Nitrites Help To Struggle Against Ischemia Retinae

Main Category: Eye Health / Blindness
Also Included In: Biology / Biochemistry;  Cardiovascular / Cardiology
Article Date: 28 Mar 2008 - 0:00 PDT

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Nitrites dilate vessels in case of hypoxia and protect retina from ischemia. The conclusion has been made by specialists of the Moscow Research Institute for Eye Diseases named after Gelmholtz and the N.M. Emanuel Institute of Biochemical Physics, Russian Academy of Sciences. Their discovery is the outcome of a series of experiments on rabbits. It is premature to talk about its clinical use.

Ischemia is a rather widespread pathology of retina and optic nerve. It is provoked by different reasons, including primary hypertension and insular diabetes. An important role in retina pathology development is played by shortage of nitric oxide, which is synthesized in the organism from arginine. Theoretically speaking, nitrites can turn into nitric oxide under the influence of some enzymes. However, till recently, nobody could prove that such reaction does take place in a living organism. The Moscow researchers succeeded to do that based on the acute ischemia retinae model developed by them.

The rabbit is a favorite object for ophthalmologists' investigations. The animals underwent laser coagulation of eye-ground vessels. The experimentalists have chosen such a place for exposure so that several impulses could capture the maximum number of vessels and if possible not to traumatize surrounding tissues. The laser provokes stable vasospasm and, consequently, ischemia. The outcomes of researchers' action were estimated by the rabbits' eye-ground photographs.

After coagulation, the rabbits' eye vessels become desolate and abruptly reduced in diameter. Right after laser exposure, sodium nitrite in physiological solution was intraperitoneally introduced to the rabbits on the basis of 20 mg per 1 kilogram of live weight. As soon as a quarter of an hour after the injection, the retina vessels directly behind the laser impact zone began to fill with blood and the blood circulation restored in them. At that, the nitrite injection to an animal with normal vessels almost did not provoke their dilation. The researchers assume that nitrite in the organism is able to quickly reduce to nitric oxide, which sharply relaxes vessels, but only in case of oxygen shortage.

In the course of a next series of experiments the researchers clarified if preliminary nitrite injection prevented vessel constriction. For this end, a rabbit was initially injected sodium nitrite, and 15 minutes later the researchers cauterized vessels by laser and observed changes in them. In this case, laser impact provoked only a short-term vasospasm of the vessel, which quickly filled with blood and restored the "flow capacity".

The same results were obtained by the researchers via an independent method when observing changes in photoelectric activity of a rabbit's retina. The electroretinogram analysis has shown that laser coagulation of vessels impairs functional state of retina, which restores within 7 days without outside interference. The sodium nitrite injection right after laser coagulation accelerates the rehabilitation process significantly, and the preparation injection prior to laser exposure virtually fully protects retina from injury. At that, even strong laser impact can not provoke abrupt constriction and desolation of animals' vessels.

Thus, the outcomes obtained by two independent methods prove that nitrites presence in vessels protects the retina from acute ischemia. Mechanism of such action, apparently, consists in the fact that under oxygen shortage in the organism, sodium nitrite can reduce to nitric oxide at concentrations that are sufficient for full vessel relaxation.

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