The fetal somatotropic axis during long term maternal undernutrition in sheep: evidence for nutritional regulation in utero.

Abstract

Nutrition is a major determinant of the somatotropic axis during postnatal life. However, little is known about the response of the fetal somatotropic axis to nutritional limitation. From day 100 of gestation (term = 147 days), singleton-bearing ewes were fed either ad libitum (control; n = 6) or 25% of the recommended energy and protein requirements (restricted; n = 7). Ewes and fetuses were chronically catheterized on day 110. On day 120, paired maternal and fetal blood samples were taken over a 6-h period at 15-min intervals. Forty-eight hours later, fetuses were given a 20-micrograms GRF bolus (i.v.), and samples were collected for 48 h. Undernourished mothers and fetuses had higher GH concentrations (P < 0.05). Although plasma GH profiles were independent in mothers and their fetuses, both maternal and fetal GH peak and nadir levels were increased (P < 0.05) by nutritional restriction, but the peak/nadir ratio and the number of pulses remained unaltered. Deconvolution analysis showed that the GH mass secreted per burst was higher in nutritionally restricted animals, whereas basal GH secretion and GH serum half-life were not influenced by undernutrition. Both maternal and fetal insulin-like growth factor-I levels were reduced (P < 0.01 and P < 0.05), whereas insulin-like growth factor-II concentrations were not influenced by the feed restriction. Fetuses from restricted mothers had higher peak GH concentrations after a GRF challenge (P < 0.001), but after correction The specific binding of [125I]ovine placental lactogen ([125I]oPL) or [125I]oGH to maternal or fetal hepatic microsomal membrane preparations was not changed by the maternal undernutrition. Maternal oPL concentrations showed considerable short term fluctuations, whereas fetal oPL levels revealed no major fluctuations. Mean maternal oPL levels tended (P < 0.06) to be elevated, whereas fetal oPL concentrations tended (P < 0.06) to be decreased in restricted animals. These results provide evidence that the somatotropic axis is functional in utero and suggest that the fetal somatotropic axis plays an active role during adaptation of the fetus to nutritional limitation.