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

Abstract

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.

The G. W. Harris Lecture Steroid Control of Brain and Pituitary Function

“…There are major differences between the priming and the releasing action of LHRH (Fink et al 1982a), the most prominent of which is that the priming but not the releasing action of LHRH involves the synthesis of a new protein and depends upon the integrity of microfilaments. The new protein synthesized as part of LHRH priming has a molecular mass of about 70 kDa (Curtis, Lyons & Fink, 1985;Fig. 19) and might be similar to the oestrogen-stimulated protein recently discovered by Mobbs, Harlan, Burrows & Pfaff (1988) in the hypothalamic ventromedial nucleus and in the mid-brain central grey.…”

Arginine Vasopressin‐lnduced Sensitization in Brain: Facilitated Inositol Phosphate Production Without Changes in Receptor Number

“…It is interesting to note here that the self-priming (sensitization) effect of luteinizing hormone-releasing hormone (LHRH) in pituitary tissue displays similar features to AVP sensitization in the brain in that pre-exposure of pituitary tissue to LHRH cause a potentiation of LHRH-induced inositol phosphate accumulation with no corresponding alterations in LHRH receptor number or affinity (35). Furthermore, evidence was provided that the facilitated secretory responses to LHRH caused by pre-exposure of pituitary tissue to LHRH appear to depend upon protein synthesis (36)(37)(38), and recently Mobbs et al (39,40) have shown the newly synthesized protein associated with enhanced LHRH responses to be an isozyme of the phospholipase C family known to be involved in PI hydrolysis. Thus, our findings and those of others suggest that the regulatory mechanism(s) underlying AVP sensitization in the brain may be similar to those underlying LHRH-induced self-priming in the pituitary.…”

Influence of folliculo-stellate cells on biphasic luteinizing hormone secretion response to gonadotropin-releasing hormone in rat pituitary cell aggregates

“…The ovarian protein factor was called gonadotropin surge-inhibiting factor (GnSIF) (14). Many studies have been devoted to the mechanisms involved in the self-priming action of GnRH (15)(16)(17)(18)(19)(20), but relatively few studies have addressed the question of how a suppressive feedback mechanism is established at the pituitary level. Recently, it was suggested that inter¬ cellular communication involving different pituitary cell types may well play a role in the establishment of a biphasic LH secretion response to GnRH (21).…”