1. In order to examine the effects of experimental hypertension on intracellular pH in mesenteric resistance arteries, intracellular pH was measured in mesenteric resistance arteries from rats with coarctation 72 h, 9 days and 28 days after the aorta was partially constricted between the origins of the renal arteries. Carotid arterial pressure was significantly raised at all time points.

2. Second-order mesenteric resistance arteries were mounted in a myograph and were loaded with the acetoxymethyl ester of the pH-sensitive dye 2′,7′-bis(carboxyethyl)-5,6-carboxyfluorescein. Morphological measurements demonstrated that arteries from rats with coarctation had an increased media volume at 9 days and at 28 days compared with vessels from sham-operated control animals, but this was only statistically significant at 28 days.

3. Resting intracellular pH was not significantly different at any time point in arteries from rats with coarctation compared with control animals, although there was a rise in intracellular pH in both groups of rats between 72 h and 9 days. The application of 4,4-di-isothiocyanatostilbene-2,2′-disulphonic acid produced a fall in intracellular pH which was significantly greater in the sham-operated rats at 9 days; this difference was not found at 28 days. Blockade of Na+/H+ exchange with 60 μmol/l ethylisopropylamiloride led to a similar fall in intracellular pH in both groups of rats at 9 days but a significantly greater fall in intracellular pH in arteries of rats with coarctation at 28 days. Activation with noradrenaline (10 μmol/l) induced acid changes in intracellular pH that were similar in both groups of rats.

4. It is concluded that induction of coarctation of the aorta was associated with the development of significant growth in mesenteric resistance arteries, but that this structural change was not associated with an intracellular pH that was significantly different from that seen in sham-operated control rats at any time. Increased regulation of intracellular pH by Na+/H+ exchange was observed only at 28 days, after medial growth had occurred, which argues against a fundamental role of this exchange system as a mediator of cell growth.

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