Discovery of components of the renin-angiotensin system (RAS) in the adenohypophysis of several species has prompted speculation concerning the location and possible function of a pituitary RAS. Although both renin and angiotensin I1 have been localized within the rat adenohypophysis, their colocalization has not been previously demonstrated within the same cells. In the present study, immunohistochemical staining by the avidin-biotin-peroxidase complex technique was used to demonstrate the coexistence of renin and angiotensin I1 in adenohypophyseal cells identified morphologically and immunocytochemically as gonadotrophs. These results support the existence of an adenohypophyseal RAS, at least part of which is under intracellular control. The influence of this system on control of fluid balance, blood pressure, and the secretion of other hypophyseal hormones is discussed.Renin (EC 3.4.99.19) is the primary enzyme in the system which produces the potent vasoconstrictor angiotensin I1 from the prohormone angiotensinogen. The components of this cascade (angiotensinogen, renin, angiotensin I (AI)) angiotensin-coverting enzyme, angiotensin I1 (AII)) are collectively referred to as the reninangiotensin system (RAS). Reninlike or immunosuppressible renin activity has been detected biochemically in the pituitary gland of rat (Haulica et al., 1975; Naruse et al., 19851, dog (Day and Reid, 1976), human (Haulica et al., 1977;Slater et al., 1980), and hog . In addition, renin has been identified immunocytochemically in the pituitary of rat Naruse et al., 1981), mouse , and human (Slater et al., 1980). Renin-positive cells of the rat pituitary have been identified as luteinizing-hormone (LH)-containing gonadotrophs (Naruse et al., 1981).The presence of A n has also been reported in the pituitary although there remains some controversy concerning its distribution. Ganten et al. (1978) presence of a complete or near-complete RAS in these cells. This system may play an important role in the control of blood pressure and fluid regulation. The purpose of the present study was, therefore, to test the above hypothesis by demonstrating the coexistence of renin and A11 in the same cells. This was attempted by analysis of serial sections immunostained for renin and A11 and by double-staining colocalization of these substances with pituitary hormones.
MATERIALS AND METHODS
Tissue PreparationsMale Sprague-Dawley rats (200-300 gm) were perfused 48 hours following bilateral nephrectomy. Under nembutal anesthesia the animals were thoroughly perfused via the left ventricle with Tyrode's buffer (pH 7.2) containing 0.8% NaCl, 0.02% KC1,0.026% CaCl2 *2H20, 0.01% MgC12.6H20, 0.1% NaHC03, 0.005% NaH2P04, 0.1% D-glucose, and 0.2% MgS04.7H20. The rats were then perfused with 200 ml cold (4°C) Perfix (Fisher, Pittsburg, PA). The pituitaries were quickly removed and fixed by immersion in Perfix for an additional 3 hours followed by dehydration in the standard ethanol/ xylene series and then embedded in paraffin. Serial sections were cut at...