The induction of hepatic somatotrophic receptors after birth in sheep is dependent on parturition-associated mechanisms.
While the GH receptor (GHR) plays a key role during adult life, its role during fetal development is not well understood. Recent data suggest that GHRs are present in ovine fetal hepatic tissue at mid-gestation. However, the levels of GHR expression are markedly lower in fetal hepatic tissue in comparison with postnatal values. The present study investigates whether the neonatal induction of the hepatic GHR and plasma levels of IGF-I follow a pattern of strictly age-related development or whether birth-associated processes stimulate this increase. Stereotaxic electrolytic lesioning of the fetal paraventricular nuclei was employed to prolong gestation markedly. We compared the hepatic binding of ovine placental lactogen (oPL) and oGH and plasma levels of IGF-I in these post-mature fetuses with those in pre-term fetuses, pregnant mothers and lambs which were of the same conceptional age as the post-mature fetuses. While specific binding of both 125I-labelled oGH and 125I-labelled oPL to hepatic microsomal membranes was fully reversible in all groups, the specific binding of 125I-labelled oGH was significantly (P < 0.001) lower than specific binding of 125I-labelled oPL in all groups of animals. There was no difference in specific 125I-labelled oGH or 125I-labelled oPL binding in livers or plasma levels of IGF-I in post-mature fetuses in comparison with pre-term fetuses. In contrast, a major increase (P < 0.001) in 125I-labelled oGH and 125I-labelled oPL binding and plasma IGF-I levels was observed in lambs.(ABSTRACT TRUNCATED AT 250 WORDS)
Breier
B H
BH
Department of Paediatrics, University of Auckland, New Zealand.
Ambler
G R
GR
Sauerwein
H
H
Surus
A
A
Gluckman
P D
PD
D000818:Animals; D000831:Animals, Newborn / Q000378:metabolism*; D005260:Female; D013006:Growth Hormone / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D007425:Intracellular Membranes / Q000378:metabolism; D008099:Liver / Q000196:embryology / Q000378:metabolism*; D008297:Male; D008862:Microsomes, Liver / Q000378:metabolism; D010928:Placental Lactogen / Q000378:metabolism; D011247:Pregnancy; D011485:Protein Binding; D011986:Receptors, Somatotropin / Q000378:metabolism*; D012756:Sheep / Q000378:metabolism*
D011986:Receptors, Somatotropin; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone; D010928:Placental Lactogen