Systemic acidosis after controlled hypotension activates catechol activity in the vasomotor center

Activation of the catechol metabolism, assessed with in vivo voltammetry, in the vasopressor area of the vasomotor center was investigated during systemic acidosis occurring after controlled hypotension. Rats anesthetized with halothane were mechanically ventilated. Sodium nitroprusside lowered mean arterial pressure to 55 mmHg for > or = 20 min. Arterial blood gases allowed us to group rats according to whether they showed symptoms of metabolic acidosis (pH < or = 7.34) immediately after controlled hypotension. To assess the effect of systemic acidosis independently of the progressive decline in pressure observed during the recovery period after controlled hypotension, we used phenylephrine infusion to maintain mean arterial pressure at baseline pressure during the recovery period after controlled hypotension in two groups of animals. Systemic acidosis increased the catechol signal in a prolonged manner [nitroprusside with acidosis (n = 7) vs. nitroprusside without acidosis (n = 5); P < 0.0001]. This catechol activation was greater when pressure was restored after hypotension [nitroprusside with acidosis plus phenylephrine (n = 5) vs. nitroprusside with acidosis over the whole interval (from -30 to +150 min); P < 0.05]. When the nitroprusside with acidosis group and nitroprusside with acidosis plus phenylephrine group were compared, hypercapnia had an involvement in the larger increase of the catechol signal observed in the nitroprusside with acidosis plus phenylephrine group [arterial PCO2: nitroprusside with acidosis vs. nitroprusside with acidosis plus phenylephrine over the whole interval (from -30 to +150 min) and at +30 and +60 min; all P < 0.05].(ABSTRACT TRUNCATED AT 250 WORDS)