Effect of adenosine-induced hypotension on the cerebral autoregulation in the anesthetized pig

The influence on cerebral blood flow (CBF) and autoregulation of systemic adenosine infusion, at doses that produced a 29 +/- 4% (0.28 +/- 0.06 mg/kg/min) or a 55 +/- 2% (0.49 +/- 0.07 mg/kg/min) reduction of mean arterial blood pressure (MABP), was evaluated in 12 normoventilated fentanyl/N2) anesthetized pigs. CBF was determined as sagittal sinus outflow and recorded continuously by an electromagnetic technique. Autoregulation was evaluated by two formal tests: infusion of angiotensin for elevation of MABP, and reduction of myocardial filling pressure by caval block for graded MABP decrease before, during and after adenosine infusion. CBF as well as cerebral metabolic rate of oxygen were unaffected during both levels of hypotension and were not significantly altered after the hypotension. Signs of impaired autoregulation were found during the angiotensin test as well as during the caval block at light hypotension (92 +/- 3 mmHg, 12.3 +/- 0.4 kPa), while autoregulation was completely abolished at moderate hypotension (59 +/- 2 mmHg, 7.9 +/- 0.3 kPa). After termination of adenosine-induced hypotension, autoregulation was restored in all animals within 60 min. It is concluded that systemically administered adenosine preserves CBF, even at low MABP levels, by a direct cerebral vasodilatory effect. However, the cerebral autoregulatory mechanisms are impaired or abolished in a dose-dependent and reversible manner.