EFFECT OF CHRONIC INFUSION OF PLACENTAL-LACTOGEN ON OVINE FETAL GROWTH IN LATE-GESTATION

To test the hypothesis that placental lactogen (PL) is a humoral regul ator of fetal growth, six singleton sheep fetuses received a continuou s intravenous fusion of 1.2 mg/d of purified ovine PL (oPL) for 14 d, beginning on Day 122 of gestation. The plasma concentration of oPL was approximately four-fold higher in infused fetuses than in six control fetuses that received a continuous infusion of saline. The circulatin g insulin-like growth factor 1 (IGF-I) concentration was also signific antly elevated in PL-infused fetuses (43.1 +/- 1.7 vs. 31.9 +/- 4.1 ng /ml; P < 0.05). Animals were slaughtered on Day 136, and the placenta and all major fetal tissues were dissected, weighed, and subsampled fo r chemical analysis. Fetal weight and crown-rump length were not signi ficantly affected by treatment; however, the aggregate weight of the b rain, liver, lungs, and heart tended to be larger (85.3 +/- 2.1 vs. 79 .9 +/- 1.5 g/kg fetus; mean +/- SE, P = 0.07) and the thyroid gland wa s smaller (0.18 +/- 0.1 vs. 0.26 +/- 0.02 g/kg fetus; P < 0.05) in the PL-infused fetuses. The livers of the PL-infused fetuses had also acc umulated additional glycogen (13.1 +/- 1.7 vs. 8.4 +/- 0.7 g; P < 0.05 ). In late gestation, PL within the fetal compartment increases fetal plasma IGF-I concentration and hepatic glycogen deposition and may aff ect the growth of several vital organs. (C) Elsevier Science Inc. 1996