Angiotensin-converting enzyme localized in the rat pituitary and adrenal glands by [³h]captopril autoradiography

We have localized angiotensin-converting enzyme (EC 3.14.5.1) in the rat pituitary and adrenal glands by [³H]captopril autoradiography. The maximal numbers of [³H] captopril-binding sites are: Posterior pituitary, 4500 fmol/mg protein; anterior pituitary, 1950 fmol/mg; intermediate pituitary, <100 fmol/mg; adrenal medulla, 480 fmol/mg; and adrenal cortex, <25 fmol/mg. The distribution within the posterior pituitary and adrenal medulla is homogeneous, whereas that in the anterior pituitary is patchy. Subcellular fractionation of the bovine adrenal medulla reveals enrichment of angiotension-converting enzyme in plasma membrane fractions, but not in chromaffin granules. [³H]Captopril autoradiography in the rat pituitary gland is unaltered by dehydration, adrenalectomy, or reserpine treatment and in Brattleboro rats. [³H]Captopril binding in the adrenal medulla is increased by 75% 3 weeks after hypophysectomy and is elevated by 80% after reserpine treatment. The change after hypophysectomy is not reversed by dexamethasone treatment.