The adult male golden hamster will undergo testicular regression when exposed to a short photoperiod, blinding, or late afternoon injections of melatonin. The present study was conducted to compare the effects of all three treatments on serum gonadotropin levels and testicular weights, and to evaluate the effects of these treatments on hypothalamic content of both immunoreactive and bioactive luteinizing hormone-releasing hormone (LHRH) levels. Hamsters were blinded (BL), exposed to a short photoperiod (SP), or received daily injections of melatonin (MEL) for 15 wk. Each treatment (BL, SP, MEL) induced a temporally similar decline in serum luteinizing hormone (LH), serum follicle-stimulating hormone (FSH), and testicular weight. Spontaneous recrudescence occurred earliest in the MEL group, with serum gonadotropins and testicular weight returning to normal by 15 wk. The SP group exhibited recovery of serum gonadotropins but not testicular weight by 15 wk. The BL group demonstrated partial recovery of serum FSH levels by 15 wk, with no recovery in either serum LH or testicular weight. Each treatment group demonstrated increased hypothalamic content of immunoreactive LHRH which was temporally correlated with the decreases of serum gonadotropins. Additionally, the MEL and SP groups demonstrated decreased immunoreactive LHRH levels during spontaneous recrudescence. Extracts of hypothalami from all treatment groups were bioactive on control hamster pituitary cells. These results indicate that there are temporal differences among the three common treatments and that these differences are manifested in serum gonadotropins, testicular weight and hypothalamic LHRH. Hypothalamic LHRH levels determined by radioimmunoassay and bioassay show periods of increase and decrease which coincide with periods of altered serum gonadotropin levels in all groups.

The ability of cultured hamster Sertoli cells to respond to FSH was studied during sexual maturation and photoperiodically induced regression and recrudescence. Serum gonadotropins were also measured in donor animals to determine if changes in LH and FSH were associated with changes in Sertoli cell response (accumulation of intracellular cAMP). There was a maturational peak of gonadotropins and an age-related decline in the ability of Sertoli cells to respond to FSH; the decline began before the peak of either gonadotropin. During regression, LH and FSH levels fell to or below prepubertal values, and the Sertoli cell response to FSH returned after the testicular weight had fallen from 2000 to 1400 mg/testis. Maximal Sertoli cell response to FSH occurred at approximately 800 mg/testis. During recrudescence, the low serum gonadotropin levels rose, reached a peak, and declined again to adult levels. The peak of gonadotropins during recrudescence was larger than that observed during maturation, and the loss of Sertoli cell response to FSH during recrudescence was delayed until after the gonadotropin peak. These data suggest that testicular recrudescence in the hamster is a dynamic process that approximates sexual maturation, but may be regulated in a somewhat different manner.

Injections of the pineal hormone melatonin reduced growth and increased doubling time of the R3327H Dunning prostatic adenocarcinoma in the Copenhagen X Fisher rat. This occurred even though testosterone levels (50% of normal) were ostensibly high enough to maintain normal tumor growth. Melatonin may act directly upon the conversion of testosterone to dihydrotestosterone to inhibit tumor growth. Alternatively, a more complicated mechanism may be involved since studies on MCF breast cancer tissue indicate an estrogen requirement for inhibition of growth by melatonin.

The pharmacokinetics of human chorionic gonadotropin (hCG) was studied in 15 normal volunteers and 15 patients undergoing in vitro fertilization (IVF). Each subject received 6000 IU hCG, intramuscularly (im), at midcycle, and serum was assayed for hCG frequently for 16 hr. All 30 subjects achieved hCG concentrations greater than or equal to 10 IU/liter within 2 hr and 19 (63%) did so within 1 hr of injection. The time taken to attain concentrations of greater than or equal to 20 and greater than or equal to 40 IU/liter correlated positively with the subjects' weight and/or surface area, but the correlation was not strong. Eleven of the 15 IVF patients had oocytes retrieved 34-35 + hr post hCG. Three of the 11 showed evidence of prior "undetected ovulation" at the time of surgery (definite in one, presumed in two). Taking into consideration the pharmacokinetics of hCG and other factors that could lead to undetected ovulation, the authors conclude that (1) hCG is rapidly absorbed in the majority of subjects following im injection, (2) ovulation may occur earlier than 36 hr following hCG in some individuals, and (3) implementation of a shorter (than 35 hr) hCG-to-oocyte retrieval interval would be advised if undetected ovulation is to be avoided.

Testicular regression was induced in adult hamsters by optic enucleation, short photoperiod, or melatonin injections. The melatonin injected group, while undergoing testicular regression, showed a quite different time course from the optic enucleated and short photoperiod groups. All three methods resulted in the restoration of Sertoli cell responsiveness to FSH in vitro from the adult level to that of Sertoli cells from immature hamsters 18-20 days of age. the melatonin injected group showed a shift in testis weight which resulted in a half maximal restoration of Sertoli cell responsiveness to FSH compared to the other groups. This restoration of Sertoli cell responsiveness to FSH was blocked by pinealectomy. These data indicate that the pineal has a specific (but not necessarily direct) effect on Sertoli cell function. In addition, the effect of melatonin injections is qualitatively but not quantitatively similar to optic enucleation and short photoperiod both with regard to testicular regression and alteration of Sertoli cell response.