Growth hormone receptor deficiency results in blunted ghrelin feeding response, obesity, and hypolipidemia in mice

We have previously shown that growth hormone (GH) overexpression in the brain increased food intake, accompanied with increased hypothalamic agouti-related protein (AgRP) expression. Ghrelin, which stimulates both appetite and GH secretion, was injected intracerebroventricularly to GH[R.sup.-/-] and littermate control (+/+) mice to determine whether ghrelin's acute effects on appetite are dependent on GHR signaling. GH[R.sup.-/-] mice were also analyzed with respect to serum levels of lipoproteins, apolipoprotein (apo)B, leptin, glucose, and insulin as well as body composition. Central injection of ghrelin into the third dorsal ventricle increased food consumption in +/+ mice, whereas no change was observed in GH[R.sup.-/-] mice. After ghrelin injection, AgRP mRNA expression in the hypothalamus was higher in +/+ littermates than in GH[R.sup.-/-] mice, indicating a possible importance of AgRP in the GHR-mediated effect of ghrelin. Compared with controls, GH[R.sup.-/-] mice had increased food intake, leptin levels, and total and intraabdominal fat mass per body weight and deceased lean mass. Moreover, serum levels of triglycerides, LDL and HDL cholesterol, and apoB, as well as glucose and insulin levels were lower in the GH[R.sup.-/-] mice. In summary, ghrelin's acute central action to increase food intake requires functionally intact GHR signaling. Long-term GHR deficiency in mice is associated with high plasma leptin levels, obesity, and increased food intake but a marked decrease in all lipoprotein fractions. agouti-related protein; appetite regulation; intracerebroventriclar injection