Twenty Four-Hour Rhythm of Gonadotropin Release Induces Cyclic Progesterone Secretion by the Ovary of Prepubertal and Adult Golden Hamsters*

Abstract

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)

Neonatal androgen abolishes clock-timed gonadotrophin release in prepubertal and adult female hamsters

“…The patterns and levels of LH, FSH, and progesterone that we report for 25-day-old oil-injected controls are similar to those reported previously for untreated females (Smith & Stetson, 1980;Donham et al, 1984). We now show that neonatal androgen abolishes the cyclic pattern of gonadotrophin release and progesterone secretion characteristic of the last part of the prepubertal period.…”

“…The influence of neonatal androgen might be exerted on the circadian oscillator itself or on the mechanisms by which the message from the oscillator is translated into the gonadotrophin secretory pattern, or both. Since male golden hamsters have normal circadian rhythms of wheel-running activity (Elliott, Stetson & Menaker, 1972) The rhythm of progesterone in the serum of untreated prepubertal females derives from the ovary since ovariectomy abolishes the rhythm (Donham et al, 1984). The source of the pro¬ gesterone is the abundant interstitium (Greenwald & Peppier, 1968;Shaha & Greenwald, 1983 fig.…”

“…The method for measurement of serum progesterone has been described previously (Donham et al, 1984). The sensitivity of the method is about 0-5 ng/ml (as determined by the smallest dose on the standard curve whose standard deviation does not overlap with that of buffer blanks).…”

“…Clock-dependent, cyclic gonadotrophin secretion has been demonstrated in prepubertal female hamsters (Smith & Stetson, 1980;Donham, DiPinto & Stetson, 1984). These daily rhythms of serum LH and FSH are initiated on Day 16 or 17 after birth and persist throughout the rest of prepubertal life until they are replaced by a 4-day rhythm as oestrous cycles begin, 2-3 weeks later.…”

Daily rhythms of pituitary--ovarian function in the immature hamster are independent of adrenal and pineal influence

“…The circadian oscillator system and the associated neuroendocrine effector system matures before puberty; daily rhythms of LH and FSH begin at about 16 days of age (Smith & Stetson, 1980;Donham et al, 1984) whereas first ovulation occurs between 30 and 40 days of age.…”