Effects of small doses of L-thyroxine and triiodo-L-thyronine on pituitary LH content of thyroidectomized rats.
Pituitary LH was studied by means of a specific radioimmunoassay (RIA) in male rats at different time intervals after thyroidectomy (T), and in rats which were T at least 30 days before and were then treated with different doses of L-thyroxine or triiodo-L-thyronine. A decrease in the pituitary LH of the T animals, with respect to the intact age-paired controls, was demonstrable from 13 days after the operation, when total pituitary LH content was taken into consideration, or from 5 days after T, when the LH concentration (mug/mg pituitary) was considered. Doses of thyroid hormones lower than the daily maintenance dose for the rat produced very little effect on the pituitary LH levels of T animals. However, a single dose of 1.75 mug of T4 or 0.2 mug of T3 (doses approximately equivalent to the T4 and T3 maintenance dose for T rats) induced such a rapid and intense increase in the pituitary LH content that it no longer differed from that of the intact age-paired controls by 12 hours. Surprisingly, 5.0 mug of T4 and 1.0 mug of T3 did not produce any increase in the pituitary LH content of T rats.
D000818:Animals; D003864:Depression, Chemical; D004305:Dose-Response Relationship, Drug; D007274:Injections, Intraperitoneal; D007986:Luteinizing Hormone / Q000378:metabolism*; D008297:Male; D009929:Organ Size / Q000187:drug effects; D010902:Pituitary Gland / Q000378:metabolism*; D010903:Pituitary Gland, Anterior / Q000187:drug effects / Q000378:metabolism*; D011863:Radioimmunoassay; D051381:Rats; D012636:Secretory Rate / Q000187:drug effects; D013960:Thyroid Function Tests; D013965:Thyroidectomy; D013974:Thyroxine / Q000008:administration & dosage / Q000494:pharmacology*; D013997:Time Factors; D014284:Triiodothyronine / Q000008:administration & dosage / Q000494:pharmacology*
D014284:Triiodothyronine; D007986:Luteinizing Hormone; D013974:Thyroxine