In vivo measurement of nitric oxide on the surface of rat cremaster muscle arterioles

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It has been established that nitric oxide (NO) plays an important role in the regulation of vascular tone. However, NO concentration [NO] in the microcirculation of skeletal muscle has not been determined. In the present study, we measured [NO] in vivo on the surface of the arterioles of the rat cremaster muscle by using NO-specific microelectrodes. The right cremaster muscles of anesthetized male Wistar-Hannover rats were surgically exteriorized using the modified Baez method (Baez S 1973). Images gained through a microscope were divided into a high speed CCD camera and into an image viewing screen with a pair of photodiodes. Vessels were classified into the order of 1A, 2A, 3A and 4A by Wiedeman's ordering system. [NO] was measured directly with a amperometric NO-selective microelectrode (7μm and 30μm, WPI Inc.) through an integrated electrochemical NO detection system (Apollo-4000, WPI). The electrode has a high detection sensitivity of 0.5 - 5.0 pA/nM and a detection limit of 1-3 nM. The microelectrode was placed immediately adjacent to the wall of arterioles on the surface of the cremaster muscle by using a micro-manipulator. [NO] was 916.4 ± 121.6 nM on the surface of 1A arterioles, 468.4 ± 62.5 nM on the 2A, 583.0 ± 131.5 nM on the 3A, and 245.0 ± 138.7 nM on the 4A arterioles. [NO] on the 1A (50 - 100μm diameter) was significantly higher than [NO] on the 4A (10- 30μm). NO concentration on the adjacent surface of the arteriolar wall gradually decreased along with the order of the arteriolar network.