Subarachnoid blood causes pial arteriolar constriction in newborn pigs

The present study was designed to determine in newborn animals the delayed effect of subarachnoid blood on pial arteriolar diameter and eicosanoid concentrations in cortical periarachnoid fluid.

Forty-eight to 96 hours after subarachnoid blood installation, closed cranial windows were implanted over the cerebral area exposed to blood in anesthetized, artificially ventilated newborn piglets. All pial arterioles greater than 60 microns in diameter were measured, and cortical periarachnoid fluid was collected for the determination of eicosanoids.

Subarachnoid blood resulted in a 20% to 30% decrease in the average diameter of pial arterioles exposed to blood for 48 to 96 hours, a decreased number of large pial arterioles (greater than 200 microns), and an increased number of small arterioles (60 to 100 microns). No changes in dilator prostanoids (prostacyclin [as 6-keto-prostaglandin F1 alpha] and prostaglandin E2) were detected. Concentrations of vasoconstrictor prostanoids in cortical cerebrospinal fluid increased. Thromboxane B2 increased to 430 +/- 70 pg/mL, and prostaglandin F2 alpha increased to 1370 +/- 180 pg/mL compared with 250 +/- 20 and 860 +/- 70 pg/mL, respectively, in the control group. The concentration of peptidoleukotrienes increased to 400 to 600 pg/mL 72 to 96 hours after blood installation, while the level in the control group was less than 80 pg/mL.

The altered balance between vasodilator and vasoconstrictor eicosanoids could contribute to cerebral vasoconstriction after subarachnoid blood installation in newborn pigs.