Effect of hypothermia on insulin-receptor interaction in different rat tissues

Experimental hypothermia caused extensive changes in the number of both classes of insulin receptors in different rat tissues. In the liver, the number of high affinity insulin receptors (HAIRs) decreased by 50% (from 25.3 to 12.6 fmol/mg membrane protein), whereas number of low affinity insulin receptors (LAIRs) was almost unchanged in comparison to normothermic animals (5.63 and 4.39 pmol/mg, respectively). In the adipose tissue, number of both classes was reduced--HAIRs by 81% (from 24.0 to 4.50 fmol/mg) and LAIRs by 92% (from 16.0 to 1.29 pmol/mg). In the skeletal muscle, capacity of HAIRs was not changed (16.2 and 19.3 fmol/mg in normo- and hypothermic animals, respectively), whereas number of LAIRs increased by 150% (from 6.65 to 16.6 pmol/mg). Hypothermic rats also showed lower amount (by 85%) of LAIRs in the heart muscle (9.37 and 1.43 pmol/mg in control and experimental animals, respectively). Simultaneously, no significant changes were found in HAIRs (16.3 and 11.9 fmol/mg, respectively) and LAIRs (4.43 and 3.88 pmol/mg, respectively) in the brain. These differences in insulin receptors responses to hypothermia may reflect different physiological role of insulin in the regulation of target cell metabolism and/or the differences in tissue distribution of the insulin receptor isoforms.