Novel Vasodilator Released by Retinal Tissue

Aseries of classical experiments within the past 20 years, all of which used the incubation of donor tissues with detector blood vessels, have yielded a rich trove of vasoactive principles, culminating in the discovery of the physiologically relevant vasodilator mediators prostacyclin1 and nitric oxide (NO).2 In a like manner, Delaey and Van de Voorde3 report in this issue of Circulation Research , evidence for the existence of yet another tissue-derived vasoactive factor that may have broad implications for vascular research.The salient finding of the study presented by Delaey and Van de Voorde3 is that adherent retinal tissue, but not a similar-sized piece of choroidal tissue, of a variety of species exerts an inhibitory effect on the contractile tone of isolated, endothelium-intact, or denuded bovine retinal arteries. Moreover, contractions induced by a variety of agents, ie, U-46619, serotonin, and endothelin-1, were also blocked in the presence of retinal tissue. Collectively, these experiments can be interpreted to mean that retinal tissue releases a diffusible vasorelaxant that not only relaxes the retinal artery but also other smooth muscle preparations such as rat mesenteric and renal arteries and rat main bronchi, as demonstrated by Delaey and Van de Voorde. Also shown is that incubation of retinal tissue yields a solution that relaxes isolated bovine retinal arteries, further confirming the involvement of a diffusible chemical substance.Previous studies by other investigators have already shown that prostaglandin (PG) E1 is capable of causing dilation of pig retinal arterioles and that administration of indomethacin into the retinal circulation reversibly inhibits retinal vasodilation induced by hypercapnia.4 In addition, in a more recent study, it was reported that intact retinal tissue of the miniature pig releases NO, as measured by an NO microprobe, most likely from glial cells and not vascular endothelial …