title: Vasoactive agonists do not change the caliber of retinal capillaries of the rat.
abstract: The pericytes of the retinal capillaries are considered to be contractile cells, based on indirect evidence. We attempted to detect pericyte contractility directly using a morphometric method following intravitreal injection of vasoconstricting (endothelin-1, norepinephrine) and vasodilating (forskolin, prostaglandin E1) agonists in rats. The technique involved measuring changes in the ratio of the (lumenal perimeter x mean lumenal radius) to the lumenal area (rP/A ratio, which we defined as "caliber"). Following intravitreal injection of endothelin-1 or norepinephrine there is an ophthalmoscopically visible constriction of the larger retinal arterioles. This constriction is also clearly demonstrable morphometrically (P = 0.001 for endothelin-1 and P = 0.047 for norepinephrine). However, neither for the vasoconstricting nor for the vasodilating agonists is there evidence of a significant change of the caliber of the capillaries. At least in the retina of the rat, therefore, we have no evidence that the pericytes perform a contractile function that alters flow in the capillaries.
mesh_terms: D000527:Alprostadil / Q000494:pharmacology; D000818:Animals; D002196:Capillaries / Q000033:anatomy & histology / Q000187:drug effects; D005576:Colforsin / Q000494:pharmacology; D016232:Endothelins / Q000494:pharmacology; D004837:Epinephrine / Q000494:pharmacology; D008297:Male; D008854:Microscopy, Electron; D051381:Rats; D017207:Rats, Sprague-Dawley; D012171:Retinal Vessels / Q000033:anatomy & histology / Q000187:drug effects*; D014661:Vasoconstriction / Q000187:drug effects; D014662:Vasoconstrictor Agents / Q000494:pharmacology*
chemical_list: D016232:Endothelins; D014662:Vasoconstrictor Agents; D005576:Colforsin; D000527:Alprostadil; D004837:Epinephrine