Changes in the dynamics of luteinizing hormone-releasing hormone- stimulated secretion of luteinizing hormone during sexual maturation of female rats

Our aim was to identify age-related changes in the dynamics of luteinizing hormone (LH) release that may contribute to the decline in pituitary sensitivity to luteinizing hormone-releasing hormone (LHRH) during sexual maturation of female rats. We studied LHRH-stimulated LH secretion curves of superfused pituitaries from rats ranging in age from 10 days to the first estrous cycle. Pituitary fragments were exposed for 10 min to medium alone or to medium plus LHRH; incubation continued in medium alone for 130 min and effluent was collected for LH analysis. Secretion curves were compared on the basis of total secretion (area under the curve), maximal change in LH secretion rate, and rates of rise and decay of the curves. The data show that total LH secretion in response to LHRH is greatest in 15-, 20-day-old and first-proestrus animals. Also, the maximal change in LH secretion rate was greater, and the increase in LH secretion rate faster in younger animals than in 30-day-old animals. Analysis of secretory granules in LH-containing gonadotropes of 15- and 30-day-old animals revealed changes in he granule population with age. We conclude that younger animals respond faster with a greater LH secretion response to LHRH than do 30-day-old or first-estrus animals, and that these age-related changes in the dynamics of LH secretion may be due in part to maturation of the LH secretory granules.