Capacity of Old Versus Young Female Rats to Secrete LH, FSH and Prolactin

Abstract

Serum LH, FSH and prolactin levels were measured by radioimmunoassays before and after ovariectomy and during and after estradiol benzoate (EB) treatment in 4-5 month old young mature female rats, in 22-24 month old constant estrous and pseudopregnant rats, and in 26-30 month old anestrous rats. Serum LH in intact old constant estrous rats was significantly higher than in young rats on the day of estrus, about the same in intact old pseudopregnant rats as in young rats in diestrus, and was undetectable in the old anestrous rats. By 7 weeks after ovariectomy, serum LH rose about 26 fold in young rats, only about 3 fold in the old constant estrous rats, about 14 fold in the old pseudopregnant rats, and remained unmeasurable in the old anestrous rats. After daily EB injection for 8 days, the relative fall in serum LH in old constant estrous and pseudopregnant rats was significantly smaller than in the young rats, and 2 weeks after estrogen treatment was terminated the rise in serum LH was significantly less in the old constant estrous and pseudopregnant than in young rats. Serum LH in the old anestrous rats remained undetectable.