Content of metallothioneins in the organs of sheep under chronic intake of lead with ration

When studying the effects of lead on mammals, one of the informative indicators is the level of metallothioneins (MTs) in organs. MTs are low molecular weight proteins (6-7 kDa) containing up to 30 % cysteine which bind heavy metal ions (Cd 2+, Zn 2+, Pb 2+, Hg 2+, Cu 2+) and act as a trap for free radicals. It is assumed that the MTs content in tissues of mammals depends not only on the amount of lead, the way of intake (with water and/or diet), the type of the tissue and its physiological functions, but on the number of cells in the body and their functional activity. At the same time, the violation in functional and synthetic activity of cells may be related to changes in the weight indices of the bodies. In this regard, the study of MT levels in farm animals as influenced by lead is of interest. In the present work we studied experimentally the MT content, the cellularity and the weight index of the organs in sheep of the Romanov breed under lead intoxication. The experiment was conducted on 27 animals of 33.0±1.1 kg in weight at the age of 1-1.5 years. The sheep were divided into four groups. The group I (4 intact animals) served as a control. For 90 days the sheep in groups II (5 animals), III (9 animals) and IV (9 animals) had a daily diet with lead nitrate at 5 mg/kg, 25 mg/kg and 150 mg/kg of feed, respectively, which corresponded to 1, 5 and 30 MPL (maximum permissible levels) of the metal in the feed. The diet consisted of 0.3 kg of concentrate and 2 kg mixed grass hay. Lead nitrate was administrated with feed once a day. Daily intake of metal (on average per animal) was 10 mg in group II, 50 mg in group III, and 300 mg in group IV, and the dose was 0.3, 1.5 and 9 mg/kg of animal weight, respectively. The study of biological indices was performed in the organs with different physiological functions (liver, kidneys, spleen), which vary in the intensity of metal accumulation and proliferation. The liver, kidneys and spleen were collected after slaughter before the beginning of the experiment (before priming) in one animal, then on days 30 and 60 of intoxication in one animal from group II, 3 animals from group III and 3 animals from group IV, and on day 90 in 3 animals from each group. It was found that constitutive MT levels differed, being higher in sheep liver and kidneys when compared to spleen, while the cell number was less. As a result of chronic intake of lead from diet, the content of MTs in the liver, the number of cells and the body weight index increased. The most pronounced changes were observed in the animals of group IV. In the kidneys there were non-linear changes in the MT level. Decrease in the MT content on day 30 of the intoxication as cell number in kidneys increased was indicative of inhibition of the cell synthetic activity, and an increase in body weight index at days 60 and 90 while the cell number reduced indicated the development of negative processes. In the spleen, the MT synthesis was inhibited, and non-linear changes in the cell number were observed. Comparison of the obtained results allows us to assume the development of negative processes in the liver, kidneys and spleen that is associated, on the one hand, with intensity of lead accumulation, and on the other hand, with the sensitivity of cells in the organs to toxic effects of this metal. It is assumed that low constitutive MT level is one of the factors of high sensitivity to lead in splenocytes.