Received for publication October 6, 2004.
Revised December 16, 2004.
Accepted for publication December 16, 2004.

Acute and chronic Captopril, but not Prazosin nor Nifedipine, normalize alterations in adrenergic intracellular Ca²⁺ handling observed in the mesenteric arterial tree of spontaneously hypertensive rats

Abstract

The effect of hypertension and acute (36h) or chronic (from age 6 to 16 weeks) antihypertensive treatment with prazosin (2 mg kg^-1 per day), nifedipine (50 mg kg^-1 per day) or captopril (50 mg kg^-1 per day) on Ca²⁺ mobilization due to ₁-adrenoceptor activation was analyzed in functional studies using arterial rings (four conductance/distributing vessels: aorta, main mesenteric, iliac and tail arteries and two resistance vessels: first and second small mesenteric branches (SMA) obtained from spontaneously hypertensive rats (SHR, 6 and 16 weeks old) and age-matched Wistar Kyoto (WKY) rats. Maximal response to noradrenaline in the presence of extracellular Ca²⁺ is not affected by hypertension nor by the antihypertensive treatment. The extracellular Ca²⁺ independent contractile responses increased with age in iliac, tail and SMA and were further increased in SMA from both young and adult SHR and in the main mesenteric artery of adult SHR. In main mesenteric artery from SHR, this increased contraction was associated with a higher increase in cytosolic [Ca²⁺] mobilized by noradrenaline without changes in the total stored Ca²⁺. Acute or chronic treatment with captopril abolished the differences observed between WKY and SHR in the NA-induced contraction in mesenteric arteries loaded in Ca²⁺-free medium. In contrast, animals acutely treated with prazosin or chronically treated with either prazosin or nifedipine exhibit the same differences in Ca²⁺ handling than untreated rats. In conclusion, these differences are not a consequence of increased blood pressure but precede it and can only be normalized by inhibition of the renin-angiotensin system.

Key words: adrenoceptors, captopril, hypertension, intracellular calcium, noradrenaline, rat mesenteric arteries