NITRIC-OXIDE INHIBITION CAUSES AN EXAGGERATED PRESSOR-RESPONSE IN YUCATAN MINIATURE SWINE

The involvement of nitric oxide (NO) in cardiovascular and renal funct ion was evaluated in 12 anesthetized Yucatan miniature swine. The effe ct of NO blockade on blood pressure was measured in six additional con scious swine. In the anesthetized swine, mean arterial pressure (MAP), heart rate, glomerular filtration rate (GFR), and urinary excretion o f water, sodium, and potassium were measured after systemic inhibition of NO synthesis by N-G-nitro-L-arginine methyl ester (L-NAME), and we re compared with values for a control period, After NO synthesis block ade, MAP increased by 63+/-5 mm Hg, a far greater increase than those observed in rats, dogs, domestic swine, or humans. The changes in GFR, urine flow rate (UFR), and sodium excretion (UNaV) were time-dependen t. The GPR decreased to 50+/-6% of control values immediately after L- NAME administration, but returned to control values within 1 h. Signif icant increases in UFR and UNaV were observed only during the third ex perimental period, 40 to 60 min after drug infusion. In the conscious swine, L-NAME administration increased MAP by 24+/-4 mm Hg. Administra tion of the sympatholytic hexamethonium bromide fully reversed the inc rease of MAP in anesthetized and conscious swine. These findings indic ate that NO has an important role in the maintenance of cardiovascular and renal function in Yucatan miniature swine. The exaggerated presse r response to NO blockade in miniature swine appears to involve the sy mpathetic nervous system.