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Department of Physiology, New York Medical College, Valhalla, New York 10595
In this study we
tested the hypothesis that insulin may differentially affect isolated
arterioles from red (RGM) and white gastrocnemius muscles (WGM) because
of their differences in function and metabolic profile. We also
determined whether the responses of these arterioles are endothelium
dependent and mediated by either prostaglandins or nitric oxide (NO).
Arterioles were isolated, pressurized to 85 mmHg, equilibrated in Krebs
bicarbonate-buffered solution (pH 7.4) gassed with 10%
O2 (5%
CO2-85%
N2), and studied in a no-flow
state. Control diameters for first-order arterioles from RGM averaged
77 ± 8 µm and from WGM averaged 77 ± 5 µm. Cumulative dose-response curves to insulin (10 µU/ml, 100 µU/ml, 1 mU/ml, and
10 mU/ml) were obtained in arterioles before and after endothelium removal or administration of either indomethacin (Indo,
10
5 M) or
NG-nitro-L-arginine
(L-NNA, 10
4 M).
Insulin evoked concentration-dependent increases in control diameter of
intact RGM and WGM arterioles of 6-26% and 9-28%, respectively. Indo was without any effect on insulin-induced dilation in RGM and WGM arterioles. Insulin-evoked dilation in both RGM and WGM
arterioles was completely inhibited and converted to vasoconstriction by endothelium removal and administration of L-NNA. These
results indicate that in endothelium-intact arterioles from RGM and
WGM, insulin evokes an endothelium-dependent dilation that is
equivalent and mediated by NO. In contrast, in the absence of a
functional endothelium, insulin evokes arteriolar constriction. The
finding that insulin can constrict arterioles, at physiological
concentrations, suggests that insulin may play a more significant role
in the regulation of vascular tone and total peripheral resistance than previously appreciated.
rat; skeletal muscle; gastrocnemius muscle; dilation; constriction; nitric oxide; microcirculation; resistance; insulin resistance
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