ALPHA-ADRENERGIC RECEPTOR ACTIVITY, CYCLIC AMP AND LIPOLYSIS IN ADIPOSE TISSUE OF HYPOTHYROID MAN AND RAT

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Abstract
SUMMARY: Lipolysis and intracellular levels of cyclic AMP of adipose tissue from man and rat in both hypothyroid and euthyroid states were studied in response to stimulation by catecholamines in vitro. Hypothyroid patients were studied before and after treatment, and were also compared with euthyroid obese controls. The experimental group of rats was rendered hypothyroid by the addition of 2·9 mm-propylthiouracil to their drinking water, and their status confirmed by plasma thyroid function tests. Evidence for α-adrenergic receptor activity was found in rat adipose tissue, but was less marked than the pronounced α-adrenergic activity in human adipose tissue. Glycerol release from adipose tissue in response to noradrenaline stimulation was less marked in hypothyroidism in both species, and was related to an increased α-adrenergic activity. No evidence was found for increased α-adrenergic effects on cyclic AMP level in hypothyroid subjects, and little evidence was found in adipose tissue from hypothyroid rats. This discrepancy may be due to the presence of the phosphodiesterase inhibitor, theophylline, in the incubation system. The possible modulatory role of thyroid hormones on receptor and phosphodiesterase activity, and on lipolysis, is discussed.

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