Comparison of the pharmacological properties of EDHF-mediated vasorelaxation in guinea-pig cerebral and mesenteric resistance vessels

Abstract

In the presence of L-NNA (100 microM), indomethacin (10 microM) and ODQ (10 microM), acetylcholine induced a concentration-dependent vasorelaxation of guinea-pig mesenteric and middle cerebral arteries precontracted with cirazoline or histamine, but not with high K(+), indicating the contribution of an endothelium-derived hyperpolarizing factor (EDHF). In cerebral arteries, charybdotoxin (ChTX; 0.1 microM) completely inhibited the indomethacin, L-NNA and ODQ-insensitive relaxation; iberiotoxin (IbTX, 0.1 microM), 4-aminopyridine (4-AP, 1 mM), or barium (30 microM) significantly reduced the response; in the mesenteric artery, ChTX and IbTX also reduced this relaxation. Glibenclamide (10 microM) had no affect in either the mesenteric or cerebral artery. Neither clotrimazole (1 microM) nor 7-ethoxyresorufin (3 microM) affected EDHF-mediated relaxation in the mesenteric artery, but abolished or attenuated EDHF-mediated relaxations in the cerebral artery. AM404 (30 microM), a selective anandamide transport inhibitor, did not affect the vasorelaxation response to acetylcholine in the cerebral artery, but in the mesenteric artery potentiated the vasorelaxation response to acetylcholine in an IbTX, and apamin-sensitive, but SR 141816A-insensitive manner. Ouabain (100 microM) almost abolished EDHF-mediated relaxation in the mesenteric artery, but enhanced the relaxation in the cerebral artery whereas the addition of K(+) (5 - 20 mM) to precontracted guinea-pig cerebral or mesenteric artery induced further vasoconstriction. These data suggest that in the guinea-pig mesenteric and cerebral arteries different EDHFs mediate acetylcholine-induced relaxation, however, EDHF is unlikely to be mediated by K(+).

Figure 1

Concentration-response curves for acetylcholine in the guinea-pig mesenteric artery (MA) and middle cerebral artery (CA) in the absence and the presence of a combination of indomethacin (10 μM) and L-NNA (100 μM) or indomethacin and L-NNA plus ODQ (10 μM) or high K⁺ PPS (40 mM). Data are shown as the mean±s.e.mean from 5–7 separate experiments.

Figure 2

Concentration-response curves for acetylcholine in the guinea-pig mesenteric artery (MA) and middle cerebral artery (CA) in the presence of a combination of L-NNA (100 μM) plus indomethacin (10 μM) as the control compared with the vessels pretreated with L-NNA plus indomethacin and K⁺ channel blockers. (a) Glibenclamide (10 μM), 4-aminopyridine (1 mM) or charybdotoxin (0.1 μM); (b) apamin (3 μM), iberiotoxin (0.1 μM) or a combination of apamin and iberiotoxin. Data are shown as the mean±s.e.mean from 5–7 separate experiments.

Figure 3

Concentration-response curves for acetylcholine in the guinea-pig mesenteric artery (MA) and middle cerebral artery (CA) in the presence of a combination of N^G-nitro-L-arginine (100 μ) plus indomethacin (10 μM) as a control and vessels pretreated with BaCl₂ (30 μM), ouabain (100 μM) or their combination. Data are shown as the mean±s.e.mean from 8–10 separate experiments.

Figure 4

Concentration-response curves for acetylcholine in the guinea-pig mesenteric artery (MA) and middle cerebral artery (CA) in the presence of a combination of L-NNA (100 μM) plus indomethacin (10 μM) as the control and vessels pretreated with: clotrimazole (1 μM), AM404 (30 μM) or combination of AM404, apamin (3 μM) and iberiotoxin (0.1 μM). Data shown as the mean±s.e.mean from 5–6 separate experiments.

Figure 5

Concentration-response curves for acetylcholine in the guinea-pig mesenteric artery (MA) and middle cerebral artery (CA) in the presence of a combination of L-NNA (100 μM) plus indomethacin (10 μM) as the control and vessels pretreated with U73122 (1 μM) or AACOCF₃ (1 μM). Data are shown as the mean±s.e.mean from six separate experiments.

Figure 6

The inhibitory effects of AM404 (30 μM) and ODQ (10 μM) on NO-mediated relaxation of endothelial-denuded guinea-pig mesenteric artery. Data shown are as the mean±s.e.mean from six separate experiments.