Interactions between bombesin / gastrin releasing peptide and ghrelin in the post-prandial control of growth hormone secretion

CANOSA LF; UNNIAPPAN S; PETER RE

Castellon, Spain

Simposio; 5th International Symposium on Fish Endocrinology; 2004

The control of pituitary growth hormone (GH) secretion in fish is multifactorial, with a balance of stimulatory and inhibitory factors. Somatostatin (SS) is the major in­hibitor, while a number of peptides stimulate GH release. Three cDNAs encoding for pre-pro-SS (PSS) have been cloned from goldfish brain; PSS-I encoding for SS-14, PSS-II potentially processed into gSS-28 that has [Glu1, Tyr7, Gly10] SS-14 at the C-terminus, and PSS-III that encodes [Pro2] SS-14 at its C-terminus. It was previously found in goldfish that GH transiently rises after meals. In goldfish, bombesin (BBS), mimicking the endogenous gastrin releasing peptide (GRP), acutely suppress food intake. BBS also stimulates GH release in goldfish and may integrate the regulation of satiation and the post-prandial increase in circulating GH levels. Ghrelin was recently characterized in goldfish as a GH secretagogue and an orexigen. In this project, we studied the changes in SS mRNA levels during feeding. We have determined the mRNA expression levels of PSS-I, PSS-II and PSS-III in goldfish forebrain by slot-blot hybridization with specific probes for each form of PSS. The results showed a 60% reduction in PSS-II mRNA expression after meals, but no changes in the expression of PSS-I and –III mRNAs were found. Intraperitoneal (IP) injections of 100 ng/g of BBS increased GH secretion and decreased PSS-I and –II gene expression.  On the other hand, IP injection of goldfish gherlin (100 ng/g) transiently increased the serum GH levels, and acted differentially on the expression of SS precursors to increase PSS-I and decrease PSS-II. Administration of ghrelin (50 ng/g) blocked the effects of BBS (100 ng/g) on the expression of PSS-I but not on PSS-II. Thus, co-administration of bombesin and ghrelin decreases only the -PSS-II gene expression. We conclude that the interactions between BBS/GRP and ghrelin can account, at least in part, for the post- prandial variations in serum GH levels and the forebrain expression of PSS-II.