[The significance of zinc for contractility of smooth muscles and ultrastructure of their microfilaments in case of hypodynamic stress]. / Cinko itaka lygiuju raumenu kontraktiliskumui ir ju mikrofilamentu ultrastrukturai hipodinaminio streso metu.

The aim of the study was to investigate the significance of zinc (added to food of the rabbits) for contractility of smooth muscles (effected by acetylcholine) and ultrastructure of their microfilaments in case of hypodynamic stress. Hypodynamic stress of 48-day duration was provoked for Chinchilla rabbits (n=20) by placing them in metal hutches. Every day (48 days) 10 rabbits, which had intervention received doses of zinc 0.3 mg/kg body wt (in form of zinc acetate). The rabbits (n=10) of the control group, which had no intervention were kept in vivarium conditions. The relaxation of smooth muscles from thoracic aorta as mediated by acetylcholine at a concentration from 10(-8) mol/l to 10(-4) mol/l was detected by means of a 6MXIC mechanotron in isometric regime. Response was expressed as the percentage of relaxation to prostaglandin F(2alpha) (10(-5) mol/l)-induced precontraction. The ultrastructure of the microfilaments of smooth muscles was evaluated by electron microscopy "Philips-300". In rabbits that received no zinc the relaxation of smooth muscles under the influence of acetylcholine was significantly lower than in rabbits that received zinc and lower in control rabbits. Also in rabbits without zinc supplement the investigation of ultrastructure of microfilaments revealed their damage (such change as irregular formation, drop out in flakes, microfilaments becoming shorter and thicker). In rabbits receiving zinc ultrastructure of microfilaments did not change.

The effect of zinc on endothelium-dependent relaxation of blood-vessels and on the ultrastructure of endothelial cells under immobilization stress.

We investigated the effects of zinc on the function and ultrastructure of endothelial cells in the case of a 48-day immobilization stress provoked in Chinchilla male rabbits (n=18) by placing them in metal hutches. Half of those rabbits (n=9) received an daily oral supplement of zinc at a dose of 0.3 mg/kg body weight (in the form of zinc acetate). The control rabbits had no intervention and received no supplement of zinc. The relaxation of smooth muscles from thoracic aorta as mediated by acetylcholine at concentrations from 10(-8) mol/L to 10(-4) mol/L was determined in isometric regime. Responses were expressed as the percentage of relaxation to prostaglandin F2alpha (2.10(-5) mol/L)-induced precontraction. The ultrastructure of endothelial cells was evaluated by electron microscopy. The level of total cholesterol and zinc in the blood serum was determined by an enzymatic method and by atomic absorption spectrometry, respectively. In rabbits receiving no zinc supplement, the relaxation of smooth muscles under the influence of acetylcholine concentrations from 10(-8) mol/L to 10(-4) mol/L was significantly (P < 0.05-0.01) lower than in rabbits receiving a supplement of zinc and lower than in control rabbits. Also, in the rabbits not receiving the zinc supplement, the level of total blood serum cholesterol was increased, but the concentration of zinc decreased. In rabbits receiving the zinc supplement, the contractility of the smooth muscles effected by acetylcholine did not change as compared with control rabbits, and we found a normal structure of endothelial cells and a normal level of total cholesterol and zinc in their blood serum. Thus, zinc played an important role in the maintenance of the normal ultrastructure and function of the endothelial cells in the rabbits receiving zinc under immobilization stress.