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Dexamethasone Pretreatment Attenuates Cerebral Vasodilative Responses to Hypercapnia and Augments Vasoconstrictive Responses to Hyperventilation in Newborn Pigs

In the perinatal period, glucocorticoids are frequently administered to enhance pulmonary maturity or prevent chronic lung disease of prematurity. Recently, it has been suggested that the perinatal exposure to glucocorticoids can be associated with unfavorable neurologic development. We studied the hypothesis that 24-h pretreatment with glucocorticoid might modify cerebrovascular responses to high and low partial arterial CO2 tension in newborn animals in vivo. A closed cranial window was implanted over the left parietal cortex of 20 anesthetized ventilated newborn (<3 d old) pigs. The actual experiments were carried out in 15 pigs: eight pretreated with a total dose of 6 mg/kg of dexamethasone and seven controls. Five pigs were used for preliminary experiments as described in the text. Pial arteriolar diameters were measured during 1) baseline conditions (normocapnia), 2) hypercapnia induced by ventilating the animals with a gas mixture containing 10% CO2, or 3) hyperventilation with resultant hypocapnia. Under these conditions, the concentrations of 6-keto-PGF1α in the CSF were measured in five experimental animals and six controls. In summary, the dexamethasone pretreatment 1) attenuated the hypercapniainduced dilator responses of pial arterioles and prevented the hypercapnia-associated fall in mean arterial blood pressure; 2) caused moderate, although not statistically significant, diminution in 6-keto-PGF1α levels in the CSF during baseline; 3) blocked hypercapnia-induced elevation of 6-keto-PGF1α; and 4) enhanced vasoconstrictive arteriolar responses to hyperventilation. We speculate that in the clinical setting, the dexamethasone effects may compromise the adjustments of global or regional cerebral blood flow to changing physiologic states in neonates.