Influence of vasoactive intestinal polypeptide (VIP) on splanchnic and central hemodynamics in healthy subjects

Intravenous vasoactive intestinal polypeptide lowers pulmonary-to-systemic vascular resistance ratio in a neonatal piglet model of pulmonary arterial hypertension

BACKGROUND

Several studies of vasoactive intestinal polypeptide (VIP) demonstrated its potent vasodilative effects on pulmonary and systemic circulation. However, no hemodynamic studies were performed to depict the effects of VIP in an in vivo model of pulmonary arterial hypertension (PAH), thereby limiting a complete understanding of the overall hemodynamic effects of VIP in PAH.

METHODS AND RESULTS

The pulmonary and systemic hemodynamic effects of intravenous infusion of 100 ng/kg per minute of VIP in control and pulmonary hypertensive piglets at 6 to 8 weeks of age were assessed. Pulmonary arterial hypertension was induced after the instillation of meconium solution in the subjects' trachea and was characterized by the establishment of a persistently elevated pulmonary arterial pressure, diminished cardiac output, and elevated pulmonary-to-systemic vascular resistance (PVR/SVR) ratio.

CONCLUSIONS

Continuous intravenous infusion of VIP markedly decreased PVR/SVR ratio in pulmonary hypertensive subjects; however, it lowered blood pressure without causing any significant changes in PVR/SVR ratio in control subjects. Collectively, these results suggest an overall pulmonary vasodilative effect of VIP in PAH.

Human VIP-alpha: an emerging biologic response modifier to treat primary pulmonary hypertension

Primary pulmonary hypertension (PPH) is a rare life-threatening disorder of unknown etiology manifested by chronic elevation of pulmonary arterial pressure. Given that pulmonary vasoconstriction, endothelial and vascular smooth muscle cell proliferation and in situ thrombosis contribute appreciably to the evolution of PPH, treatment with vasodilators, antiproliferative drugs and anticoagulants, alone or in combination, constitute the pharmacologic standard of care. To this end, long-term administration of oral calcium channel blockers, prostacyclin analogs by various routes and oral endothelin-1 receptor antagonists, alone or in combination, is efficacious in treating patients with PPH. Unfortunately, efficacy is hampered by poor stability, delivery and bioavailability, and by systemic toxicity. Hence, there is an ongoing need to develop and test new drugs to treat patients with PPH. To address this issue, a novel, targeted, long-acting, biocompatible and safe sterically stabilized liposomal and micellar formulation of human vasoactive intestinal peptide (VIP) was developed and tested for human use: the 28-amino acid pleiotropic biologic response modifier, human VIP-alpha. The long-lasting salutary effects of phospholipid-associated VIP on vasomotor tone and arterial pressure were expressed at low concentrations solely in diseased animals and were independent of its route of administration. Thus, the author proposes that human VIP-alpha could be developed as a safe long-acting drug to treat patients with PPH.

The gastroenteroinsular response to glucose ingestion during postexercise recovery

This study examined gastrointestinal hormone and peptide responses when glucose was ingested after prolonged exercise. Six endurance-trained male athletes ran on a treadmill for 2 h at 60% VO2 max. Immediately after the run, the athletes consumed 75 g of glucose in 250 ml of water (ExGLU) or flavored water as a placebo control (ExPL). On a separate visit, the athletes rested for 2 h and then consumed glucose (ConGLU). During the first 60 min of recovery from exercise alone (ExPL), plasma vasoactive intestinal peptide (VIP), gastrin, and glucagon-like peptide-1 (GLP-1) all increased significantly, whereas glucose, insulin, and gastric inhibitory polypeptide (GIP) were unchanged from the immediate postexercise value. When glucose was ingested after exercise (ExGLU), glucose, insulin, VIP, gastrin, GLP-1, and GIP were all increased (P < 0.01). However, when glucose was ingested after resting for 2 h (ConGLU), VIP levels were unaffected, although glucose, insulin, gastrin, GLP-1, and GIP levels increased (P < 0.05). The plasma glucose response was greater (P < 0.03) and the plasma insulin response lower (P < 0.004) during ExGLU compared with ConGLU. There was a significantly higher (P < 0.01) VIP response during the initial period of recovery in ExGLU than there was with both ExPL and ConGLU. Plasma VIP showed a modest negative correlation with circulating glucose (r = -0.35, P < 0.03) and insulin (r = -0.37, P < 0.03) during the ExGLU recovery period. In summary, when glucose is ingested after prolonged exercise, there is mild insulin resistance and a corresponding rapid transitory increase in plasma VIP. These data suggest that VIP may play an important glucoregulatory role when glucose is ingested during the immediate postexercise recovery period.

Mediators, cytokines, and growth factors in liver-lung interactions

Multiple mediators have been implicated in the interactions between the liver and the lungs in various disease states. The best characterized mediator of liver-lung interaction is alpha 1-antitrypsin. Several cytokines and mediators may be involved in the pathogenesis of the hepatopulmonary syndrome and in the cytokine cascades that are activated in systemic inflammatory states such as acute respiratory distress syndrome. Hepatocyte growth factor or scatter factor is a recently described peptide with a broad range of biologic effects that may mediate lung-liver interactions.

Ventilation-perfusion relationships and central haemodynamics in patients with cirrhosis. Effects of a somatostatin analogue

The ventilation-perfusion relationships of the lung (VA/Q) and central haemodynamics were studied in seven patients with cirrhosis before and 30 min after a bolus injection of a somatostatin analogue, octreotide (Sandostatin, 50 micrograms i.v.), to elucidate the role of this substance in the hepatopulmonary syndrome. In the basal state all patients had normal spirometry but reduced diffusing capacity. Three patients had various degrees of hypoxaemia (6.9-8.3 kPa) and three had clubbing of the fingers. In the basal state VA/Q distributions, determined by inert gas elimination technique, showed an intrapulmonary shunt of 7.9 +/- 2.2% of cardiac output (range 1.5 to 17.1) and perfusion of lung regions with "low VA/Q" of 4.4 +/- 2.2% of cardiac output (range 0 to 15.4). After octreotide, the amount of shunting increased (10.9 +/- 4.4% of cardiac output; non-significant), while "low VAQ" was unchanged (3.7 +/- 1.3% of cardiac output). Arterial oxygen tension decreased from 10.2 +/- 1.1 to 9.7 +/- 1.1 kPa (non-significant). The mean pulmonary arterial pressure increased from 14.5 +/- 1.9 to 16.3 +/- 1.8 mmHg (p < 0.01). No alterations were seen in heart rate, stroke volume, cardiac output, central pressures or vascular resistances. The results of the present study do not support the hypothesis that octreotide improves hypoxaemia and ventilation-perfusion relationships in patients with hepatopulmonary syndrome.

Vasoactive intestinal polypeptide increases whole pancreatic blood flow but does not affect islet blood flow in the rat

To evaluate the effects of vasoactive intestinal peptide (VIP) on whole pancreatic blood flow and islet blood flow in the rat, anaesthetized adult rats were injected intravenously for 90 s with VIP (500 ng/kg body weight). Immediately after the injection, the whole pancreatic and islet blood flows were measured with a microsphere technique. VIP markedly increased the former but did not affect the latter. Thus, the fraction of the whole pancreatic blood flow diverted through the islets was decreased. In separate experiments, the effects of VIP on the blood glucose and serum insulin concentrations of anaesthetized animals were investigated. VIP caused an acute increase (after 2 min) in the latter, but did not affect the former. It is concluded that VIP exerts its blood flow stimulatory properties only on the exocrine pancreas, and that it may increase the serum insulin concentrations without an associated change in islet blood perfusion.

CNS effects of peptides: a cross-listing of peptides and their central actions published in the journal Peptides, 1986-1993

The centrally mediated effects of peptides as published in the journal Peptides from 1986 to 1993 are tabulated in two ways. In one table, the peptides are listed alphabetically. In another table, the effects are arranged alphabetically. Most of the effects observed after administration of peptides are grouped, wherever possible, into categories such as cardiovascular and gastrointestinal. The species used in most cases has been rats; where other animals were used, the species is noted. The route of administration of peptides and source of information also are included in the tables, with a complete listing provided at the end. Many peptides have been shown to exert a large number of centrally mediated effects.

Effect of vasoactive intestinal polypeptide (VIP) on pulmonary ventilation-perfusion relationships and central haemodynamics in healthy subjects

Ventilation-perfusion relationships of the lung (VA/Q) and central haemodynamics were studied in nine healthy subjects before and during 30 min of vasoactive intestinal polypeptide (VIP) infusion (20 ng kg.min-1). During the infusion, arterial concentrations of VIP rose from 16.1 +/- 6.1 to 420 +/- 110 pmol l-1 and noradrenaline concentrations doubled (P < 0.01). VA/Q distributions, determined by inert gas elimination technique, were significantly shifted to lower values for VA/Q with slight increases in dispersions, but arterial oxygen tension remained unchanged. Heart rate, stroke volume and cardiac output rose 27, 44 and 80% respectively (P < 0.01). Systematic arterial pressure stabilized at a slightly lower level compared to basal (base line: 93 +/- 5 mmHg, VIP; 88 +/- 6 mmHg, P < 0.05). Right atrial and pulmonary capillary wedge pressures remained unchanged during VIP infusion, while pulmonary vascular resistance and systematic vascular resistance decreased significantly, by 25% (P < 0.03) and 53% (P < 0.01), respectively. It is concluded that VIP causes: (1) alterations in ventilation-perfusion distributions, but generates no shunt and does not cause hypoxaemia during 30 min infusion, (2) reduction of pulmonary and systemic vascular resistances and afterload reduction of the left ventricle, (3) reflex sympathoadrenal stimulation with increasing heart rate and myocardial contractility, and (4) a direct positive inotropic effect on the myocardium.

The effect of vasoactive intestinal polypeptide on the lower esophageal sphincter in achalasia

Vasoactive intestinal polypeptide (VIP) is one of the main neurotransmitters implicated in the relaxation of the lower esophageal sphincter (LES). The effect of exogenous VIP on LES motor activity was determined by esophageal manometry. LES pressure (LESP) and LES relaxation were compared in four healthy volunteers and in six patients with achalasia. The effects of intravenous doses of 1.5, 3, and 5 pmol.kg-1.min-1 of VIP were compared with placebo. Neither placebo nor 3 and 5 pmol.kg-1.min-1 of VIP produced any effect on esophageal motility in healthy volunteers. In achalasia the three doses of VIP caused a dose-dependent decrease in LESP with a significant improvement in LES relaxation. A dose of 5 pmol.kg-1.min-1 produced a maximal decrease of 51% in LESP. A beta-adrenergic agonist, isoproterenol, caused a decrease in LESP both in healthy volunteers and in patients with achalasia without improving LES relaxation. In summary, intravenous VIP improved LES relaxation and caused a decrease in LESP in patients with achalasia without affecting LESP in healthy volunteers, indicating that the LES muscle in achalasia is supersensitive to VIP. The current study suggests that a selective damage in the noncholinergic nonadrenergic innervation of the esophagus is in part responsible for the motor alteration seen in these patients. The findings and the inability of isoproterenol to improve LES relaxation despite decreasing LESP support a role in VIP as a indicator of LES relaxation.