Effects of an antiserum to rat growth hormone and bromocriptine on cholesterol-metabolizing enzymes in the lactating rat mammary gland.
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.
Shand
J H
JH
Hannah Research Institute, Ayr.
West
D W
DW
D000818:Animals; D001971:Bromocriptine / Q000494:pharmacology*; D002784:Cholesterol / Q000378:metabolism*; D002788:Cholesterol Esters / Q000378:metabolism; D005260:Female; D013006:Growth Hormone / Q000276:immunology*; D006903:Hydroxymethylglutaryl CoA Reductases / Q000378:metabolism; D007106:Immune Sera / Q000494:pharmacology*; D007774:Lactation / Q000378:metabolism*; D008321:Mammary Glands, Animal / Q000201:enzymology*; D008861:Microsomes / Q000201:enzymology; D011247:Pregnancy; D051381:Rats; D002785:Sterol O-Acyltransferase / Q000378:metabolism
D002788:Cholesterol Esters; D007106:Immune Sera; D001971:Bromocriptine; D013006:Growth Hormone; D002784:Cholesterol; D006903:Hydroxymethylglutaryl CoA Reductases; D002785:Sterol O-Acyltransferase