Interplay of sino-aortic reflexes and haemodynamic changes during natural sleep in the cat

1. When the sino-aortic afferents are intact, desynchronized sleep causes a small decrease in the blood pressure, a vasodilation in the mesenteric and renal beds, and a vasoconstriction in the external iliac bed. 2. After sino-aortic deafferentation desynchronized sleep causes a larger fall in the blood pressure, a greater vasodilatation in the mesenteric and renal beds, and a vasodilatation replaces the vasoconstriction in the external iliac bed. 3. The sino-aortic reflexes play an active role in controlling circulation during desynchronized sleep by opposing the centrally induced reduction in adrenergic sympathetic tone. This effect of sino-aortic reflexes is similar on both visceral and muscular vessels. In addition, the muscular bed, but not the visceral one, is regulated by a spinal reflex vasoconstriction mechanism which is apparent only when the sino-aortic reflexes are intact.