[Thyroid protein synthesis and insulin: influence of the hormone concentration (author's transl)]

Canine thyroid slices were preincubated at 37 degrees C in the glucose-free TC 199 medium following in vitro addition of monocomponent insulin at increasing concentrations: from 10(-5) to 1 IU/ml. After 30 minutes, the incubation was continued in the presence of 3H-leucine (20 microCi/ml) for 1 h. The incorporation of radioleucine in the homogenates was determined as dpm/mg of protein. Insulin added in vitro significantly enhanced the mean 3H-leucine incorporation in the thyroid proteins at all concentrations tested. A maximal effect was obtained within the range 10(-3)-1 IU per ml. The response at lower concentrations, close to the physiologic conditions in man, was still pronounced. These data suggest that insulin strongly stimulates the thyroid synthesis up to a concentration of 10(-5) IU = 0.4 ng/ml, which has been found to be effective in the hormone-receptor binding studies.