Effect of endotoxicosis on plasma and tissue levels of calcitonin gene-related peptide.

This study was designed to investigate the changes in tissue content and plasma concentrations of CGRP, a 37 amino acid vasoactive peptide, in male Sprague Dawley rats injected intravenously with a nonlethal dose of 3 mg/kg E. coli endotoxin. Plasma CGRP concentrations in nonendotoxemic animals, measured by a specific RIA, were initially 30.5 +/- 3.3 pg/ml, and were significantly increased to 63.7 +/- 4.6 pg/ml 2 hr after induction of endotoxemia (P less than 0.001; n = 13). A higher dose of LPS did not further elevate plasma CGRP levels, indicating that the maximal response occurred following a dose of 3 mg/kg LPS. CGRP levels in abdominal aorta, inferior vena cava, stomach, kidney, and left ventricular myocardium (4.11, 8.5, 2.61, 0.69, and 0.25 pmol/g wet weight tissue, respectively) were not changed significantly following the injection of endotoxin. However, in lung and mesenteric artery the levels increased significantly from 1.47 +/- 0.12 and 7.97 +/- 1.32 pmol/g wet weight tissue to 1.96 +/- 0.19 (P less than 0.05, n = 11) and 15.02 +/- 2.3 pmol/g (P less than 0.01; n = 7), respectively. In contrast, CGRP levels in the duodenum were significantly decreased from 11.3 +/- 0.93 pmol/g wet weight tissue to 6.2 +/- 0.68 pmol/g (P less than 0.001; n = 6). The changes in plasma concentration and tissue content of CGRP suggest that splanchnic organs may be the source of the elevated plasma CGRP levels in endotoxemia and that selective organ CGRP levels reflect a role in the pathogenesis of the response to endotoxemia.

Endothelin stimulates 86Rb efflux in rat glioma C6-Bu-1 cells.

Endothelin-1 (ET) elevates intracellular calcium ([Ca2+]i) and increased [Ca2+]i has been associated with K+ efflux. Therefore, we investigated ET stimulation of K+ efflux in rat glioma C6-BU-1 cells. K+ efflux was measured by monitoring the release of 86Rb+ from cells pre-loaded with 86RbCl. ET stimulated 86Rb+ efflux with an EC50 of 5.9 nM. ET-stimulated 86Rb+ efflux was insensitive to Ca2+ channel blockade, however it was reduced by 68% in Ca(2+)-free buffer, suggesting a sizable dependence on an extracellular source of Ca2+ influx through non voltage-operated Ca2+ channels. ET-stimulated 45Ca2+ efflux slightly preceded 86Rb+ efflux, again suggesting the presence of Ca2+ dependent K+ channels. ET-stimulated 86Rb+ efflux was insensitive to glyburide suggesting that efflux is not through ATP-sensitive K+ channels. ET-stimulated 86Rb+ efflux was insensitive to pertussis toxin (PTX) pre-treatment. Pre-incubation with the protein kinase C (PKC) inhibitor, staurosporine, inhibited 86Rb+ efflux by 66%, suggesting the involvement of PKC activation in ET-mediated 86Rb+ efflux. In summary, in C6-BU-1 cells, ET stimulates Ca2+ dependent K+ efflux which is mediated in part by protein kinase C activation, but not a PTX sensitive G-protein, nor through an ATP-sensitive K+ channel. These data extend the intracellular mechanisms initiated by ET to include Ca2+ dependent K+ efflux in glial cells and further support a neuromodulatory role for ET.