INFLUENCE OF ANTI‐HYPERTENSIVE DRUG TREATMENT ON VASCULAR REACTIVITY IN SPONTANEOUSLY HYPERTENSIVE RATS

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Abstract
1 The effect of prolonged anti-hypertensive drug treatment on the blood pressure of conscious spontaneously hypertensive rats (SH-rats), and of age-matched normotensive Sprague-Dawley rats was determined during the development of hypertension in SH-rats and in the early stages of established hypertension. A comparison of the vascular reactivity to noradrenaline (NA) and 5-hydroxytryptamine (5-HT) was also made in isolated perfused mesenteric artery preparations from treated and control SH- and Sprague-Dawley rats. 2 Chronic treatment from age 4 to 16 weeks with hydrallazine alone, or a combination of hydrallazine/hydrochlorothiazide/reserpine, ad libitum in the drinking water, prevented the development of hypertension in SH-rats and also reduced the vascular reactivity to NA and 5-HT in isolated vessel preparations from treated compared to control rats. 3 Similar drug treatments started in early established hypertension reduced blood pressure in SH-rats over the 12 week treatment period (from age 8 to 20 weeks) without affecting vascular reactivity to NA and 5-HT in the isolated vessel preparation. 4 Drug treatments had little effect on blood pressure of age-matched Sprague-Dawley rats and no effect on vascular reactivity to NA and 5-HT in the isolated perfused mesenteric artery preparation from treated compared to control rats. 5 These results indicate that the development of increased vascular reactivity and of hypertension in SH-rats occurs simultaneously and, therefore, the vascular changes may be a consequence of the structural changes induced by the raised blood pressure. 6 In established hypertension, no regression of vascular changes was observed despite prolonged reduction of blood pressure. The rǒle of an increased vascular reactivity in the maintenance of hypertension is therefore questionable.