Circulating LH and FSH Levels and Testicular Function in Hamsters During Light Deprivation and Subsequent Photoperiodic Stimulation1

The relationship between testicular function and peripheral gonadotropin levels was investigated in adult hamsters throughout a 60-day period of light deprivation and then again after a return to normal light cycles (L:D, 14:10). Hypophyseal LH and plasma LH and FSH concentrations declined slowly and progressively (at least 5-fold) during the 60-day period of constant darkness. Thedecline in gonadotropin release was associated with a 73% decrease in plasma testosterone concentrations and a 4-fold reduction in the capacity of testicular tissue to convert [7-3H]progesterone to [3H]testosterone in vitro (p < 0.05). Testis atrophy accompanied the collapse of the hypophysealgonadonal endocrine system as evidenced by a 98% reduction in the relative number of step 7 spermatids and the absence of step 17 spermatids from the seminiferous epithelium. Once previously light-deprived hamsters (i.e., 60 days) were exposed o L:D, 14:10 cycles, hypophyseal LH and plasma LH and FSH levels returned to near control levels within 10 days. However, restoration of normal concentrations of plasma testosterone and of the capacity of teased testicular tissue to convert [7-3H]- progesterone to [3H]testosterone in vitro occurred gradually after exposure to long days. These findings conform with those anticipated after subjecting male hamsters to constant darkness followed by long days and demonstrate striking differential responses in the rate of gonadotropin release after exposure to nonstimulatory and stimulatory photoperiods. (Endocrinology95: 195, 1974)