In nonhuman primates intracarotid adenosine, but not sodium nitroprusside, increases cerebral blood flow

Intracarotid infusion of short-acting vasodilators, such as adenosine and nitroprusside, in doses that lack significant systemic side effects, may permit controlled manipulation of cerebrovascular resistance. In this experiment we assessed changes in cerebral blood flow (CBF) after intracarotid infusion of nitroprusside and adenosine. The study was conducted on six adult baboons under isoflurane anesthesia and controlled ventilation. Intracarotid drug infusion protocol avoided hypotension during nitroprusside infusion and tested for autoregulatory vasoconstriction. CBF (intraarterial 133 Xe technique) was measured four times during infusions of 1) intracarotid saline, 2) IV phenylephrine (0.2 μg.kg -1 .min -1 ) aimed to increase mean arterial pressure by 10-15 mm Hg, 3) IV phenylephrine and intracarotid nitroprusside (0.5 μg.kg -1 .min -1 ), and 4) intracarotid adenosine (1 mg/min). IV phenylephrine increased mean arterial pressure (69 ± 8 to 91 ± 9 mm Hg, P < 0.0001, n = 6), and concurrent infusion of intracarotid nitroprusside reversed this effect. However, compared with baseline, CBF did not change with IV phenylephrine or with concurrent infusion of IV phenylephrine and intracarotid nitroprusside. Intracarotid adenosine profoundly increased CBF (from 29 ± 8 to 75 ± 32 mL.100 g -1 .min -1 ; P < 0.0001). In nonhuman primates, intracarotid adenosine increases CBF in doses that lack significant systemic side effects, whereas intracarotid nitroprusside has no effect. Intracarotid adenosine may be useful for manipulating cerebrovascular resistance and augmenting CBF during cerebral ischemia.