Insulin and the lung

The lung in relation to vasoactive polypeptides

Among the metabolic functions of the lungs are the formation, release, activation and inactivation of biologically active peptides. The following peptides may be present or formed in normal lung: vasoactive intestinal peptide or a peptide closely related to it, a spasmogenic peptide not yet fully identified, bradykinin, substance P, a bombesin-like peptide (especially in fetal and neonatal lung), and eosinophil-chemotactic peptides. These peptides are found in special neuroendocrine cells, in neurons, or in mast cells. Normal lung also inactivates bradykinin and activates angiotensin; both processes are catalysed by the same enzyme (kininase II or angiotensin-converting enzyme), located in pulmonary vascular endothelium. Pulmonary tumours and certain non-tumorous lesions can produce and release a variety of peptide hormones that are not normally generated by the lung in substantial amounts. This 'ectopic' secretion of hormones may be detectable only by sensitive assays or may result in specific clinical syndromes.

The lung, whole-body metabolism and disease

It is well recognized that the lung has its own hormonally responsive endogenous metabolism. Less well recognized is the potential of the lung to influence and, in turn, be influenced by the homeostatic mechanisms of the body. It is suggested that the lung could modulate concentrations of circulating hormones and thereby play an indirect exogenous metabolic role in whole-body metabolism. Investigations of patients undergoing cardiopulmonary bypass as well as studies with the perfused rat lung suggest that the lung could make an important direct contribution to whole-body lactate and perhaps alanine production. The control of the endogenous and exogenous metabolism of the lung may be exerted through circulating hormones, substrates, blood gases and lung movement. Disorders of the lung or the whole body may disturb these relationships. In patients with chronic lung disease circulating blood metabolites are affected and conversely in diabetes there are effects on lung metabolism. The unified concept of lung/whole-body metabolism is discussed in relation to therapeutic approaches for the prevention and investigation of neonatal and adult respiratory distress syndromes.

The mechanism of insulin secretion after oral glucose administration V. Portal venous IRI concentration in dogs after ingestion of glucose

Concentrations of immunoreactive insulin activity and of blood glucose were measured in portal and peripheral venous blood in six conscious dogs after oral administration of 1.0 g/kg glucose. Portal venous samples were obtained either by chronic catheterization or by direct puncture of the portal vein through a London-cannula. Portal venous IRI was already significantly increased 5 min after the onset of the stimulus. Peripheral venous IRI pattern reflected this early increase, but the peripheral venous blood glucose level was unchanged. The results indicate that the early peripheral venous IRI increase reflects a pancreatic insulin secretory reflex.

"A spoonful of sugar" - trans-alveolar nutrition

In this initial study, it has been postulated that even the simple bronchial administration of isotonic glucose and insulin can maintain alveolar cell metabolism as measured by A.T.P. activity; further studies, using aerosolized glucose solutions, will test the validity of the hypothesis that alveolar metabolism can be maintained by the administration of substrate in aerosolized form by the alveolar route and will determine whether this form of substrate administration has clinical potential.