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Cardiovascular effects of tolazoline and ranitidine
Insights
Ranitidine administration reversed the blood vessel dilating effects of tolazoline in children with congenital heart disease. This suggests H2 receptors may play a role in cardiovascular regulation.
Area of Science:
- Pediatric Cardiology
- Pharmacology
- Cardiovascular Physiology
Background:
- Congenital heart disease (CHD) often requires interventions to manage pulmonary and systemic vascular resistances.
- Tolazoline is a pulmonary vasodilator used in pediatric patients with CHD.
- Gastrointestinal hemorrhage is a potential side effect of tolazoline therapy.
Purpose of the Study:
- To investigate the cardiovascular effects of ranitidine in children with CHD.
- To determine if ranitidine influences the hemodynamic effects of tolazoline.
- To explore the potential role of H2 receptors in cardiovascular regulation.
Main Methods:
- Prospective study involving 12 children with CHD.
- Administration of tolazoline (1-2 mg/kg) to assess its effects on vascular resistance and heart rate.
- Intravenous administration of ranitidine (3 mg/kg) to evaluate its impact on hemodynamics.
Main Results:
- Tolazoline significantly decreased pulmonary and systemic vascular resistances and increased heart rate.
- Ranitidine administration reversed these effects, returning resistances to baseline levels.
- Ranitidine also caused a significant decrease in heart rate compared to baseline.
Conclusions:
- Ranitidine may antagonize the vasodilatory effects of tolazoline, suggesting the involvement of H2 receptors.
- Tolazoline's mechanism of action might involve H2 receptors, not solely alpha-adrenergic blockade.
- Further research is needed to assess the safety of H2 blockade in pediatric patients, especially those with pulmonary hypertension.
Abstract:
The cardiovascular effects of ranitidine were studied in 12 children with congenital heart disease who had been given tolazoline as a pulmonary vasodilator. Ranitidine was given as prophylaxis against gastrointestinal haemorrhage induced by tolazoline. Tolazoline 1-2 mg/kg caused significant falls in pulmonary and systemic vascular resistances and a rise in heart rate. After intravenous administration of ranitidine 3 mg/kg both resistances rose again and neither resistance then differed significantly from baseline levels. Heart rate also fell and the final heart rate was significantly below baseline levels. We conclude that there may be H2 receptors within the pulmonary and systemic circulations and that tolazoline may mediate some of its effects through these H2 receptors rather than by alpha adrenergic receptor blockade. The safety of H2 blockade in children, particularly those with pulmonary hypertension, needs further investigation.