N ω-nitro-l-arginine, l-NNA, N ω-nitro-l-arginine
methyl ester (l-NAME), l-arginine, atropine methylnitrate,
aminoguanidine, carbamylcholine, methylene blue, substance
P, N-acetyl-l-tryptophane 3,5-bis
(trifluoromethyl)-benzyl ester (ATTB), and prazosin were purchased
from Sigma (St. Louis, MO). 2-(4-Carboxyphenyl)-
4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide
(carboxy-PTIO) was produced by Calbiochem (La Jolla, CA). Bupranolol
was a gift of Schwartz Pharma, Monheim, Germany. Tetrodotoxin (TTX) was
purchased from Alomone Laboratories (Jerusalem, Israel). All other
chemicals were of analytical grade. The composition of the
Krebs–Ringer bicarbonate solution was (in mM): 118 NaCl, 4.7 KCl, 1.2
MgCl2, 2.5 CaCl2, 25
NaHCO3, 1.2
KH2PO4, and 11 glucose (pH
7.4).