To investigate the physiological importance of oestradiol-17beta and inhibin in the regulation of gonadotrophin secretion in the cyclic golden hamster, females were passively immunized against two hormones. When 200 microL antiserum against oestradiol-17beta (oestradiol-AS) was given on Day 3 (Day 1 = day of ovulation), the preovulatory gonadotrophin surge was completely blocked for 24 h and the length of the oestrous cycle was also prolonged for one day. In the group given 200 microL oestradiol-AS on Day 3, basal levels of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) increased slightly and superovulation (19.6+/-0.8, mean+/-s.e.m.) occurred. When 200 microL antiserum against inhibin (inhibin-AS) was given at 1100 hours on Day 3, a dramatic increase in plasma FSH and a slight increase in LH were noted, resulting in superovulation (38.2+/-2.6) on the expected Day 1. The present study indicates clearly that inhibin plays a major role in regulating the specific ovulation rate in the hamster through the control of FSH secretion. Present results also indicate that oestradiol-17beta suppresses basal LH secretion. Oestradiol-17beta may act as an indicator of the follicular maturation, and the high plasma concentration of oestradiol-17beta noted from Day 3 to Day 4 may play an important role in determining the timing of initiation of the preovulatory gonadotrophin surge.

Gonadal function in the male golden hamster (Mesocricetus auratus) was investigated during exposure to a short photoperiod condition. Within 3 weeks of exposure to the short photoperiod condition, FSH and testosterone in the plasma significantly decreased, and subsequently immunoreactive (ir)-inhibin significantly decreased. Testicular contents of ir-inhibin and testosterone, and pituitary contents of LH and FSH also significantly decreased by 3 weeks with regression of weight of testes, epididymis and seminal vesicles and sperm head count. Circulating LH varied but not significantly. Thereafter, all reproductive parameters and secretion of LH, FSH, ir-inhibin and testosterone gradually recovered after 17 weeks of exposure even though animals continued to be subjected to the short photoperiod condition. Plasma concentrations of inhibin B and inhibin pro-alphaC were detectable and were significantly decreased after 15 weeks of exposure to the short photoperiod, but their levels were still detectable. Immunopositive reaction of inhibin alpha and betaB subunits was found in Sertoli cells and Leydig cells in the regressed testes of animals subjected to short photoperiod as was also seen in animals before exposure to the short photoperiod. Although the spermatogenic cycle was suppressed like prepubertal animals, the present study showed that the testicular recovery, so-called refractoriness, is functionally different from the developing stage of immature animals, especially with regard to inhibin secretion. The present results showed that changes in FSH preceded changes in inhibin during the regression and recovery phases, indicating that FSH is a major regulatory factor of inhibin secretion in male golden hamsters. The present study also demonstrated that regressed testes still secrete a small amount of bioactive inhibin during exposure to a short-photoperiod condition.

Abstract. We studied developmental reproduction of male golden hamsters (Mesocricetus auratus) by determining hormone secretion, observing morphological changes including distribution of immunoexpression of inhibin α subunit, 3β-hydroxysteroid dehydrogenase (HSD), and investigating sperm head count from birth to adulthood. Immunoexpression of inhibin α subunit was found in interstitial cells of not well organized testes of neonatal animals, and positive staining was also found in Sertoli cells in developing animals. However, the intensity of immunostaining in Sertoli cells varied when the spematogenic cycle of the seminiferous epithelium began. Testosterone levels in the plasma and testicular contents of testosterone and immunoreactive (ir)-inhibin increased from around 25 days of age, about 10 days before the presence of the first sperm in the testis. On the other hand, plasma concentrations of ir-inhibin progressively increased from birth to 10 days of age, when it reached peak levels. A reciprocal pattern of change between plasma concentrations of ir-inhibin and FSH was found from 10 days of age. Plasma concentrations and pituitary contents of LH increased from 15 days of age and reached adult levels about 40 days of age. The present results suggest that inhibin is an important factor in the regulation of FSH secretion even in infant male golden hamsters, and the regulated FSH may control the increasing the number of germ cells. Inhibin might be not the only endocrine factor as the regulator of FSH secretion, but also a paracrine or autocrine factor which is involved in spermatogenesis in the golden hamster. Key words: Inhibin, Hamster, Development, Testis (J. Reprod. Dev. 48: [343][344][345][346][347][348][349][350][351][352][353] 2002) arly 20 th century experiments, which were the initial proposal for the existence of inhibin, showed that destruction of the germinal epithelium by irradiation caused hyperfunction in the absence of atrophy of the second sex glands [1], and that injection of aqueous testicular extracts to castrated rats prevented the appearance of enlarged "castration cells" in the pituitary [2,3]. These