Hypothalamo-pituitary regulation of thyrotrophin secretion in chronically catheterized Brattleboro rats.
Plasma TSH rhythms were measured in Brattleboro (DI) and control Long-Evans (LE) rats with an intracardiac catheter allowing repeated sampling in conscious unstressed animals. The TSH response to thyrotrophin-releasing hormone (TRH; 500 ng/100 g body weight) was also determined. Finally, hypothalamic and pancreatic TRH concentrations and TRH-degrading activity (TRH-DA) were measured by specific radioimmunoassay. Long-Evans rats had a 24-h rhythm with a major modulatory 8-h component. In DI rats, only the 24-h rhythm was detected. The mean 24-h rhythm-adjusted mean TSH level was higher in DI than in LE rats (1.38 +/- 0.05 and 1.14 +/- 0.06 micrograms/l respectively, P less than 0.01). The peak TSH response to TRH was significantly increased in DI rats while the pituitary concentration of TSH was also higher (0.93 +/- 0.09 vs 0.39 +/- 0.06 micrograms/mg wet weight in LE, P less than 0.001). Hypothalamic TRH and TRH-DA were similar in both strains. The response to propylthiouracil-induced hypothyroidism was identical in both strains. We conclude that DI rats have a normal pituitary sensitivity to tri-iodothyronine but a central dysfunction in the pituitary environment leading to some alterations of TSH secretion.
D000818:Animals; D002940:Circadian Rhythm; D005260:Female; D007031:Hypothalamus / Q000378:metabolism / Q000502:physiology*; D010179:Pancreas / Q000378:metabolism; D010902:Pituitary Gland / Q000378:metabolism / Q000502:physiology*; D051381:Rats; D011910:Rats, Brattleboro / Q000502:physiology*; D011919:Rats, Inbred Strains; D011922:Rats, Mutant Strains / Q000502:physiology*; D013972:Thyrotropin / Q000097:blood / Q000378:metabolism*; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology / Q000502:physiology*
D013973:Thyrotropin-Releasing Hormone; D013972:Thyrotropin