REFLEX CARDIAC INHIBITION OF BRANCHIO-VASCULAR ORIGIN IN THE ELASMOBRANCH, SQUALUS ACANTHIAS

Abstract

1. Cardiac inhibition follows sudden increase of pressure within the gill blood vessels of Squalus acanthias. An average increase of 10.7 mm. Hg above the average systolic pressure existing in the dorsal aorta constitutes an adequate stimulus for the inhibitory response.2. The cardio-inhibitory response is a reflex, with afferent pathways located in the branchial nerves and efferent pathways in the vagus supply to the heart. The reflex is both unilateral and crossed.3. The average ventral aortic systolic blood pressure in Squalus acanthias is found to be 28.2 mm. Hg, the average dorsal aortic systolic pressure 15.4 mm. Hg, and the average ventral aortic pulse pressure 13.3 mm. Hg. The inhibitory reflex to increased ventral aortic pressure modifies the diastolic blood pressure to a significant degree.4. The adaptive nature of the reflex is pointed out and its phylogenetic significance is discussed.