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.