Direct In Situ Measurement of Nitric Oxide in Mesenteric Resistance Arteries

Abstract

The endothelium plays a critical role in maintaining vascular tone by releasing vasoconstrictor and vasodilator substances. Endothelium-derived nitric oxide is a vasodilator that can be rapidly inactivated by superoxide (reaction rate constant, K = 3.6 x 10(9) L/mol per second). The measurement of nitric oxide concentration in biological systems is a challenging analytic problem because nitric oxide is also rapidly inactivated by Fe(II), Fe(III), and O2, all of which are found in great abundance in biological systems. To date, no currently used instrumental technique has been suitable for direct in situ measurement of NO in isolated resistance arteries. We designed the present study to perform for the first time direct in situ measurements of NO in rat mesenteric resistance arteries and to delineate the effects of hypertension on the release of NO and/or its interaction with superoxide. We describe here an adaptation of the recently published design of a porphyrinic sensor for direct in vitro measurement of NO in a single cell. The most significant advantage of this modified porphyrinic microsensor is that its small size makes it ideal for NO measurement in resistance arteries with an internal diameter of 200 microns or less. Small segments of the third-order branch of the mesenteric artery were isolated from normotensive Wistar-Kyoto rats and stroke-prone spontaneously hypertensive rats and placed in an organ chamber filled with Hanks' balanced salt solution buffer (2 mL, 37 degrees C). The tip of the porphyrinic microsensor was inserted into the lumen of an isolated vascular ring, and NO release was monitored in situ after maximal stimulation of NO synthase with the receptor-independent agonist calcium ionophore A23187 (10 mumol/L). Maximal surface concentration of NO measured after A23187 administration was significantly smaller in 15-week-old hypertensive rats (0.28 +/- 0.03 mumol/L, n = 10) than in age-matched normotensive rats (0.38 +/- 0.03 mumol/L, n = 10, P < .03). However, in the presence of the superoxide scavenger superoxide dismutase (100 U/mL), the peak NO level from the hypertensive rats was 0.37 +/- 0.04 mumol/L (n = 10), which was comparable to that observed for the normotensive rats in the absence and presence of superoxide dismutase. In summary, our results demonstrate that in rat mesenteric resistance arteries hypertension is associated with increased NO decomposition by superoxide, whereas NO release remains unaffected. This may be important in the pathogenesis of hypertension and its cardiovascular complications.

Nifedipine Indirectly Upregulates Superoxide Dismutase Expression in Endothelial Cells via Vascular Smooth Muscle Cell–Dependent Pathways

“…For example, hypertension is associated with increased inhibition of NO signaling by superoxide, whereas NO release remains unaffected. 17 Bauersachs et al 18 also reported that endothelial dysfunction in ischemic heart failure was induced by an increase in vascular superoxide production despite enhanced vascular endothelial nitric oxide synthase (eNOS) and soluble guanylate cyclase expression. Importantly, eNOS is a cytochrome P450 reductase-like enzyme that produces superoxide under certain pathological conditions.…”

Beneficial Effects of Trandolapril in Uninephrectomized Spontaneously Hypertensive Rats: Role of Cyclooxygenase Pathway

“…Other authors (Nava & Luscher 1995) have showed that, at least in the SHR, vascular nitric oxide production is augmented, but some overproduction of nitric oxide scavengers from the superoxide dismutase pathway break down the nitric oxide leading to endothelial dysfunction (Tschudi et al 1996). We have demonstrated that aortas from SHR-UNX do not show myogenic tone as a consequence of the nitric oxide released on the basal tone.…”

Mecanismos de hipertensión en obesidad

“…Estudios llevados a cabo en pacientes hipertensos, han mostrado que presenta una alteración de la respuesta vasodilatadora a los estimulantes del NO, pudiendo deberse a una reducción en su síntesis [26][27][28] , sin estar relacionado en exclusiva a una menor disponibilidad de sustrato 29 , debido a una mayor descomposición del NO por superóxido 30 o por la inhibición por sustancias ciclooxigenasa dependientes 31 .…”