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Reproductive aging in female mammals is characterized by a progressive decline in fertility and fecundity. Many women delay their first full-term pregnancy until an age at which their reproductive potential has already declined. No treatment is presently available to delay the aging process. In a limited number of rodent species, caloric restriction sustained reproductive function in older females, and in most investigations, sexual maturation was delayed because caloric restriction was initiated at weaning. We have previously reported similar outcomes in female Siberian hamsters that were reared in short photoperiod (SP), which profoundly inhibits reproductive physiology. When compared to hamsters held in long photoperiod (LP), females reared in SP matured much later and had greater reproductive success at 9 mo of age. Herein, we determined if delayed onset of sexual maturation was necessary for SP to decelerate reproductive aging. We initiated a 6-mo period of SP before or after sexual maturation and measured the reproductive success of females at 12 mo of age. Maintenance of hamsters in SP beginning after puberty was associated with significantly greater litter success (77%) compared to imposition of SP before puberty (35%); the difference in weaning success was even greater (73% and 12%, respectively). Regardless of which SP regime was used, litter success of females exposed to SP was substantially greater than that of 12-mo-old females held continuously in LP (6%). The efficacy of SP in decelerating female reproductive aging is manifest at several life stages and is greater when treatment is initiated after rather than before puberty.

In most seasonal breeders, photoperiod influences the timing of the transition to sexual maturity. In sheep, males and females express reproductive maturity under different photoperiods. Spring-born males begin the maturational process during lengthening days (spring), whereas females do so during shortening days (autumn). We hypothesized that photoperiod differentially influences the transition to sexual maturity in each sex, and that this difference results from the presence or absence of androgens prenatally. We monitored the timing of sexual maturity in male and female lambs (n = 8 each) and in prenatally masculinized female lambs (n = 7) maintained under controlled photoperiods (natural-simulate or reverse natural-simulate). Circulating LH was analyzed to reveal the timing of the pubertal gonadotropin rise; lambs were gonadectomized and implanted with estradiol to provide a constant feedback on LH secretion. Under natural-simulate photoperiod, LH increased in males at 7.0 +/- 0.3 wk when days were lengthening. In females treated similarly, sexual maturity occurred at 27.0 +/- 0.8 wk when day lengths were decreasing. The reverse photoperiod had no effect on males, but it delayed the expression of sexual maturity in females. Thus, LH also increased in males at 7.1 +/- 0.9 wk, while none of the females maintained under the same photoperiod had elevated LH secretion when the experiment was terminated (32 wk of age). Prenatal treatment with androgens masculinized the reproductive response to photoperiod; as in the males, LH increased in the androgenized females maintained under a reverse natural-simulate photoperiod at 7.1 +/- 0.4 wk.(ABSTRACT TRUNCATED AT 250 WORDS)

In woodchucks (Marmota monax), as in other marmotine rodents, endogenous circannual metabolic and reproductive cycles persist and free-run at intervals of 10-12 mo for up to 4 yr in a neutral photoperiod of 12L:12D. The annual metabolic cycle is not altered by exposure to constant long days or short days for several months. In the wild, changes in food intake cause body weight to peak in late summer and reach nadirs in early spring, and there is a single annual breeding season in late winter. To determine whether normal changes in photoperiod entrain the endogenous circannual cycle, aspects of reproduction, food intake, and body weight were studied for 28 mo in eight groups of woodchucks housed in light-controlled rooms. These included four groups of 7-10 males and four groups of 7-10 females exposed to automated and continuous daily changes in photoperiod. The imposed changes in photoperiod resembled native Northern Hemisphere (boreal) changes or Southern Hemisphere (austral) changes in photoperiod. The treatments started at the summer solstice shortly after capture as 2.5-mo-old juveniles or 14.5-mo-old yearling adults. In austral vs. boreal woodchucks, started as juveniles, annual increases in testosterone and testis descent at 5, 14, and 23 mo of study were advanced by 2, 5, and 6 mo, respectively. Annual increases in progesterone at 7, 16, and 25 mo of study were advanced by 4, 5, and 6 mo, respectively. The older woodchucks were significantly but less dramatically affected by austral photoperiod for the first 6 mo of study, and by 8-12 mo were advanced the same as the younger animals. At 16-17 and 26-27 mo of photoperiod reversal, 16 austral females had normal pregnancy rates (78%) and produced normal-sized litters (4.3 +/- 0.2) that were advanced by 5 and 6 mo, respectively, relative to those of boreal controls. Body weights in austral vs. boreal juveniles were reduced at 3-5 mo of study but not in older woodchucks. At 1 and then 2 yr of austral lighting, peaks in body weight were advanced by 4 and then 5 mo relative to boreal controls in young animals, and by 2 and then 5 mo in older animals. Between 1 and 2 yr of austral lighting in both age groups the nadirs in food intake (45 g per day) were about 16-25% of peak food intake 6-8 mo earlier, as in boreals, but advanced by 5-6 mo relative to boreals.(ABSTRACT TRUNCATED AT 400 WORDS)

A direct effect of prolactin (Prl) on gonadotropin secretion has been suggested but not convincingly demonstrated. The secretion of LH in response to photostimulation (phs) and ovariectomy (ovx) was evaluated in adult female turkeys that had received injections of ovine Prl (124 IU/bird/day for 14 days). In experiment 1, oPrl administration initiated on the day of ovx and phs in reproductively quiescent birds suppressed (p less than 0.05) the elevated LH from a peak level of 11.7 +/- 3.5 ng/ml to 5.1 +/- 0.8 ng/ml in ovx hens. The photo-induced LH increase was unaffected by the oPrl treatment in intact birds. In experiment 2, the oPrl treatment was initiated 7 days before ovx and/or phs. This treatment blunted the peak increase in LH level that follows phs in intact (p less than 0.05) and in ovx (p less than 0.05) hens. In both experiments, onset of lay following phs was delayed (p less than 0.05) in the oPrl-treated groups (29.4 +/- 0.9 days vs. 22.3 +/- 0.9 days; 34.8 +/- 0.5 days vs. 25.0 +/- 0.9 days). In experiment 3, administration of oPrl after ovx of laying hens suppressed the LH rise at essentially all sampling times tested. At the end of the experimental period, 6 of the 7 sham-operated, oPrl-treated laying hens, but none of the sham controls, displayed incubation behavior and had Prl levels of 1020 +/- 370 ng/ml compared to 34 +/- 7 ng/ml in vehicle-treated controls. The results suggest a role for Prl in incubation behavior and LH secretion in the turkey.

An ambient temperature of 30 degrees C compared to 18 degrees C accelerated the increase in serum prolactin (Prl) level induced by photostimulation of female turkeys. The contribution of reproductive stage and nesting behavior to this serum Prl elevation was assessed by housing adult female turkeys in individual wire cages while allowing other females free access to nests on the floor. Birds of both groups were exposed to 10 degrees C, 24 degrees C or 30 degrees C beginning 4 wk prior to photostimulation and continuing throughout the reproductive phase. Lapsed time between the onset of photostimulation and onset of sexual maturity, and between the onset of sexual maturity and onset of incubation behavior was shorter in birds housed at 30 degrees C with access to nests than in corresponding birds housed at 24 degrees C and 10 degrees C. The increases in serum Prl associated with sexual maturity or incubation behavior occurred at a greater rate in the birds maintained at 30 degrees C. Cage-reared birds had the same lapsed time between onset of photostimulation and onset of sexual maturity and the same sustained low Prl level regardless of ambient temperature exposure. All groups exhibited similar luteinizing hormone profiles. These findings indicate that the accelerated increase in Prl under elevated temperature in floor-reared turkeys is related to accelerated development of reproductive function, and not the direct effect of ambient temperature on mechanisms controlling Prl.

Female deer mice were exposed to a short day (SD, 6L:18D) photoperiod beginning during 1 of 3 stages of life. In the first experiment, exposure to SD during adulthood resulted in a minimal disruption of reproductive condition; many females bore 2 litters after the onset of this treatment. In the second experiment, females reared on SD from weaning matured normally, as measured by vaginal introitus; however, vaginal closure occurred in approximately one-half of these females by 9 weeks of age. In the third experiment, females were born of mothers housed on either an SD or a long day photoperiod, and were continued on the maternal photoperiod until 6 weeks of postnatal age. The SD photoperiod markedly inhibited reproductive maturation as measured by vaginal patency, ovarian weight, and uterine weight. A comparison of reproductive organ weights and vaginal condition provided evidence for the validity of the latter measure as an index of reproductive state. As assayed by the present testing procedure, the sensitivity of the reproductive system to photoperiod decreases as a function of age in female deer mice.

Basal serum gonadotropin levels were monitored weekly in female hamsters from birth to 10 weeks of age. Hamsters raised on three different photoperiods presented uniform pre- and postpubertal patterns of serum LH and FSH, suggesting that gonadotropin release in the young hamster occurs independently of ambient photoperiod. In all groups, serum LH levels increased gradually in animals up to 4 weeks of age, after which levels plateaued at 50--100 ng/ml. Serum FSH was markedly elevated in 2- and 3-week-old hamsters (800--1200 ng/ml), but remained at 200--400 ng/ml in all other groups. We next examined the change in the responsiveness of the pituitary to exogenous gonadotropin-releasing hormone (GnRH) challenge. Female hamsters 2 days of age failed to respond to any dose (0.025--1000 ng) of GnRH, while 10-day old females responded in typical dose-dependent fashion. GnRH-stimulated LH release first occurred in 6-day-old hamsters and was maximal by day 9, whereas FSH release first occurred on day 8 and was maximal by day 9. The prepubertal pattern of gonadotropin release can, in part, be explained on the basis of the development of pituitary GnRH sensitivity, which occurs independently of photoperiod.

Photoperiod is an important environmental cue timing puberty in the domestic female sheep, a seasonal breeder. Because the effects of photoperiod on reproductive function in the adult sheep are mediated by the pineal melatonin rhythm, the present study determined whether the pineal through its secretion of melatonin is involved in the pubertal process. Neonatal denervation of the pineal by removal of the superior cervical ganglia (SGX) abolished the nocturnal melatonin rhythm and delayed the onset of reproductive cycles beyond 1 yr of age in female lambs reared under natural conditions. Puberty was also delayed in SGX lambs reared under an artificial photoperiod sequence of long days (experienced at 17-22 weeks of age) followed by short days. By comparison, intact lambs under this same photoperiod treatment began cycles at the normal age. Another group of SGX lambs was treated each night with melatonin; the infusion replicated the duration of the nighttime rise in serum melatonin occurring in intact lambs exposed to 5 weeks of long days followed by short days (9-h or 15-h infusions, respectively). Melatonin treatment of these SGX lambs restored puberty to the normal age. These findings suggest that the pineal melatonin rhythm is an essential component of the photoperiodic mechanism timing puberty in the female sheep.