal titre of plasma testosterone, whereas a significant increase in TIF testosterone concentration was evident when compared with controls. All other groups of rats subjected to transient neonatal hypothyroidism had consistently low titres of plasma and TIF testosterone. Plasma DHT concentrations in rats subjected to transient neonatal hypothyroidism remained unaltered. However, TIF DHT increased in 10 days     

The acute effect of oestrogens on testosterone production appears not to be mediated by testicular oestrogen receptors

Scatchard binding analysis was performed to measure the cytoplasmic oestrogen receptor in the testis of rats. After treatment of rats with the antioestrogen tamoxifen no oestrogen receptor binding was found in testicular low speed supernatant between 12 and 96 h after treatment. Such tamoxifen-treated rats were used to study the acute effect of oestrogens on testosterone secretion, both in vivo and in vitro. Injection of oestradiol benzoate (50 μg, 24 h prior to experiment) resulted in a significant depression of basal and LH-stimulated plasma testosterone levels in control rats and this effect was unchanged in tamoxifen-pretreated rats. In vitro, oestradiol-17β also inhibited the LH-induced rise in testosterone secretion by isolated testicular interstitial cells. This inhibition was not affected if the rats had been pretreated with tamoxifen. These results indicate that the inhibitory effects of exogenous oestrogens on testicular testosterone production are probably not mediated by the oestrogen receptor.     

Circulating maternal immunoreactive inhibin levels during pregnancy in the rat: effects of oophorectomy, hypophysectomy, hemihysterectomy, delayed implantation and pseudopregnancy.

This study examines the source of inhibin in the maternal circulation of pregnant rats by measuring serum immunoactive inhibin levels following a range of experimental procedures. Ovariectomy at days 7, 13 or 19 of gestation, with maintenance of pregnancy by supplementation with progesterone and oestradiol dipropionate, led to a profound fall of serum inhibin levels in comparison with controls, demonstrating that the ovary is a major source of circulating inhibin. This conclusion was supported by the inhibition of the late rise (days 16-22) in serum inhibin in pregnant rats which were hypophysectomized on day 15 and maintained with oestrogen and progesterone supplementation. These data support the view that the rise in serum inhibin from days 16 to 22 is due to re-activation of follicular development in preparation for the post-partum oestrus. Reduction of fetal numbers by hemihysterectomy on days 7, 13 or 19 did not alter serum inhibin levels. Induction of delayed implantation by ovariectomy on day 3 and progesterone supplementation together with initiation of reimplantation by the addition of oestradiol dipropionate on day 7 or 11 did not significantly alter inhibin levels. The induction of pseudopregnancy by mating to vasectomized rats did not result in the maintenance of stable serum inhibin levels until oestrous cycles recommenced. Taken together, the studies have identified the ovary as the predominant source of circulating maternal inhibin levels throughout pregnancy in the rat.