Role for endogenous endothelin in the regulation of plasma volume and albumin escape during endotoxin shock in conscious rats

Abstract

To explore the role of endogenous endothelin (ET) in the regulation of vascular functions, we studied the effects endothelin receptor blockade on blood pressure, plasma volume and albumin escape during endotoxin shock in conscious, chronically catheterized rats. Red blood cell volume and plasma volume were determined by using chromium-51-tagged erythrocytes and iodine-125-labelled albumin, respectively. Intravenous injection of lipopolysaccharide (LPS, 10 mg kg(-1)) resulted in hypotension, haemoconcentration, and increased total-body albumin escape, which is reflected by a 30% reduction in plasma volume. Plasma ET-1 concentrations increased 2.1 fold and 5.4 fold at 30 and 120 min post-LPS, respectively. LPS-induced losses in plasma volume and albumin escape were significantly attenuated by pretreatment of animals with the dual ET(A)/ET(B) receptor antagonist bosentan (17.4 micromol kg(-1), i.v. 15 min prior to LPS) or the ET(A) receptor antagonist FR 139317 (3.8 micromol kg(-1), i.v.) during both the immediate and delayed phases of endotoxin shock. The inhibitory actions of bosentan and FR 139317 were similar. Both antagonists augmented the hypotensive action of LPS. Administration of bosentan or FR 139317 70 min after injection of LPS also attenuated further losses in plasma volume and increases in total body and organ albumin escape rates with the exception of the lung and kidney. These results indicate a role for endogenous endothelin in mediating losses in plasma volume and albumin escape elicited by LPS predominantly through activation of ET(A) receptors, and suggest that by attenuating these events, ET(A) or dual ET(A)/ET(B) receptor blockers may be useful agents in the therapy of septic shock.

Figure 1

Experimental protocols. ⁵¹Cr-RBC indicates ⁵¹Cr-tagged rat red blood cells; [¹²⁵I]-HSA, ¹²⁵I-labelled human serum albumin.

Figure 2

Changes in mean arterial blood pressure (MABP) and in pressor responses to norepinephrine in conscious rats treated with LPS during endothelin receptor blockade. (A) Different groups of animals were injected intravenously with vehicle (saline, control), bosentan (17.4 μmol kg⁻¹) or FR 139317 (3.8 μmol kg⁻¹) at 15 min (arrow a) followed by LPS (10 mg kg⁻¹) or saline 10 min later (arrow b). (B) Different groups of rats received saline, bosentan or FR 139317 at time 0 (arrow a) followed by LPS 10 min later (arrow b). (C) Different groups of rats received LPS at 10 min (arrow a) followed by vehicle (saline), bosentan or FR 139317 70 min later (arrow b). (D) Pressor responses to intravenous norepinephrine (3.1 nmol kg⁻¹) in rats pretreated with saline (control), bosentan or FR 139317 for 10 min before injection of LPS (at time 0). Values are means±s.e.mean. ^*P<0.05 for both bosentan and FR 139317 compared with LPS at the same time point).

Figure 3

Effects of bosentan (17.4 μmol kg⁻¹), FR 139317 (3.8 μmol kg⁻¹) or their vehicle (saline, control) on haematocrit, plasma volume, and red blood cell volume and total-body albumin escape during the early phase of endotoxin shock in conscious rats. The animals were pretreated with bosentan, FR 139317 or vehicle for 10 min before administration of LPS (10 mg kg⁻¹, i.v.). Values are mean±s.e.mean and were obtained at 50 min after injection of [¹²⁵I]-HSA. ^***P<0.001 (compared with control), # P<0.05; ## P<0.01 (compared with LPS by Dunn's test).

Figure 4

Effects of bosentan (17.4 μmol kg⁻¹), FR 139317 (3.8 μmol kg⁻¹) or their vehicle (saline, control) on albumin escape rates in various vascular beds during the early phase of endotoxic shock in conscious rats. The animals were pretreated with bosentan, FR 139317 or vehicle for 10 min before administration of LPS (10 mg kg⁻¹, i.v.). Values are mean±s.e.mean. ^***P<0.001 (compared with control), # P<0.05; ## P<0.01 (compared with LPS by Dunn's test).

Figure 5

Effects of bosentan (17.4 μmol kg⁻¹), FR 139317 (3.8 μmol kg⁻¹) or their vehicle (saline, control) on haematocrit, plasma volume, and red blood cell volume and total-body albumin escape during the delayed phase of endotoxic shock in conscious rats. The animals were either pretreated with bosentan, FR 139317 or vehicle for 10 min before administration of LPS (10 mg kg⁻¹, i.v.) (Pretreatment) or they first received saline at time 0 then LPS at 10 min and 70 min later bosentan or FR 139317 (Treatment). [¹²⁵I]-labelled human serum albumin was injected at 100 min and measurements were performed at 105 min and at 150 min after injection of LPS. Values are mean±s.e.mean. ^*P<0.05; ^**P<0.01 (compared with measurements at 105 min in the same group), # P<0.05, ## P<0.01 (compared with LPS by Dunn's test).

Figure 6

Effects of bosentan (17.4 μmol kg⁻¹), FR 139317 (3.8 μmol kg⁻¹) or their vehicle (saline, control) on albumin escape rates in various vascular beds during the delayed phase of endotoxic shock in conscious rats. The animals were pretreated with bosentan, FR 139317 or vehicle for 10 min before administration of LPS (10 mg kg⁻¹, i.v.) or they first received saline at time 0 then LPS at 10 min and 70 min later they were treated with bosentan or FR 139317. ¹²⁵I-labelled human serum albumin was injected at 100 min and the animals were killed at 150 min after injection of LPS. Values are mean±s.e.mean. ^*P<0.05; ^**P<0.01 (compared with LPS by Dunn's test).