Related Experiment Videos
Inhibition of vascular myogenic tone and reactivity by calcium antagonists
1Hässle Cardiovascular Research Laboratories, Mölndal, Sweden.
Insights
Calcium antagonists, commonly used for hypertension, directly inhibit myogenic tone in vascular smooth muscle. These drugs reduce peripheral resistance by interfering with the activation of myogenically active smooth muscle.
Area of Science:
- Cardiovascular Physiology
- Pharmacology
Background:
- Basal vascular tone is primarily maintained by myogenic tone in resistance vessels.
- Antihypertensive calcium antagonists reduce peripheral resistance, suggesting an inhibition of myogenic tone.
Purpose of the Study:
- To review evidence supporting the hypothesis that calcium antagonists directly inhibit myogenic tone.
- To investigate the effects of calcium antagonists on myogenic tone and reactivity in vascular smooth muscle.
Main Methods:
- Review of existing studies on calcium antagonists and myogenic tone.
- Experimental evidence from anesthetized cats (hindleg) and rat portal vein preparations.
- Assessment of basal myogenic tone, responses to nerve stimulation, spontaneous contractions, and pressure-induced vasoconstriction.
Main Results:
- Calcium antagonists (felodipine, verapamil, diltiazem) dose-dependently reduced basal myogenic tone.
- These drugs also depressed nerve-stimulated vasoconstriction and spontaneous myogenic activity.
- Effects on myogenic reactivity were more pronounced than on basal tone, as evidenced by reduced transient vasoconstriction and attenuated autoregulation.
Conclusions:
- Calcium antagonists directly interfere with the activation of myogenically active vascular smooth muscle.
- This interference leads to reductions in both myogenic tone and reactivity.
- Findings support the direct inhibitory effect of calcium antagonists on myogenic tone, impacting vascular resistance and blood flow regulation.
Abstract:
In most organs basal vascular tone is maintained by the myogenic tone in the smooth muscles of the resistance vessels. Commonly used antihypertensive calcium antagonists reduce peripheral resistance and hence vascular tone, suggesting inhibition of myogenic tone. The findings supporting this hypothesis are reviewed here. Evidence for direct inhibition of myogenic tone by calcium antagonists includes findings in the hindleg of the anaesthetized cat, in which basal myogenic tone (prevailing resistance minus the resistance at maximal dilation) was dose-dependently reduced by felodipine. Furthermore, induced responses to vasomotor nerve stimulation were depressed by felodipine to the same relative extent as was the basal myogenic tone. The phasic spontaneous force development, which is of myogenic origin in the rat portal vein, was reduced after the administration of verapamil, diltiazem or felodipine. The adrenergic potentiation of this myogenic activity was also depressed to the same relative extent as felodipine depressed the spontaneous contractile force. The effect of calcium antagonists on myogenic reactivity seems to be even more pronounced than their effect on myogenic tone. Thus, transient vasoconstriction in response to a rapid increase in transmural pressure in the hindleg of the anaesthetized cat was reduced to a relatively greater extent by calcium antagonists than the basal myogenic tone. The attenuation of renal and cerebral blood flow autoregulation that has been observed after the administration of calcium antagonists also suggests a direct effect on myogenic reactivity. These results suggest that calcium antagonists interfere with activation in myogenically active vascular smooth muscle, resulting in reductions in myogenic tone.(ABSTRACT TRUNCATED AT 250 WORDS)