Abstract
Sildenafil citrate is a type-5 phosphodiesterase inhibitor (PDE-5), able to inhibit type-6 phosphodiesterase (PDE-6) as well, providing clinical benefits and paraeffects, some of them potentially related to the retina. The effects of the sildenafil on the retrobulbar and retinal circulation were studied in 27 adult male rabbits of the White New Zealand breed. The electric activity of the retina was evaluated before and at the end of the treatments, and immunohistochemistry studies were conducted. An amplitude increase of the b wave was found in the mixed response of cones and rods after 7 days of treatment with sildenafil citrate. However, in the other evaluations and periods, the values did not differ from the basal ones. Through immunohistochemistry, no significant decrease of the expression of PDE-5 and PDE-6 proteins was observed. Based on the results obtained, it is possible to admit that the sildenafil citrate did not change the expression of PDE-5 and PDE-6, neither the electroretinographic activity of the retina of male rabbits of the White New Zealand breed.
Highlights
The sildenafil citrate is able to promote vasodilatation in sites where the type-5 phosphodiesterase (PDE-5) is present
The electroretinogram may be used in studies on toxicity to drugs, once it is able to evaluate the retina functionally (Sims, 2007)
The effects of the sildenafil were evaluated in 18 adult male, albino, homozygote rabbits, of the White New Zealand breed, randomly divided into 3 groups of 6 animals, for treatment with the drug at a dose of 3.5mg/kg every 24 hours, for 7, 15 and 30 days and in 9 control animals, totaling 27 individuals
Summary
The sildenafil citrate is able to promote vasodilatation in sites where the type-5 phosphodiesterase (PDE-5) is present. Wave a results from the activity of cones and rods (Schaeppi and Liverani, 1977). It reflects the negative change in the intracellular load of photoreceptors (hyperpolarization) occasioned by the light evoked and by the closure of the sodium channels of the cell membrane. Wave b has controversial origin (Sims, 2007) It is admitted as resulting from the depolarization of the Müller cells and the bipolar cells. Rods are not able to receive stimuli over 15 pulses of light per second. Cones are able to receive them, noticing flicker stimuli from 30 Hz to 50 Hz (Sims, 1999; Oriá et al, 2004; Manzano, 2010)
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