Loss of plasma glucose lowering response to cold stress in opioid mu-receptor knock-out diabetic mice.

Opioid mu-receptor plays an important role in the regulation of glucose homeostasis in diabetic rats lacking insulin. Opioid mu-receptor knockout mice were employed to identify the essential role of this receptor in the present study. Western blotting analysis characterized the deletion of opioid mu-receptor in liver of knockout mice as compared to that of normal (wild-type) mice. We found that the plasma glucose concentration of diabetic mice induced by intraperitoneal injection of streptozotocin was markedly decreased after exposure to cold-stress in a cold room for 1 h. However, this plasma glucose lowering response to cold-stress was disappeared in diabetic mice lacking opioid mu-receptor. The important role of opioid mu-receptor in the plasma glucose lowering response to cold stress can thus be considered. Moreover, bilateral adrenalectomy abolished this plasma glucose lowering response to cold stress in diabetic mice with opioid mu-receptor, as compared to the shamed-operated animals. Therefore, activation of opioid mu-receptor by opioid from adrenal gland appears to be responsible for the plasma glucose lowering response to cold-stress in diabetic mice with insulin deficiency.

Inactivation of yeast alcohol dehydrogenase by nitrilopropionamides.

A series of halonitrilopropionamides have been examined as potential inhibitors of yeast alcohol dehydrogenase. Analogues with a good leaving group on the alpha-carbon, and a geminal electronegative atom, were found to be initial competitive inhibitors against NAD with inhibition constants as low as 0.6 microM. Incubation of the enzyme with these inhibitors leads to a slow, irreversible inactivation, with an inactivation constant for 2,2-dibromo-3-nitropropionamide of about 100 microM. No protection against inactivation was observed with the substrate ethanol, while the presence of saturating levels of NAD slowed the rate, but not the final extent, of enzyme inactivation. The resulting enzyme-inactivator complex is stable to a range of conditions that are known to denature the enzyme, indicating that a covalent modification of yeast alcohol dehydrogenase has led to the inactivation. A bimodal inactivation model is proposed to account for the observed interactions of these halonitrilopropionamides with yeast alcohol dehydrogenase.