Inhibin: measurement and role in the immature female rat.

The possible physiological significance of endogenous inhibin has been evaluated in the female rat during sexual maturation. Plasma inhibin levels measured by a specific RIA were very low, but detectable at 5 days of age, then progressively increased until day 17, when they showed an abrupt rise. This rise was concurrent with a dramatic fall in plasma FSH levels. At day 30, inhibin values were not significantly (P greater than 0.05) different from those of adult females. The immunoneutralization of endogenous inhibin had no statistically significant (P greater than 0.05) effect on plasma FSH levels in 10-day-old immature female rats, but markedly (P less than 0.01) increased them at day 20 and 30. These results suggest that endogenous inhibin plays a physiological role in modulating FSH secretion from day 20 of age in the female rat.