Release of endogenous catecholamines in the nucleus tractus solitarii during experimentally induced blood pressure changes.

The nucleus tractus solitarii (subnucleus medialis) of anaesthetized cats was bilaterally superfused through push-pull cannulae and the release of endogenous catecholamines (dopamine, noradrenaline and adrenaline) determined in the superfusates. A moderate increase in blood pressure elicited by intravenously injected noradrenaline (0.3 micrograms per kg body weight) reduced the rate of release of endogenous adrenaline, while a pronounced rise in blood pressure (at least 47 mm Hg) evoked by noradrenaline (3 micrograms per kg) or blood injection inhibited the release of adrenaline and noradrenaline in the nucleus tractus solitarii. Bilateral carotid occlusion also diminished the release rates of adrenaline and noradrenaline. Decreases in blood pressure induced by controlled bleeding, intravenous injection of chlorisondamine or nitroprusside did not alter the rates of release of adrenaline or noradrenaline, but the rate of release of endogenous dopamine seemed to be reduced. The decreased adrenaline and noradrenaline release elicited by increases in blood pressure and the reduced release of dopamine induced by decreases in blood pressure may reflect a counteracting mechanism in the nucleus tractus solitarii so as to normalize alterations in blood pressure. The results suggest a hypertensive function of noradrenaline, and possibly a hypotensive role of dopamine at the level of the nucleus tractus solitarii.