AGE-DEPENDENT DIFFERENCES IN TESTICULAR INACTIVATION OF FSH AND IN INHIBITION OF FSH BINDING TO RAT TESTIS

The maximum binding of iodinated rat FSH ([125I]r-FSH) to rat testicular tissue, in the presence of an excess of homogenate, was highly age dependent with a decrease in maximal binding in the maturing rat from 14 days to 30 days of age. Thereafter, there was no difference to at least 60 days of age. There was a concurrent increase in the concentration of FSH-binding inhibitor which could be extracted from the testis, although extracts of liver and kidney also showed an age dependent increase in FSH-binding inhibition. Extractable binding inhibitors do not offer the complete explanation of age dependent maxima in FSH binding because apparent removal of the inhibitor from homogenate did not affect the pattern of maximum binding. Hormonal inactivation was greater by testicular tissue from 60-day-old rats than by this tissue from 14-day-old rats. The maximum binding to a mixture of these two homogenates was not significantly different from the maximum binding to homogenate from 14-day-old rats alone. Once the extractable inhibitor had been removed from homogenate there was no detectable release of any substance into the buffering medium which would affect the binding of [125I]r-FSH. It is suggested that the age dependent systems described, which act to decrease the binding of FSH to its receptor by inhibition or inactivation, may have a role in the control of the effects of FSH during sexual maturation.