Effect of tyrosine kinase inhibitors on luteinizing hormone-releasing hormone (LHRH)-induced gonadotropin release from the anterior pituitary.
A range of selective tyrosine kinase inhibitors, piceatannol, methyl-2,5-dihydroxycinnamate (MDC), genistein, psi-tectorigenin and lavendustin A, all reduced luteinizing hormone-releasing hormone (LHRH)-induced luteinizing hormone (LH) and follicle-stimulating hormone (FSH) release from pro-oestrous rat hemipituitaries incubated in vitro. In general, both 'initial' release and the augmented release resulting from LHRH self-priming, were reduced in parallel in a concentration-dependent fashion. The effects of piceatannol were independent of the steroidal status of the pituitary tissue. Both piceatannol and MDC greatly reduced LH release by ionomycin and a protein kinase C (PKC) activator, phorbol 12,13-dibutyrate (PDBu), suggesting that the tyrosine kinase(s)-dependent step is in the later stages of the stimulus-secretion pathway activated by the LHRH receptor. These data were supported by immunoblots for phosphotyrosine showing that in the gonadotrope-derived alpha T3-1 cell line, treatment with LHRH caused piceatannol-sensitive increases in specific tyrosine phosphorylation of several proteins (major bands at 65-75 and 120-130 kDa). Treatment of cells with PDBu mimicked the tyrosine phosphorylations evoked by LHRH whereas the PKC inhibitor, GF109203X, partially reduced both LHRH- and PDBu-induced tyrosine phosphorylations. Direct effects of MDC and piceatannol on PKC were assessed in an in vitro PKC assay; piceatannol, but not MDC, inhibited PKC activity but at considerably higher concentrations than required for inhibition of LHRH-induced gonadotropin secretion. These data support a role for tyrosine kinase activation in LHRH-induced secretion.
Johnson
M S
MS
MRC Brain Metabolism Unit, University Department of Pharmacology, Edinburgh, UK.
Wolbers
W B
WB
Noble
J
J
Fennell
M
M
Mitchell
R
R
D000818:Animals; D002934:Cinnamates / Q000494:pharmacology; D005260:Female; D005640:Follicle Stimulating Hormone / Q000378:metabolism*; D019833:Genistein; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology*; D066298:In Vitro Techniques; D015759:Ionomycin / Q000494:pharmacology; D007529:Isoflavones / Q000494:pharmacology; D007986:Luteinizing Hormone / Q000378:metabolism*; D010636:Phenols / Q000494:pharmacology; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D010903:Pituitary Gland, Anterior / Q000187:drug effects / Q000378:metabolism*; D011359:Proestrus; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors*; D051381:Rats; D013267:Stilbenes / Q000494:pharmacology
D002934:Cinnamates; D007529:Isoflavones; D010636:Phenols; D013267:Stilbenes; D007987:Gonadotropin-Releasing Hormone; D015240:Phorbol 12,13-Dibutyrate; C062898:lavendustin A; D015759:Ionomycin; C067472:methyl 2,5-dihydroxycinnamate; C041525:3,3',4,5'-tetrahydroxystilbene; C055439:psi-tectorigenin; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone; D019833:Genistein; D011505:Protein-Tyrosine Kinases