Combined effect of low doses of propranolol and ethanol on cardiac function: a comparative study by radionuclide ventriculography in conscious dogs.

Trained, chronically instrumented, conscious dogs were used to evaluate the effect of propranolol (PRO), ethanol (ETH) or their combination (P + E) on the left ventricular (LV) function by first-pass radionuclide ventriculography (RNV). Six dogs were trained prior to a sterile left thoracotomy, where a left atrial catheter was implanted. After recovery of four days RNV was carried out by injecting a bolus of technetium-99m diethylenetriamine pentaacetic acid via the catheter to the left atrium. The data was collected for 12 sec. to a computer by frame rate of 20 frames/sec. from left lateral view of the dog. The experiments were performed both in four-leg standing and in 60-degree head-up tilted positions. After control measurements the data were obtained with 0.5 mg/kg of PRO, 0.45 g/kg of ETH and their combination. The P + E combination increased significantly LV end-diastolic and end-systolic volumes, whereas LV peak ejection rate and ejection fraction were decreased. Upright position diminished the LV volume and increased heart rate, while ejection fraction and cardiac output remained unchanged. The first-pass RNV method proved to be promising for measuring the cardiac pharmacological effects in conscious dogs. The combination of propranolol and ethanol in low doses induced an unexpectedly strong depression of LV function, which is supposed to be followed of latent cardiac depressing effect of ETH revealed by blockade of compensatory adrenergic mechanisms with PRO.