Indirect vascular actions of (Gln4)-neurotensin in canine adipose tissue

Research note: cardiovascular effects of neurotensin in anesthetized White Leghorn hens

Solutions of neurotensin (NT) at 0, 12, 60, 120, and 600 nM were infused i.v. into anesthetized, 16- to 34-wk-old hens at 60 microL/kg per minute for 30 min. These infusates increased plasma NT concentrations to steady state values of about .1, .2, 1, 2, and 10 times the postprandial concentrations of NT in hepatic portal blood, respectively. None of these concentrations significantly affected heart rate or arterial (carotid) or central venous (jugular) blood pressure.

Antidiuretic effects of neurotensin in chloralose anaesthetized dogs

1. Effects of cerebroventricular and/or intravenous infusions of neurotensin (NT), an endogenous tridecapeptide, on haemodynamics and renal function were investigated in chloralose anaesthetized dogs. 2. Cerebroventricular infusions (i.c.v.) of NT (10-6 mol/L and 10-5 mol/L, 0.1 mL/min) for 30 min did not produce any significant alterations in the measured variables. In the vagotomized dogs, intravenous (i.v.) infusion of NT (10(-5) mol/L) at a rate of 0.1 mL/min for 30 min significantly lowered the arterial blood pressure and glomerular filtration rate; these effects were accompanied by pronounced reductions in the urine flow and urinary sodium excretion and marked increases in urine osmolality. 3. In the dogs with vagi intact, i.v. infusions of NT failed to produce any alterations in the blood pressure; however, renal effects of NT were essentially identical to those observed in the vagotomized dogs. 4. Infusions of NT (10(-6) mol/L) and/or NT-metabolites NT1-8 and NT8-13 (10(-5) mol/L) directly into the renal artery failed to produce any significant alterations in the urine flow. Antidiuretic effects of i.v. NT were not prevented by acute renal denervation, adrenalectomy, or pretreatment of the animals with naloxone. However, morphine pretreatment completely abolished the hypotensive and anti-diuretic effects of NT. 5. It is proposed that i.v. infusion of NT rapidly facilitates the secretion of an endogenous substance possessing potent antidiuretic properties and opiate mechanisms are involved in mediating such an effect. Although it appears unlikely, a role for vasopressin cannot be ruled out.

Localization of neurotensin binding sites in rat kidney

[3H]Neurotensin ([3H]NT) appears to bind specifically to a single class of sites in slide-mounted rat kidney sections (KD = 8.3 nM; Bmax = 31.6 fmol/mg tissue). Bound [3H]NT can be displaced by nonradioactive NT and a series of its fragments and analogues with relative potencies that correlate well (r = 0.91; p less than 0.005) to their potencies in the rat stomach strip bioassay. These results suggest that NT receptors are similar in both systems. However, they are probably slightly different from those present in the guinea pig atria (r = 0.78; p less than 0.1). We visualized these sites by using the tritium-sensitive LKB film technique analysed by computerized densitometry. [3H]NT binding sites are highly concentrated in the renal cortex while low levels are observed in the renal medulla. The possible physiological and/or pathophysiological significances of the presence of [3H]NT binding sites in the kidney are discussed.

Blood flow in human adipose tissue after infusion of (Gln4)-neurotensin

(Gln4)-neurotensin, 18 pmolXkg-1Xmin-1, was infused i.v. during 20 min in 10 healthy male volunteers. Adipose tissue blood flow was continuously monitored by measuring the disappearance rate of 99mTc-pertechnetate injected s.c. on the abdomen and thigh. Heart rate and blood pressure were measured and calf blood flow studied by venous occlusion plethysmography. Neurotensin-like immunoreactivity (NTLI) in serum was determined. Infusion of isotonic saline served as control. During intravenous infusion of (Gln4)-neurotensin the first order rate constants of 99mTc-pertechnetate from the abdomen decreased by 21.9 +/- 5.9% from a basal value of 8.3 +/- 0.5% min-1 (p less than 0.01). The reduction in blood flow started after a latent period of 5-10 min and persisted throughout the thirty minute observation period following infusion. A significant correlation (r=0.87, p less than 0.001) was found between the percentage decrease in blood flow from abdominal fat and the body fat content of the subjects as determined from the sum of four skinfolds. Blood flow from thigh fat did not change significantly, nor did heart rate, blood pressure or calf blood flow. During infusion of (Gln4)-neurotensin plasma neurotensin-like immunoreactivity (NTLI) increased successively. Ten minutes after starting the infusion the mean plasma NTLI level had increased from 20 +/- 5 pM to 302 +/- 31 pM; at 20 min it was 473 +/- 51 pM. These concentrations are within the range found after eating a fatty meal. The results indicate that neurotensin plays a physiological role in the regulation of human adipose tissue blood flow and may be of importance for the postprandial uptake of substrates in adipose tissue in certain regions. We suggest that neurotensin deserves consideration as an endocrine hormone affecting the regional deposition of fat postprandially.

Fat inhibition of gastric acid secretion in man and plasma concentrations of neurotensin-like immunoreactivity

The effects of intraduodenal administration of oleic acid (5, 10, 20, and 40 ml) on gastric acid secretion stimulated by a submaximal intravenous pentagastrin infusion and on plasma concentrations on neurotensin-like plasma immunoreactivity (NTLI) were studied in 18 healthy subjects. Each volume of oleic acid or saline (controls) was tested in six subjects except the volume of 20 ml, which was given to ten subjects. Gastric acid secretion was studied for a 2-h period at 15-min intervals after intraduodenal infusion. Five milliliters oleic acid evoked a significant inhibition (29%) of gastric acid secretion. Maximal inhibition by oleic acid appeared after 20 ml (43%), which was significantly greater than after 10 ml. In seven duodenal ulcer (DU) patients 20 ml oleic acid evoked an inhibition of 20%, which was significantly lower than in the healthy subjects. Proximal gastric vagotomy (PGV) abolished the fat inhibition in DU patients. Basal and peak NTLI concentrations after 20 ml oleic acid were significantly lower in DU patients than in health subjects. In DU patients there was no significant difference in the integrated response of NTLI before and after PGV. The 2-h integrated NTLI response was dependent on the administered volume of oleic acid in healthy subjects. There was a correlation between acid inhibition and the integrated response ot NTLI in healthy subjects. This suggests that immunoreactive neurotensin may be involved in the oleic-acid-induced inhibition of gastric acid secretion. Neurotensin, or a neurotensin metabolite, apparently exerts its inhibitory effect at a synaptic level, which explains the finding that oleic acid did not inhibit gastric acid secretion after PGV. Neurotensin may have a physiological role as a hormone with enterogastrone functions.

Plasma concentration of neurotensin-like immunoreactivity (NTLI) and lower esophageal sphincter (LES) pressure in man following infusion of (Gln4)-neurotensin

(Gln4)-neurotensin was infused i.v. for 5 to 70 min at 3 different infusion rates (6, 12 and 18 pmol X kg-1 X min-1, respectively) in 19 male volunteers, aged 26-47. The plasma concentration of neurotensin-like immunoreactivity (NTLI), the lower esophageal sphincter (LES) pressure, blood pressure, heart rate. ECG and blood glucose concentration were measured. The volunteers did not report any subjective effects during the infusion. Following infusion periods of 30 min or more the volunteers often reported bowel movements starting 5 min or more after cessation of the infusion. Neither blood pressure nor heart rate changed significantly. No changes were noted in the continuous ECG or in the blood glucose concentration. Apparent steady state levels of about 300 pM NTLI were reached at about 40 min during infusion of 12 pmol X kg-1 X min-1 (Gln4)-neurotensin. In all volunteers the LES pressure was significantly reduced within 5 min of starting the infusion. In 6 volunteers 12 pmol X kg-1 X min-1 (Gln4)-neurotensin was infused i.v. for 5 min. The LES pressure decreased significantly (P less than 0.01) from 13.7 +/- 1.3 mmHg to 5.3 +/- 0.8 mmHg. The decrease in the LES pressure occurred at plasma NTLI concentrations of approximately 50 pM, i.e. at levels below those obtained in man after a meal or the ingestion of fat. The present data further support the hypothesis that in man plasma neurotensin, or a neurotensin metabolite is an endocrine hormone involved in the postprandial regulation of the motor functions of the gastrointestinal tract.

The effect of ingestion of amino acids, glucose and fat on circulating neurotensin-like immunoreactivity (NTLI) in man

The effect of ingestion of amino acids (Vamin N), glucose, and fat (Intralipid) on the concentration of neurotensin-like immunoreactivity (NTLI) in plasma was determined in 6 healthy male volunteers. After ingestion of Intralipid (55 ml, 200 mgxml-1) there was a significant increase in the plasma concentration of NTLI. The calculated integrated total NTLI response (6.7 +/- 2.5 nM over 180 min) was statistically significant. Although isocaloric amounts of Vamin and glucose also increased the plasma concentration of NTLI, these increases were not statistically significant. The data indicate that fat is an important stimulus for the release of NTLI from the small intestine. It is suggested that neurotensin, or a metabolite, in blood may be a hormone involved in the postprandial inhibition of gastric motility and gastric acid secretion elicited from the small intestine.