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Metabolism Unit, Center for Metabolism and Endocrinology, Department of Medicine and Molecular Nutrition Unit, Center for Nutrition and Toxicology, NOVUM, Karolinska Institute at Karolinska University Hospital at Huddinge, S-141 86 Huddinge, Sweden
Submitted 10 December 2003 ; accepted in final form 10 March 2004
Previous studies have established that growth hormone (GH) has many important effects on the regulation of cholesterol and lipoprotein metabolism. However, human GH (hGH) can also bind to prolactin receptors, eliciting prolactin receptor-mediated effects. In this study, we evaluated whether hGH can exert such responses in currently used animal models and whether prolactin affects lipoprotein and/or hepatic cholesterol metabolism. Normal and hypophysectomized (Hx) male rats were given either hGH or bovine GH, the latter unable to bind to the prolactin receptor. The hormones were continuously infused by use of subcutaneous osmotic mini-pumps for 7 days; blood and livers were collected after euthanasia. Both hormones stimulated hepatic LDL receptor expression and bile acid synthesis to a similar extent and normalized the altered plasma lipoprotein pattern in Hx rats. Prolactin, injected twice daily to Hx male rats, did not exert any effects on the plasma lipoprotein pattern or on cholesterol metabolism. We conclude that previously established effects of hGH on cholesterol metabolism are not mediated by prolactin in male rats.
plasma cholesterol; low-density lipoprotein receptor; cholesterol-7
-hydroxylase
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