Prostanoids Modulate Opiold Cerebrovascular Responses in Newborn Pigs1

The influences of oploids on pial artenolar diameter and cortical periarachnoid cerebrospinal fluid prostanoid concentration were investigated in piglets with closed cranial windows. Methionine enkephalin (1 O_12_1 O M) increased pial arteriolar diameter (139 ± 4, 1 49 ± 3, 1 78 ± 3 m, for control, 1 O_12, and 1 O M, respectively). Leucine enkephalin produced similar pial arteriolar dilation. In contrast, dynorphin elicited dilation during normoten-sion and constriction during hypotension. f-Endorphin (1 0_12_ 1 0- M) decreased pial artenolar diameter (1 37 ± 6, 128±6,92 ± 7 m, for control, 1 O_12 and 1 O_6 M, respectively). All four opioids increased cerebrospinaJ fluid 6-keto-prostaglandin (PG)Fia, PGE2, PGF2a and thrombloxane B. lndomethacin (5 mg/kg i.v.) blocked methionine and leucine enkephalin and dy-norphin-induced pial arteriolar dilation, but potentiated fi-endor