Midcycle and luteal elevations of follicle stimulating hormone in squirrelmonkeys (Saimiri boliviensis) during the estrous cycle

Follicle stimulating hormone (FSH) has fundamental importance in reproducti ve function, but its cyclic pattern has not previously been described in th e squirrel monkey, due primarily to the lack of a suitable assay. An homolo gous radioimmunoassay (RIA) based on recombinant cynomolgus FSH measured ch anges in serum FSH relative to patterns of bioactive luteinizing hormone (L H), estradiol, and progesterone during the estrous cycle. FSH was observed to have a sharp peak during the late follicular phase coincident with the L H surge and then rose again during the luteal phase. Estradiol was low exce pt for the midcycle rise, suggesting an inhibitory relationship. The rat gr anulosa cell in vitro FSH bioassay confirmed high levels of this hormone. M easurement of FSH in the squirrel monkey has found a pattern different from Old World primates in the luteal phase, which may provide insight into the reproductive mechanisms of this species. (C) 2000 Wiley-Liss, Inc.