Role of the adrenergic receptors in the central mechanism of the cardiovagal component of the arterial baroreceptor reflex.

The effects of clonidine (1.5 mcg/kg of body weight), L-DOPA (4 mg/kg) and propranolol (0.1 mg/kg) on the reflex bradycardia caused by stimulation of the arterial baroreceptors were studied in 46 waking cats in encephale isole preparations. The drugs were administered into the vertebral artery. They increased the gain of the cardiovagal reflex from the arterial baroreceptors by 162%, 162.5%, 150% respectively with regard to the control values. A similar effect of clonidine and propranolol was manifested also in cats with spinal cord destroyed between the segments C1 to Th12. The effects of clonidine and L-DOPA on the cardiovagal component of the reflex were abolished by aceperon (4 mg/kg) injected into the vertebral artery.