The effect of space flight on the board of the satellite Cosmos 2044 on plasma hormone levels and liver enzyme activities of rats

Abstract

The aim of present experiment was to study the changes of corticosterone, insulin and glucose levels in plasma, of the activity of enzymes involved in aminoacid metabolism in liver and the binding of insulin to specific receptors of cell membrane from liver and also of adipose tissue of rats exposed to space flight for 14 days on biosatellite Cosmos 2044. Adult male Wistar rats (body mass 300-370 g) were divided into five groups: intact control rats (AC), rats exposed to space flight (F), animals in synchronous model experiment (S), rats in antiorthostatic hypokinesia (A) and so called operated control group (C). Half of all groups (5 animals) except the intact control were operated 3 days before the experiment (fibulas on both hind legs were broken). The flight animals were sacrificed 5-6 hours after landing. It was observed that plasma insulin levels are increased in rat exposed to 14-day space flight and in synchron experiments. A significant increase of plasma glucose levels was found in flight rats in spite of high insulin concentrations suggesting that in rats exposed to 14-day space a deterioration of tissue sensitivity to insulin could by present. No significant differences of specific insulin binding to liver plasma membrane fraction in flight and intact control animals were observed. A decrease of insulin binding capacity in liver was found in rats in antiorthostatic hypokinesia (A). However in the membrane of adipocytes an important increase of insulin receptors was noted in rats subjected to space flight. These results suggest, that the liver and adipocyte insulin receptors of flight rats did not respond to the increased plasma insulin levels by "down regulation". The determination of plasma corticosterone levels showed that in flight rats and animals exposed to antiorthostatic hypokinesia the plasma hormone levels are significantly elevated. A significant increase of tyrosine aminotransferase and tryptophan pyrrolase activities in liver of flight rats and those exposed to hypokinesia was observed. Also the elevation of alanine amino-transferase in liver was observed in flight rats, while, the activity of aspartate aminotransferase in liver was similar in control and flight animals. These results showed that the changes in liver enzyme activities in rats after 14-day space flight are in agreement with the results observed in previous experiments after a shorter space flight (7 days).