A possible general corollary between α1-receptor density in brown adipose tissue and the degree of activation of the tissue was investigated. For this purpose, the effect of cafeteria feeding on α1-adrenergic receptors in brown adipose tissue of seven-week-old female rats was studied by the use of the α1-antagonist (3H)prazosin. In cafeteria-fed rats, the KD of the α1-receptor for (3H)prazosin was unchanged (about 0.35 nM), but the receptor density was doubled (up to 40 fmol per mg of membrane protein). This was also observed when the results were expressed per unit of a plasma-membrane marker (5′-nucleotidase). It was concluded that an increased α1-receptor density is seen not only in cold-acclimated rats, but also in other conditions where brown fat is activated, and a possible general physiological significance of α1-adrenergic pathways in brown adipose tissue is discussed.

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