Hypothalam ic-Pitu itary-Gonadal Interactions during Spontaneous Testicular Recrudescence in

Golden hamsters exposed to short days (<12.5 h Iight/24 h) show a decrease in serum FSH and LH resulting, after 10-12 weeks, in testicular regression. This is followed by a spontaneous rise in serum FSH and LH (weeks 15-23) and a concomitant maturation of the reproductive system. In this study, we examined the interaction of negative feedback mechanisms and photoperiodic effects during the period of spontaneous recrudescence in hamsters exposed to continual short day treatment (LD 6 h:18 h). After 2 weeks, animals were divided into 4 groups. One group served as intact controls. Another group of intact males received 5 mm testosterone implants (in Silastic tubing). The others were castrated; half of these received testosterone implants. Five animals were sacrificed every 2 weeks in the control group and every week in the treatment groups. Spontaneous testicular recrudescence occurred between weeks 15-27 in control animals and weeks 20-29 in animals with testosterone implants. Analysis of serum gonadotropins in each treatment group revealed a temporal difference in the peak of FSH and LH that appears to correlate with circulating levels of testosterone. These data suggest that alternations in gonadotropin release during spontan-eous testicular recrudescence may be controlled by a gradual change in the set point of the sensitiv-ity of the hypothalamic-pituitary axis to testosterone