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1. The present study examined the effects of concurrent manipulation of dietary calcium and salt on contractile responses of vascular smooth muscle (VSM) and endothelial function of aortic rings from Sprague-Dawley rats. 2. Salt loading enhanced the contractile response of the aortic rings to noradrenaline (NA), an effect that was blunted by a high calcium intake. 3. Removal of the endothelium and incubation of aortic rings in physiological salt solution containing methylene blue increased the sensitivity of the rings to NA. 4. The increase in the sensitivity of aortic rings induced by endothelium removal was more pronounced in aortic rings from salt-loaded rats. 5. Acetylcholine caused similar degrees of relaxation in all experimental groups, but the relaxation to histamine was smaller (P < 0.05) in salt-loaded rats than in other groups of rats; however, after removal of the endothelium, the contractile response to histamine was higher in salt-loaded rats. 6. The results indicate that the hypersensitivity of isolated aortic rings to agonists, as observed in salt-loaded rats, is due to altered responses of the VSM and not as a result of changes in the endothelium. In addition, salt loading tends to increase the synthesis of endothelium-dependent relaxing factor. The ability of salt loading to enhance the contractile responses of VSM to agonists can be prevented by supplementing the diet with high calcium.

The effects of chloroquine on resting blood pressure, forearm blood flow (FBF), and forearm vascular resistance (FVR) and on the responses to cold stimulation were studied in healthy young adults. Chloroquine sulphate (800 mg) reduced systolic pressure and increased FBF (P < 0.05) but had no effect on resting FVR. Cold immersion increased systolic pressure (from 108.8 +/- 1.7 mmHg to 127.8 +/- 6.9 mmHg; P < 0.05) diastolic pressure (from 73.4 +/- 2.7 to 95.2 +/- 6.2 mmHg; P < 0.01) and FVR (from 5.9 +/- 0.9 to 13.0 +/- 1.9 a.u.; P < 0.001) but reduced FBF (from 14.3 +/- 1.64 to 10.1 +/- 1.29 ml min-1; P < 0.05). Chloroquine reduced the increase in FVR reduced by cold stimulation (P < 0.01), but had little effect on the BF and FBF responses to cold stimulation. The hypotensive effect of chloroquine could be attributed, at least in part, to the observed fall in vascular resistance.

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1. The effect of chronic ethanol (10%) consumption for 5 months on vascular smooth muscle (VSM) using aortic rings of both sexes of Sprague-Dawley rats was studied. 2. Chronic ethanol consumption increased the sensitivity of VSM to noradrenaline (NA) in both male and female ethanol-treated rats. 3. There was no significant difference in the contractile response of male and female ethanol-treated rats to NA. Hence, the enhancement of vascular contractility to the agonist due to chronic ethanol consumption is independent of gender. 4. Vascular relaxation induced by acetylcholine showed similar responses in all experimental groups. Thus, chronic ethanol consumption seems to have no significant effect on the production of endothelium-dependent relaxing factor. 5. However, the VSM sensitivity to potassium chloride was increased in female ethanol-treated rats, whereas male ethanol-treated rats had similar responses as controls. 6. The results suggest that the effect of chronic ethanol consumption on VSM varies with gender. Impairment of VSM in male ethanol-treated rats is due partly to changes in the receptor-operated channel, whereas in females it is due to changes in both receptor- and potential-operated channels.