PLASMA NEUROTENSIN LEVELS IN HUMANS - RELATION TO HORMONE LEVELS IN DISEASES INVOLVING THE HYPOTHALAMO-PITUITARY-THYROID AXIS

This study was aimed to investigate, in humans, the possible relations hip between plasma neurotensin (NT) levels and the activity of the hyp othalamo-pituitary-thyroid axis. Neurotensin was measured by radioimmu noassay in 14 healthy adult volunteers and in 41 patients among whom 1 0 were considered as controls and 31 had thyroid dysfunction according to free thyroxine and thyrotropin plasma values. Basal NT levels were not significantly different in healthy adults and in control patients : 9.7+/-1.1 fmol/ml (mean+/-SEM) vs 13.3+/-2.9 fmol/ml, respectively. In patients with central hypothyroidism the NT level was significantly lower (5.7+/-1.2 vs healthy volunteers and controls; p < 0.05) and in patients with peripheral hypothyroidism and hyperthyroidism the NT le vel was significantly higher (35.9+/-12.8 and 29.9+/-9.5 fmol/ml, resp ectively, vs healthy adults (p < 0.01) and vs controls (p < 0.05)). Af ter thyrotropin-releasing hormone (TRH) injection (250 mu g iv) in nin e subjects (two control patients, five patients with hypothyroidism an d two patients with hyperthyroidism), NT levels decreased independentl y of the endocrine status from mean values of 13.4+/-8.4 at basal leve l to 7.3+/-0.8 fmol/ml 30 min after injection (p < 0.01 on paired perc entage decrease values). These data suggest that plasma NT levels in h umans depend upon the pituitary-thyroid status and indicate that TRH c ould exert a negative regulation on circulating NT levels.