FSH and testosterone levels in the plasma of juvenile male rats after application of ovine FSH, HCG and PMS at different ages.

Male rats of the Wistar/Han strain are treated with ovine FSH, hCG or PMS in various doses for twelve days, beginning on the 1st, 12th, 24th or 36th day of life each. The determination of FSH in plasma by radioimmunoassay at the end of the treatment shows that all exogenous gonadotropins depress the FSH levels to immeasurable values. Plasma testosterone increases after application of hCG and PMS, not ovine FSH. To explain these findings a hypothalamic inhibition of the FSH release by a "short feedback" mechanism is discussed.