Effects of hypo- and hyperthyroidism on pancreatic TRH-degrading activity and TRH concentrations in developing rat pancreas.
High concentrations of thyrotrophin-releasing hormone (TRH) in the rat pancreas were detected during the first few days of life decreasing thereafter while pancreatic TRH-degrading activity (TRH-DA) absent at birth appeared on day 14 and increased to reach adult values by day 21. This period of life is also remarkable by the low level of circulating thyroid hormones. Since TRH-degrading activity may be thyroid hormone dependent it was of interest to study the effects of thyroid status fluctuations both on TRH-DA and TRH content during the neonatal period. In this study, hypo- and hyperthyroidism were induced by 6-n-propyl-2-thiouracil (PTU) and triiodothyronine (T3) respectively. Pancreatic TRH-DA and TRH concentrations were measured at different ages from birth until day 29, in treated animals and results compared to control age-matched rats. In hypothyroid rats, pancreatic TRH concentrations remained significantly higher after day 16 while TRH-DA was lower during the whole period studied. Following T3 treatment, pancreatic TRH concentrations decreased significantly from day 3 onwards. However, no significant changes were found for TRH-DA except a two-fold increase on day 28. These results suggest that two different mechanisms may account for thyroid hormones action: 1) a direct effect on pancreatic TRH 2) an inductive saturable effect on TRH-DA. Furthermore a fine tuner modulatory role of TRH-DA on TRH concentrations cannot be excluded.
D000367:Age Factors; D000818:Animals; D005260:Female; D006980:Hyperthyroidism / Q000378:metabolism*; D007037:Hypothyroidism / Q000378:metabolism*; D010179:Pancreas / Q000254:growth & development / Q000378:metabolism*; D011247:Pregnancy; D011441:Propylthiouracil / Q000494:pharmacology; D011863:Radioimmunoassay; D051381:Rats; D011919:Rats, Inbred Strains; D013973:Thyrotropin-Releasing Hormone / Q000378:metabolism*; D014284:Triiodothyronine / Q000494:pharmacology
D014284:Triiodothyronine; D013973:Thyrotropin-Releasing Hormone; D011441:Propylthiouracil