EFFECTS OF THE ADRENERGIC DRUGS ON THE CHRONO- AND INOTROPIC RESPONSES TO THE CHOLINERGIC STIMULATION OF THE ISOLATED GUINEA-PIG’S ATRIA

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Abstract
Effects of adrenergic drugs on the negative chrono- and inotropic responses of the guinea-pig''s and rabbit''s atria to the vagal stimulation were studied in the isolated vagus-atrial preparations. Epinephrine usually did not affect the negative chrono- and inotropic responses of the atria to the vagal stimulation, while norepinephrine depressed the responses. The negative responses to the vagal stimulation of the atria of the guinea-pig treated with reserpine did not quantitatively differ from those of the non-treated atria. After the reserpinization, epinephrine usually augmented the responses to the vagal stimulation, while noreprinephrine did not affect the responses. The megative responses of the atria to the vagal stimulation and to the administration of acetylcholine were markedly depressed by adrenolytics, such as dibenzyline and tolazoline. Dichloroisopropyl-norepinephrine in the concentrations of 10-7 and 5 x 10-7 did not affect the vagal and acetylcholine responses of the guinea-pig''s atria. The negative responses of the atria to the vagal stimulation as well as to acetylcholine were markedly depressed by the administration of brety-lium. The role of endogenously released and exogenously administered catecholamine on the cholinergic transmission mechanism in the isolated atria was discussed.