EXPRESSION AND EFFECT OF ADRENOMEDULLIN ON RAT GRANULOSA-CELL

Adrenomedullin (AM) is a potent hypotensive peptide recently discovere d in extracts of human pheochromocytoma. To elucidate the relation of AM? production in the ovary, the effect of,gonadotropin on the product ion of AM was studied in the cultured rat granulosa cells. A Northern blot analysis of the LH receptor and adrenomedullin yielded a major hy bridizing band at 5.4 kb and 1.6 kb, respectively. In our culture syst em of rat granulosa cells, without any stimulus, the LH receptor mRNA was undetectable and the; Am mRNA level was stably expressed for 6 day s. FSH significantly induced LH receptor mRNA and suppressed AM mRNA f or 4 days of culture and with the addition of hCG after 2 days of pret reatment with FSH, AM mRNA levels were markedly suppressed. FSH and 8- Br-cAMP significantly increase LH receptor mRNA and suppress AM mRNA i n a dose-dependent manner. These data indicated that the differentiati on of granulosa cells mediated by gonadotropins were associated by sup pression in AM expression through a cAMP-dependent mechanism. On the o ther hand, AM stimulated a rapid rise in intracellular cAMP levels, wh ich peaked within 15 min of addition, in a dose-dependent manner with a maximal response seen at 100 nM. Additionally, AM enhanced the effec ts of FSH, acting additionally to produce cAMP in the cells. it-M may play a role in the process of granulosa cell differentiation as a loca l regulator through an autocrine/paracrine mechanism.