Thyroid hormone replacement restores circulating enkephalin concentrations in hypophysectomized fetal sheep.
We have investigated the effects of fetal hypophysectomy (HX) with or without thyroxine (T4)replacement on the plasma concentrations of free methionine-enkephalin (free Met-Enk), noradrenaline, and adrenaline in late gestation sheep fetus. Plasma adrenaline concentrations were significantly higher in intact fetal sheep (1.05 +/- 0.12 pmol/L) between 125 and 140 days of gestation when compared with the HX + saline (0.64 +/- 0.10 pmol/L) and HX + T4 (0.61 +/- 0.08 pmol/L) groups. During the first 15 days of the T4 or saline infusion, the plasma concentrations of free Met-Enk were significantly higher in the HX + T4 group (392 +/- 40 pmol/L) than in the HX + saline group (299 +/- 43 pmol/L). At this stage of gestation, however, circulating concentrations of free Met-Enk were significantly higher in intact fetal sheep (556 +/- 51 pmol/L) than in either of the HX groups. Between 125 and 140 days of gestation, plasma free Met-Enk concentrations were similar and significantly higher in the intact and HX + T4 groups than those measured in the HX + saline fetal sheep. We conclude that the decrease in circulating free Met-Enk concentrations after removal of the fetal pituitary is primarily a consequence of functional athyroidism.
Simonetta
G
G
Department of Physiology, Monash University, Clayton, Victoria, Australia.
Young
I R
IR
McMillen
I C
IC
D000818:Animals; D004744:Enkephalin, Methionine / Q000097:blood*; D004837:Epinephrine / Q000097:blood; D005260:Female; D005312:Fetal Blood / Q000378:metabolism; D005333:Fetus / Q000502:physiology*; D005865:Gestational Age; D007016:Hypophysectomy; D007262:Infusions, Intravenous; D009638:Norepinephrine / Q000097:blood; D011247:Pregnancy; D012756:Sheep; D013974:Thyroxine / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology*
D004744:Enkephalin, Methionine; D013974:Thyroxine; D009638:Norepinephrine; D004837:Epinephrine