Role of dexamethasone on vasopressin release during endotoxemic shock.

The present study was designed to assess the hypothesis that dexamethasone (DEX) through the control of nitric oxide (NO) synthesis could regulate the release of vasopressin (AVP), which plays an important role in the regulation of arterial pressure and plasma osmolality. Endotoxemic shock was induced by intravenous (i.v.) injection of 1.5 mg/kg lipopolisaccharide (LPS) in male Wistar rats weighing 250-300 g. After LPS administration, a group of animals were treated with DEX (1.0 mg/kg of body weight), whereas saline-injected rats served as controls. The LPS administration induced a significant decrease in mean arterial pressure (MAP) with a concomitant increase in heart rate (HR) (Delta VMAP: -16.1+/-4.2 mm Hg; Delta VHR: 47.3+/-8.1 bpm). An increase in plasma AVP concentration occurred and was present for 2 h after LPS administration (11.1+/-0.9 pg/mL) returning close to basal levels thereafter and remaining unchanged until the end of the experiment. When LPS was combined with i.v. administration of a low dose of DEX, we observed an attenuation in the drop of MAP (Delta VMAP: -2.2+/-1.9 mm Hg) and a decrease in NO plasma concentration [NO] after LPS administration (1098.1+/-68.1 microM) compared to [NO] after DEX administration (523.4+/-75.2 microM). However, this attenuation in the drop of MAP was accompanied by a decrease in AVP plasma concentration (3.7+/-0.4 pg/mL). These data suggest that AVP does not participate in the recovery of MAP when DEX is administered in this endotoxemic shock model.