Effects of Norepinephrine, Angiotensin, Dihydroergotamine, Papaverine, Isoproterenol, Histamine, Nicotinic Acid, and Xanthinol Nicotinate on Retinal Oxygen Tension in Cats

Abstract

The oxygen tension in the vitreous body close to the retina, P,,02, was determined continuously in cats. The effects on Pvr02 of intraarterial injections of various vasoactive drugs were determined. The vasoconstrictors norepinephrine, angiotensin and dihydroergotamine did not change PvrOZ in five cats. The same result was obtained with the vasodilators isoproterenol, histamine and xanthinol nicotinate in five cats, and with nicotinic acid in six cats, while papaverine invariably increased Pvro2 in seven cats when injected intraarterially and in two cats when injected intravenously. It is suggested that the ability to penetrate the blood-retinal barrier may play an important role in determining the effect of vasoactive drugs on retinal blood flow.

Oxygen Sensing in Retinal Health and Disease

“…In the cat, oxygen tension peaks in the inner and outer plexiform layers correspond to the superficial and deep retinal vascular plexi, respectively. The mean pO 2 in the inner retina of the cat during dark adaptation is 18.5 mm Hg [16], which is consistent with measurements of preretinal oxygen tension in cats of 18.9 mm Hg [17]. Although no difference in oxygen consumption has been demonstrated between darkness and steady illumination [18,19], the oxygen tension in the inner retina is slightly reduced in light adaptation compared with darkness [16].…”

Autoregulation of optic nerve head blood flow and its role in open-angle glaucoma

“…As noted previously, autonomic nerves are absent in the anterior ONH [85] and branches of the retinal vessels [86][87][88]. Although adrenergic receptors have been found in the retinal and choroidal vasculature [108,110], other work has shown little influence of these mechanisms on blood flow to the optic nerve [5,[126][127][128].…”

“…Changes in both systemic blood pressure and IOP ultimately affect the main hemodynamic parameter in the eye, the ocular perfusion pressure (OPP). While the association between glaucoma and impaired ocular blood flow has been theorized for centuries, the relationship between autoregulation of blood flow and glaucoma was first proposed investigated in the 1970s [5,6,22], and there have been a number of scholarly articles written on this subject since. A continuous blood supply, especially to tissues with heavy metabolic activity, is critical to survival.…”

“…Since then, clear evidence of a vascular component to the disease has arisen, including largescale epidemiologic studies [2][3][4], animal studies [5][6][7][8][9][10], histopathologic studies [11] and human studies of ocular blood flow [12][13][14][15][16][17][18][19].…”

The Role of Adrenoceptors in the Retina

“…The results, however, are partly contradictory, which makes it difficult to draw unequivocal conclusions regarding the functional role of α 1 -ARs in the regulation of retinal vascular resistance and perfusion. While Mori et al observed a dose-dependent constriction of rat retinal arterioles in response to intravenous administration of noradrenaline, Alm et al did not observe any effect of exogenously administered noradrenaline on retinal blood flow in cats [84,85]. Dollery et al reported that intravenously administered noradrenaline decreased retinal vascular diameter in healthy humans, whereas other studies detected only a negligible impact of circulating noradrenaline and the α 1 -adrenergic agonist, phenylephrine, on human retinal vessel diameter and blood flow [86][87][88].…”