INFLUENCE OF POLYENES ON CYCLIC 3',5'-AMP FORMATION AND GLUCOSE UTILIZATION IN THYROID

The membrane modifying polyenes, filipin and nystatin, have been studied with respect to their ability to alter thyroid cell metabolism. Filipin, believed to modify membranes through interaction with phospholipids and/or cholesterol, appears to induce either no effect or mild inhibition of baseline [14C]glucose oxidation in dog thyroid slices. Nystatin, which has been shown to react with membrane cholesterol, stimulates labeled glucose oxidation to 14CO2. [6-14C]Glucose oxidation to 14CO2 is stimulated more extensively than [i-14C]glucose oxidation (3-fold). Thyroid-stimulating hormone (TSH) stimulation, in contrast, is greater with [i-14C]-glucose than [6-14C]glucose. These observation would suggest that the nystatin stimulation is effected by a different mechanism than that induced by TSH. This probability is supported by the further observation that both nystatin and filipin are antagonistic to TSH-increased glucose oxidation. The nystatin stimulation may be due to increased movement of glucose through the cell membrane. A new radiometric assay has been developed for cyclic 3′,5′-AMP which permits measurement of samples as amall as 5.10-13 mole. With this assay it was observed that nystatin and filipin reduced thyroid-slice 3′,5′-AMP levels. In order to determine if this reduction was due to a direct action on thyroid adenyl cyclase, a TSH-responsive 9000 × g particulate preparation was isolated and evaluated with respect to polyene effects. Both nystatin and filipin inhibit thyroid particulate adenyl cyclase activities. It is suggested that this subcellular inhibition may be correlated in part with polyene inhibitions of TSH-stimulated glucose oxidation and 3′,5′-AMP formation observed at the intact cell level. © 1969.