Sphingosine-1-phosphate reduces rat renal and mesenteric blood flow in vivo in a pertussis toxin-sensitive manner

Abstract

Sphingolipids such as sphingosine-1-phosphate (SPP) and sphingosylphosphorylcholine constrict isolated rat intrarenal and mesenteric microvessels in vitro. The present study investigates their effects on the cardiovascular system in vivo in anaesthetized rats. The animals were given intravenous or intrarenal arterial bolus injections of sphingolipids (0.1-100 microg kg(-1)) with subsequent measurements of mean arterial pressure, heart rate and renal and mesenteric blood flows (RBF, MBF) using a pressure transducer and electromagnetic flow probes, respectively. Intravenous injection of SPP rapidly (within 30 s), transiently and dose-dependently reduced RBF (maximally -4.0+/-0.3 ml min(-1)) and MBF (maximally -1.4+/-0.2 ml min(-1)), without affecting mean arterial pressure or heart rate. Other sphingolipids had no significant effect. Intrarenal arterial SPP administration caused greater blood flow reductions (maximally -6.4+/-0.3 ml min(-1)) than systemic administration. Upon intrarenal administration, sphingosylphos- phorylcholine also lowered RBF (maximally -2.8+/-0.6 ml min(-1)), while the other sphingolipids remained without effect. Pretreatment with pertussis toxin (PTX, 10 microg kg(-1)) 3 days before the acute experiment abolished the SPP-induced reductions of RBF and MBF. These data demonstrate, that SPP is a potent vasoconstrictor in vivo, particularly in the renal vasculature, while the other structurally related sphingolipids had little if any effects. The PTX-sensitivity strongly suggests that the effects of SPP on renal and mesenteric blood flow are mediated by receptors coupled to G(i)-type G-proteins.

Figure 1

Effects of 100 μg kg⁻¹ intravenously injected sphingolipids on RBF and MBF in anaesthetized rats. Data are mean±s.e.mean (n=4–8) of alterations relative to baseline values. Start of the bolus injections was indicated by an arrow. RBF (A) and MBF (B) were rapidly and transiently reduced by injection of 100 μg kg⁻¹ of SPP (4.0±0.3 and 1.4±0.2 ml min⁻¹, respectively, ^** P<0.01 in a one-way analysis of variance). BSA, SPPC, sphingosine (SPH) or glucopsychosine (GLU) had no effect.

Figure 2

Dose-response curves of intravenously injected sphingolipids on RBF and MBF in anaesthetized rats. Data are mean±s.e.mean (n=4–8) of alterations relative to baseline values. RBF (A) and MBF (B) were dose-dependently reduced by SPP (P<0.0001 in a two-way analysis of variance) but not by BSA, SPPC, sphingosine (SPH) or glucopsychosine (GLU).

Figure 3

Effects of 100 μg kg⁻¹ intravenously injected sphingolipids on MAP and HR in anaesthetized rats. Data are mean±s.e.mean (n=4–8) of alterations relative to baseline values. Start of the bolus injections was indicated by an arrow. Injection of BSA, SPP, SPPC, sphingosine (SPH) or glucopsychosine (GLU) did not detectably alter MAP (A) or HR (B) up to 100 μg kg⁻¹.

Figure 4

Effects of 100 μg kg⁻¹ intrarenally injected sphingolipids on RBF and MBF in anaesthetized rats. Data are mean±s.e.mean (n=5–7) of alterations relative to baseline values. Start of the bolus injections was indicated by an arrow. RBF (A) and MBF (B) were rapidly and transiently reduced by injection of SPP (^**P<0.01 in a one-way analysis of variance); the blood flow reduction was more pronounced than upon intravenous injection. SPPC also reduced RBF but not MBF to a lower extent compared to SPP (^**P<0.01 in a one-way analysis of variance). BSA and sphingosine (SPH) had no effects.

Figure 5

Dose-response curves of intrarenally injected sphingolipids on RBF and MBF in anaesthetized rats. Data are mean±s.e.mean (n=5–7) of alterations relative to baseline values. RBF (A) and MBF (B) were dose-dependently reduced by SPP (P<0.0001 in a two-way analysis of variance) but not by BSA or sphingosine (SPH). SPPC had a small inhibitory effect at 100 μg kg⁻¹.

Figure 6

Dose-response curves of systemically injected SPP on MAP, RBF and MBF in PTX- and vehicle-treated anaesthetized rats. Data are mean±s.e.mean (n=5–6) of alterations relative to baseline values. SPP did not alter MAP (A), but dose-dependently reduced RBF (B) and MBF (C) in vehicle- but not in PTX-treated rats (P<0.0001 in a two-way analysis of variance).