Effect of triiodothyronine augmentation on rat lung surfactant phospholipids during sepsis SERGEY M. KSENZENKO, SCOTT B. DAVIDSON, AMER A. SABA, ALEXANDER P. FRANKO, AML M. RAAFAT, LAWRENCE N. DIEBEL, AND SCOTT A. DULCHAVSKY Department of Surgery, Wayne State University School of Medicine, Detroit, Michigan 48201 Ksenzenko, Sergey M., Scott B. Davidson, Amer A. Saba, Alexander P. Franko, Aml M. Raafat, Lawrence N. Diebel, and Scott A. Dulchavsky. Effect of triiodothyronine augmentation on rat lung surfactant phospholipids during sepsis. J. Appl. Physiol. 82(6): 2020–2027, 1997.—Surfactant functional effectiveness is dependent on phospholipid compo- sitional integrity; sepsis decreases this through an undefined mechanism. Sepsis-induced hypothyroidism is commensu- rate and may be related. This study examines the effect of 3,38,5-triiodo-L-thyronine (T 3 ) supplementation on surfactant composition and function during sepsis. Male Sprague- Dawley rats underwent sham laparotomy (Sham) or cecal ligation and puncture (CLP) with or without T 3 supplementa- tion [CLP/T 3 (3 ng/h)]. After 6, 12, or 24 h, surfactant was obtained by lavage. Function was assessed by a pulsating bubble surfactometer and in vivo compliance studies. Sepsis produced a decrease in surfactant phosphatidylglycerol and phosphatidic acid, with an increase in lesser surface-active lipids phosphatidylserine and phosphatidylinositol. Phospha- tidylcholine content was not significantly changed. Sepsis caused an alteration in the fatty acid composition and an increase in saturation in most phospholipids. Hormonal replacement attenuated these changes. Lung compliance and surfactant adsorption were reduced by sepsis and maintained by T 3 treatment. Thyroid hormone may have an active role in lung functional preservation through maintenance of surfac- tant homeostasis during sepsis. fatty acids; respiratory distress THE PULMONARY SURFACTANT SYSTEM is of primary impor- tance in normal lung function and homeostasis. Surfac- tant consists of a complex mixture of phospholids and lipoproteins which act in concert to reduce lung surface tension, maintain fluid balance, and possibly reduce infection. Acute alterations in the availability and functional integrity of lung surfactant have been dem- onstrated in animal models of respiratory distress and during the acute respiratory distress syndrome (ARDS) in humans (8). Similar changes in lung surfactant are noted during sepsis, which is often remote from the lung (17). Although it is estimated that 200,000 people die of ARDS annually in the US, the acute biochemical changes in lung surfactant during infection remain poorly characterized. 3,38,5-Triiodo-L-thyronine (T 3 ) is a ubiquitous growth hormone and is necessary for the maintenance of lung morphology, type II alveolar cell function (surfactant synthesis), and lung repair after injury (2, 22). The ‘‘Sick Euthyroid’’ or ‘‘Low T 3 ’’ syndrome is frequently coexistent with ARDS and consists of a normal or low serum thyroxine, with a profound reduction in circulat- ing levels of metabolically active T 3 (1, 3, 11, 12). The physiological ramifications of these acute changes in thyroid economy are not clear. An acute decrease in thyroid hormone-dependent metabolism may provide a beneficial reduction in energy requirements during periods of stress. In contrast, thyroid hormone is neces- sary for optimal cellular repair after injury and for normal homeostasis. Furthermore, recent studies have suggested that an intact thyroid axis is essential for survival during hemorrhagic and septic shock (10, 14). The purpose of this study was to determine the time course and effect of sepsis with or without T 3 augmenta- tion on surfactant compositional and functional integ- rity. METHODS Animals and surfactant preparation. The experiments described herein conform to the NIH Guidelines for the Care of Laboratory Animals and were approved by the Wayne State University Animal Care Committee. Adult male Sprague- Dawley rats (250–350 g) were acclimated to the animal care facility for 1 wk and fed standard rat chow. Animals were anesthetized and underwent sham laparotomy (Sham; n 5 60), cecal ligation and puncture (CLP; n 5 60), or CLP with T 3 replacement (CLP/T 3 ; n 5 60). T 3 replacement was adminis- tered by a subcutaneous Alzet osmotic pump at 3 ng/h, which has previously been shown to correct the sepsis-induced decrease in serum free T 3 levels (10). In each group, animals were randomly killed at 6, 12, or 24 h after CLP. Alveolar surfactant was obtained by repeated lavage through a tra- cheostomy with 0.15 M sodium chloride to total lung capacity 3 3. The surfactant pellet was isolated, following the procedures of Curstedt and co-workers (7), with a low-speed centrifugation to remove the cellular pellet followed by high- speed centrifugation to isolate the surfactant fraction. Measurements of lung compliance and surface tension. In situ dynamic pulmonary compliance was determined in a subset of animals from the slope of the pressure curve during serial lung inflation. The animals were anesthetized, and a tracheostomy was performed. The lungs were inflated with humidified room air at 4 ml/min, and the change in pressure was monitored with a pressure transducer. Dynamic lung compliance was calculated from the midslope region of the pressure-volume curve. Stock solutions of surfactant extract were prepared from pelleted surfactant from each animal group and dissolved in 0.15 M sodium chloride to a concentra- tion of 4 mg phospholipid/ml and dispersed by mechanical vortexing. Surfactant adsorption and surface tension were measured on a pulsating bubble surfactometer (Electronetics, Amherst, NY), as described by Enhorning (15). Surfactant adsorption was calculated from the pressure-volume loop during initial bubble inflation over a 10-s interval. Surface tensions are calculated from the Young-Laplace equation for a sphere (P 5 2 3 T/r), where P is the pressure drop across the bubble interface, T is the surface tension, and r is the bubble radius. Temperature was set at 37°C, and the pulsation rate was 20 cycles/min. Oscillation was continued for 15 min or until the minimum tension (T min ) was ,3 mN/m; surface T min and maximum tension were continuously recorded. 0161-7567/97 $5.00 Copyright r 1997 the American Physiological Society 2020 http://www.jap.org Downloaded from journals.physiology.org/journal/jappl (035.173.036.035) on July 14, 2020.