Comparison of the ability of thyroxine and triiodothyronine to suppress TRH-induced TSH secretion by perfused rat anterior pituitary fragments.
Adenohypophyseal fragments from 8 rats were perifused in small 0.2-ml chambers with medium alone or with medium containing 0.2 or 2 micrograms/dl T3 or 20 micrograms/dl T4. The TSH secretion in response to 1-min perifusion with 3 X 10(-8) M TRH was measured before and at 20- to 40-min intervals after beginning T4 or T3 perifusions. A similar temporal course of inhibition of TRH-induced TSH secretion was produced by both iodothyronines, suggesting but not proving that T4 may inhibit the TSH secretion by a direct effect not dependent on its prior intra- or extrapituitary conversion to T3.
D000818:Animals; D005260:Female; D066298:In Vitro Techniques; D007700:Kinetics; D010903:Pituitary Gland, Anterior / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013972:Thyrotropin / Q000378:metabolism*; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology*; D014284:Triiodothyronine / Q000494:pharmacology*; D014443:Tyrosine / Q000494:pharmacology*
D014284:Triiodothyronine; D014443:Tyrosine; D013973:Thyrotropin-Releasing Hormone; D013972:Thyrotropin