[Cardiovascular effects of salbutamol in rabbits anesthetized with sodium pentobarbital]

1) Heart rate, instantaneous carotid blood flow (electromagnetic probe) and arterial blood pressure were recorded for 60 minutes in rabbits anesthetized with sodium pentobarbital (40 mg/kg). Anesthetic induction was made one hour before starting the measurements to allow animal preparation. These measurements were performed on three experimental groups--(A) group: anesthetized animals without any treatment (control group); (A + SA) group: anesthetized animals + intravenous (I.V.) infusion of salbutamol (300 micrograms/kg); (A + SE) group : anesthetized animal + I.V. infusion of a saline solution in the same volume and time conditions than for (A + SA) group, that is to say (10 ml within 10 min): this series was conducted to explore the specific effects of hypervolemia. 2) Comparing the SE and SA groups, it appeared, within 30 to 120 seconds, that I.V. infusion of salbutamol induced a decrease in systolic and diastolic blood pressures and a significant increase in heart rate and carotid blood flow. While heart rate and blood pressures returned progressively to their control values (A group), carotid blood flow was still higher 60 minutes after starting salbutamol infusion. 3) The possible mechanisms involved in the observed cardiovascular responses to salbutamol are discussed. The predominant effect is probably the hypotension resulting from a peripheral vasodilatation by direct stimulation of beta 2-adrenergic receptors in vascular smooth muscle. The increase in heart rate and carotid blood flow may be explained by a two fold mechanisms: direct stimulation of the beta-adrenergic receptors (beta 1 and/or beta 2) and consequences of the vasodilatation.