ACTIVATION OF MAP KINASE ASSOCIATED WITH THE PRIMING EFFECT OF LHRH

A MAP kinase activity assay was developed to determine whether the LHR H receptor could activate this enzyme (particularly during LHRH primin g). In anterior pituitary tissue from pro-oestrous rats LHRH caused co ncentration-dependent activation of MAP kinase after 5-10 min and cont inued for up to 60 min of incubation. The magnitude of this response c orrelated with that of LHRH priming on various days of the oestrous cy cle but not with the magnitude of 1st hour (unprimed) LHRH-induced LH release. The response to LHRH was mimicked by a phorbol ester but not by ionomycin and was blocked with high potency by GF 109203X but not b y H7 (in a similar manner to the PKC species that mediates LHRH primin g). Neither the tyrosine kinase inhibitor lavendustin A nor the protei n synthesis inhibitor cycloheximide blocked LHRH-induced MAP kinase ac tivation. The possible functional significance of MAP kinase activatio n in gonadotrophs is considered with respect to LHRH priming.