Age dependent changes in FSH responsive adenylyl cyclase and FSH binding in rat testes

FSH responsive adenylyl cyclase (AC) activities were examined in both homogenates and membrane particles from 9-71 days old rat testes, and FSH binding was determined in membrane particles from the same animals. FSH responsive AC was measured in the presence of either GTP (0.04 mM) or the non-metabolizable GTP analogue, GMP-P(NH)P (0.04 mM). From days 9 and 11 there was a gradual decrease in both basal and FSH stimulated AC activities and a very similar decrease in FSH binding. The relative stimulation by FSH, however, was fairly constant (2-3 fold stimulation). The excellent correlation between specific FSH binding and FSH responsive AC activities during sexual maturation does not support the notion that uncoupling of the FSH receptors from the AC is a primary reason for the attenuated FSH response during pubertal development. The age dependent decrease in both basal and FSH stimulated AC activities during sexual maturation is a reflection of the relative increase in germ cells (containing no FSH receptors and FSH responsive AC). The LH/hCG responsive AC in membrane particles from the same ages showed an age dependent increase in both absolute activities and relative responses, probably indicating the increased number of Leydig cells in the developing testis.