PRODUCTION OF ENDOTHELINS BY THE VENTILATORY MUSCLES IN SEPTIC SHOCK

Circulating endothelin-1 (ET-1) concentration increases significantly in animal models of sepsis. The main mechanism responsible for this ri se in ET-1 levels is believed to be upregulation of ET-1 synthesis in various organs, such as the lungs and heart. In this study we investig ated whether ET-1 is synthesized in the ventilatory muscles and whethe r this synthesis is regulated in septic shock. Conscious rats were inj ected with Escherichia coli endotoxin (lipopolysaccharide [LPS]) and k illed 6, 12, and 24 h later. A fourth group of rats was injected with normal saline and served as a control. The diaphragm was excised at th e end of the experiment and quickly frozen. Diaphragmatic ET-1 level w as measured with radioimmunoassay, and messenger RNA (mRNA) expression of ET-1 precursor prohormone (preproET-1), preproET-3, and endothelin -converting enzyme was measured with reverse transcription-polymerase chain reaction. LPS injection elicited an early (within 6 h) and prolo nged rise in diaphragmatic ET-1 concentration. In addition, mRNA level s of preproET-1 and preproET-3 rose by about 4- and 3-fold within 6 to 12 h of LPS injection, whereas mRNA of endothelin-converting enzyme i ncreased by more than 10-fold and peaked within 24 h of LPS injection. Immunostaining with anti-ET-1 antibody revealed positive ET-1 stainin g in the endothelium and somatic muscle fibers of septic diaphragms. T hese results indicate that diaphragmatic muscle fibers synthesize sign ificant amounts of ET-1 in septic shock and that the rise in ET-1 prod uction is due to upregulation of ET precursors and the converting enzy me.