An in vitro procedure for the estimation of thyroid hormone releasing factors in sera of thyrotoxic patients.

LATS containing sera and a number of Graves' disease sera stimulated T4 release from mouse thyroids in vitro as determined by RIA, thus confirming the presence of a thyroid hormone releasing factor in sera of thyrotoxic patients. The pattern of stimulation was similar to that previously shown for TSH in terms of T4 release time sequence. cAMP increase and catecholamine inhibition via alpha-adrenergic receptors. In the same in vitro system, neutralization with a human thyroid homogenate showed presence of LATS-Protector (LPA) in LATS negative thyrotoxic sera. The present study describes a simpler procedure for estimating LATS or similar activity, as compared to the McKenzie assay, and suggests identical receptor sites for TSH and other thyroid stimulators.