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Effect of activation of the H1 receptor on coronary hemodynamics in man
Insights
Selective H1 receptor stimulation in patients with heart conditions reduced coronary vascular resistance, but triggered angina and coronary artery spasm in some individuals with coronary artery disease.
Area of Science:
- Cardiology
- Pharmacology
Background:
- Histamine H1 receptors play a role in cardiovascular function.
- Understanding H1 receptor effects on coronary circulation is crucial for managing cardiac conditions.
Purpose of the Study:
- To investigate the impact of selective H1 receptor activation on coronary hemodynamics.
- To assess the potential for H1 receptor stimulation to induce angina or coronary spasm.
Main Methods:
- 16 patients with cardiac conditions were divided into two groups based on coronary health.
- Histamine was infused to selectively stimulate H1 receptors, with heart rate controlled and coronary blood flow measured.
- Cimetidine was used for pretreatment.
Main Results:
- H1 receptor stimulation reduced coronary vascular resistance in patients without significant coronary artery disease.
- In patients with coronary artery disease, H1 receptor activation led to angina, decreased coronary blood flow, and increased coronary vascular resistance.
- Coronary artery spasm was observed in one patient during histamine infusion.
Conclusions:
- H1 receptor stimulation can cause coronary vasodilation in healthy vessels.
- Selective H1 receptor activation poses a risk of inducing angina and coronary spasm in patients with coronary artery disease.
Abstract:
We evaluated the effects of selective activation of H1 receptors on coronary hemodynamics in 16 patients divided into two groups: group A, 11 patients with atypical angina or valvular heart disease and normal coronary arteries, and group B, five patients with spontaneous angina, four of whom had significant (greater than 70% stenosis) coronary artery disease and one with normal coronaries. Selective H1 receptor stimulation was achieved by infusing 0.5 microgram/kg/min of histamine intravenously for 5 min after pretreatment with cimetidine (25 mg/kg). Heart rate was maintained constant (100 beats/min) by coronary sinus pacing and coronary blood flow (CBF) was measured by thermodilution. In group A, during histamine infusion mean aortic pressure fell from 99 +/- 5 to 77 +/- 4 mm Hg (mean +/- SEM, p less than .001), coronary vascular resistance (CVR) decreased from 1.07 +/- 0.17 to 0.82 +/- 0.14 mm Hg/ml/min (p less than .02), and CBF and myocardial oxygen consumption remained unchanged. None of the patients in this subgroup developed angina during histamine infusion. In group B, while no significant average changes in mean arterial pressure, CVR, or CBF were observed, two of the five patients (40%) developed angina during histamine infusion, accompanied by ST-T elevation, a decrease in CBF, and an increase in CVR. In one of these two patients circumflex coronary arterial spasm was angiographically demonstrated during histamine-induced angina. Our results suggest that stimulation of the H1 receptor induces a reduction of CVR, probably resulting from vasodilation of small coronary resistance vessels.(ABSTRACT TRUNCATED AT 250 WORDS)