Differential effects of estrogen and growth hormone on uterine and hepatic insulin-like growth factor I gene expression in the ovariectomized hypophysectomized rat.
The acute and chronic effects of 17 beta-estradiol (E2) and GH on uterine and hepatic insulin-like growth factor I (IGF-I) gene expression in ovariectomized hypophysectomized (ovx-hypox) rats were examined. Six hours after a single injection of E2 (5 micrograms/100 g BW), uterine IGF-I gene expression was increased 22.5 +/- 5.4-fold (P less than 0.005) above that in untreated rats. In the same experiment E2 alone had no significant effect on hepatic IGF-I gene expression. Similarly, in chronic experiments uterine IGF-I in ovx-hypox rats receiving 0.1 or 1 microgram/rat.day E2 for 10 days was significantly increased compared to that in ovx-hypox rats that did not receive E2 [5.38 +/- 0.79 vs. 1.10 +/- 0.15 (P less than 0.005) and 6.64 +/- 0.28 vs. 0.93 +/- 0.06 (P less than 0.005), respectively]. While administration of human GH alone significantly increased uterine IGF-I expression (3.76 +/- 1.61-fold compared to that in untreated rats; P less than 0.05), a significant and reproducible attenuation of E2-induced IGF-I expression was seen in the two acute experiments where GH reduced the E2-induced response by 36 +/- 3.7% and 53 +/- 19.4%. While chronic administration of E2 to ovx-hypox rats resulted in uterine growth, a significant decrease in body weight was seen in rats treated with 1 microgram/day E2 compared to that in untreated ovx-hypox controls (-4.3 +/- 1.5 vs. 2.5 +/- 0.6 g; P less than 0.0005). E2 treatment also significantly decreased the GH-induced increase in weight gain at each GH dose by approximately 40%. GH-induced hepatic IGF-I gene expression and serum IGF-I concentration were similarly reduced by chronic E2 administration. In contrast, in acute experiments where E2 alone had no effect on hepatic IGF-I expression, it acted in a synergistic fashion with GH and resulted in significantly greater accumulation of IGF-I mRNA. From these observations we conclude that 1) both E2 and human GH are potent stimulators of IGF-I gene expression in appropriate target tissues; and 2) in addition to any effects E2 has on GH secretion and IGF-I action, the growth-retarding effect of estrogen in the rat involves inhibition of GH-dependent hepatic IGF-I expression.
Murphy
L J
LJ
Department of Physiology, Faculty of Medicine, University of Manitoba, Winnipeg, Canada.
Friesen
H G
HG
D000818:Animals; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D005796:Genes; D013006:Growth Hormone / Q000494:pharmacology*; D007016:Hypophysectomy; D007334:Insulin-Like Growth Factor I / Q000235:genetics*; D007700:Kinetics; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D009693:Nucleic Acid Hybridization; D010052:Ovariectomy; D051381:Rats; D011919:Rats, Inbred Strains; D013002:Somatomedins / Q000235:genetics*; D014158:Transcription, Genetic / Q000187:drug effects*; D014599:Uterus / Q000187:drug effects / Q000378:metabolism*
D013002:Somatomedins; D004958:Estradiol; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone