Regulation of endothelial nitric oxide synthase by PGD(2) in the developing choroid

We investigated if prostaglandins might regulate the increased choroidal en dothelial (e) nitric oxide synthase (NOS) expression in the perinate. Prost aglandins, eNOS mRNA, immunoreactive protein and activity, and nitrite [sta ble metabolite of nitric oxide (NO)] production were markedly higher in new born (1 day old) than juvenile (6-8 wk old) pig choroid. Treatment of isola ted newborn choroids with the prostaglandin synthase inhibitor ibuprofen fo r 24 h reduced eNOS mRNA and nitrite production to values in juveniles. Thi s effect was equally observed with the PGD(2) receptor CDP) blocker BW A868 C and was prevented by cotreatment with PGD(2) but not other prostaglandins ; similar observations were made on NOS activity in vivo. PGD(2) also incre ased eNOS expression on choroids of juveniles, and this effect was blocked by BW A868C. The manifestation of this upregulation of eNOS by PGD2 on the control of choroidal vasomotor response was tested by using NO-dependent va sorelaxants, ACh, bradykinin (Bk), and substance P (SP. ACh-, Bk-, and SP-e licited choroidal vasorelaxation was greater in saline-treated newborn than juvenile pigs. Ibuprofen (24 h) decreased ACh-, Bk-, and SP-evoked vasorel axation in newborns, whereas PGD(2) increased that in juveniles and prevent ed the ibuprofen-induced attenuated relaxation in newborns; infusion of N-o mega-monomethyl-L-arginine in choroids of those animals treated with PGD2 r eversed the augmented vasorelaxation to ACh, Bk, and SP. Finally, PGD(2)-in duced upregulation of NOS in the perinate was also reflected by curtailed c horoidal blood flow autoregulatory response to increased perfusion pressure . In conclusion, PGD(2) exhibits a major role in upregulating eNOS expressi on and activity in the choroid, which in turn results in greater NO-mediate d vasorelaxation; a new mechanism for eNOS regulation via DP is hereby disc losed. The relationship between PGD2 and eNOS in the developing subject pro vides an explanation for the interactive role of these two factors in the a bsent choroidal blood flow autoregulation in the perinate.