INVITRO EFFECT OF INSULIN ON THE UPTAKE OF GLUCOSE AND ALPHA-AMINOISOBUTYRIC-ACID IN THE THYROID-GLAND OF THE TURTLE (CHRYSEMYS-DORBIGNI)

The presence of specific insulin binding sites in the thyroid gland of the turtle Chrysemys dorbigni has been previously reported. The purpose of the present work was to investigate the probable action of insulin on the uptake of [14C]deoxy-d-glucose ([14C]DG) and [14C]α-aminoisobutyric acid ([14C]AIB) in turtle (C. dorbigni) thyroid glands in vitro. Thyroid fragments (±40 mg) were incubated at 25° in Krebs-Ringer-bicarbonate buffer containing 0.2 μCi of [14C]DG or [14C]AIB without or with bovine insulin at different periods of time. The uptake of [14C]DG and [14C]AIB increased with incubation time. The presence of insulin (7 × 10-6 M) in the incubation medium during 240 min did not modify the [14C]DG uptake. However if the thyroid fragments were previously incubated with insulin (60 min) and then incubated (240 min) with the same concentration of the hormone, the [14C]DG uptake was markedly increased. This stimulatory effect of insulin was dose-dependent. In similar experimental conditions, insulin also produced a significant increase in the uptake of [14C]AIB. Therefore, these findings strongly support the hypothesis that insulin might exert a direct action on the thyroid function. © 1991.