Plasma radioimmunoassayable neurotensin responses to the administration of various nutrients.

Abstract

In order to elucidate the releasing mechanism of gut neurotensin, plasma radioimmunoassayable neurotensin (RNT) was measured in dogs after intrajejunal administration of various nutrients. Transient and slight increases of plasma RNT were found after administration of glucose and saturated fatty acid. In contrast, remarkably raised plasma RNT levels were seen after administration of an amino acid mixture and of unsaturated fatty acid. The findings suggested that gut neurotensin may play roles in digestion and adsorption of amino acid and some fatty acids. --neurotensin; plasma; radioimmunoassay; nutrientsIn spite of the findings on the distribution in the gut and the pharmacological effects of neurotensin, its releasing mechanism still remains obscure.In view of the morphological feature that neurotensin immunoreactive cells in the gut reached the gut lumen with their cytoplasmic processes (Ito et al. 1979), it seems probable that neutrotensin containing cells may receive stimuli directly from the gut lumen and may secrete neurotensin into blood.To elucidate the releasing mechanism of neurotensin in the gut, plasma levels of radioimmunoassayable neurotensin (RNT) were measured in the dogs after intrajejunal administration of various nutrients. MATERIALS AND METHODSMongrel dogs, weighing 12-16 kg, were employed in the present study. Operations for intrajugular catheterization and catheter jejunostomy were performed under anesthesia 3 days before examinations. After overnight fast, 50 ml each of 33% glucose, oleic acid, caprionic acid and an amino acid mixture (12% crystalline z-amino acid solution containing essential and nonessential amino acids) were administered to the dogs intrajejunally. Blood samples were taken into chilled tubes containing 1.2 mg of EDTA Nat and 500 units of trasylol/ml of blood before and at 5, 10, 20 and 30 min after administration of nutrients. Plasma was separated by centrifugation at 4°C and stored at -25°C until assay. Radioimmunoassay for neurotensin was carried out using anti-NT3 antiserum which had a negligible cross-reactivity to other gut hormones (Ito et al. 1980). The least detectable level of RNT in the assay was 300 pg/ml. Within assay coefficients were less than 6%. RESULTS AND DISCUSSIONAs shown in Table 1, slight and transient enhancement of RNT release was found after intrajejunal administration of glucose and oleic acid which is a saturated fatty acid. In contrast, remarkably raised RNT levels were seen after intrajejunal administration of the amino acid mixture and caprionic acid which is an unsaturated fatty acid. Thus, it seems