Gonadal growth and gonadal hormones do not participate in the development of responsiveness to photoperiod in the golden hamster.

Photoperiod regulates seasonal reproductive cycles in adult golden hamsters but does not influence the timing of puberty in juvenile hamsters. We examined whether pubertal gonadal growth or gonadal hormones were important for the development of photoperiodic responsiveness in hamsters. In one experiment, hamsters raised on long or short days were implanted with 20 mm of testosterone-filled Silastic capsules between 2 and 12 weeks of age. This treatment completely prevented testis growth in 50% of the hamsters on short days and retarded testis growth in hamsters on long days. When the capsules were removed at Week 12, the testes of hamsters on long days matured to adult size within 4 weeks. The testes of hamsters on short days showed no signs of growth for 9 weeks after testosterone was removed whether testis growth had been completely suppressed or only partially suppressed through Week 12. In the second experiment, hamsters born and maintained on long days for 8 weeks were castrated either at 1 week of age or at 8 weeks of age. Half of the animals in each of these groups were exposed to short days from 8 to 19 weeks of age. All hamsters were challenged with various doses of testosterone between 15 and 19 weeks and blood samples were collected after each dose for measurement of luteinizing hormone (LH) and follicle-stimulating hormone (FSH). Hamsters exposed to short days were more sensitive to the negative feedback effects of testosterone on gonadotropin secretion than hamsters on long days, whether castrated as neonates or as adults.(ABSTRACT TRUNCATED AT 250 WORDS)