Prostaglandin G/H Synthase-2 Is a Major Contributor of Brain Prostaglandins in the Newborn

Abstract

In order to understand the molecular basis of the elevated cerebral prostaglandin levels in the newborn, we compared the expression of the mRNAs and proteins of prostaglandin G/H synthases (PGHS), PGHS-1 and PGHS-2, in various regions of the brain and the microvasculature of newborn (1-2-day-old) and juvenile (4 -7-week-old) pigs and also measured the relative contribution of PGHS-2 to cerebral prostaglandin synthesis both in vivo and in vitro by using a novel inhibitor of PGHS-2, NS-398. Ribonuclease protection assays using total RNA isolated from various regions of the porcine brain revealed that, unlike PGHS-1 mRNA, PGHS-2 mRNA was abundantly expressed in the cortex and the microvasculature of the newborn compared with those of the juvenile animal. PGHS-2 immunoreactive protein comprised the majority of total PGHS enzyme in neonatal cerebral microvasculature due to a 2-3-fold lower expression of immunoreactive PGHS-1 protein. Inhibition of PGHS-2 by NS-398 decreased the rate of prostaglandin synthesis by purified cerebral microvessels of the newborn by approximately 65% and of juvenile pigs by 30%. The decrease in brain tissue prostaglandin concentrations following intravenous administration of NS-398 was greater in newborn pigs ( 90%) than in the juvenile animals ( 30%). Furthermore, NS-398 substantially reduced the net in vivo cerebrovascular production of prostaglandins in newborn pigs. Taken together, these results indicate that PGHS-2 is the predominant form of prostaglandin G/H synthase in the newborn brain and cerebral microvasculature and the main contributor to the brain prostaglandin levels in the newborn animal.

Selective Inhibitors Differentially Affect Cyclooxygenase-Dependent Pial Arteriolar Responses in Newborn Pigs

“…Our present in vivo results using COX isoform-selective pharmacological tools are in accordance with the dominant, strong expression of COX-2 in the piglet brain and cerebral arteries, especially the microvascular endothelium (2), and the COX-2 dependency of in vivo cerebrovascular prostanoid production in piglets (13). The assessed COX-dependent responses mainly require COXproducts from endothelial cells, since selective endothelial injury diminishes the responsiveness to these stimuli (14,15).…”

N-methyl-d-aspartate-induced vasodilation is mediated by endothelium-independent nitric oxide release in piglets

“…ROS, which promote dilation to bradykinin, apparently arise from metabolism of arachidonic acid by cyclooxygenase (COX)-1 in mice (32). Whether this same mechanism occurs in piglets is unclear, because in this species COX-2 is the predominant isoform present under normal conditions both in brain and cerebral arteries (34). However, our finding that NMDA-induced dilation of pial arterioles was intact after PDB injection indicates that a contribution of endothelial NO or other endothelial-derived dilator substances to vasodilation is very unlikely.…”

Proinflammatory Gene Induction by Platelet-Activating Factor Mediated Via Its Cognate Nuclear Receptor

“…For inhibition of receptor translocation treatments, C-PAF stimulation was done under potassium-depleted conditions (DMEM:water, 1:1). Total cellular RNA and nRNA (1 g) were subject to RT-PCR for COX-2 (209 bp) and iNOS (417 bp) genes as described previously (35). Each PCR cycle was 94°C, 30 s; 58°C, 45 s; 72°C, 1 min and was repeated 40 times.…”