NO and prostanoids: age dependence of hypercapniaand histamine-induced dilations of pig pial arterioles.

Responses to hypercapnia and acetylcholine by newborn piglet pial arterioles are prostanoid dependent but appear to require both prostanoids and nitric oxide in juvenile pigs. We hypothesized that cerebrovascular dilatory responses become less prostanoid dependent and more NO dependent with development. Pial arteriolar responses to hypercapnia and histamine were recorded from α-chloralose-anesthetized newborn and juvenile pigs with closed cranial windows. Responses were recorded during control, after indomethacin or N ω-nitro-l-arginine (l-NNA), and after inhibitor plus iloprost or sodium nitroprusside. Indomethacin blocked newborn hypercapnic responses and markedly attenuated histamine dilations, but only reduced the dilations to about half in juveniles. Iloprost at subdilator concentrations restored newborn responses to hypercapnia and histamine but did not alter either response in indomethacin-treated juveniles. l-NNA attenuated juvenile, but not newborn, hypercapnia-induced dilations. Sodium nitroprusside did not restore the response.l-NNA did not alter responses to histamine in either age group. Cerebrovascular dilations to hypercapnia and histamine are prostanoid dependent and nitric oxide independent in the newborn pig, whereas nitric oxide assumes an increasing role in hypercapnic, but not histamine, responses with development.