Prostanoids, but not nitric oxide, counterregulate angiotensin II mediatedvasoconstriction in vivo

To evaluate the modulating effects of nitric oxide and prostanoids during a ngiotensin II-mediated vasoconstriction, male Wistar rats (n = 25) were inf used with increasing doses of angiotensin II following pretreatment with th e cyclooxygenase inhibitor indomethacin, the nitric oxide-synthase inhibito r NG-nitro-L-arginine methyl ester (L-NAME) plus sodium nitroprusside to re store mean arterial blood pressure. or saline. Hemodynamics were studied wi th the radioactive microsphere method. Indomethacin did not alter systemic or regional hemodynamics. L-NAME + sodium nitroprusside reduced cardiac out put, as well as systemic and renal vascular conductance. Angiotensin II inc reased mean arterial blood pressure and heart rate, and decreased systemic vascular conductance as well as vascular conductance in gastrointestinal tr act, kidney, skeletal muscle, skin, mesentery + pancreas, spleen and adrena l. Indomethacin enhanced the angiotensin II-mediated effects in all vascula r beds, whereas L-NAME + sodium nitroprusside enhanced its effect in mesent ery + pancreas only. In conclusion, vasodilator prostanoids, but not nitric oxide, counterregulate angiotensin II-mediated vasoconstriction in vivo. ( C) 2001 Elsevier Science B.V. All rights reserved.