Obestatin, acylated and total ghrelin concentrations in the perinatal rat pancreas

Background: Ghrelin and obestatin are encoded by the preproghrelin gene and originate from posttranslational processing of the preproghrelin peptide. The fetal rat pancreas contains acylated and desacylated ghrelin peptides, as well as growth hormone secretagogue receptor -1a mRNA. Acylated ghrelin inhibits insulin secretion. We investigated the plasma and tissue ontogeny of ghrelin and obestatin in the rat. Methods:We measured obestatin and acylated and total ghrelin concentrations in plasma, pancreas and stomach from rat fetuses (F20) and neonates at postnatal day (PN) 1, 6,12 and 21). Results: Overall, obestatin concentrations were markedly lower than total ghrelin concentrations. In plasma, total ghrelin concentrations decreased abruptly after birth (p < 0.05), contrasting with a 3 times increase in the concentration of acylated ghrelin between F20 and PN1 (p < 0.05). In pancreas, total ghrelin and obestatin concentrations decreased progressively from PN1 to PN21 but acylated ghrelin concentrations increased 6-7 times from F20 (18 [61 pg/ml) to PN6 (122 [591 pg/ml). The percent of acylated ghrelin increased from 1.8 (0.6) at F20 to 39.7 (13.0) % of total ghrelin immunareactivity at PN12 (p < 0.05). There were significant positive correlations between postnatal obestatin, acylated or total ghrelin and insulin concentrations in the pancreas (all p < 0.02, r(2) > 0.21) and between postnatal total ghrelin and obestatin (in pancreas, r(2) = 0.37) or acylated ghrelin (in stomach, r(2) = 0.27) (p < 0.001). Conclusion: Ghrelin and obestatin are present in the perinatal pancreas where they could potentially affect insulin secretion.