Plasma and pituitary concentrations of LH, FSH, and prolactin in aging C57BL/6 mice at various times of the estrous cycle.

Plasma and pituitary concentrations of LH, FSH, and prolactin (Prl) were measured by RIA in 2-4, 7-8, 12-13 and 16-20 month-old female C57BL/6 mice during various stages of the estrous cycle. In general, gonadotropin concentrations tended to rise with increasing age and Prl concentrations tended to decline. Pronounced differences existed, however, between the four age groups around the time of the LH surge. LH secretion declined progressively with increasing age at 21.00 hr of proestrus. Aged mice, 16-20 months old, had significantly lower plasma concentrations of LH than did other age groups. It is not known whether age-related changes in the ovary, pituitary, or hypothalamus are largely responsible for differences in the secretion of LH, FSH and Prl in aging C57BL/6 mice.