Kinetic evidence for two components in the priming effect of LH-releasing hormone in the rat. 
The priming effect of LHRH on LH release from prooestrous rat hemipituitary glands in vitro was analysed by kinetic approaches.  Concentration-response curves for LHRH-, K(+)- and ionomycin-induced LH release were constructed for initial exposure to the secretagogues and after 'priming' with a low dose of LHRH (100 pg/ml).  These data were analysed by a non-linear curve-fitting programme to reveal the potency and maxima of the responses before and after priming.  The parameters obtained from the curves fitted to the LHRH concentration-response curves showed that two changes had occurred as a result of priming.  There was an increase in the maximum amount of hormone released and also a relatively greater ability for low concentrations of LHRH to cause release (increased potency).  The data for K+ and ionomycin revealed only one change as a result of priming, an increase in the maximum amount of hormone available for release.  The data indicate that LHRH, after self-priming, releases more hormone by at least two routes, one represented by a general increase in stimulus-secretion coupling (which is available to K+ and ionomycin), the other a specific up-regulation of signal transduction by the LHRH receptor-effector system.