EFFECTS OF EPINEPHRINE, PHENOXYBENZAMINE, AND PROPRANOLOL ON MAXIMAL EXERCISE IN SHEEP

Abstract : The effect of sympathomimetic epinephrine (10 ug/kg, i.v.), beta- adrenergic antagonist propranolol (0.2 mg/kg, i.v.) and alpha-adrenergic antagonist phenoxybenzamine (1 mg/kg, i.v.) on maximal exercise in normal sheep was investigated. Maximal exercise in control sheep showed a mean maximum oxygen consumption (VO2) of 47.6 + or - 6.7 ml O2/min/kg. Maximum VO2 after pretreatment with epinephrine, 51.6 + or - 8.7 ml O2/min/kg, was not significantly different from control. Maximum VO2 after pretreatment with propranolol and phenoxybenzamine, 35.4 + or - 15.3 and 40.8 + or - 8.3 ml O2/ min/kg, respectively, were both significantly less than control (p<.05). The anaerobic threshold (AT) was unaffected by either epinephrine, propranolol or phenoxybenzamine. Maximum exercise in sheep caused a mean 42% increase in hematocrit and 44% increase in hemoglobin. This exercise-induced hemoconcentration was unaffected by propranolol but was partially blocked by phenoxybenzamine. Maximal exercise in sheep caused significant decreases in bicarbonate and pH and significant increases in jugular venous P02 and O2 content. Increases in O2 content from rest to maximal exercise, 7.6 + or - to 12.7 + or - 1.8 g/100ml (p<.05), were less when sheep were exercised after pretreatment with phenoxybenzamine, 7.9 + or - 1.2 to 10.8 + or - 0.7 g/100ml (p<.05).