MORPHOMETRIC INDICATORS OF CHANGES IN THE CILIARY BODY OF RABBITS WITH EXPERIMENTAL HYPOPINEALISM UNDER THE INFLUENCE OF A COURSE OF MELATONIN

Abstract

There is a close physiological connection between the organ of vision and the pineal gland, which is manifested in the fact that under the influence of light falling on the retina, signals are transmitted along the retinohypothalamic pathways to the brain and, reaching the pineal gland, inhibit the production of the hormone melatonin (M). It was found that a decrease in nighttime production of M leads to disruption of free-radical processes in the cell, disruptions in the immune and endocrine systems, etc. As a result, pathological changes develop in various tissues of the body. Modern studies have identified M in such eye tissues as the retina, ciliary body (CB), and lens epithelium. A connection has also been established between M production, production of intraocular fluid by the ciliary body, intraocular pressure and the development of certain types of glaucoma.

The aim of the work was to investigate the features of morphological changes in the CB of rabbits under the influence of the course of M injections at different times of manifestation of experimental hypopinealism, which developed against the background of 24-hour lighting.

Materials and methods. The experimental study was carried out on rabbits in compliance with the "European Convention for the Protection of Vertebrate Animals Used for Experimental and Other Scientific Purposes" (Strasbourg, 1986) and Law of Ukraine “On the Protection of Animals from Cruelty” No. 3447-IV (Kyiv, 2006). The formation of hypopinealism in animals was achieved by exposing them to 24-hour lighting. The groups were: the control group (CG) - 23 intact animals, which were in vivarium with natural change of day and night; a group with hypopinealism (HG) - 32 rabbits that were in the round-the-clock illumination (RCI); the HG+M group - 29 rabbits that were in the RCI, but before being withdrawn from the experiment, received a course of injections of M for 14 days. Depending on the duration of the experiment, subgroups were identified: 1-2, 3-5, 8-12, 18-19, 26-28 months. When conducting a morphological study of the CB of enucleated eyes of rabbits, morphometric analysis was used using the "field" method. To determine the M content in the blood during the day and night, an enzyme immunoassay was used.

Results. Nighttime melatonin levels in blood decreased under RCI conditions to 62.26±5.27 pmol/L (control: 369.45±14.35 pmol/L; p<0.005).

After 1-2 months of experiment in the HG+M_1-2 subgroup, the average vascular wall thickness (AVWT) indicator (50.71±1.30×10^-6 m) decreased compared to HG_1-2 (59.20±1.21×10^-6 m; p<0.005) and the indicator was similar to CG_1-2 (51.31±1.22×10^-6 m, р<0.005); the average relative area of the vessels (ARAV) indicator (6.61±0.25%) was lower than the HG_1-2 indicator (7.80±0.27%; p<0.005), and significantly exceeds the indicator CG_1-2 (4.51±0.21%; p<0.005). According to morphological and morphometric analysis, after 18-19 months of experimentation in the CB, circulatory disorders completely disappear and pronounced sclerotic changes increase. After 26-28 months in the subgroup HG+M_26-28 the indicator of AVWT increased (207.92±8.6×10^-6 m), not differing from the HG_26-28 indicator (217.42±8.72×10^-6 m; p>0.05), but remaining higher than the CG_26-28 indicator (107.22±5.21×10^-6 m; р<0.005). The ARAV indicator decreases to 3.43±0.13% (p<0.005) and is similar to the indicators of subgroups CG_26-28 and HG_26-28 (3.81±0.11% and 3.42±0.15%; p>0.05).

Conclusions. Thus, according to morphometric and morphological indices, the course of melatonin injections used up to 5 months of the experiment reduces reactive edema and vascular disorders characteristic of the early stages of hypopinealism formation under round-the-clock illumination conditions. After 26-28 months of round-the-clock illumination, the course of melatonin does not have a therapeutic effect on morphological changes in the ciliary body, apparently due to irreversible sclerotic changes in the vessels.