Plasma and pituitary concentrations of LH, FSH and prolactin in aged female C57BL/6 mice

Abstract

Plasma and pituitary concentrations of luteinizing hormone [LH], follicle-stimulating hormone [FSH] and prolactin were determined by radioimmunoassay in 2-mo.-old (young) and 16- to 20-mo.-old (old) C57BL/6 mice. There were no statistical differences in hormonal levels between aged females in estrus (those exhibiting a copulatory plug) and those in constant diestrus. In the old females, plasma levels of LH (P < 0.002) and FSH (P < 0.001) were significantly elevated, while levels of prolactin (P < 0.001) were significantly depressed compared with those from young animals. Pituitary homogenates from old females also contained more gonadotropins (P < 0.001) and less prolactin (P < 0.001) than those of the young females. A radioreceptor assay utilizing a plasma membrane of luteinized rat or mouse ovaries indicated that LH from 2-mo.-old animals bound better to ovarian receptors (P < 0.05) than did LH from old mice, although radioimmunoassay of the same samples gave higher (P < 0.01) plasma LH levels for the old mice. Since the radioreceptor assay is considered to be a more sensitive test for biologically active LH, the results from these 2 types of assays suggest that there may be an alteration in the mouse LH molecule with age.