Effects of an antiserum to rat growth hormone and bromocriptine on cholesterol-metabolizing enzymes in the lactating rat mammary gland

in Journal of Endocrinology
Authors:
J. H. Shand
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D. W. West
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ABSTRACT

Rats in mid-lactation were treated, for 2 days, with anti-rat GH serum (anti-rGH) and/or bromocriptine before microsomes were prepared from the freeze-clamped mammary glands. The effects of these anti-hormone treatments on the concentrations of microsomal cholesterol and cholesterol esters and on the activities of acyl-CoA:cholesterol acyltransferase (ACAT), neutral cholesterol ester hydrolase and 3-hydroxy-3-methylglutaryl-CoA reductase (HMG-CoA reductase) were measured. HMG-CoA reductase was determined in microsomes prepared in both the presence and absence of phosphatase inhibitors to determine the expressed and total activities respectively.

Anti-rGH reduced HMG-CoA reductase and increased microsomal cholesterol and cholesterol esters. Bromocriptine reduced HMG-CoA reductase but increased all of the other parameters. The results indicate that the initial stage in the stimulation of milk secretion involves a decrease in the activity of ACAT and that the phosphorylation level of HMG-CoA reductase is modulated by both prolactin and GH acting in opposition.

Journal of Endocrinology (1991) 128, 287–295

 

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