The Effects And The Possible Mechanism Involved In Vivo And Vitro Of Ghrelin On Rat Vascular Calcification

Objective Ghrelin is a new peptide with regulatory actions in growth hormone secretion in anterior pituitary and energy metabolism. Currently, studies showed that ghrelin has potently protective effects in cardiovascular diseases. We employed rats vascular calcific model induced by vitamin D3 intramuscular injection and nicotine (P.O), and rats calcific vascular smooth muscular cells (VSMCs) induced byβ-glycerophosphate to study the possible mechanism which was involved in the regulatory action of ghrelin in vascular calcification.Methods The total aorta Ca²⁺ content in aorta and VSMCs were measured by atom absorptive spectrophotography; the alkaline phosphatase (ALP) activity in plasma, aorta and VSMCs were determined by the use of phenyl diphosphate-2-sodium; aortic 45Ca²⁺-deposition was detected with the using of 45CaCl2; the mRNA expression of ghrelin, osteopontin (OPN) and endothelin were analysized by reverse-transcript PCR, and the levels of ghrelin in plasma, endothelin in plasma and aorta were determined by radioimmunoassay.Results Vitamin D3 and nicotine induced vascular calcification in rats andβ-glycerophosphate induced calcification in VSMCs too, with increase in the total Ca²⁺ content and 45Ca²⁺-deposition in aorta and VSMCs, and ALP activity in plasma, aorta and VSMCs. However, significant decrease in OPN mRNA expression in aorta and VSMCs, and ghrelin levels in plasma (-21.8%) and its mRNA expression in aorta (-41.6%) were also observed. The calcification in aorta was significantly attenuated by subcutaneous injection administration with ghrelin 30 and 300 nmol/kg for 4 weeks, and the latter dosage was more potent than the former. After the ghrelin treatment, the total aorta Ca²⁺ contents were less by 24.4% and 28.1%, aortic 45Ca²⁺-deposition less by 18.4% and 24.9%, plasma ALP activity less by 36.6% and 76.7%, and aortic ALP activity less by 10.3% and 47.6%, respectively, than those in the rats with vascular calcification, but the OPN mRNA was up-expressed. After treated with ghrelin 10-8¹0-6mol/L, the calcification in VSMCs was also attenuated, with decrease in the total Ca²⁺content, 45Ca²⁺-deposition and ALP activity in VSMCs in a concentration-dependent manner, so did the increase in OPN mRNA expression. In addition, we observed that endothelin levels of plasma and aortic endothelin mRNA expression significantly increased in the rats with vascular calcification, and ghrelin treatment significantly decreased them, with high dosage more portent than the lower. Conclusions Our results indicated that ghrelin can significantly attenuate the calcification in aorta and VSMCs partly through the antagonism with endothelin system in circulation and vascular tissues.