Abstract-Administration of adrenocorticotropic hormone (ACTH) leads to the development of hypertension. Because glucocorticoids can affect the nitric oxide system at several sites, the present study tested the hypothesis that nitric oxide synthase (NOS) expression may be altered in ACTH-induced and corticosterone-induced hypertension in the rat. This was addressed by measuring Nos1, Nos2, and Nos3 mRNA in the kidney, adrenal gland, heart, and hypothalamus of 16 ACTH-treated and 16 vehicle-treated rats as well as in 10 corticosterone-treated and 10 control rats. In addition, in situ hybridization and immunohistochemistry were used to confirm changes by detection of Nos in RNA and NOS protein in tissues. Systolic blood pressure of ACTH and corticosterone rats was elevated (165Ϯ6 and 162Ϯ11 mm Hg; PϽ0.001 versus control). Each Nos isoform mRNA was measured by reverse transcriptase-polymerase chain reaction technique. In ACTH rats, mRNA for Nos2 was reduced in renal cortex by 58Ϯ5% and in medulla by 68Ϯ7%; for Nos3, mRNA reductions of 59Ϯ6% and 51Ϯ11% were seen (PϽ0.001 after Hochberg correction for multiple comparisons). In corticosterone rats, Nos2 mRNA decreased in cortex by 68Ϯ5% and in medulla by 62Ϯ6%; Nos3 mRNA by 50Ϯ8% in cortex, and Nos1 by 29Ϯ7% in medulla (all PϽ0.001 after Hochberg correction). Reductions seen in kidney were supported by in situ hybridization and immunohistochemistry. Apart from a 62Ϯ2% decrease in Nos2 mRNA in adrenal of ACTH rats (corrected PϽ0.05), no significant changes were seen in the other nonrenal tissues for any isoform. Key Words: immunohistochemistry Ⅲ hybridization Ⅲ RNA Ⅲ nitric oxide Ⅲ isoenzymes Ⅲ reverse transcriptase-polymerase chain reaction A dministration of adrenocorticotropin (ACTH) produces hypertension in humans, rats, dogs, and sheep, and excess endogenous secretion is associated with Cushing's syndrome. 1 The elevation in blood pressure (BP) is explicable by the action of cortisol in humans 2 and corticosterone in the rat, 3 but the mechanism by which these steroids raise BP is still not well understood. Studies of ACTH-induced and corticosterone-induced hypertension in the rat and cortisolinduced hypertension in humans suggest a role for the nitric oxide (NO) system in these forms of hypertension. [3][4][5] Given that glucocorticoids are known to have several potential sites of action in the NO system, including an inhibitory effect on transmembrane L-arginine transport 6 and suppression of nitric oxide synthase (NOS)2 7 as well as tetrahydrobiopterin synthesis, 6 we wanted to define whether elements of the NO system are altered in ACTH-induced hypertension. Contrary to early views, reflected in their nomenclature, each NOS has varying degrees of constitutive and inducible capabilities. 8,9 The aim of the present study was to examine NOS expression in ACTH, corticosterone, and vehicle-treated rats. Because dexamethasone can reduce human NOS3 promoter activity and mRNA stability 10 and NOS2 control is at the level of transcription and protein stability, 11 we lo...
