Administration of Growth Hormone to Pregnant Rats on a Reduced Diet Inhibits Growth of Their Fetuses*

Abstract

During gestation, female rats become resistant to the anabolic actions of GH. The importance of this resistance for conceptus growth was investigated by treating pregnant dams on a reduced diet with ovine (o) or bovine (b) GH during days 10-20 of gestation. Reducing food intake to 60% that of ad libitum-fed controls significantly depleted maternal inguinal fat stores by day 20 of gestation, but it did not affect the growth of the fetuses or the placentas. In the food-restricted dams, twice daily injections of oGH (1 mg/day) or bGH (5 mg/day) during days 10-20 of gestation increased their inguinal fat pad wet weight by 28% and 62%, respectively, but had no effect on the wet weight of maternal heart, liver, or spleen. The dams treated with bGH had significantly heavier kidneys than the PBS- or oGH-treated females. On day 20 of gestation, control animals fed a 60%-diet had total serum insulin-like growth factor-I levels that were depressed to the same extent as those in ad libitum fed dams (i.e. to about 25% of the levels in nonpregnant females). Both the oGH and bGH treatments significantly elevated maternal serum insulin-like growth factor-I to 42% and 300%, respectively, of the levels in the untreated underfed dams. Compared to virgin controls, maternal tibial epiphyseal plate width was also significantly diminished in dams fed ad libitum or a 60% diet. Nevertheless, oGH and bGH were effective at augmenting maternal tibial epiphyseal plate width to equal those in virgin controls. Both doses of GH significantly reduced placental and fetal weights compared to those of PBS-injected dams on a 60% diet, and dams treated with the higher dose of GH were in an advanced stage of fetal and placental resorption by day 20 of gestation. Thus, maternal resistance to the anabolic actions of GH appears to be an important adaptation for diverting nutrients from the mother to the fetus.