Effects of immobilization with medetomidine and reversal with atipamezole on blood chemistry of semi-domesticated reindeer (Rangifer tarandus tarandus L.) in autumn and late winter

Blood chemistry was studied in 8 adult female reindeer, of which 5 were pregnant. Half of them received only medetomidine (150 micrograms/kg i.m.) and half of them medetomidine and atipamezole (750 micrograms/kg) in March. Three weeks later the drug regimens were reversed. The same procedure was carried out during the next September and October. Seasonal differences in pretreatment values could be seen in serum urea, phosphorous, and cholesterol, with the highest concentrations during the autumn; and creatinine, ASAT, ALAT, and CK values, which were higher in the non-pregnant reindeer in late winter. Their low-protein and low-energy diet during the winter explains most of the differences. Increased enzyme activities in serum indicate decreased membrane stability of certain organs in late winter, possibly due to nutritional deficiencies. Treatment effects could be seen in several parameters. The increase in blood glucose and decrease in serum FFA were most probably due to alpha 2-adrenoceptor activation, which inhibits insulin release and lipolysis. These effects were partly or totally inhibited after treatment with the antagonist atipamezole. The earlier increase in serum CK and ASAT activities in those receiving atipamezole can be explained by increased tissue perfusion due to atipamezole itself and the fact that these animals stood up and began to move much earlier than did those which received medetomidine only. A significant decrease in serum Na+, K+, Cl-, Pi, cholesterol, total Ca, and total protein concentration observed during the first 10 to 40 min of the medetomidine sedation could be explained by possible haemodilution and diuresis. More effective metabolism of medetomidine in autumn could explain the shorter recovery times of reindeer receiving only medetomidine and most of the differences in treatment effects between the seasons: faster increase in protein and cholesterol concentrations after the decrease, and the antagonistic effect of atipamezole on glucose and Pi changes in autumn. Based on these results, medetomidine seems to be a good sedation agent for reindeer both in autumn and in late winter; the effects of medetomidine can be rather effectively antagonized by atipamezole.