Pituitary-thyroid axis sensitivity and neonatal changes in plasma iodothyronine, thyreostimulin and cortisol levels in the preterm lamb: comparison of two experimental models.
The influence of a 7 days prematurity, induced by oestrogen or dexamethasone injection to the mothers, on neonatal changes in plasma T4, T3, reverse T3 (rT3), TSH and cortisol levels was studied in 6 full term, 6 oestrogen preterm and 6 dexamethasone preterm lambs. In addition, the pituitary-thyroid axis sensitivity was assessed by the magnitude of the response to TRH administration. At birth, plasma cortisol and T3 levels, as the value of the T3/T4 ratio, were significantly lower in the two groups of preterm lambs than in full term animals; however, whereas plasma T3 concentrations and values of the T3/T4 ratio remained low in oestrogen lambs, they were quickly restored and elevated T3 levels associated to high T4 levels could be even observed in dexamethasone lambs; in this last group, these abrupt changes could be a consequence of raised TSH plasma concentrations recorded at birth. Moreover, if plasma rT3 levels and values of the rT3/T4 ratio were similar during the first hours of life in dexamethasone and full-term lambs, they were significantly higher in oestrogen animals. The responsiveness of the pituitary-thyroid axis to TRH was normal in dexamethasone animals, but was significantly enhanced in oestrogen ones, probably as a consequence of low T3 levels.
Cabello
G
G
Unité de Différenciation Cellulaire et Croissance, INRA-ENSA, Montpellier, France.
Wrutniak
C
C
D000818:Animals; D000831:Animals, Newborn / Q000502:physiology*; D003907:Dexamethasone / Q000494:pharmacology; D005865:Gestational Age; D006854:Hydrocortisone / Q000097:blood*; D008954:Models, Biological; D010902:Pituitary Gland / Q000378:metabolism*; D012756:Sheep; D013961:Thyroid Gland / Q000378:metabolism*; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology; D013974:Thyroxine / Q000097:blood; D014284:Triiodothyronine / Q000097:blood; D014285:Triiodothyronine, Reverse / Q000097:blood
D014284:Triiodothyronine; D014285:Triiodothyronine, Reverse; D013973:Thyrotropin-Releasing Hormone; D003907:Dexamethasone; D013974:Thyroxine; D006854:Hydrocortisone