Transplanted XY germ cells produce spermatozoa in testes of XXY mice.

XXY mouse has been characterized as an experimental model for men with Klinefelter's syndrome (XXY male phenotype). To test whether donor XY germ cells could proliferate and differentiate in the XXY testicular environment, donor testicular cells from adult (2-3 months old) and immature (10 days old) XY green fluorescence protein (GFP) transgenic mice were transplanted into the seminiferous tubules of adult (4-7 months old) and young (6 weeks old) XXY recipient mice respectively. Twelve weeks after transplantation, GFP positive spermatogonia were found in 21.74% (five out of 23) of adult XXY recipients who received adult donor cells. The GFP positive segments of seminiferous tubules were observed in 44.44% (four out of nine) young XXY recipients who received donor cells from 10 days old GFP mice. We found using immunohistochemistry and cell morphology that donor-derived GFP positive germ cells were spermatogonia, spermatocytes, round spermatids and spermatozoa in some of the seminiferous tubules of young XXY recipient mice. The results demonstrated that the donor XY germ cells were able to qualitatively complete spermatogenesis in some of the seminiferous tubules of XXY mice.

Male contraception; synergism of gonadotropin-releasing hormone analog and testosterone in suppressing gonadotropin.

Long-term administration of either superactive analog's of gonadotropin-releasing hormone or of testosterone suppresses gonadotropin secretion in male animals and humans. Testosterone administered in combination with gonadotropin-releasing hormone analog further suppresses serum gonadotropin levels in male rats. This observation indicates synergistic activity and suggests that the gonadotropin-releasing hormone analog and testosterone act at independent sites within the hypothalamic-pituitary axis. The primary actions of superactive analog are probably mediated by changes at a postreceptor site in the pituitary gonadotropin-secreting cells.

Pituitary receptor site blockade by a gonadotropin-releasing hormone antagonist in vivo: mechanism of action.

Administration of a potent gonadotropin-releasing hormone (GnRH) antagonist [Nac-L-Ala1,pCl-D-Phe2,D-Trp3,6]GnRH as a single subcutaneous injection to castrated adult male rats reduced, by more than 90 percent, both serum luteinizing hormone concentrations and specific pituitary GnRH receptor binding. This effect persisted for 24 hours. The dissociation rate of the antagonist from pituitary membrane homogenates was fourfold slower than the dissociation rate of a potent agonist. The prolonged in vivo inhibition of pituitary GnRH receptor binding and luteinizing hormone secretion by the GnRH antagonist may be mediated by the slower dissociation rate of the antagonist from its specific pituitary membrane receptor site.

Combined nestorone-testosterone gel suppresses serum gonadotropins to concentrations associated with effective hormonal contraception in men.

BACKGROUND: Novel male-based contraceptives are needed to broaden family planning choices. A progestin, Nestorone® (Nes) gel, plus a testosterone (T) gel suppresses sperm concentrations to levels associated with effective contraception in normal men. However, administration of two gels on different parts of the body daily is impractical. OBJECTIVE: Compare the effectiveness of daily application of a single, combined 8.3 mg Nes-62.5 mg T gel (Nes-T) vs. 62.7 mg T gel to suppress serum FSH and LH concentrations to ≤1.0 IU/L (a threshold associated with suppression of sperm concentrations to ≤1 million and effective contraception) and to compare the pharmacokinetics of serum Nes and T concentrations between the gel groups. DESIGN: We conducted a 28-day, double-blind, controlled trial of 44 healthy men randomized to daily Nes-T or T gel with measurement of hormones at baseline, treatment, and recovery and during 24-h pharmacokinetic studies on days 1 and 28 of treatment. RESULTS: Of the subjects who met pre-defined inclusion criteria, 84% of the Nes-T group suppressed serum gonadotropin concentrations to ≤1.0 IU/L at days 21-28 vs. 16.7% in the T group (p < 0.001). On day 1, Nes concentrations rose significantly above baseline by 2 h and continued to rise up to 24 h after Nes-T gel application. Nes concentrations were not detectable in the T group. Serum total T concentrations rose and were significantly higher in the T gel group compared to the Nes-T group at 24 h on day 1 and days 11, 14, and 21 (p < 0.01). There were no serious adverse events in either group. About 80% of the subjects reported satisfaction with both gels. CONCLUSION: Daily Nes-T gel effectively and safely suppresses serum gonadotropins and is acceptable to most men. It should be studied further in efficacy trials of hormonal male contraception.

Preventing secondary exposure to women from men applying a novel nestorone/testosterone contraceptive gel.

BACKGROUND: Testosterone (T)/Nestorone (NES) combination gel is a potential transdermal male contraceptive that suppresses gonadotropins and spermatogenesis. Transfer of transdermal T from men to women can be prevented by washing or covering application sites with clothing. OBJECTIVES: We hypothesized that showering or wearing a shirt over gel application sites would prevent secondary exposure of T and NES to a woman after close skin contact. MATERIALS AND METHODS: Twelve healthy male and 12 healthy female participants were recruited. Men applied T/NES 62 mg/8 mg gel to their shoulders and upper arms. Two hours after application, female partners rubbed the application site for 15 min. Exposure in the female partner was assessed under three conditions: a shirt covered the application site; the man showered prior to skin contact; or without intervention to reduce transfer. Serum T and NES concentrations were measured by LC-MS/MS in serial blood samples for 24 h after gel exposure. MAIN OUTCOMES: Change in female serum T and NES levels as measured by average concentration over 24 h (Cavg ). RESULTS: Median female serum T Cavg was 23.9 ng/dL (interquartile range, 19.3, 33.9) with the shirt barrier and 26.7 ng/dL (20.7, 33.9) after showering, which was higher than baseline 20.9 ng/dL (16.7, 25.0), both p < 0.03) but lower than without intervention (58.2 ng/dL [30.9, 89.1], both p < 0.01). Female serum NES Cavg and maximum concentration were below the lower limit of quantification with the shirt barrier and after showering, but increased without intervention in six of 12 women (maximum concentration <60 pg/mL). Men had lower average serum NES levels after showering (47 pg/ml [20, 94] compared to no intervention (153.3 pg/mL [51, 241], p < 0.02). CONCLUSION: Secondary transfer of T and NES occurs after intensive skin contact with the gel application site. Secondary transfer is decreased by a shirt barrier or showering before contact.

Mechanisms of gonadotropin-releasing hormone agonist action in the human male.

Agonist analogs of GnRH are being increasingly utilized to induce medical castration for treatment of a variety of hormonally responsive clinical disorders. However, the mechanism/s of their paradoxical antigonadal action in the human male remain poorly understood. Basal and integrated concentrations of immunoreactive LH after intermediate term (4-16 weeks) GnRH agonist treatment are only modestly decreased and cannot fully account for the far greater decline in serum testosterone (T) concentrations. Bioassayable LH concentrations, however, decrease markedly and parallel the fall in serum T suggesting secretion of qualitatively different LH species with diminished biological activity while the circulating concentrations of beta-subunit parallel the measured bioassayable LH concentrations, free alpha-subunit secretion remains persistently and disproportionately elevated during chronic GnRH agonist treatment. Cross-reactivity of free alpha-subunits in the human LH RIA contributes to this disparity between the LH immuno and bioactivity. Chromatography of serum LH during GnRH agonist treatment suggests secretion of a qualitatively different LH species. Unlike the rat, in which the antifertility effects of the agonist are mediated predominantly by direct inhibition of testicular steroidogenesis, significant direct gonadal effects have not been demonstrated in man. Thus the bulk of evidence points to a predominant pituitary site of action in the human male. The molecular basis of the heterogeneity of LH during GnRH agonist, however, remains to be elucidated. The hypothesis that co- or posttranslational modification by the agonist may attenuate biologic activity of LH has not yet been directly tested.

Male sexual function and its disorders: physiology, pathophysiology, clinical investigation, and treatment.

This review is designed to help the reproductive endocrinologist integrate his or her professional activity with those of other disciplines including urology, radiology, neurology, and psychology in order to successfully manage all of the inseparable aspects of male sexual and reproductive functioning. Significant advances in the field of male sexual physiology and pathophysiology and new methods of investigation and treatment of male sexual disorders are outlined. The review synthesizes available data on the following: norms of sexual organs, aging and sexuality, role of central and peripheral neurochemicals in each stage of the sexual cycle, role of corporeal smooth muscles in the hemodynamic control of erection and detumescence, influence of psychological factors, drugs, and disease on all aspects of sexual functioning, and use of nocturnal penile tumescence monitoring, imaging investigations, and neurophysiologic studies in the diagnostic workup of males with sexual dysfunction. Clinical algorithms are presented where appropriate. Extensive discussions on newly developed strategies in psychological and behavioral counseling, drug therapy, tissue engineering, nonsurgical devices, and surgical treatments for all forms of sexual disorders are also provided. Lastly, the effect of sexual dysfunction and its treatment on quality of life in affected men is addressed, along with recommendations for future research endeavors.

Comparison of the single dose pharmacokinetics, pharmacodynamics, and safety of two novel oral formulations of dimethandrolone undecanoate (DMAU): a potential oral, male contraceptive.

Dimethandrolone (DMA, 7α,11ß-dimethyl-19-nortestosterone) has both androgenic and progestational activities, ideal properties for a male hormonal contraceptive. In vivo, dimethandrolone undecanoate (DMAU) is hydrolyzed to DMA. We showed previously that single oral doses of DMAU powder in capsule taken with food are well tolerated and effective at suppressing both LH and testosterone (T), but absorption was low. We compared the pharmacokinetics and pharmacodynamics of two new formulations of DMAU, in castor oil and in self-emulsifying drug delivery systems (SEDDS), with the previously tested powder formulation. DMAU was dosed orally in healthy adult male volunteers at two academic medical centers. For each formulation tested in this double-blind, placebo-controlled study, 10 men received single, escalating, oral doses of DMAU (100, 200, and 400 mg) and two subjects received placebo. All doses were evaluated for both fasting and with a high fat meal. All three formulations were well tolerated without clinically significant changes in vital signs, blood counts, or serum chemistries. For all formulations, DMA and DMAU showed higher maximum (p < 0.007) and average concentrations (p < 0.002) at the 400 mg dose, compared with the 200 mg dose. The powder formulation resulted in a lower conversion of DMAU to DMA (p = 0.027) compared with both castor oil and SEDDS formulations. DMAU in SEDDS given fasting resulted in higher serum DMA and DMAU concentrations compared to the other two formulations. Serum LH and sex hormone concentrations were suppressed by all formulations of 200 and 400 mg DMAU when administered with food, but only the SEDDS formulation was effectively suppressed serum T when given fasting. We conclude that while all three formulations of oral DMAU are effective and well tolerated when administered with food, DMAU in oil and SEDDS increased conversion to DMA, and SEDDS may have some effectiveness when given fasting. These properties might be advantageous for the application of DMAU as a male contraceptive.

The structural brain correlates of cognitive deficits in adults with Klinefelter's syndrome.

CONTEXT: Adults with Klinefelter's syndrome (KS) are known to present disturbances of language skills and delayed learning abilities. OBJECTIVES: The aim of this study was to assess brain morphometry in KS and to correlate eventual volumetric changes with performance on neuropsychological tests. PATIENTS: Patients included 18 KS adults and 20 age-matched controls. METHODS: All participants underwent prospectively double-spin-echo brain magnetic resonance imaging and neuropsychological testing of verbal and nonverbal domains. On the axial stack of magnetic resonance imaging slices, regional brain volumes were measured either by automated segmentation (full brain, total cerebrospinal fluid, and ventricular volume) or manual drawing with help of a neuroanatomy atlas (frontal, temporal, and parietal lobes, gray matter component of the lobes, cerebellar hemispheres, and hippocampal complexes). RESULTS: KS patients performed significantly lower than controls on language-related tasks exploring verbal processing speed and verbal executive function. They were diagnosed with significant enlargement of ventricular volume and bilateral reduction of cerebellar hemispheres. Furthermore, after separation of participants according to handedness and after correction of regional brain volumes for atrophy, a significant reduction of left temporal lobe volume was found in KS compared with controls. Ventricular volume was inversely correlated with cognitive function, whereas left temporal lobe volume was positively correlated with language-related tasks. CONCLUSION: This study hypothesizes that supernumerary X-chromosome and/or congenital hypogonadism provoke structural alterations in the subcortical pathways involved in language processing, thus providing a neurobiological substrate for cognitive deficits in KS.

Humanin protects against chemotherapy-induced stage-specific male germ cell apoptosis in rats.

Humanin (HN) has cytoprotective action on male germ cells after testicular stress induced by heat and hormonal deprivation. To examine whether HN has protective effects on chemotherapy-induced male germ cell apoptosis, we treated four groups of adult rats with (i) vehicle (control), (ii) HN, (iii) cyclophosphamide (CP); or (iv) HN+CP. To investigate whether the protective effects of HN on germ cells require the presence of Leydig cells, another four groups of rats were pre-treated with ethane dimethanesulfonate (EDS), a Leydig cell toxicant, to eliminate Leydig cells. After 3 days, when Leydig cells were depleted by EDS, we administered: (i) vehicle, (ii) HN, (iii) CP; or (iv) HN+CP to rats. All rats were killed 12 h after the injection of HN and/or CP. Germ cell apoptosis was detected by TUNEL assay and quantified by numerical count. Compared with control and HN (alone), CP significantly increased germ cell apoptosis; HN +CP significantly reduced CP-induced apoptosis at early (I-VI) and late stages (IX-XIV) but not at middle stages (VII-VIII) of the seminiferous epithelial cycle. Pre-treatment with EDS markedly suppressed serum and intratesticular testosterone (T) levels, and significantly increased germ cell apoptosis at the middle (VII-VIII) stages. CP did not further increase germ cell apoptosis in the EDS-pre-treated rats. HN significantly attenuated germ cell apoptosis at the middle stages in EDS pre-treated rats. To investigate whether HN has any direct effects on Leydig cell function, adult Leydig cells were isolated and treated with ketoconazole (KTZ) to block testosterone synthesis. HN was not effective in preventing the reduction of T production by KTZ in vitro. We conclude that HN decreases CP and/or EDS-induced germ cell apoptosis in a stage-specific fashion. HN acts directly on germ cells to protect against EDS-induced apoptosis in the absence of Leydig cells and intratesticular testosterone levels are very low.

The role of hypothalamic adrenergic receptors in preventing testosterone-induced androgenization in the female rat brain.

Androgenization of the female neonatal rat brain by testosterone and the subsequent development of persistent estrus in the adult can be blocked by drugs which interfere with normal hypothalamic neuronal function. The mechanism of action of these drugs was studied. A 25-micrograms dose of testosterone propionate at 5 days of age produced a 69% incidence of persistent estrus at 90 days of age. alpha-Methyl-p-tyrosine given with testosterone propionate resulted in an 81% incidence of persistent estrus. Therefore, hypothalamic norepinephrine depletion did not prevent androgenization. Tyramine (100 micrograms) inhibited androgenization to an incidence of 27% by 90 days. Phenoxybenzamine (50 micrograms) and phentolamine (50 micrograms) each reduced the incidence to 0%. Combining the beta-antagonist propranolol with phenoxybenzamine or phentolamine reversed the block in androgenization, resulting in 37% and 50% incidences of persistent estrus, respectively. Tyramine causes the release of neuronal stores of norepinephrine which is turn stimulates alpha- and beta-adrenergic receptors. The action of tyramine implicates adrenergic stimulation as a mechanism for the inhibition of androgenization, but does not define which receptor type is involved. In addition to postsynaptic alpha-blockade, phenoxybenzamine and phentolamine can cause presynaptic alpha-blockade, resulting in increased neuronal norepinephrine release and beta-stimulation. When the beta-antagonist propranolol was added to the alpha-antagonists, the block in androgenization was reversed. Therefore, we conclude that beta-adrenergic receptor stimulation prevents androgenization of the neonatal rat brain.

Gonadotropin-releasing hormone analog and testosterone synergistically inhibit spermatogenesis.

We recently demonstrated that superactive gonadotropin-releasing hormone (GnRH) analogs and testosterone synergistically suppress gonadotropin secretion in castrate rats. We proposed that these two classes of agents used in combination would lead to enhanced suppression of spermatogenesis by synergistically inhibiting gonadotropin secretion. This hypothesis was tested in the present study in which synergistic inhibition of spermatogenesis was produced by combined analog and testosterone treatment. The mechanism of the synergistic action observed differed from that hypothesized in that the analog had both primary inhibitory actions directly on the testis and effects at a pituitary level. The addition of testosterone to the regimen further inhibited spermatogenesis by decreasing the secretion of gonadotropins thereby attenuating the compensatory rise in LH and FSH secretion expected with direct analog inhibition of the testis. These studies demonstrate the potential of combined GnRH analog and testosterone administration as a male contraceptive agent and indicate the complexity of their synergistic interactions.

The interaction between beta-endorphin and gonadal steroids in regulation of luteinizing hormone (LH) secretion and sex steroid regulation of LH and proopiomelanocortin peptide secretion by individual pituitary cells.

Reported studies using the conventional pituitary cell culture technique suggest that beta-endorphin (B-EP) produced locally in the pituitary or reaching it from the hypothalamus acts in conjunction with estradiol (E2) to initiate and in conjunction with progesterone (P4) to terminate the midcycle surge of LH. In addition, the reverse hemolytic plaque assay (RHPA) was used to investigate the effects of E2 and P4 on the secretory activity of individual pituitary cells. The results of these experiments indicate that 1) E2 enhances the secretion of LH, ACTH, and B-EP by individual pituitary cells; 2) E2 increases the number of secreting cells for each of the three hormones; 3) the rise in B-EP and ACTH secretion antecede that of LH; 4) P4 augments ACTH and B-EP secretion by individual pituitary cells; and 5) P4 has dual effects, acutely (1 h) potentiating LH secretion from already active cells and subsequently (8 h) recruiting cells that formerly had little or no secretory activities. Collectively, the above studies support a role for steroid hormones in regulation of midcycle LH secretion at the pituitary level. The results also suggest that intrapituitary (paracrine/autocrine) and extrapituitary (endocrine) B-EP modulates gonadal steroid effects on LH secretion by pituitary gonadotrophs.

Time course of recovery of spermatogenesis and Leydig cell function after cessation of gonadotropin-releasing hormone antagonist treatment in the adult rat.

This study examined the time course of recovery of spermatogenesis and its relationship to the temporal changes in circulating levels of gonadotropin and testosterone (T) and intratesticular T levels after cessation of treatment with a potent GnRH antagonist (GnRH-A). Adult male rats were given a daily sc injection of Nal-Glu-GnRH antagonist (1250 micrograms/kg BW) for 4 weeks and killed in groups of five 0, 1, 2, 3, 4, and 6 weeks after discontinuation of treatment. After cessation of treatment, plasma FSH levels returned to control values by 6 weeks, whereas LH levels returned to control values within 1 week. Both circulating as well as intratesticular levels of T returned to normal levels by 3 and 4 weeks, respectively. Interestingly, a rebound in both FSH and intratesticular T, but not in plasma T, beyond control levels occurred early in the recovery phase. The total volume of Leydig cells, which was only 15% of control values, increased 4.3-fold within 1 week and was not significantly different from control values (92% recovery) by 2 weeks posttreatment. Enumeration of earlier phases of germ cells as well as homogenization-resistant advanced (steps 17-19) spermatids revealed a progressive increase in germ cell numbers with time. Complete restoration of the numbers of preleptotene spermatocytes, pachytene spermatocytes, step 7 spermatids, and advanced spermatids occurred 1, 3, 4, and 6 weeks, respectively, after termination of GnRH-A treatment. There was also a complete reversal of GnRH-A-induced changes in testicular weight, tubule diameter, and volume of seminiferous tubules and their lumens by 6 weeks posttreatment, paralleling the recovery of spermatogenesis. These results suggest that 1) complete recovery of spermatogenesis and various other testicular parameters can be achieved in GnRH-A-treated rats after cessation of treatment; 2) the progression of various germ cells during the recovery period follows the normal time schedule of germ cell development; and 3) the recovery of spermatogenesis is preceded by supranormal levels of FSH and intratesticular T. These findings further emphasize the suitability of antagonistic analogs of GnRH for male fertility control.

The effect of hypothalamic catecholamine synthesis inhibition by alpha-methyltyrosine on gonadotropin secretion during sexual maturation in the male Wistar rat.

alpha-Methyl-p-tyrosine (AMPT), a competitive inhibitor of tyrosine hydroxylase, was used to block the synthesis of hypothalamic catecholamines in six different age groups (15, 23, 30, 38, 56, and 72 days of age) in both intact and castrated male rats. Castrated rats received testosterone-filled Silastic capsules of various lengths to give four graded serum concentrations of testosterone in each age group. Intact and castrate animals of all ages were killed 1 week after the castrate group was orchiectomized and outfitted with Silastic capsules. On the day of death, 250 mg/kg BW AMPT base were given ip at zero time, and a second dose (125 mg/kg BW) was given 2 h after the first injection. Rats were killed at zero time and 2 and 4 h after the first AMPT injection. Serum was collected for LH, FSH, and testosterone determinations. AMPT had marked biphasic effects on LH and T secretion, causing both to increase (less than 70% above basal) in the intact immature rats (15 and 23 days of age) and fall (greater than 60% below basal) in the mature rats (38, 56, and 72 days of age). LH increased (up to 307%) in the castrated immature rats in response to AMPT, but no change occurred in the mature castrated rats until moderate concentrations of testosterone were present (1000-2000 pg/ml). Then, LH, as in intact rats, decreased (up to 90%) during exposure to AMPT. These data suggest that the ratio of stimulatory and inhibitory effects of hypothalamic norepinephrine and dopamine changes during sexual maturation, with inhibitory effects predominating in the prepubertal rat.

Temporal and stage-specific effects of recombinant human follicle-stimulating hormone on the maintenance of spermatogenesis in gonadotropin-releasing hormone antagonist-treated rat.

Despite considerable attention to the hormonal regulation of spermatogenesis, the role of FSH in adult mammals remains controversial. This is mainly due to the unavailability until recently of FSH preparations free of contaminating LH and discrepant results in various species. Using LH-free recombinant human FSH (rhFSH), we sought to determine if FSH is able to maintain spermatogenesis in rats in which both LH and FSH, but not other pituitary hormones, are markedly suppressed by GnRH-A treatment. Groups of five adult SD rats were given daily sc injections of vehicle, Nal-Glu-GnRH-A (1.25 mg/kg BW) or GnRH-A + 10 IU rhFSH for up to 4 weeks. In agreement with our previous report, GnRH-A treatment for 1 week led to a significant (P < 0.05) reduction in testis weight (26.6%) and in the number of specific germ cells involving preleptotene (27.7%) and pachytene spermatocytes (36.7%) and step 7 spermatids (30.3%) at stage VII of the seminiferous epithelial cycle. The number of advanced spermatids declined by 44.3%. Concomitant administration of rhFSH for 1 week resulted in a significant increase in testicular weight, tubular areas at stage VII-VIII, and in the absolute volumes of seminiferous tubules and their lumens compared to GnRH-A alone. Most importantly, FSH replacement to GnRH-A-treated rats fully attenuated the early (1 week) GnRH-A-induced reduction in germ cell numbers at stage VII as well as the number of advanced (steps 17-19) spermatids, and effectively prevented GnRH-A-induced reduction in the number of pachytene spermatocytes and step 7 spermatids for 2 weeks. In addition, FSH replacement to GnRH-A-treated rats was able to increase the number of B spermatogonia available for entry into meiosis and maintain the number of preleptotene spermatocytes throughout the treatment period. The observed beneficial effects of rhFSH on spermatogenesis in GnRH-A-treated rats are most likely not due to the stimulation of the Leydig cell function (via paracrine interaction between Sertoli and the Leydig cells), because FSH addition to GnRH-A had no discernible effect on intratesticular or plasma T levels, accessory organs weight, and the total volume of the Leydig cells when compared with GnRH-A alone.(ABSTRACT TRUNCATED AT 400 WORDS)

Serum gonadotropins in rats fed a low-valine diet.

Female rats fed a low-valine diet from the time of weaning have been shown to have delayed puberty compared to growth-matched controls. To explore the mechanism of this delay, serum LH and FSH were measured in rats fed the low-valine diet and in growth-matched control rats at several ages prior to puberty. Hormonal determinations at each time point were made both in the basal state and after LHRH administration or castration. After age 27 days, the mean basal serum FSH was lower in the low-valine group than in the control group. The mean serum levels of LH and FSH after oophorectomy were significantly lower in the low-valine group than in the control group, although the mean serum levels of LH and FSH after LHRH administration to intact animals were similar in both groups. The combination of impaired response to castration with unimpaired pituitary response to LHRH suggests that the low-valine group had a hypothalamic defect which accounts for their delayed sexual maturation when compared to growth-matched animals.

Regulation of alpha and rat luteinizing hormone-beta messenger ribonucleic acids during gonadotropin-releasing hormone agonist treatment in vivo in the male rat.

Agonist analogs of GnRH, after an initial period of stimulation, down-regulate gonadotropin secretion in both man and experimental animals. To study the pretranslational changes in LH subunits during GnRH agonist (GnRH-A) treatment in vivo, 55-day-old male Wistar rats were divided into two groups as follows: 1) sham operated, and 2) testosterone (T)-replaced castrated animals. T replacement was given by 20-mm T implants. Each group was subdivided into two subgroups to receive either saline or 1 microgram GnRH-A (D-Leu6,Des,Gly10-GnRH Net) by daily sc injection. Pituitaries were harvested after 1, 7, and 28 days of GnRH-A treatment for measurements of LH subunit mRNAs by dot hybridization assay. Serum LH concentrations were measured by a RIA. In intact animals, serum LH concentrations, measured 24 h after the GnRH-A injection, were higher in the GnRH-A group than in saline controls on day 1, but not on days 7 and 28. However, alpha and LH beta mRNA levels were higher in the GnRH-A-treated animals than in saline controls only on day 28, but not on days 1 and 7, however, in T-replaced castrated rats, in which testicular feedback to the pituitary was clamped by orchiectomy and replacement with a fixed dose of exogenous T, GnRH-A decreased serum LH and LH beta mRNA levels compared to those in saline controls. alpha mRNA levels were, however, not different between GnRH-A- and saline-treated animals at any time. We conclude that 1) an early increase in serum LH after 1 day of GnRH-A treatment probably reflects the release of preformed LH rather than increased synthesis; 2) in T-replaced castrated animals where the testicular feedback is clamped, GnRH-A-induced down-regulation of LH can be explained by a decrease in LH beta mRNA; and 3) differences in the LH subunit responses of intact and T-replaced castrated animals provide further evidence for testicular modulation of the LH response to GnRH-A.

Differential regulation of rat luteinizing hormone alpha- and beta-subunits during the stimulatory and down-regulatory phases of gonadotropin-releasing hormone action.

Chronic treatment with agonist analogs of GnRH or long term continuous administration of GnRH results in down-regulation of pituitary LH secretion. We investigated the changes in the LH subunits during the stimulatory and down-regulatory phases of GnRH action in rat pituitary cell monolayer culture. The rat pituitary cells in culture, pretreated with medium alone or GnRH agonist for 48 h, were incubated with graded doses of GnRH for 4 h, and LH, LH alpha, and LH beta concentrations in the media and cell pellets were measured by specific and sensitive RIAs. Cells pretreated with medium alone responded to GnRH with a dose-dependent increase in LH, LH alpha, and LH beta immunoreactivity in the medium. However, rat LH, LH alpha, and LH beta concentrations in the cell pellets showed a dose-dependent decrease with GnRH treatment. Pretreatment with GnRH agonist led to a marked decrease in the LH response of cells to graded doses of GnRH. During this down-regulatory phase, the concentrations of LH beta in the medium remained undetectable even though LH alpha immunoreactivity remained persistently and disproportionately elevated. These data suggest that the alpha- and beta-subunits of rat LH are both coordinately and differentially regulated. During the stimulatory phase of GnRH action, both subunits rise concordantly, but during the down-regulatory phase the secretion of the two subunits becomes unbalanced. The changes in the beta-subunit closely parallel the changes in the concentrations of LH dimer, pointing to the key role of beta-subunit in regulation of LH secretion.

In vitro inhibition of testosterone biosynthesis by ketoconazole.

Oral ketoconazole has been demonstrated to lower plasma testosterone in man. Measurement of blood precursors of testosterone suggest that ketoconazole may have its effect inhibiting the 17,20-desmolase enzyme within the testis. To substantiate this, a series of in vitro experiments was conducted using the rat testis to determine where in the testosterone biosynthetic pathway ketoconazole has its effect. To accomplish this, an assay system to measure 17 alpha-hydroxylase, 17,20-desmolase, and 17 beta-hydroxysteroid dehydrogenase activities involved in the delta 4-testosterone biosynthetic pathway was developed. It was demonstrated from dose-response and time-course experiments that a dose of approximately 10 micrograms/ml ketoconazole was sufficient to inhibit in vitro testicular steroidogenesis. Using dosages between 10 and 300 micrograms/ml ketoconazole, a marked inhibition of both the 17 alpha-hydroxylase and the 17,20-desmolase activities occurred. Ketoconazole under these conditions had no effect on 17 beta-hydroxysteroid dehydrogenase activity. Ketoconazole also inhibited the increased activity of these enzymes induced by hCG (1 IU). These data confirm the observation that in vitro ketoconazole has a direct inhibitory effect on 17,20-desmolase activity. These results further suggest that ketoconazole has more than one site of action in inhibiting testosterone biosynthesis in the testis and may indeed be a suitable agent for the treatment of patients with disseminated prostate cancer.