THE RELEASE OF ENDOGENOUS CATECHOLAMINES IN THE CAT HYPOTHALAMUS IS AFFECTED BY SPINAL TRANSECTION AND DRUGS WHICH CHANGE THE ARTERIAL BLOOD PRESSURE

Abstract

In anesthetized cats, posterior and anterior hypothalamic areas were superfused with CSF through double-walled cannulae. The release of endogenous catecholamines [dopamine, noradrenaline [norepinephrine] and adrenaline [epinephrine)] was determined in the superfusate by a radioenzymatic assay. Transection of the brain caudal to the hypothalamus almost abolished the release of catecholamines in the posterior hypothalamic area, while that in the anterior hypothalamic area was moderately decreased. A circular transection around the hypothalamus greatly reduced the release of catecholamines in the anterior hypothalamic area. The catecholaminergic nerve endings of the anterior hypothalamic area probably do not originate entirely from cell bodies located in the brain stem. Spinal transection elicited a pressor response which was followed by fall of the arterial blood pressure. The pressor response was associated with increased rates of release of the catecholamines in the anterior hypothalamic area, while the release of catecholamines in the posterior hypothalamic area was reduced. The fall of blood pressure enhanced the rates of release of the catecholamines in the posterior hypothalamic area and reduced their release in the anterior hypothalamic area. Chlorisondamine i.v., caused a fall of blood pressure which was associated with an increased release of catecholamines in the posterior hypothalamic area and a decrease in the rates of release in the anterior hypothalamic area while i.v. tramazoline elicited a pressor response and enhanced the rates of release of the catecholamines in the anterior hypothalamic area. Pronounced changes in the arterial blood pressure may affect the release of catecholamines in opposite direction in the 2 hypothalamic areas to counteract the blood pressure change.