Effects of in vivo triiodothyronine and long acting thyroid stimulator (LATS) administration on the vitro thyroid cAMP response to thyrotrophin and LATS.

The present study was undertaken to examine the effects of prolonged in vivo treatment with T3 and long acting thyroid stimulator (LATS) on in vitro responsiveness of mouse thyroid cyclic AMP to thyrotrophin (TSH) and LATS-immunoglobulin G (IgG). In control mice, thyroid cAMP concentrations after incubation with normal-IgG (10 mg/ml) for 2 h, TSH (10 mU/ml) for 10 min and LATS-IgG (10 mg/ml) for 2 h were 1.25 +/- 0.11 (mean +/- SE) (n = 5), 15.87 +/- 3.47 (n = 6) and 2.17 +/- 0.25 pmoles/mg wet weight (n = 6), respectively. In mice given T3 (5 micrograms/ml) in drinking water for 5 days, thyroid cAMP concentrations after an incubation with TSH were reduced by 50%, as compared to those of the control mice. They were also decreased in mice injected ip with 5 mg of LATS-IgG (1000%/5 mg in the McKenzie bioassay) daily for 5 days. Combined treatment with T3 and LATS decreased the cAMP response to TSH only to the same extent as did T3 alone, indicating that the inhibitory effects of T3 and LATS were not additive. Similar findings were observed with the thyroid cAMP response to LATS-IgG in vitro; either T3 or LATS treatment in vivo decreased cAMP response to LATS-IgG in vitro, but combined treatment with T3 and LATS did not cause further inhibition as compared with T3 or LATS treatment alone.(ABSTRACT TRUNCATED AT 250 WORDS)