Masashi Kurahashi

Calorigenic effects of noradrenaline and glucagon on white adipocytes in cold- and heat-acclimated rats.

Calorigenic actions of noradrenaline and glucagon on isolated epididymal fat cells from warmacclimated controls, cold-acclimated and heatacclimated rats were measured by the use of a twin-type conduction microcalorimeter. Both noradrenaline and glucagon stimulated heat production in isolated adipocytes maximally in doses of 1 μg/ml and 10μg/ml, respectively. Maximal responsiveness of adipocytes per unit cell to noradrenaline was not influenced by cold acclimation, while it was reduced by heat acclimation. Maximal response in total epididymal fat cells to noradrenaline was increased in cold acclimation and not changed in heat acclimation at increased numbers of adipocytes in both cold-acclimated and heatacclimated animals. Maximal response per unit cell as well as per total epididymal fat cells to glucagon was increased in cold acclimation and reduced in heat acclimation.The present results indicate that the modified responses of target adipocytes to noradrenaline and glucagon are involved in the development of temperature acclimation.

GLUCAGON AND TEMPERATURE ACCLIMATION

Publisher Summary Physiological and pathological significance of glucagon has been evidenced for several years. Glucagon is believed to be responsible for the physiological responses to energy need such as fasting and physical exercise. Glucagon plays a part in the metabolic aspects of temperature acclimation in concert with other humoral factors such as catecholamines, thyroid, and adrenocortical hormones that have been shown to be involved in temperature acclimation. This chapter describes an experiment involving a few cold-acclimated rats, in which plasma glucagon level significantly increased at the early stage of acclimation at 2 weeks, but it returned to the control value with the development of cold acclimation. As for the heat-acclimated rats, the plasma glucagon level was reduced and remained low throughout the acclimation period for 4 weeks. The blood free fatty acid (FFA) level also exhibited the corresponding changes to those observed in plasma glucagon, and there was a positive correlation between plasma glucagon and blood FFA levels.