Ghrelin blunted vascular calcification in vivo and in vitro in rats

Ghrelin is a new peptide with regulatory actions in growth hormone secretion in the anterior pituitary gland and in energy metabolism. Currently, ghrelin has potently protective effects in cardiovascular diseases. We used an in vivo model of rat vascular calcification induced by vitamin D-3 and nicotine and one of cultured rat vascular smooth muscular cells (VSMCs) calcification induced by beta-glycerophosphate to study the possible mechanism in the regulatory action of ghrelin in vascular calcification. Calcification increased total Ca2+ content and Ca-45(2+) deposition in aortas and VSMCs and alkaline phosphatase (ALP) activation in plasma, aortas and VSMCs. However, calcified aortas and VSMCs showed a significant decrease in osteopontin (OPN) mRNA expression and a marked reduction of ghrelin levels in plasma and its mRNA expression in aortas. The aortic calcification was significantly attenuated by subcutaneous administration of ghrelin 30 and 300 nmol kg(-1) day(-1) for 4 weeks, and the latter dosage was snore potent than the former. Ghrelin treatment at the two dosages reduced the total aorta Ca2+ content by 24.4% and 28.1%, aortic Ca-45(2+) deposition by 18.4% and 24.9%, plasma ALP activity by 36.6% and 76.7%, and aortic ALP activity by 10.3% and 47.6% (all P < 0.01 or 0.05), respectively. Ghrelin at 10(-8)-10(-6) mol/L attenuated the calcification in cultured VSMCs, with decreased total Ca2+ content, Ca-45(2+) deposition and ALP activity and increased OPN mRNA expression, in a concentration-dependent manner. In addition, endothelia levels in plasma and aortas and its mRNA expression in aortas significantly increased with calcification. but ghrelin treatment significantly decreased endothelia levels and mRNA expression, with the high dosage being more potent than the lower dosage. These results indicate that local ghrelin in vascular was down-regulated during vascular calcification, whereas administration of ghrelin effectively attenuated vascular and VSMCs calcification. (c) 2005 Elsevier B.V. All rights reserved.