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 relationship between plasma neurotensin (NT) levels and the activity of the hypothalamo-pituitary-thyroid axis. Neurotensin was measured by radioimmunoassay in 14 healthy adult volunteers and in 41 patients among whom 10 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 level was significantly higher (35.9 +/- 12.8 and 29.9 +/- 9.5 fmol/ml, respectively, vs healthy adults (p < 0.01) and vs controls (p < 0.05)). After thyrotropin-releasing hormone (TRH) injection (250 micrograms iv) in nine subjects (two control patients, five patients with hypothyroidism and two patients with hyperthyroidism), NT levels decreased independently of the endocrine status from mean values of 13.4 +/- 8.4 at basal level to 7.3 +/- 0.8 fmol/ml 30 min after injection (p < 0.01 on paired percentage decrease values). These data suggest that plasma NT levels in humans depend upon the pituitary-thyroid status and indicate that TRH could exert a negative regulation on circulating NT levels.