Regulation of serum insulin-like growth factor-I (IGF-I), hepatic growth hormone binding and IGF-I gene expression in the rat during pregnancy and lactation.
An apparent GH resistance occurs in pregnancy, since GH concentrations in serum are reported to be normal or elevated, whereas serum IGF-I falls to very low levels. To determine whether this GH resistance is manifest at the level of the hepatic GH receptor or in the ability of GH to initiate IGF-I gene expression, we have determined hepatic IGF-I mRNA expression, circulating IGF-I and hepatic GH binding during various stages of pregnancy and lactation in the rat. The concentration of IGF-I in serum fell from 37 +/- 5 nmol/l (means +/- S.E.M.) in virgin rats to 17 +/- 1 nmol/l in rats in late pregnancy, recovered in early lactation (31 +/- 3 nmol/l) but was again significantly lower than in virgin animals by mid-lactation (22 +/- 3 nmol/l). Hepatic GH binding did not vary significantly during pregnancy but showed a small significant decrease in early lactation when expressed per mg membrane protein. When expressed as GH binding per liver, however, there were no significant changes in GH binding at any stage. Liver weight increased significantly between virgin and early pregnant animals (7.1 +/- 0.2 g compared with 9.2 +/- 0.5 g respectively, P < 0.01) and continued to increase up to late lactation (14.3 +/- 0.4 g).(ABSTRACT TRUNCATED AT 250 WORDS)
Travers
M T
MT
Hannah Research Institute, Ayr, U.K.
Madon
R J
RJ
Flint
D J
DJ
D000818:Animals; D005260:Female; D005786:Gene Expression Regulation / Q000502:physiology; D013006:Growth Hormone / Q000378:metabolism*; D007334:Insulin-Like Growth Factor I / Q000235:genetics / Q000378:metabolism*; D007774:Lactation / Q000378:metabolism*; D008099:Liver / Q000033:anatomy & histology / Q000378:metabolism*; D009929:Organ Size / Q000502:physiology; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000378:metabolism*; D011485:Protein Binding; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017208:Rats, Wistar
D012333:RNA, Messenger; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone