Type II cell response to chronic beta adrenergic agonist and antagonist infusions

Beta adrenergic agonists stimulate the secretion of lamellar bodies by lung alveolar type II cells. Most studies of such stimuli have been for short time periods; we wished to determine the effects of longer infusions of beta adrenergic agonists and antagonists upon biochemical and morphometric measures of type II cell surfactant pools. We implanted osmotic minipumps which infused 10 micrograms/kg/min of isoproterenol, 10 micrograms/kg/min of terbutaline or 0.2 microgram/kg/min of propranolol into the s.c. tissue of rats for 7 days. Saline-infused rats and untreated rats were studied concurrently. Seven days after pump implantation, we measured body, lung and heart weight and lamellar body and lavage disaturated phosphatidylcholine content. A group of rats with saline-, isoproterenol- or propranolol-filled osmotic minipumps had lungs fixed and processed for morphometric volume determination of type II cell organelles. Lung and body weights were unaffected by beta agonists and by propranolol, whereas heart weights were increased 14 to 47%. Lamellar body disaturated phosphatidylcholine was elevated 20 to 30% after 7 days of beta agonist infusion and was 20% lower after 7 days of propranolol, compared to saline infusion. Morphometric estimates of total lamellar body volume per lung showed a 22% increase after 7 days of isoproterenol and a 40% decrease after 7 days of propranolol. These changes were found to be due to an increase in lamellar body volume per cell after isoproterenol and a decrease in both lamellar body volume per cell and total number of type II cells per lung after propranolol infusion.