Studies On The Effect Of Endothelin On The Secretion Of Ghrelin In Ruminants

Ghrelin plays an important role in promoting growth and appetite. Previous study showed that endothelin(ET) increased the levels of ghrelin, but it was unclear that the endothelin receptor subtypes which mediated ET-induced of the release of Ghrelin. This study investigated the ET receptor subtypes of which increasing ghrelin levels by inteavenous injection and immunohistochemistry methods. We hope the present study could provide a theoretical basis for regulatory mechanism of ghrelin in ruminant.To clarify effect of ET on physiological and biochemical indexes in ruminants, sheep were intravenously injected with 0.1% BSA saline(control group), 0.7 nmol/kg ET-1(ET-1 group) and 0.7 nmol/kg ET-3(ET-3 group) according to incomplete Latin Square Design. The results showed that heart rates in ET-1 and ET-3 groups were reduced(P < 0.05), while plasma levels of glucose, values of red blood cell, hemoglobin and hematocrit were increased compared with those of control group(P < 0.05), and ET-3 was more effective than ET-1 in terms of the effects and duration. Respiratory rate, values of white blood cell and its classification, and plasma protein concentration had not significant difference after injecting ET-1 or ET-3 compared with those of control group(P > 0.05).To explore ET receptor subtypes mediate the ET-induced secretion of ghrelin, steers were intravenously injected with 0.1% BSA saline(control group),(0.1 ?g/kg, 0.4 ?g/kg, 0.7 ?g/kg, 1.0 ?g/kg) ET-3, 2.0 ?g/kg IRL1620(the ET-B receptor highly specific agonist), 20.0 ?g/kg [D-Lys3]-GHRP-6(the GHS-R receptor antagonist) and 1.0 ?g/kg ET-3 combined with 20.0 ?g/kg [D-Lys3]-GHRP-6 by complete Latin Square Design. The results showed that ET-3 dose-dependently increased plasma levels of ghrelin compared with those of control group(P < 0.05). IRL 1620 and ET-3 had the same effect. [D-Lys3]-GHRP-6 did not block ET-3-induced elevation of acyl ghrelin and total ghrelin levels(P > 0.05).To explore Whether there may be endogenous ET receptors on the ghrelin endogenous endocrine cells By using the combination of antigen and antibody immunological principles, Anti-acylated ghrelin immunoreactive cells were found in sheep abomasum, especially the bottom of fundus gastric glands using rabbit anti-acylated N-terminus ghrelin antisera by immunohistochemistry method. Anti-ET-A and ET-B receptor immunoreactive substance was observed in sheep abomasums fundus, especially with high concentration in the neck and bottom cavity of gastric glands.The present results demonstrated that ET reduced heart rate, but increased values which connected with red blood cells in plasma through ET-A receptors, and ET-B receptors might involve in ET-induced secretion of ghrelin in rminants.