Differential effects of continuous versus intermittent administration of growth hormone to hypophysectomized female rats on serum lipoproteins and their apoproteins.
The effects of the plasma pattern of GH on serum and lipoprotein levels of total cholesterol, triglycerides, apolipoprotein A-I (apo A-I), apolipoprotein B 48/100 (apo B), and apolipoprotein E (apo E) were studied in hypophysectomized female Sprague-Dawley rats, which had been given replacement therapy with L-T4 and hydrocortisone. Bovine GH (1 mg/kg.day) was administered sc either continuously by means of osmotic minipumps or by two daily injections. Serum lipoproteins were separated by sequential ultracentrifugation into very low density lipoproteins [density (d) less than 1.006 g/ml], low density lipoproteins (LDL; d 1.006-1.063 g/ml) and high density lipoproteins (HDL; d 1.063-1.21 g/ml). The content of total cholesterol and triglycerides were then determined. Apo A-I, apo B, and apo E were isolated from rat serum and antibodies raised in rabbits. In serum and in lipoprotein fractions, the content of apo A-I, apo-B, and apo E were determined by electroimmunoassay. After hypophysectomy, there occurred a decrease in serum cholesterol and serum levels of apo A-I and apo E, in spite of replacement therapy with T4 and cortisone. Similar changes were also observed in HDL. In contrast, apo B, cholesterol, and triglycerides were increased in LDL. Estradiol treatment had no effect on these changes. Continuous infusion of GH resulted in an increase in cholesterol and apo E in serum and HDL to the levels of intact females. In contrast, GH given twice daily had no effect. Therefore, the sexually dimorphic secretion of GH may be important for the regulation of sex differences in apo E and HDL cholesterol levels. There were no consistent effects of GH treatment on the levels of apo A-I in serum or HDL, but GH treatment resulted in a decrease in apo B and triglycerides in both serum and LDL, regardless of the mode of administration. This suggests that GH regulates the serum and LDL levels of apo B and triglycerides independently of the secretory pattern.
Department of Physiology, University of Göteborg, Sweden.
J
J
Oscarsson
S O
SO
Olofsson
G
G
Bondjers
S
S
Edén
D000818:Animals; D001053:Apolipoproteins / Q000097:blood*; D001835:Body Weight / Q000187:drug effects; D002784:Cholesterol / Q000097:blood; D004334:Drug Administration Schedule; D004343:Drug Implants; D005260:Female; D013006:Growth Hormone / Q000008:administration & dosage / Q000494:pharmacology*; D007016:Hypophysectomy; D007262:Infusions, Intravenous; D007279:Injections, Subcutaneous; D008074:Lipoproteins / Q000097:blood* / Q000302:isolation & purification; D008970:Molecular Weight; D051381:Rats; D011919:Rats, Inbred Strains; D012016:Reference Values; D014280:Triglycerides / Q000097:blood
D001053:Apolipoproteins; D004343:Drug Implants; D008074:Lipoproteins; D014280:Triglycerides; D013006:Growth Hormone; D002784:Cholesterol