Abstract
1. 1. Intravenous injections of epinephrine produced an increase in dorsal aortic blood pressure and heart rate. Low dose levels of epinephrine caused a reflex slowing of the heart, a response abolished by atropine injections into the pericardial cavity. 2. 2. Phenoxybenzamine injections blocked the pressor response to epinephrine. Changes in blood pressure during activity and excitement also disappear after α-adrenergic receptor blockage with phenoxybenzamine. 3. 3. It is concluded that there are α-adrenergic receptors in blood vessels in the gills and in the general body circulation. Epinephrine probably causes a vasodilation in the gills and a vasoconstriction of blood vessels peripherally in the systemic circulation. 4. 4. Blood pressure changes occuring during swimming can be explained by the interaction of epinephrine with α-adrenergic receptors. 5. 5. Dichloroisoproterenal or propranolol, when injected intravenously in fish, had little effect on the response of the heart to epinephrine, but caused a marked fall in dorsal aortic blood pressure and heart rate.
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