The effect of acute and chronic insulin administration on insulin-like growth factor-I expression in the pituitary-intact and hypophysectomised rat.
Although growth hormone is known to be the main regulator of insulin-like growth factor-I, insulin has also been shown to play a role in regulating serum insulin-like growth factor I levels in diabetic animals. While this effect is thought to be due to correction of metabolic perturbations, some studies have suggest that insulin may have a direct effect on growth and/or insulin-like growth factor-I levels. We have examined the effects of acute and chronic insulin administration to non-diabetic, pituitary-intact and hypophysectomised rats. Rats were injected intraperitoneally with insulin as an acute bolus (10 U) or a chronic subcutanious infusion (low dose; 2.4 U/day, high dose; 12 U/day) over 5 days. Insulin-like growth factor-I mRNA was quantitated by Northern and slot blots of RNA from various tissues. A small (less than 2-fold) but significant increase (p less than 0.05) was seen in hepatic insulin-like growth factor-I mRNA abundance in pituitary-intact rats following acute insulin injection and chronic low dose insulin infusion. An increase in insulin-like growth factor-I mRNA levels was also seen in other tissues including diaphragm, lung, kidney and heart. A significant increase (p less than 0.05) in serum insulin-like growth factor-I levels was also observed 6 h after insulin injection. In contrast, in pituitary-intact rats which received high dose insulin infusion and were hypoglycaemic at the time of death, tissue levels of insulin-like growth factor-I mRNA were reduced compared to saline-treated control groups.(ABSTRACT TRUNCATED AT 250 WORDS)
Salamon
E A
EA
Department of Internal Medicine, Faculty of Medicine, University of Manitoba, Winnipeg, Canada.
Luo
J
J
Murphy
L J
LJ
D000818:Animals; D004334:Drug Administration Schedule; D005260:Female; D006321:Heart / Q000187:drug effects; D007016:Hypophysectomy; D007328:Insulin / Q000008:administration & dosage / Q000494:pharmacology*; D007334:Insulin-Like Growth Factor I / Q000096:biosynthesis / Q000235:genetics*; D007668:Kidney / Q000187:drug effects / Q000378:metabolism; D007700:Kinetics; D008099:Liver / Q000187:drug effects / Q000378:metabolism; D009132:Muscles / Q000187:drug effects / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism; D009693:Nucleic Acid Hybridization; D009928:Organ Specificity; D012333:RNA, Messenger / Q000187:drug effects / Q000235:genetics; D051381:Rats; D011919:Rats, Inbred Strains; D012016:Reference Values; D013002:Somatomedins / Q000235:genetics*
D007328:Insulin; D012333:RNA, Messenger; D013002:Somatomedins; D007334:Insulin-Like Growth Factor I