HYPOTHERMIA ENHANCES CONTRACTILITY IN CEREBRAL-ARTERIES OF NEWBORN LAMBS

Hypothermia is the major factor influencing autoregulatory properties of the cerebral circulation in human infants undergoing hypothermic ca rdiopulmonary bypass. The present investigation evaluated the effect o f decreased temperature on the contractility of isolated middle cerebr al arteries obtained from newborn lambs. Reducing bath temperature fro m 37 to 21 degrees C caused a temperature-dependent increase in contra ctile tension, achieving 1.32 +/- 0.09 g above resting tension (0.75 g ). Pretreatment with nonselective (alpha(1) and alpha(2)) alpha-adreno ceptor antagonist, phentolamine (10(-5) M), with an inhibitor of nitri c oxide synthase, N-G-nitro-L-arginine methyl ester hydrochloride (10( -4) M), and with a cyclooxygenase inhibitor, indomethacin (10(-5) M), did not affect the contractile response to a decrease in bath temperat ure from 37 to 21 degrees C. Furthermore, cerebral arteries were respo nsive to both norepinephrine (constriction) and sodium nitroprusside ( relaxation) and the sensitivity of cerebral arteries to the sympatheti c neurotransmitter norepinephrine appears to be enhanced at low temper atures. We postulate that direct cerebral vasoconstriction and enhance d adrenergic contractility may be responsible for increased cerebrovas cular resistance during and after hypothermic cardiopulmonary bypass w ith possible ischemic cerebral injury and neurological sequelae. (C) 1 994 Academic Press, Inc.