Endothelium-derived hyperpolarizing factor as an in vivo back-up mechanism in the cutaneous microcirculation in old mice

Abstract

There is now strong evidence that an endothelium-derived hyperpolarizing factor (EDHF), other than nitric oxide (NO) or prostaglandin (PG), exists for dilating arteries and arterioles. In vitro studies on isolated vessels pointed out a role for EDHF as a back-up mechanism when the NO pathway is impaired, but there was a lack of in vivo studies showing a functional role for EDHF. Ageing has pronounced effects on vascular function and particularly on endothelium-dependent relaxation, providing a novel situation in which to assess the contributions of EDHF. The purpose of the present study was thus to determine if, in vivo, there was a functional role for EDHF as a back-up mechanism in the cutaneous microcirculation in the ageing process. We investigated in vivo the contribution of each endothelial factor (NO, PG and EDHF) in the cutaneous vasodilatation induced by iontophoretic delivery of acetylcholine and local pressure application in young adult (6-7 months) and old (22-25 months) mice, using pharmacological inhibitors. The cutaneous vasodilator responses induced by acetylcholine and local pressure application were dependent upon NO and PG pathways in young adult mice, whereas they were EDHF-dependent in old mice. EDHF appears to serve as a back-up mechanism when ageing reaches pathological states in terms of the ability for NO and PG to relax cutaneous microvessels, allowing for persistent cutaneous vasodilatator responses in old mice. However, as a back-up mechanism, EDHF did not completely restore cutaneous vasodilatation, since endothelial responses were reduced in old mice compared to young adult mice.

Figure 1

Percentage changes in skin blood flow in response to local iontophoretic delivery of acetylcholine (ACh) in young adult and old mice without inhibition (untreated), following the inhibition of NOS using N^ω-nitro-l-arginine (LNNA), following the inhibition of COX using indomethacin (INDO), following the combined inhibition of NOS and COX (LNNA + INDO) and following the blockade of endothelium-derived hyperpolarizing factor (EDHF) using apamin and charybdotoxin (APA + ChTX). Error bars represent s.e.m. n = 9 in each group, except for young adult mice treated with LNNA + INDO (n = 5) and old mice treated with APA + ChTX (n = 5). * P < 0.05 untreated old mice compared to untreated young adult mice. # P < 0.05, ## P < 0.01 treated compared to age-matched untreated mice.

Figure 2

Changes in skin blood flow, expressed in arbitrary units (a.u.), in response to local pressure application in untreated young adult and old mice (n = 10 in each group). Error bars represent s.e.m.

Figure 3

Percentage changes in skin blood flow in response to local pressure application in young adult and old mice without inhibition (untreated, n = 10 in each group), following the inhibition of NOS and COX using N^ω-nitro-l-arginine and indomethacin (LNNA + INDO, n = 5 in young adult mice and n = 8 in old mice) and following the blockade of endothelium-derived hyperpolarizing factor (EDHF) using apamin and charybdotoxin (APA + ChTX, n = 6 in young adult mice and n = 5 in old mice). Error bars represent s.e.m. * P < 0.05 old mice compared to young adult mice. # P < 0.05 treated compared to age-matched untreated mice.