Effects of angiotensin-converting enzyme inhibition on arterial, venous and capillary functions in cat skeletal muscle in vivo

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T1 - Effects of angiotensin-converting enzyme inhibition on arterial, venous and capillary functions in cat skeletal muscle in vivo

AU - Ekelund, Ulf

PY - 1996

Y1 - 1996

N2 - The aim of the present study was to analyse quantitatively, on a cat gastrocnemius muscle preparation in vivo, the effects of local angiotensin-converting enzyme (ACE) inhibition by enalaprilat on total regional vascular resistance (tone) and its distribution to the large-bore arterial resistance vessels (> 25 microns), the small arterioles (< 25 microns) and the veins. Associated effects on capillary pressure and fluid exchange were also studied. Close-arterial infusion of enalaprilat (0.05-0.20 mg kg muscle tissue min-1) elicited a moderate dilator response in all three consecutive sections of the muscle vascular bed, an increase in capillary pressure and transcapillary fluid filtration. This dilation could be abolished by the selective bradykinin B2-receptor antagonist Hoe 140 (2 mg kg-1 min-1, i.a.), indicating that the dilator mechanism of ACE inhibition was an increased local concentration of bradykinin, and hardly at all a decreased concentration of angiotensin (AT) II. The generalized dilator response to ACE inhibition along the vascular bed suggested a relatively uniform distribution of ACE from artery to vein and this was further supported by the finding that a close-arterial infusion of AT I (0.04-0.32 microgram kg-1 min-1), which was vasoactive only after conversion to AT II by local ACE, elicited a generalized constrictor response in all three vascular sections. In contrast, infused AT II (0.01-0.16 microgram kg-1 min-1) constricted almost selectively the large-bore arterial vessels. The specific angiotensin AT1-receptor antagonist losartan (2 mg kg-1 min-1, i.a.) abolished the constrictor response to AT II but did not affect vascular tone under control conditions, indicating that AT II is not involved in the initiation of basal vascular tone in muscle. These results, taken together, indicate that under basal conditions vascular ACE contributes to the local control of vascular tone in skeletal muscle by degrading the endogenous dilator bradykinin, and not by converting AT I into vasoconstrictor AT II.

AB - The aim of the present study was to analyse quantitatively, on a cat gastrocnemius muscle preparation in vivo, the effects of local angiotensin-converting enzyme (ACE) inhibition by enalaprilat on total regional vascular resistance (tone) and its distribution to the large-bore arterial resistance vessels (> 25 microns), the small arterioles (< 25 microns) and the veins. Associated effects on capillary pressure and fluid exchange were also studied. Close-arterial infusion of enalaprilat (0.05-0.20 mg kg muscle tissue min-1) elicited a moderate dilator response in all three consecutive sections of the muscle vascular bed, an increase in capillary pressure and transcapillary fluid filtration. This dilation could be abolished by the selective bradykinin B2-receptor antagonist Hoe 140 (2 mg kg-1 min-1, i.a.), indicating that the dilator mechanism of ACE inhibition was an increased local concentration of bradykinin, and hardly at all a decreased concentration of angiotensin (AT) II. The generalized dilator response to ACE inhibition along the vascular bed suggested a relatively uniform distribution of ACE from artery to vein and this was further supported by the finding that a close-arterial infusion of AT I (0.04-0.32 microgram kg-1 min-1), which was vasoactive only after conversion to AT II by local ACE, elicited a generalized constrictor response in all three vascular sections. In contrast, infused AT II (0.01-0.16 microgram kg-1 min-1) constricted almost selectively the large-bore arterial vessels. The specific angiotensin AT1-receptor antagonist losartan (2 mg kg-1 min-1, i.a.) abolished the constrictor response to AT II but did not affect vascular tone under control conditions, indicating that AT II is not involved in the initiation of basal vascular tone in muscle. These results, taken together, indicate that under basal conditions vascular ACE contributes to the local control of vascular tone in skeletal muscle by degrading the endogenous dilator bradykinin, and not by converting AT I into vasoconstrictor AT II.

KW - angiotensin-converting enzyme

KW - arteries

KW - bradykinin

KW - capillary pressure

KW - losartan

KW - microcirculation

KW - nitric oxide

KW - vascular tone

KW - veins

U2 - 10.1046/j.1365-201X.1996.517281000.x

DO - 10.1046/j.1365-201X.1996.517281000.x

M3 - Article

VL - 158

SP - 29

EP - 37

JO - Acta Physiologica

JF - Acta Physiologica

SN - 1748-1716

IS - 1

ER -