The priming effect of LH-releasing hormone: effects of cold and involvement of new protein synthesis.

The possible involvement of protein synthesis in the priming effect of LH-releasing hormone (LHRH) has been investigated in vitro using hemipituitary glands from pro-oestrous rats. Cycloheximide (7.1 mumol/l) blocked the priming effect of LHRH (elicited by 8.5 nmol LHRH/l) and protein synthesis (assessed by gel electrophoresis of 35S-labelled pituitary proteins). Pituitary glands were also incubated at 0-1 degrees C followed by incubation at 37 degrees C. While incubation at 0 degrees C for either 1 or 2 h reduced LH release and blocked protein synthesis, the LH response to LHRH in a subsequent 1-h incubation at 37 degrees C was similar to that during the corresponding period in pituitary glands incubated throughout at 37 degrees C. Incubation with medium alone at 0 degrees C during the first hour followed by incubation with LHRH at 37 degrees C during the second hour resulted in an LH response to LHRH which was similar to that in glands incubated with LHRH for 2 successive hours at 37 degrees C. Two-dimensional gel electrophoresis showed that LHRH priming was associated with the synthesis of a new protein of approximately 69 000 molecular weight and with changes in the isoelectric point of two other high molecular weight proteins. These results suggest that the priming effect of LHRH involves the synthesis of a new protein as well as post-translational changes (possibly phosphorylation) in two other proteins and that exposure to cold may prime the pituitary gland to LHRH possibly by stimulating intracellular Ca2+ release and/or protein phosphorylation.