Adenosine causes dilatation and constriction of hypothalamic blood vessels.

The effect of adenosine on intraparenchymal cerebral blood flow was examined in conscious rabbits with the 133Xe clearance technique. Perivascular application of 10(-3) and 10(-4) M adenosine to hypothalamic blood vessels increased hypothalamic blood flow by approximately 50% (p less than 0.005). This vasodilatation was attenuated by the intrahypothalamic injection of the beta-adrenergic receptor antagonist propranolol, but was unaffected by alpha-adrenoreceptor blockade with phenoxybenzamine, or depression of neuronal activity with barbiturate. 2-Chloroadenosine, a stable analogue of adenosine, also increased hypothalamic blood flow by 50% (p less than 0.005), but this dilatation was unaffected by propranolol. These results suggest that adenosine increased hypothalamic blood flow at high concentrations by vascular receptor systems dependent on adenosine receptors and adrenergic receptors. Adenosine (10(-6) M) reduced hypothalamic blood flow by approximately 25% (p less than 0.005). This vasoconstriction was unaffected by adrenergic blockade with propranolol or phenoxybenzamine, or by inhibition of neuronal activity with barbiturate. The results suggest that adenosine decreases hypothalamic blood flow at low concentrations by stimulation of adenosine receptors associated with vascular smooth muscle.