Colloid Droplet Formation in Dog Thyroid in Vitro

Sutherland et al. have proposed that many hormones including thyroid-stimulating hormone (TSH) act by elevating the intracellular levels of cyclic 3'5'-adenosine monophosphate (c-AMP) (1). TSH increases the levels of c-AMP in thyroid homogenates (2) and slices (3). It is important to determine the extent to which the variety of biochemical and morphological changes produced by TSH can be duplicated by increasing the concentration of thyroidal c-AMP. Although c-AMP does not appear to stimulate thyroid tissue in vitro, dibutyryl c-AMP, a c-AMP analogue that appears to enter cells more rapidly than c-AMP and that is more resistant to enzymatic hydrolysis (4), stimulates glucose oxidation in dog slices and phospholipid metabolism in beef thyroid slices, like TSH (5). A striking early morphological effect of TSH on the thyroid is the formation of pseudopods and colloid droplets in thyroid epithelial cells (6, 7). This paper shows that dibutyryl c-AMP, like TSH, causes the formation of pseudopods and intracellular colloid droplets when incubated with dog thyroid slices.