Long-term effects of heavy metal salts on morphometric parameters and functional state of the sexually mature rats' pineal gland

Environmental pollution with heavy metals poses a great threat to living organisms and constitutes one of the major problems of modern society. The pineal gland controls the endocrine, nervous, and immune systems, integrates the systemic response to adverse factors affecting the body’s resistance. The aim of the study is to investigate the correlation relationships between the dimensions of the pineal gland in sexually mature rats and its other morphometric parameters under conditions of prolonged exposure to a complex of heavy metal salts. Animals from 3 experimental groups were subjected for 30, 60, and 90 days to simulated microelementosis by adding to their drinking water a mixture of heavy metal salts: zinc (ZnSO4×7H2O) – 5 mg/L, copper (CuSO4×5H2O) – 1 mg/L, iron (FeSO4) – 10 mg/L, manganese (MnSO4×5H2O) – 0.1 mg/L, lead (Pb(NO3)2) – 0.1 mg/L, and chromium (K2Cr2O7) – 0.1 mg/L. Morphological, morphometric, and statistical research methods were used. In the pineal gland of experimental animals, as a result of exposure to heavy metal salts, adaptive-compensatory processes developed and rearrangements occurred in the correlation relationships between the parameters of pineal dimensions and other morphometric indicators of the gland. A decrease in organometric parameters of the gland was observed on the 30th and 90th days of the experiment, with their increase on the 60th day of the study. The strongest correlation between the length of the pineal gland and the glial cell-neuronal index was observed on the 30th day of the experiment; between the length and width of the pineal gland, the length and the average diameter of the karyon/optical density of nuclei on the 60th day; and between the width of the gland and the average diameter of the karyon on the 90th day of the experiment. Adaptive rearrangements in the pineal gland at different stages of pollutant exposure had a wave-like pattern and were determined by the tension of adaptive-compensatory processes at the early stages of the study (30th day), which were replaced by compensatory hypertrophy of the organ on the 60th day of the experiment and by the gradual exhaustion of the functional adaptive capacities of the pineal gland in response to long-term exposure to heavy metal salts (90th day).