Effects of tri-iodothyronine, thyroxine and isopropyl-di-iodothyronine on thyroid-stimulating hormone in serum and pituitary gland and on pituitary concentrations of prolactin, growth hormone, luteinizing hormone and follicle-stimulating hormone in hypothyroid rats.
Replacement of the 3'-halogen of the tri-iodothyronine (T3) molecule by a propyl-group produces a thyromimetic analogue, 3'-isopropyl-3,5-di-iodo-L-thyronine (T2iPr), with high biological potency. A serum thyroid-stimulating hormone (TSH) suppression test with one single intraperitoneal injection of 3 or 30 nM-T3 or T2iPr or with 30 or 300 nM-thyroxine (T4) per kg body weight was performed on 56 adult male Lewis rats which were maintained for 3 weeks on an iodine-deficient diet containing 0.2% 6n-propyl-2-thiouracil (PTU). Blood was withdrawn from each rat by cardiac puncture 24 h before and 3, 7, 24 and 48 h after application of the iodothyronines. Raised serum levels of TSH, due to the treatment with PTU, were significantly reduced within 3 h of treatment with 30 nM-T3, 300 nM-T4, 3 or 30 nM-T2iPr and they remained low throughout the observation period. Treatment with 3 nM-T3, or 30 nM-T4 per kg body weight was less effective. Pituitary concentrations of growth hormone, TSH, prolactin and FSH were significantly reduced by the treatment with PTU. There was also a slight, but insignificant reduction of pituitary concentrations of LH. Treatment with T3, T4 or T2iPr stimulated the reaccumulation of growth hormone, TSH, prolactin, LH and FSH in the pituitary gland.
D000818:Animals; D004104:Diiodothyronines / Q000494:pharmacology*; D005640:Follicle Stimulating Hormone / Q000378:metabolism; D013006:Growth Hormone / Q000378:metabolism; D006728:Hormones / Q000494:pharmacology*; D007037:Hypothyroidism / Q000378:metabolism*; D007986:Luteinizing Hormone / Q000378:metabolism; D008297:Male; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism*; D011388:Prolactin / Q000378:metabolism; D051381:Rats; D013970:Thyronines / Q000494:pharmacology*; D013972:Thyrotropin / Q000097:blood / Q000378:metabolism*; D013974:Thyroxine / Q000494:pharmacology*; D014284:Triiodothyronine / Q000494:pharmacology*
D004104:Diiodothyronines; D006728:Hormones; D013970:Thyronines; D014284:Triiodothyronine; C027594:isopropyl-diiodothyronine; D011388:Prolactin; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone; D013972:Thyrotropin; D013006:Growth Hormone; D013974:Thyroxine