EFFECT OF DEXAMETHASONE ON CEREBRAL PROSTANOID FORMATION AND PIAL ARTERIOLAR REACTIVITY TO CO2 IN NEWBORN PIGS

This study investigates the effect of glucocorticoid treatment on the relationship between arteriolar Pco2 and cortical prostanoid production and on cerebrovascular responsiveness to elevated CO2 in newborn piglets. The response of pial arteries to hypercapnia (fractional inspired CO2 = 0.035 and 0.07) was studied in 18 anesthetized newborn piglets, 9 of which were pretreated with dexamethasone (2 mg.kg-1.day-1 for 36-48 h). Pial arterioles (77-122-mu-m diam) were monitored using a closed cranial window and intravital microscopy. Perivascular cerebrospinal fluid (CSF) was sampled from the cortical surface and analyzed for 6-ketoprostaglandin F1-alpha and thromboxane B2 (TxB2) using radio-immunoassay. In the dexamethasone-treated animals the increase in arteriolar diameter to CO2 was diminished by approximately 50% for each respective CO2 concentration vs. the control group. Acute sympathetic denervation did not restore the CO2 dilator response. Dexamethasone did not alter baseline cortical CSF prostanoid concentrations but abolished the CO2-induced increase in CSF prostanoids. The dilator response to exogenously applied prostaglandin E2 was inhibited in dexamethasone-treated animals. However, the dilator response to exogenous adenosine and the contractile response to prostaglandin F2-alpha were not altered in the dexamethasone-treated piglets. The data support the concept that metabolites of arachidonic acid participate in the cerebrovascular response to CO2 and suggest that glucocorticoid treatment may influence cerebrovascular tone via this mechanism.