Studies on Pituitary Follitropin. XI. Induction of Hormonal Antagonistic Activity by Chemical Deglycosylation

Chemically deglycosylated ovine follitropin (DG-FSH) retained its binding ability to bovine and rat testicular membrane fractions but was completely inactive in stimulating cyclic AMP accumulation in immature rat seminiferous tubular suspensions. The native hormone induced cyclic AMP accumulation in a dose-dependent manner but no significant response was detectable at any dose of DG-FSH even in the presence of a potent phosphodiesterase inhibitor. By virtue of these different biological characteristics all preparations of DG-FSH exerted potent inhibitory action when added to the cells along with the native hormone. Complete inhibition of FSH action was observed at equivalent concentrations of the DG-FSH. It was also effective against hFSH. DG-FSH had no effect on hCG action in rat interstitial cells. The accumulation of cyclic AMP induced by a non-hormonal agent such as cholera toxin in the tubular suspensions was unaffected by the concomitant presence of DG-FSH indicating that its antagonistic activity is mediated through its binding to specific follitropin receptors.