Growth hormone secretion during pregnancy: altered effects of growth hormone releasing factor and insulin-like growth factor-I in vitro.
Growth hormone (GH) secretion is controlled by growth hormone releasing factor (GRF) but changes in the circulating level of this hormone are difficult to measure. Insulin-like growth factor (IGF-I) is a GH-dependent growth factor which significantly but slightly inhibits stimulated GH release in vitro. We have tested the effects of GRF and IGF-I on GH release in pregnancy, a state in which serum concentrations of GH are elevated and levels of IGF-I are lowered. We have found, in a system of acutely dispersed adenohypophysial cells prepared from pregnant (day 21-23) or control cycling female rats, that adenohypophysial cells from pregnant rats have an increased GH release with GRF. In contrast, IGF-I inhibition is similar but slightly smaller. These altered responses may result in elevated serum GH levels during pregnancy.
D000818:Animals; D002478:Cells, Cultured; D005260:Female; D013006:Growth Hormone / Q000378:metabolism*; D013007:Growth Hormone-Releasing Hormone / Q000494:pharmacology*; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D007700:Kinetics; D010903:Pituitary Gland, Anterior / Q000187:drug effects / Q000378:metabolism*; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D012016:Reference Values; D013002:Somatomedins / Q000494:pharmacology*; D013004:Somatostatin / Q000494:pharmacology
D013002:Somatomedins; D013004:Somatostatin; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone