Rat visceral yolk sac: a target for parathyroid hormone action

The stimulation of cAMP production by parathyroid hormone [human PTH-(1-34)] in fetal membranes was studied over the last 9 days of pregnancy in the rat. PTH significantly stimulated cAMP production in the placental and capsular parts of the visceral yolk sac at all days studied. In contrast PTH stimulated cAMP production in the amnion only at days 14 and 17 and had no effect in the maternal and fetal sides of the placenta nor in the parietal yolk sac before it degenerated (day 14). The biochemical characteristics of PTH-stimulated cAMP production in visceral yolk sac are similar to those reported in other systems: a) maximal stimulation was obtained with 1.2 X 10(-7) M hPTH-(1-34) and 50% stimulation achieved by 2-3 X 10(-8) M; and b) the antagonist [Nle8,Nle18,Tyr34] bovine PTH-(3-34) amide competitively inhibited the stimulation of cAMP production by hPTH-(1-34). These results strongly suggest that the rat visceral yolk sac is a target organ for PTH during the last 9 days of pregnancy.