Effects of Subunits of TSH and LH on TSH Stimulation of Cyclic AMP Accumulation in Dog Thyroid Slices

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Abstract
The effects of subunits of TSH on basal and TSH-stimulated cyclic AMP concentrations were evaluated in dog thyroid slices. Botfrl TSH-α and TSH-β increased cyclic AMP levels, I but they were much less potent than equivalent amounts of intact TSH. Stimulation by the subunits could reflect contamination with small amounts of intact hormone. A 40-fold excess of either TSH-α or TSH-β did not inhibit the stimulation induced by submaximal doses of TSH. These results suggest that the subunits do not interfere with binding of TSH to its receptor sites and activation of adenylate cyclase activity. Subunits of LH also increased cyclic AMP concentrations in dog thyroid slices to about the same extent as equivalent amounts of the TSH subunits. LH stimulated cyclic AMP levels to a greater extent than could be accounted for by the reported contamination with TSH, sugesting that LH has intrinsic activity on dog thyroid slices. However, since the TSH contamination was determined by in vivo bioasay and the present experiments involved in vitro bioassay, the TSH content of LH may be greater in the latter system. As with the subunits, LH did not inhibit the effects of TSH and usually produced additive effects.(Endocrinology92: 642, 1973)

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