Aims: 

Despite wide investigation of Mg²⁺ influence upon vascular smooth muscle, few studies analyse its impact on endothelium-dependent relaxation (EDR). Chronic inhibition of nitric oxide synthase (NOS) induces hypertension and Mg²⁺ load doesn't influence its development but may reduce it later. Beside this we studied the influence of chronic Mg²⁺ upon acute effects of two antihypertensives in L-NAME hypertension.

Methods: 

24 male Wistar rats were divided in 4 groups, which received (1 ml saline solution i.p. twice a day): isotonic NaCl, isotonic MgCl₂ 1 mmol/kg/day, and L-NAME 40 mg/kg/ day, either in NaCl or in MgCl₂ solution. Arterial pressure and heart rate were measured with a tail-cuff sphygmomanometer. Single-dose rilmenidine (1 mg/ kg i.p.) and captopril (50 mg/kg i.p.) were assesed acutely (10, 20 and 30 min after injection). Rings from aorta and mesenteric artery branches were studied by isometric myography.

Results: 

L-NAME induced hypertension starting day 3, reaching in 14 days 135 ± 3.5 vs.104 ± 3.8 mmHg. This is not altered by concomitant i.p. MgCl₂ (126 ± 4.3 mmHg, day 14) and can be normalized acutely by i.p. rilmenidine (97 ± 7 mmHg after 30') or captopril (104 ± 5.3 mmHg after 30'), but this effect tends to be reduced by chronic Mg²⁺ (103 ± 5.6 and 116 ± 5.1 mmHg, respectively). In vitro data indicate that chronic Mg²⁺ promotes partial preservation of EDR in resistance arteries of L-NAME treated animals by fostering EDHF.

Conclusion: 

Our combined approach brings novel evidence regarding the effects of Mg²⁺ upon EDR and the mechanisms involved.

*CNCSIS grant A/1222, **CNCSIS grant interdisciplinary platform /68.