Late pregnancy increases hepatic expression of insulin-like growth factor-I in well nourished guinea pigs

Blood IGF-I concentrations are persistently elevated throughout pregnancy in humans and guinea pigs and may regulate substrate partitioning between mother and conceptus. In the guinea pig, liver and adipose tissue have recently been suggested to contribute to the increased levels of circulating IGF-I in mid-pregnancy, but whether this persists in late pregnancy in undernutrition is not known. Therefore the effect of pregnancy and undernutrition on circulating IGF-I and hepatic expression of IGF-I in late gestation in the guinea pig was examined. Female guinea pigs (Cavia porcellus) were fed ad libitum throughout pregnancy or 70% of ad libitum intake for 28 days prior to and throughout pregnancy (term is 69 d). Non-pregnant animals were maintained for 88 days on the same diets. Plasma IGF-I was measured by RIA after molecular sieving chromatography at low pH. Abundances of IGF-I and beta-actin mRNA in maternal liver were quantified by digoxigenin-ELISA after RT PCR. Late pregnancy increased both the concentration of IGF-I protein (p<0.001) in plasma and the relative abundance of liver IGF-I mRNA (p<0.001) in ad libitum fed, but not in feed restricted pregnant guinea pigs. The concentration of IGF-I protein in plasma correlated positively with the relative abundance of IGF-I mRNA in liver overall (p<0.002), suggesting the liver as a major source of endocrine IGF-I in late pregnant guinea pigs. This study demonstrates that hepatic expression of IGF-I remains elevated during late pregnancy in the well fed guinea pig, which is in contrast to that observed in other non-human species.