Assessment of bioactivity of WHO/NIH research standard for inhibin (code 86/690) using two separate pituitary...

The Research Standard for inhibin, porcine (No. 86/690) distributed by the National Institute for Biological Standards and Control, U.K. for the bioassay of inhibin was tested for its bioactivity in vitro in two rat pituitary cell culture systems. The system A was obtained from pituitaries of 12 day old immature rats while system B was obtained from pituitaries of mature male rats. The inhibin preparation failed to inhibit basal secretion of FSH in the system A. Instead it stimulated the release of both LH and FSH. 1 ng LHRH induced release of LH was inhibited by 32, 80 and 43% by 0.1, 1 and 10 IU inhibin, respectively. 10 ng LHRH induced release of FSH was inhibited in a none-dose related manner and the maximum inhibition was by 10 IU inhibin (25%). The same dose of 10 IU inhibin stimulated LHRH-induced release of LH by 35%. In system B, 1, 10, 50, 100 and 200 IU inhibin suppressed basal secretion of FSH by 0, 44, 72, 70 and 48%, respectively, while LH was suppressed by 13, 24, 46, 22 and 21% respectively. The pattern of inhibition of 10 ng LHRH induced release of LH and FSH by inhibin was similar to its effect on basal secretion. A specific dose-related inhibition of FSH was not observed. Our data question the utility of the inhibin standard (86/690).