Control of pulmonary surfactant secretion from type II pneumocytes isolated from the lizard Pogona vitticeps

Pulmonary surfactant, a mixture consisting of lipids and proteins and secreted by type II cells, functions to reduce the surface tension of the fluid lining of the lung, and thereby decreases the work of breathing. In mammals, surfactant secretion appears to be influenced primarily by the sympathetic nervous system and changes in ventilatory pattern. The parasympathetic nervous system is not believed to affect surfactant secretion in mammals. Very little is known about the factors that control surfactant secretion in nonmammalian vertebrates. Here, a new methodology for the isolation and culture of type II pneumocytes from the lizard Pogona vitticeps is presented. We examined the effects of the major autonomic neurotransmitters, epinephrine (Epi) and ACh, on total phospholipid (PL), disaturated PL (DSP), and cholesterol (Chol) secretion. At 37 degrees C, only Epi stimulated secretion of total PL and DSP from primary cultures of lizard type II cells, and secretion was blocked by the beta-adrenoreceptor antagonist propranolol. Neither of the agonists affected Chol secretion. At 18 degrees C, Epi and ACh both stimulated DSP and PL secretion but not Chol secretion. The secretion of surfactant Chol does not appear to be under autonomic control. It appears that the secretion of surfactant PL is predominantly controlled by the autonomic nervous system in lizards. The sympathetic nervous system may control surfactant secretion at high temperatures, whereas the parasympathetic nervous system may predominate at lower body temperatures, stimulating surfactant secretion without elevating metabolic rate.