Primary monolayer cultures of heterogeneous pituitary cells have shown age- related decreases in LH secretion after administration of PMA, a protein- kinase C activator as well as after nifedipine, a calcium channel blocker. Observations suggest that long vs. short term LH release may proceed through separate mechanisms which are differentially affected by aging. New techniques for examining the cellular, biochemical, and molecular events responsible for age-related alterations in LH and PRL secretion have been introduced. These include; centrifugal elutriation, reverse hemolytic plaque assay, immunocytochemistry and immunofluorescence, RIA of G-protein subunits, and HPLC measurement of PIP metabolites. We have found that it is possible to achieve highly enriched gonadotropic cell populations using small number of rats. Paracine effects from the other separated pituitary cells do not appear necessary for GnRH mediated secretion of LH so that gonadotropes enriched in this manner are functional. Preliminary measurements of LH release confirm an age-related decrease in both basal and GnRH-stimulated LH secretion in enriched gonadotrope populations. In pituitary homogenate preparations from young and old rats, we have shown by ADP-ribosylation, that G alphas levels do not change. This result, in conjunction with the previous finding that bypassing the plasma membrane reverses the age related LH-secretion deficit, suggests that a signal transduction mechanism is involved in the LH secretion deficit. Levels of membrane inositol 1, 4, 5-triphosphate do increase upon stimulation with GnRH, but inositol 1,3,4,5-tetrakisphosphate also appears to be involved in the release of LH. This result may explain why, in previous studies, IP3 alone did not alter the age-deficit in LH release.
