Brown adipose tissue and thermogenesis in hypophysectomized rats in relation to temperature acclimation.

The aim of this work was to test the role of pituitary dependent hormones in cold-induced non-shivering thermogenesis. In the 28 degrees C-acclimated rat, hypophysectomy inhibited body growth and led to an atrophy of thyroid and adrenals. In brown adipose tissue (BAT) some alterations were induced which are usually observed after cold acclimation of the animal: increase in relative weight, decreases in the relative amount of lipids, increases in the amounts of protein and DNA and modification of the proportions of several phospholipid fatty acids; moreover, basal lipolysis, in vitro, was enhanced to the same extent as that following cold acclimation of the normal rat. The in vivo stimulation by norepinephrine (NE) of O2 consumption (test for nonshivering thermogenesis) and of fatty acid release into blood were suppressed. Progressive cold acclimation of the hypophysectomized rats at 15 degrees C led to a hypertrophy of BAT to the same extent as in the sham-operated animals. The in vivo sensitivity to NE was partially restored. The results suggest that hypophysectomy does not suppress the ability to acclimate to moderate cold by means of BAT dependent non-shivering thermogenesis. However, the low ability to produce heat seems to indicate that pituitary or pituitary-dependent hormones are necessary to optimize the cold stimulation of brown fat thermogenesis.

Effects of cold acclimation on adipose tissue lipolysis and cellularity in the hypophysectomized rat.

The study investigated the effects of hypophysectomy and cold acclimation on cellularity and lipolytic capacity of adipose tissue. Hypophysectomized rats (H) were compared to age matched or weight matched controls. Rats were exposed to either 28 degrees C or 15 degrees C ambient temperature for five weeks. In H, despite the inhibition of body growth, it was observed that the growth of epididymal adipose tissue is not entirely inhibited. In comparison with weight matched controls, increase in tissue weight is found to be due to an adipocyte hypertrophy without changes in cell number. No effect of cold acclimation on adipose tissue weight, cellularity and insulinemia were observed in the H group. The in vitro lipolysis effect of norepinephrine was suppressed in 28 degrees C H; a partial recovery of this effect was observed after cold acclimation. This fact is not dependent on adipocyte size, but possibly on structural or metabolic modifications.