Prostaglandin E-binding sites in the fetal adrenal

Prostaglandin E2 (PGE2) is specifically and reversibly bound by particulate fractions from adrenals from fetal calves and lambs. These binding sites appear to be located primarily in the adrenal medulla and have properties very similar to those which we have detected in adult human, bovine, and ovine adrenal medulla. The rate constant for the association reaction between [3H]PGE2 and its binding sites in fetal calf adrenals is 1.8 X 10(5) M-1 sec-1. The [3H]PGE2-binding site complex dissociates in a biphasic manner, with rate constants of 6.7 X 10(-4) sec-1 and 4.2 X 10(-5) sec-1 for the fast and slow phases, respectively. The Kd values for the interactions of PGE2 with particulate fractions from adrenals of fetal calves and lambs are 2.3 and 3.5 nM, respectively. The [3H]PGE2-binding sites are very specific for PGE1 and PGE2. The affinities of other prostaglandins (PGF2 alpha greater than PGA2 greater than 13,14-dihydro-15-oxo-PGE2 greater than PGD2 greater than 6-oxo-PGF1 alpha) are 130- to 1300-fold lower. We have detected binding sites in adrenals from fetal calves as early as 112 days of gestation. The concentration of binding sites in fetal calf adrenals increases from 0.11 to 0.18 pmol/mg protein between about 130 days of gestation and term. The concentration of binding sites in fetal lamb adrenals (approximately 0.07 pmol/mg protein) does not change appreciably between about 100 days of gestation and term. These results suggest that PGE-binding sites are present in fetal adrenal medulla in mid- and late gestation and are consistent with a role for PGEs in controlling catecholamine release from the fetal adrenal.