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Parallel reduction of calcium-influx-dependent vasoconstriction and platelet-free calcium concentration with calcium
Insights
Essential hypertension involves increased vasoconstriction and platelet calcium. Both calcium entry blockers and beta-blockers reduced vasoconstriction and platelet calcium levels in patients.
Area of Science:
- Cardiovascular Pharmacology
- Hypertension Research
Background:
- Essential hypertension is characterized by enhanced calcium-influx-dependent vasoconstriction.
- Elevated free calcium concentration in platelets is observed in patients with essential hypertension.
Purpose of the Study:
- To investigate the relationship between calcium-influx-dependent vasoconstriction, platelet calcium concentration, and blood pressure in essential hypertension.
- To assess the effects of nitrendipine (calcium entry blocker) and acebutolol (beta-blocker) on these parameters.
Main Methods:
- Measurements of forearm blood flow (FAF) and platelet free calcium concentration were performed in five hypertensive patients.
- Assessments were conducted before and after a 6-week treatment with either nitrendipine or acebutolol.
- Vasodilator responses to intra-arterial nitrendipine, sodium nitroprusside, and post-ischemic reperfusion were evaluated.
Main Results:
- Chronic nitrendipine treatment significantly reduced the increase in FAF in response to intra-arterial nitrendipine (p < 0.05).
- Chronic acebutolol treatment also showed a reduction in FAF response, though not statistically significant.
- Both nitrendipine and acebutolol treatments led to a significant decrease in platelet free calcium concentration (p < 0.05 and p < 0.01, respectively).
- Non-specific vasodilator responses remained unchanged during treatment.
Conclusions:
- Antihypertensive treatment with calcium entry blockers or beta-blockers effectively reduces calcium-influx-dependent vasoconstriction.
- A decrease in free calcium concentration in platelets correlates with reduced vasoconstriction, suggesting platelets may reflect vascular smooth muscle calcium levels.
Abstract:
In essential hypertension, calcium-influx-dependent vasoconstriction is enhanced, and free calcium concentration in platelets is elevated. To investigate calcium-influx-dependent vasoconstriction as related to platelet calcium concentration blood pressure, forearm blood flow (FAF) and free calcium concentration in platelets were measured in five patients with essential hypertension before and after a 6-week treatment with nitrendipine or acebutolol. Starting from comparable basal values, the increase in FAF (ml/min/100 ml tissue) to intraarterially infused nitrendipine (20 micrograms/100 ml tissue) was 40.7 +/- 6.1 before and 30.7 +/- 12.3 after chronic nitrendipine treatment (p less than 0.05) and 41.6 +/- 6.2 before and 34.6 +/- 14.9 after chronic acebutolol treatment. The "nonspecific" vasodilator response to intraarterial sodium nitroprusside or to postischaemic reperfusion were similar before and during treatment. Platelet-free calcium concentration fell on nitrendipine (p less than 0.05) and on acebutolol (p less than 0.01) treatment. Antihypertensive treatment with calcium entry as well as beta-adrenoceptor blockade resulted in a reduction of calcium-influx-dependent vasoconstriction and a fall in free calcium concentration in platelets. Thus, increased calcium platelets may reflect increased calcium in vascular smooth muscle cells and arteriolar tone.