Cyclic Adenosine 3′,5′-Monophosphate Concentration in Plasma, Adipose Tissue and Skeletal Muscle in Normal Subjects and in Patients with Hyper- and Hypothyroidism

Abstract

Plasma and tissue concentrations of cyclic AMP were studied in 11 hyperthyroid patients (mean PBI 14.6 μg/100 ml) and 10 patients with primary hypothyroidism (mean PBI 1.6 μg/100ml). These results were compared with the values obtained in 13 euthyroid control subjects (mean PBI 5.6 μg/100 ml). Mean ± SEM plasma concentrations for the groups were: hyperthyroidism 23.6 ± 2.2 nm, primary hypothyroidism 5.1 ± 0.7 nm. Both these levels differed significantly (p < 0.001) from that of euthyroid control subjects (10.7 ± 0.6 nm). Treatment with propranolol 160 mg/day orally in 5 hyperthyroid patients resulted in reduction of plasma cyclic AMP levels to that of euthyroid subjects. Plasma concentrations of cyclic AMP were found to be about 1% of the tissue levels. Cyclic AMP levels in skeletal muscle averaged 1.5 ± 0.3 nmole/g wet weight in hyperthyroid patients and in adipose tissue 1.5 ± 0.3 nmole/g. Both these levels were significantly higher than in euthyroid subjects (p < 0.02). In hypothyroid patients cyclic AMP in skeletal muscle averaged 0.5 ±0.1 nmole/g and in adipose tissue 0.4 ±0.1 nmole/g, not statistically different from normal subjects. Infusion of propranolol (0.1 mg/min) in 2 hyperthyroid patients lowered plasma cyclic AMP to normal levels while the cyclic AMP plasma level in 2 euthyroid subjects remained unchanged. It is suggested that in hyperthyroidism β-adrenergic receptor responses are enhanced as compared to the normal state.