Role of catecholamines and vasopressin in cardiovascular responses to bilateral dorsolateral transection of the medulla oblongata in the rat

The role of sympathetic and other pressor systems in the development of fulminant hypertension induced by baroreceptor deafferentation is still unclear. We studied the effects of acute hypertension produced by bilateral dorsomedullary knife cuts lateral to the nucleus tractus solitarii (DMK-cut) on plasma norepinephrine (NE), epinephrine (E), and vasopressin (VP) in conscious, tail-artery-cannulated rats. In saline-pretreated (SAL) rats, DMK-cut caused a significant (p less than 0.001) rise in mean blood pressure (MAP, +68 +/- 3 mm Hg), heart rate (HR, +97 +/- 19 bpm), NE (+2.5 +/- 0.3 ng/ml), E (+2.7 +/- 0.4 ng/ml), and VP (+115 +/- 34 pg/ml) compared to sham-operated rats. Neither sympathetic blockade with chlorisondamine (CHLO, 10 mg/kg, s.c.) nor elimination of the pressor effects of VP by use of Brattleboro rats or the VP pressor antagonist resulted in a maximal MAP response significantly different from that in the SAL + DMK-cut group. However, CHLO-pretreatment of Brattleboro rats completely abolished the increase in MAP and HR. It is suggested that the bilateral DMK-cut causes acute hypertension, probably due to the abolition of baroreceptor reflexes by central interruption of neural connections of the nucleus tractus solitarii. It appears that both the increased sympathoadrenomedullary activity and VP release normally contribute to this hypertension; however, either one is sufficient to sustain the elevated blood pressure.