Fast cold-induced activation of the external pathway of NADH oxidation in liver mitochondria of hyperthyroid rats.

The exposure of a cold-adapted rat for 15 min at 4 degrees C results in the appearance of measurable oxidation of added NADH via the external amytal- and antimycin-A-resistant pathway in liver mitochondria. This effect increases if the animal has been treated with thyroid gland preparation for 4-5 days. In vitro, the addition of Mg2+ or increase in the tonicity of incubation mixture suppresses external NADH oxidation. Addition of 70 mg X ml-1 serum albumin or 70 mg X ml-1 polyvinylpyrrolidone in the presence of Mg2+ and addition of 20 microM palmitic or 20 microM oleic acids induces to some extent external NADH oxidation in the mitochondria of control (nontreated) and of cold-adapted, thyroidgland-preparation-treated rats. It is concluded that hyperthyroid rats can be used as a model of cold-induced initiation of the external pathway of NADH oxidation. A relation between the increase of exogenous NADH oxidation and phospholipase A2 activity in liver mitochondria is discussed.