The development of a homologous radioimmunoassay (RIA) for the measurement of serum hamster prolactin (PRL) has facilitated our studies on monitoring the secretion patterns of this hormone during different states of reproduction. Four salient findings emerge from the present studies. First, rapid cardiac puncture without anesthesia does not affect serum PRL levels during selected times in the estrous cycle or during pregnancy. Second, serum PRL levels during the estrous cycle describe a daily rhythm of PRL release with maximum serum concentrations each day occurring in the afternoon and the highest of these occurring on proestrus (day 4 of cycle). Third, PRL release during pregnancy is characterized by a single surge each day; although the time of maximum PRL release varies, levels increase during the hours of darkness and decline to basal during the light. Fourth, the amount of PRL released during pregnancy diminishes with time; on day 15 the total amount of PRL in the serum is less than 10% of that measured on day 5.

Cyclic release of gonadotropin (GTH) begins on day 16 or 17 of age, about 2 weeks before ovulatory estrous cycles are initiated in female golden hamsters (Mesocricetus auratus). The daily cycles of LH and FSH are characterized by surges that peak at about 1700 h. The timing of this daily surge is similar to that observed in adult photoperiod-induced anovulatory or lactating females and to that of ovulatory females on the afternoon of proestrus. The purpose of this investigation was to determine if initiation of cyclic GTH release during the prepubertal period results in significant changes in ovarian function. A second objective was to examine the similarity between cyclic secretion of GTH in the prepubertal animal and that in the short day anovulatory adult. Groups of prepubertal females were killed throughout a 24-h period on days 13-14, 19-20, and 27-28, i.e. both before and after the expected onset of cyclic GTH release. LH did not vary significantly on days 13-14, but thereafter showed a significant rhythm, with a maximum at 1700 h. Levels of progesterone (P) were low and nonvarying on days 13-14, but a significant rhythm was measured in samples collected on days 27-28. When samples were collected from photoperiod-induced anovulatory adults, the rhythm of circulating LH and P was similar to that in the late prepubertal female. Ovariectomy of 22-day-old females resulted in low and tonic levels of P when the animals were killed 3 days later at 1400, 1700, and 2000 h, showing that the cyclical rhythm of P measured in these samples results from ovarian, not adrenal, secretion. The response of the daily cycle of LH to phenobarbital (PB) blockade in prepubertal females was identical to that in the adult: the LH surge did not occur on the afternoon of PB injection, but reappeared 24 h later at the expected time. The late afternoon surge of P was also blocked by PB administration. These results show 1) that the initiation of cyclic GTH secretion by the prepubertal female hamster influences ovarian maturation as reflected by changes in the levels and patterns of secretion of P; 2) that the rhythms of LH, FSH, and P secretion in the prepubertal female are similar to those in the photoperiod-induced anovulatory adult; and 3) that the response of the prepubertal female to barbiturate blockade is identical to that of the adult.(ABSTRACT TRUNCATED AT 400 WORDS)

In the absence of the ovary,

The age dependency of the time delay preceding a gonadal response to short photoperiod, blinding, and daily evening melatonin injection in young male and female hamsters has been examined to determine why the reproductive system of prepubertal golden hamsters is apparently unaffected by short-day treatment. Anestrous occurred in 50% of the female hamsters during the 10th week after blinding whether or not blinding occurred at 3, 5, 7, or 9 weeks of age. A similar latency was found following initiation of melatonin injections although the variance was greater (50% became anestrous during the 8th, 11th, 9th, and 8th week after initiation at ages of 3, 5, 7, and 9 weeks, respectively). After transfer to short days, however, females were 18 to 22 weeks old before 50% had become anestrous and the latency intervals were 19, 13, 11, and 10 weeks for transfer at 3, 5, 7, and 9 weeks of age, respectively. In males, mean testicular weights decreased to 50% of control values during the 9th and 10th week following blinding regardless of the age at which blinding occurred; the latency following initiation of melatonin injection or transfer to short days ranged between 8 and 11 weeks. These data support the conclusion that prepubertal male and female golden hamsters 3 weeks of age and older respond to light deprivation and melatonin treatment in the same manner as adults, but that the latency of the response is such that sexual maturity is attained before regression occurs. The response of 3-week-old female hamsters to short photoperiods, however, is apparently confounded by factors not governed by the pineal gland.