Intravenously Administered Vasodilatory Prostaglandins Increase Retinal and Choroidal Blood Flow in Rats

Abstract

Abstract. We established an experimental system for measuring blood flow in the rat fundus and examined whether intravenously administered vasodilatory prostaglandins (PGE 1 , PGE 2 , and PGI 2 ), 8-(4-chlorophenylthio)-cAMP (a cAMP analogue), and nicardipine (a Ca 2+ -channel blocker) increase fundus blood flow (FBF). Under artificial ventilation, rats were injected with tetrodotoxin (50 µg / kg, i.v.) to eliminate any nerve activity and prevent movement of the eye.After tetrodotoxin, the rats were infused with norepinephrine (0.3 -0.5 µg ⋅ kg) and) simultaneously to maintain adequate systemic circulation.We found that intravenous infusion of PGE 1 (2 -10 µg ⋅ kg), and PGI 2 (1 -10 µg ⋅ kg −1 ⋅ min −1 ) increased the FBF in a dose-dependent manner. The vasodilatory PGs decreased arterial pressure, whereas they did not affect heart rate. Like vasodilatory PGs, 8-(4-chlorophenylthio)-cAMP (30 µmol / kg, i.v.) increased FBF and decreased arterial pressure. While infusion of nicardipine (0.3 -3 µg ⋅ kg −1 ⋅ min −1 ) produced comparable depressor responses with those to vasodilatory PGs and the cAMP analogue, it did not increase FBF. These results suggest that vasodilatory PGs and cAMP act more selectively than Ca 2+ -channel blockers on retinal / choroidal blood vessels. Therefore, the vasodilatory PGs might be considered to be possible candidates for the therapeutics to treat disorders of retinal / choroidal circulation.

Role of Calcium-Activated Potassium Channels with Small Conductance in Bradykinin-Induced Vasodilation of Porcine Retinal Arterioles

“…In isolated bovine retinal small arteries, acetylcholine relaxation is not inhibited by indomethacin, suggesting release of NO and no involvement of prostaglandins. 31 However, prostaglandins were found to be involved in vasodilator responses in rat, 32,38,39 canine, 33,34 bovine, 36 and porcine 35,37 eyes. In previous studies of pressurized porcine retinal arteries, we observed that inhibition of cyclooxygenase induced a significant right shift of the bradykinin concentration response, 6 and in the present study the effect of the cyclooxygenase inhibitor, indomethacin, on bradykinin relaxation was even more pronounced.…”

Nitric oxide dilates rat retinal blood vessels by cyclooxygenase-dependent mechanisms

“…Because TTX decreased blood pressure and HR, a mixture solution of norepinephrine (NE) and epinephrine (Epi) (NE:Epi ϭ 1:9) was continuously injected into the right jugular vein at a constant rate by means of a syringe pump (Model 1140 -001, Harvard Apparatus) to maintain systemic blood pressure and HR at the control level (19,20). This procedure also abolished the pressor response to spinal cord stimulation and the ACh-induced reflex tachycardia observed in anesthetized rats for several hours (4).…”

Variation in Lipid-Associated Genes as They Relate to Risk of Advanced Age-Related Macular Degeneration

“…LCPUFAs are precursors to vasoregulatory thromboxanes (TX) and prostaglandins (PG) affecting blood flow [143], vasomotility, platelet activity, and platelet aggregation [88][89][90][91]. As precursors to lipid mediators and endogenous ligands to nuclear transcription factors, ω-3 LCPUFAs are associated with beneficial or non-damaging cellular response in vascular systems subjected to physiologic stresses that alter blood flow, oxygen delivery [70,[143][144][145][146][147][148] and lipoprotein metabolism [50,149,150]. Chronic Light Exposure and AMD.…”