Effect of Urate on Nitric Oxide Microcirculatory Response in the Rat Tail to Body Heating

Abstract

Objective: The objective of this study was to determine if nitric oxide (NO)-mediated cutaneous vasodilation depends on urate concentrations. Methods: Capillary blood cell velocities (BCV) in the tail capillary vessels of anesthetized, heat-stressed Sprague-Dawley rats were measured by the videomicroscopy method, and the femoral mean arterial pressure (MAP) was recorded on a Grass polygraph. The effects of urate or urate and NO production on the above parameters were determined by using specific inhibitors of these compounds, for example, allopurinol (All) or All or N-nitro-L-arginine (NNA), respectively. Urate concentrations were determined by an enzymatic, colorimetric method, and total nitrite levels were measured fluorometrically. Results: During heat stress, All or All and NNA significantly decreased plasma urate or urate and total nitrite concentrations, respectively, and the response of vascular conductance (estimated as a ratio of BCV to MAP). Urate administration, after All and NNA pretreatment, restored plasma urate and total nitrite concentrations and increased BCV/MAP. Conclusions: Urate at physiological concentration helps to maintain vascular conductance of cutaneous capillaries in the rat tail during body heating. The effect of urate on vascular conductance may be mediated by NO.