Testosterone selectively increases serum follicle-stimulating hormonal (FSH) but not luteinizing hormone (LH) in gonadotropin-releasing hormone antagonist-treated male rats: evidence for differential regulation of LH and FSH secretion

Both testosterone (T) and gonadotropin-releasing hormone (GnRH)-antagonist (GnRH-A) when given alone lower serum luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in intact and castrated rats. However, when graded doses of testosterone enanthate (T.E.) were given to GnRH-A-treated intact male rats, a paradoxical dose-dependent increase in serum FSH occurred; whereas serum LH remained suppressed. This surprising finding led us to ask whether the paradoxical increase in serum FSH in GnRH-A-suppressed animals was a direct stimulatory effect of T on the hypothalamic-pituitary axis or the result of a T effect on a testicular regulator of FSH. To test these hypotheses, we treated adult male castrated rats with GnRH-A and graded doses of T.E. In both intact and castrated rats, serum LH remained undetectable in GnRH-A-treated rats with or without T.E. However, addition of T.E. to GnRH-A led to a dose-dependent increase in serum FSH in castrated animals as well, thus pointing against mediation by a selective testicular regulator of FSH. These data provide evidence that pituitary LH and FSH responses may be differentially regulated under certain conditions. When the action of GnRH is blocked (such as in GnRH-A-treated animals), T directly and selectively increases pituitary FSH secretion.     

Testicular modulation of luteinizing hormone response to gonadotropin-releasing hormone (GnRH)-agonist treatment

We and others have observed that the response of serum luteinizing hormone (LH) and follicle-stimulating hormone (FSH) to chronic gonadotropin-releasing hormone-agonist (GnRH-A) treatment is substantially different in normal compared to hypogonadal males. These data suggested that products of the testes determine the gonadotropin response to GnRH-A. The present studies were designed to determine whether this effect is mediated by products of the interstitial (steroids) or the tubular compartment. To create experimental states with selective impairment of interstitial, tubular, or both compartments, 100 male sexually mature Wistar rats were divided into five groups: I, intact; II, castrated; III, castrated with 20-mm testosterone (T) implants; IV, bilaterally cryptorchid; and V, ketoconazole-treated animals. Cryptorchid animals have been shown to have impairment of tubular function while ketoconazole inhibits T biosynthesis. Each of the 5 groups was divided into 2 subgroups to receive daily injections of either saline or 1 microgram of a potent GnRH agonist, D-leu6 des-Gly10 GnRH N-ethylamide, for 4 wk. Unlike the intact animals, which showed an elevation of basal serum LH concentration after 4 wk of GnRH-A treatment, the castrated animals showed significant suppression below baseline. Animals with preferential impairment of tubular function (cryptorchid and castrated + T) also showed significant suppression of LH after GnRH-A treatment. However, the ketoconazole-treated animals (with inhibition of T biosynthesis and intact tubular function), behaved similarly to intact animals and demonstrated an elevation of LH after GnRH-A treatment.(ABSTRACT TRUNCATED AT 250 WORDS)     

Testosterone and estrogen differently effect Th1 and Th2 cytokine release following trauma-haemorrhage.

The object of the study was to determine whether male and female sex steroids produce divergent effects on Th1 and Th2 cytokine release following trauma-haemorrhage. Recent studies indicate that androgens are responsible for the depressed splenocyte Th1 cytokine release in males following trauma-haemorrhage. In contrast, female mice maintain their Th1 cytokine release capacity following trauma-haemorrhage. Nonetheless, the effect of male and female sex steroids on Th1 and Th2 cytokine release following trauma-haemorrhage remains unknown. Male C3H/HeN mice were castrated and treated with pellets containing either vehicle, 5alpha-dihydrotestosterone (DHT), 17beta-estradiol (estradiol), or a combination of both steroid hormones, for 14 days prior to soft-tissue trauma (i.e. laparotomy) and haemorrhagic shock (35+/-5 mmHg for 90 min followed by adequate fluid resuscitation) or sham operation. Untreated male and female mice, as well as DHT treated female mice, served as control groups. Twenty-four hours later the animals were sacrificed, plasma obtained and splenocytes harvested. Plasma DHT and estradiol levels in treated animals were comparable with intact male and female mice, respectively. A significant depression of splenocyte Th1 cytokines, i.e. IL-2, IFN-gamma, was observed in DHT treated castrated animals, DHT treated females, and untreated males following trauma-haemorrhage, as opposed to maintained Th1 cytokine release in estradiol treated and estradiol/DHT treated castrated animals and females. The release of the anti-inflammatory cytokine IL-10 was markedly increased in DHT treated mice and males subjected to trauma-haemorrhage compared to shams, but decreased in estrogen treated mice and females under such conditions. These results suggest that male and female sex steroids differentially affect the release of Th1 and Th2 cytokines following trauma-haemorrhage and should be further studied for their potential to modulate splenocyte function in trauma victims.     

Effects of short days on aromatization and accumulation of nuclear estrogen receptors in the hamster brain

Exposure of hamsters to short days increases sensitivity to the negative feedback effects of testosterone (T) but decreases responsiveness to the behavioral effects of the hormone. Since T is metabolized in the brain to 5 alpha-dihydrotestosterone (DHT) and estradiol, which differentially affect gonadotropin secretion and sex behavior, it is reasonable to postulate that daylength can modulate neural responses by quantitative or qualitative alterations in T metabolism and subsequent receptor binding of active hormone. Experiments reported here focused on aromatization and the nuclear accumulation of estrogen receptors. Adult male hamsters were maintained for 6-12 wk in long (14:10 LD) or short (8:16 LD) daily photoperiods. Both intact and castrated animals were used to assess direct effects of short days versus changes due to short-day-induced testicular regression. Discretely dissected regions of the brain (preoptic area, POA; hypothalamus, HTH; and corticomedial amygdala, CMA) or limbic blocks (LIM) comprised of all three regions were assayed for estrogen-synthesizing activity (aromatase) and estrogen-binding activity (receptors). Aromatase was estimated in vitro by conversion of [7-(3)H] androstenedione to [3H] estrogen and in vivo by measuring increases in nuclear estrogen receptor levels after injection of aromatizable androgen. Receptor-binding activity was assayed in crude cytosolic and nuclear extracts by incubating samples with [3H] estradiol +/- 100-fold excess inert estradiol, and separating free and bound steroids by Sephadex LH-20 gel filtration. When aromatase was assayed in homogenates prepared from discrete brain regions of individual hamsters, significantly lower activity was found in the HTH of short-day animals than in long-day controls. This effect was seen in both intact and castrated animals, which indicates that it was not mediated by the testis. Decreased enzyme activity in the POA and CMA of short-day hamsters was not significant, nor was there an effect of castration independent of short days. Low levels of nuclear estrogen receptors were present in LIM of intact males, but these were reduced after castration or concomitant with testicular regression after short-day exposure. This suggests that the hamster testis normally secretes estrogen or aromatizable androgen. A single injection of estradiol or aromatizable androgen (T or androstenedione) increased nuclear receptors in LIM of castrated animals. Cytosolic receptors were not different in short-day vs. long-day hamsters, nor were there differences in nuclear receptor levels after a single estradiol injection.(ABSTRACT TRUNCATED AT 400 WORDS)     

Effect of steroid milieu on gonadotropin-releasing hormone-1 neuron firing pattern and luteinizing hormone levels in male mice

GnRH neuronal function is regulated by gonadal hormone feedback. In males, testosterone can act directly or be converted to either dihydrotestosterone (DHT) or estradiol (E2). We examined central steroid feedback by recording firing of green fluorescent protein (GFP)-identified GnRH neurons in brain slices from male mice that were intact, castrated, or castrated and treated with implants containing DHT, E2, or E2 + DHT. Castration increased LH levels. DHT or E2 alone partially suppressed LH, whereas E2 + DHT reduced LH to intact levels. Despite the inhibitory actions on LH, the combination of E2 + DHT increased GnRH neuron activity relative to other treatments, reflected in mean firing rate, amplitude of peaks in firing rate, and area under the curve of firing rate vs. time. Cluster8 was used to identify peaks in firing activity that may be correlated with hormone release. Castration increased the frequency of peaks in firing rate. Treatment with DHT failed to reduce frequency of these peaks. In contrast, treatment with E2 reduced peak frequency to intact levels. The frequency of peaks in firing rate was intermediate in animals treated with E2 + DHT, perhaps suggesting the activating effects of this combination partially counteracts the inhibitory actions of E2. These data indicate that E2 mediates central negative feedback in males primarily by affecting the pattern of GnRH neuron activity, and that androgens combined with estrogens have a central activating effect on GnRH neurons. The negative feedback induced by E2 + DHT to restore LH to intact levels may mask an excitatory central effect of this combination.     

Regulation of pro-gonadotropin-releasing hormone gene expression by sex steroids in the brain of male and female rats

The fine modulation of gonadotropin gene expression and secretion is well recognized to be regulated by sex steroids through their direct action both at the anterior pituitary level and on the pulsatile pattern of GnRH secretion at the hypothalamic level. Since the influence of sex steroids on hypothalamic GnRH mRNA levels remains to be elucidated, quantitative in situ hybridization was used to study the effect of sex steroids on cellular levels of pro-GnRH mRNA in adult rats of both sexes. The effects of 14-day gonadectomy as well as administration of 17 beta-estradiol (E2, 0.25 micrograms) or dihydrotestosterone (DHT, 100 micrograms) twice a day during 14 days to gonadectomized animals were evaluated. In addition, the effect of progesterone (P, 2 mg, twice daily) alone or in the presence of E2 was also studied in ovariectomized animals. Hybridization was performed using a 35S-labeled cDNA probe encoding rat pro-GnRH and the corresponding mRNA levels were assessed by counting the number of silver grains overlying labeled neurons. In male rats, castration induced a highly significant 65% increase (compared to intact rats) in the mean number of grains per neuron. Administration of E2 or DHT to castrated animals completely prevented the post castration rise in pro-GnRH mRNA levels. In female animals, the effect of ovariectomy was less striking than in the male, a 25% increase (P less than 0.001) being observed. Treatment with E2 or DHT also completely prevented the increase in pro-GnRH mRNA levels induced by ovariectomy. Moreover, treatment with P in ovariectomized animals markedly potentiated the inhibitory effect of E2 on pro-GnRH mRNA levels.(ABSTRACT TRUNCATED AT 250 WORDS)     

Castration inhibits exercise-induced accumulation of Hsp70 in male rodent hearts

Intense exercise leads to accumulation of the inducible member of the 70-kDa family of heat shock proteins, Hsp70, in male, but not female, hearts. Estrogen is at least partially responsible for this difference. Because androgen receptors are expressed in the heart and castration leads to decreases in calcium regulatory proteins and altered cardiac function, testosterone (T) or its metabolites could also be involved. We hypothesized that removal of endogenous T production through castration would reduce cardiac Hsp70 accumulation after an acute exercise bout, whereas castrated animals supplemented with 5alpha-dihydrotestosterone (DHT) would show the intact male response. Fifty-four 8-wk-old male Sprague-Dawley rats were divided into intact, castrated, or castrated + DHT groups (n = 18/group). At 11 wk of age, 12 animals in each group undertook a 60-min bout of treadmill running at 30 m/min (2% incline) while the remaining 6 in each group remained sedentary. At 30 min or 24 h after exercise (n = 6/time point), blood and hearts were harvested for analysis. Serum T was undetectable in castrated and DHT-treated castrated rats, whereas serum DHT was significantly reduced in castrated animals only (approximately 60% reduction) (P < 0.05). Although there were no differences in constitutive levels of Hsp70 protein, exercise significantly increased cardiac hsp70 mRNA and protein in intact and DHT-supplemented rats, but not in castrated animals (P < 0.05). To examine whether castration eliminated the ability to respond to stress, another six intact and six castrated animals were subjected to a 15-min period of hyperthermia (core temperature raised to 42 degrees C) and killed 24 h later. As opposed to exercise, castrated animals subjected to heat shock exhibited increases in Hsp70 above nonshocked (i.e., sedentary) animals, similarly to intact males (P < 0.05). These data suggest that androgens, in addition to estrogen, play a role in the sexual dimorphism observed in the stress response to exercise but not heat shock.     

Immunization against luteinizing hormone-releasing hormone fusion proteins does not decrease prostate cancer in the transgenic adenocarcinoma mouse prostate model

This study was undertaken to test the effect of immunization against luteinizing hormone-releasing hormone (LHRH) fusion proteins on the development and progression of prostate cancer in the transgenic adenocarcinoma mouse prostate (TRAMP) model. Two LHRH fusion proteins, ovalbumin with seven LHRH peptides (OV-LHRH-7), and thioredoxin with seven LHRH peptides (TH-LHRH-7) were used in a cocktail vaccine. Two groups of male TRAMP mice were immunized with the cocktail. Primary immunizations were at either 4 or 8 weeks of age. LHRH immunized mice (n=19) were compared with castrated (n=19) and intact mice (n=18) for testosterone concentration, tumor weight, and lifespan. Immunization against LHRH in the TRAMP mice resulted in significant production of antibodies to LHRH compared with surgically castrated and intact control mice. Testicular weight was significantly reduced in the LHRH immunized groups compared with intact control mice. Serum testosterone was reduced (P<0.05) in the immunized mice compared with intact control mice and was not different from that of castrated mice (P>0.05). Tumor weight was variable and inconsistent throughout all treatment groups. Lifespan was not increased by immunization against LHRH or castration. Intact control mice (lived the longest (227+/-11 days), whereas immunized mice lived 206+/-11 days and castrated mice lived 213+/-13 days. Tumors from immunized TRAMP mice appeared more aggressive than tumors of castrated and intact mice, as demonstrated by 35% expression of gross lung tumors in the immunized mice whereas none were observed in the castrated or intact TRAMP mice. Prostate cancer is initially dependent upon androgens for growth and development, but cells have the ability to escape androgen dependence and progress to an androgen independent state, which was evident in this study. The TRAMP mouse model immunized against LHRH may have utility in future studies and treatments of the androgen independent prostate cancer.     

A comparison of the effects of castration and 6-methylene progesterone, a 5 alpha-reductase inhibitor, on the rat ventral prostate

6-Methylene progesterone (6MP) is an irreversible in vitro kcat inhibitor of rat prostate 5 alpha-reductase, the enzyme which converts testosterone (T) to dihydrotestosterone (DHT). Treatment of adult rats with 6MP or diethylstilbestrol (DES) decreased the weight of the ventral prostate (VP) by 45%, while castration reduced it by 86%. Histologically, the 6MP-treated VP were indistinguishable from those of controls, while the VP from DES-treated rats showed fibrous stromal hypertrophy as in castrated rats. The prostatic hydroxyproline content, an index of collagen levels, was enhanced by castration or DES, but was not significantly increased by 6MP. Within 2 days of 6MP treatment, the 5 alpha-reductase activity was reduced by 46% and ornithine decarboxylase (ODC) activity was lowered by 27%. During this time the prostatic acid phosphatase activity increased 42% and remained elevated with continued exposure to 6MP up to 13 days. The castration-induced involution of the VP was accompanied by a reduction in serum T and an increase in serum luteinizing hormone (LH). 6MP had no effect on T and LH serum levels but reduced the DHT content within the VP by 64%. Our results indicate that the structure and secretory acid phosphatase activity of the VP are less sensitive to changes in the ratio of T:DHT than is cell proliferation. Thus, the relative amounts of DHT and T within the VP may prove to be more significant than the absolute amount of either androgen in controlling prostate growth or its attendant neoplasms.     

Sexual incentive motivation in male rats requires both androgens and estrogens

In Experiment 1 castrated male rats were implanted with a Silastic capsule containing either E or cholesterol (CHOL) 35 days after castration. They were then tested for sexual incentive motivation and copulatory behaviors every 5th day for 3 weeks. None of the treatments affected sexual incentive motivation. After the last test, all subjects were implanted with DHT-containing Silastic capsules, and tests continued for another 3 weeks. While E + DHT enhanced sexual incentive motivation and copulatory behavior, DHT alone failed to do so. In Experiment 2 the aromatase inhibitor fadrozole (F) was combined with testosterone (T). T restored all behaviors to the level seen in intact rats, and F significantly reduced these effects. In fact, T + F was not different from DHT. T and DHT restored the weight of the prostate and seminal vesicles to levels close to those of intact rats. In Experiment 3 a lower dose of E was employed. Also this dose of E failed to affect sexual incentive motivation while E + DHT restored it to the level of intact animals. Castration enhanced the serum concentrations of LH and FSH. E alone caused a marked reduction, and E + DHT brought both gonadotropins back to the level of intact animals. It was concluded that the doses of E and DHT employed in these experiments were within or close to the physiological range, and that such doses of E completely fail to enhance sexual incentive motivation in castrated animals. DHT has small or no effects. It appears that sexual incentive motivation and copulation require simultaneous stimulation of androgen and estrogen receptors.     

Effects of castration and androgen treatment on androgen-receptor levels in rat skeletal muscles.

The effects of castration and dihydrotestosterone (DHT) treatment on levels of skeletal muscle androgen receptor (AR) were examined in three groups of adult male rats: 1) intact normal rats, 2) rats castrated at 16 wk of age, and 3) rats castrated at 16 wk of age and given DHT for 1 wk starting at week 17. All animals were killed at 18 wk of age. Castration caused a decrease (P < 0.05) in the weights of the levator ani and bulbocavernosus muscles. The administration of DHT to the castrated rats increased (P < 0.05) the weights of the levator ani and bulbocavernosus muscles. Castration caused a significant downregulation of AR levels in the bulbocavernosus (P < 0.05) but had no significant effect on AR levels in the levator ani muscle. DHT administration to the castrated group upregulated AR levels in the bulbocavernosus and levator ani muscles. The plantaris muscle did not significantly (P > 0.05) change for any of the treatments. These findings suggest that the effects of castration and androgen replacement differentially affect skeletal muscle mass and AR levels.     

The prostate response to prolactin modulation in adult castrated rats subjected to testosterone replacement

Despite the androgenic dependence, other hormones, growth factors, and cytokines are necessary to support prostatic growth and maintain the glandular structure; among them, prolactin is a non-steroidal hormone secreted mainly by the pituitary gland. However, extra-pituitary expression of prolactin, such as in the prostate, has also been demonstrated, highlighting the paracrine and autocrine actions of prolactin within the prostate. Here, we investigated whether prolactin modulation alters ventral prostate (VP) morphophysiology in adult castrated rats. Sprague Dawley rats were castrated and after 21 days, divided into ten experimental groups (n?=?6/group): castrated control: castrated animals that did not receive treatment; castrated+testosterone: castrated animals that received T (4 mg/kg/day); castrated+PRL (PRL): castrated animals receiving prolactin (0.3 mg/kg/day); castrated+T+PRL: castrated animals that received a combination of testosterone and prolactin; and castrated+bromocriptine (BR): castrated animals that received bromocriptine (0.4 mg/kg/day). The control group included intact animals. The animals were treated for 3 or 10 consecutive days. At the end of experimental period, the animals were euthanized, and the blood and VP lobes were collected and analyzed by different methods. The main findings were that the administration of prolactin to castrated rats did not exert anabolic effects on the VP. Although we observed activation of downstream prolactin signaling after prolactin administration, this was not enough to overcome the prostatic androgen deficiency. Likewise, there was no additional glandular involution in the castrated group treated with bromocriptine. We concluded that despite stimulating the downstream signaling pathway, exogenous prolactin does not act on VP in the absence or presence of high levels of testosterone.     

Androgens are not major down-regulators of androgen receptor levels during growth of the immature rat penis

This study was undertaken to investigate the prevalent hypothesis that androgens are responsible for the organ-specific down-regulation of penile androgen receptors (ARs) and decline of penile growth in the rat during sexual maturation. Sexually immature male rats (21 days old) were castrated and treated for 3 days (“short-term”), with high doses of: (a) testosterone and the -reductase inhibitor finasteride (T/F); (b) dihydrotestosterone (DHT); or (c) finasteride alone (F). Intact and castrate controls received vehicle only. PolyA + RNA was analysed by Northern blot hybridization and ARs were estimated in the penis and ventral prostates by (3-H)R-1881 binding in the cytosol. Short-term castration, with or without F, increased penile AR mRNA, whereas high doses of T/F and DHT reduced it considerably. Although penile cytosol AR concentration in the control castrates, with or without F, paralleled the AR mRNA rise, treatment with androgens left cytosol AR content per organ and AR concentration above those of the intact rat penis despite the drop in AR mRNA. A “long-term” treatment (10 days) on 19-day-old rats with either medium or high doses of T/F and DHT also failed to down-regulate penile cytosol ARs below the intact controls. Western blot analysis of penile cytosol AR levels confirmed these results. Block of pituitary FSH and LH release by a GnRH antagonist in castrates receiving T/F or DHT at high doses did not modify the response. In the case of intact rats, high doses of T/F or DHT actually increased penile cytosol AR content. No difference was observed between T/F and DHT effects. In contrast to what occurs during sexual maturation, the prostate ARs and growth rate responded to all treatments in a similar way to what was observed in the penis. Our results suggest that increases in serum T or DHT are not major factors in the physiological down-regulation of ARs and androgen-dependent growth in the rat corpora cavernosa.     

Sexual behavior in male rats treated with estrogen in combination with dihydrotestosterone

Male rats castrated at 30 days of age were treated with estradiol benzoate (dose range: 0.05–50 μg EB for 26 days) and dihydrotestosterone (1 mg DHT for 36 days) as adults. The combined EB and DHT treatments resulted in display of male sexual behavior which did not differ from the behavior shown by intact untreated males or castrated, testosterone propionate (1 mg TP for 26 days) treated males. EB alone or DHT alone were relatively ineffective in activating male behavior in castrated males.     

Differential proliferative response of the ventral prostate and seminal vesicle to testosterone replacement

We have investigated epithelial cell proliferation and the rate of glandular recovery of the ventral prostate (VP) and seminal vesicle (SV) promoted by testosterone replacement (TR) in castration-induced regressed glands. Adult male Wistar rats were castrated and, after 21 days, they were treated with testosterone propionate (4 mg/kg/day). Intact (CT) and castrated rats without TR (CS) were also analysed. VP and SV were processed for histochemistry, morphometric-stereological analysis and immunocytochemistry to determine the PCNA index (PI). After 10 days of TR, the VP weight reached approximately 72% of the CT values, while the SV weight exceeded approximately 17% of the CT values. By the third day of TR, VP and SV presented a mean PI of 34% and 94% for distal region and 14% and 22% for proximal region, respectively. SV also had more luminal cells PCNA-positive than VP, mainly in the distal region. The PI values fell on days 5, 7 and 10, but were still higher than CT. These findings indicate that epithelial cells from involuted SV are more responsive to TR than those from VP when stimulated to proliferate and replace the luminal cell population, suggesting a different mechanism regulating cell proliferation in response to androgenic stimuli.     

Short duration testosterone infusions maintain male sex behavior in Syrian hamsters

In most mammalian species, reduced androgen availability is associated with marked reductions in male sexuality; conversely, androgen replacement in castrated males restores sex behavior within a few weeks. Testosterone (T) pulse duration, amplitude, frequency, and inter-pulse interval may be as important as total amount of hormone in determining target tissue responsiveness. We remain ignorant of the number and duration of daily T pulses necessary and sufficient to sustain male mating behavior. An in-dwelling infusion system was employed to vary T-pulse frequencies and durations. Daily 4 h infusions of aqueous T (100 microg/0.064 ml) and twice daily 4 h pulses of T (each 50 microg/0.064 ml) were sufficient to maintain ejaculatory behavior of sexually experienced castrated hamsters for 11 weeks post-castration; castrated hamsters infused with vehicle ceased to display the ejaculatory pattern 3 weeks after gonadectomy. Circulating T concentrations of hormone-infused hamsters declined markedly 7 h after the termination of each infusion. These results establish that male sex behavior can be sustained with infusions of relatively low T concentrations for 4 h/day and suggests that the basal concentrations of T sustained by the gonad during inter-pulse intervals may not be necessary for maintenance of sex behavior. 4 h T infusions were sufficient to maintain penile and seminal vesicles weights, but not ventral prostate weights or flank gland dimensions; the threshold for maintaining male sex behavior is lower than that for some androgen-dependent peripheral structures. Development of effective androgen replacement regimens that sustain sex behavior in castrated animals may be useful in the design of androgen replacement therapy for hypogonadal men.     

Effects of elevated gonadotropin levels on thyroid function in the male rat

In order to determine if thyroid disease in hypogonadal men is the result of chronic elevation of serum gonadotropins, thyroid histology and serum thyroid hormone levels were evaluated in male rats that had been castrated either 2 weeks or 15 months previously. Despite significantly elevating serum LH levels, castration did not affect thyroid structure or function. Serum total T4 levels were reduced with age in both short and long-term castrate animals but returned to the levels seen in young rats when testosterone was replaced. Testosterone replacement also increased free T4 levels in both the young and old castrate rats. Neither age nor testosterone replacement affected serum T3 or TSH levels.     

Delay in the age of balano-preputial skinfold cleavage and alterations in serum profiles of testosterone, 5 alpha-androstane-3 alpha,17 beta-diol, and gonadotropins in adult rats treated during puberty with luteinizing hormone releasing hormone

Previous work has shown that chronic treatment of intact, immature male rats with luteinizing hormone releasing hormone (LHRH) decreases sex accessory gland weights and results in retardation of the normal developmental increase in the ratio of serum testosterone (T)/5 alpha-androstane-3 alpha,17 beta-diol (3 alpha-Diol) via an apparent enhancement of testicular 5 alpha-reductase or 3 alpha-hydroxysteroid oxidoreductase activities. In the present work, androgen dependent balano-preputial skinfold cleavage was significantly delayed by approximately one week in intact, immature male rats which were treated daily for two weeks with either 1.0 micrograms, 2.5 micrograms or 5.0 micrograms of LHRH during a discrete phase of pubertal development (28-41 days of age). In intact, adult (62 day old) animals which received LHRH treatments during pubertal development, serum T concentrations and sex accessory gland weights were reduced compared to control animal values. Serum 3 alpha-Diol content in the adult rats was either unaltered or increased significantly depending on the LHRH dosage employed during sexual development. Serum luteinizing hormone concentrations were not different between control and LHRH-pretreated adult rats whereas the highest dosage of LHRH employed (5.0 micrograms) during puberty resulted in a significant elevation of adult serum follicle stimulating hormone levels. It is suggested that chronic LHRH treatment of the male rat during puberty results in a perturbation in testicular androgen biosynthetic activities and an impairment of pituitary-testicular hormone feedback mechanisms which persist at least through early adulthood.     

Inhibitory control of the pituitary LH secretion by LH-RH in male rats.

Luteinizing hormone-releasing hormone (LH-RH) was administered to prepubertal male rats (intact, castrate or castrate-adrenalectomized, 60 g body weight) for 28 days (1 microgram LH-RH/day, s.c.), at a 10-fold physiological dose, as compared to the minimal FSH-releasing dose of 100 ng/rat s.c. In intact rats, serum LH and weight of androgen-dependent organs (vented prostate, seminal vesicles) were reduced after 14 days of treatment. In castrate rats, the postcastration rise in serum LH was abolished by treatment. Pituitary LH content, FSH secretion and prolactin secretion were not suppressed. Hypothalamic LH-RH was increased at 14 and 21 days. In castrate adrenalectomized male rats, LH secretion was also suppressed by 1 microgram LH-RH s.c. x 28 days. The hypothalamic LH-RH content did not increase. The pituitary LH-RH receptor level was not down-regulated after 14 days treatment either in intact or castrate male rats. Pituitary inhibition (LH release) in rats by a supraphysiological dose of LH-RH given for 28 days indicates that the optimal regime for chronic treatment has to be determined by monitoring LH release at regular intervals. Direct pituitary inhibition by LH-RH may explain some of the unexpected antifertility effects observed with high doses of LH-RH.     

Effects of testosterone and estradiol on ventral prostate and body weights of castrated rats

Administration of 100 μg of testosterone (T) daily for 14 and 28 days to 7-day castrate rats restored the weight of the ventral prostate to a level which slightly exceeded that of the controls. Ventral prostate weight in groups receiving estradiol-17β (E₂) doses of 10, 50, 100, 200, or 500 μg administered simultaneously with 100 μg of T did not differ significantly from intact controls, although the weights were lower at E₂ levels greater than 100 μg. Body weights of the castrated rats receiving 100 μg of T did not differ from those of sham castrated controls. However, mean body weights of all groups which received E₂ (10 to 500 μg) simultaneously with 100 μg of T were significantly less than (p< .025 or less) those of the sham castrated controls. Analysis of normalized ventral prostate weights, i.e., mg ventral prostate/100 gm body weight, showed that E₂ does not antagonize T and revealed a trend which suggested that low levels of E₂ (10, 50 and 100 μg) may have enhanced the restorative effects of 100 μg T. Our data indicate that 100 μg of T approaches a physiological dosage for castrated rats and that in contrast to the possible enhancement of its restorative effects on the ventral prostate by low leve E₂, its body weight stimulating effects are clearly impaired by E₂.