A COMPARISON OF THE EFFECTS OF SALBUTAMOL, ETILEFRINE AND DEXTRAN DURING HYPOTENSION AND LOW CARDIAC OUTPUT STATES IN RABBIT

SUMMARY 1. The effects of salbutamol (25 and 50 μg/kg), etilefrine (50 and 200 μg/kg) and dextran (8 ml/kg) on cardiovascular function have been studied in the rabbit. 2. The three drugs raised the resting cardiac output (with salbutamol producing Δ max 52%, P<0.001, n=5) and right heart filling pressure (RHFP, Δ max from dextran 3.5 cmH2O; P<0.001, n=6) and lowered total peripheral resistance (TPR, Δ max from salbutamol 46%, P<0.001, n=5). However, TPR rose with the 200 μg/kg etilefrine (P<0.05, n=5). Pulse pressure rose with salbutamol (P<0.001, n=6) and etilefrine (P<0.05, n=6). Etilefrine raised resting BP (Δ max, P<0.001, n=6); salbutamol lowered resting BP (Δ max, P<0.001, n=6) while dextran (n=6) had little effect on resting BP. 3. The actions of salbutamol are mediated mainly through β2-adrenoceptors although the drug also has some minor β1-adrenoceptor action. With etilefrine, the increase in cardiac output and the reduction in TPR are mediated through (β-adrenoceptors while the increases in RHFP, blood pressure and TPR are a direct action on the α-adrenoceptors. 4. However, during haemorrhage the fall in diastolic pressure produced by salbutamol was considerably reduced while the reduction in mean BP and systolic pressure (which sometimes rose) was abolished. Dextran raised BP during hypotension produced by either sympathectomy or haemorrahge but not during normotension. 5. The reflex recovery in RHFP and the reflex tachycardia were slightly attenuated during lower body negative pressure (LBNP) after salbutamol or dextran. The reflex recovery in blood pressure was complete and the pressure sometimes exceeded the resting level by up to 10 mmHg during LBNP after salbutamol, etilefrine (50 μg/kg only) and dextran. 6. The reduced TPR (presumably due to vasodilation) and the increases in cardiac output and RHFP at an adequately maintained blood pressure produced by suitable doses of the three drugs may be useful in the management of circulatory shock and related states.