Haemodynamic profile and responsiveness to anandamide of TRPV1 receptor knock-out mice

Abstract

The endocannabinoid anandamide and cannabinoid (CB) receptors have been implicated in the hypotension in various forms of shock and in advanced liver cirrhosis. Anandamide also activates vanilloid TRPV(1) receptors on sensory nerve terminals, triggering the release of calcitonin gene-related peptide which elicits vasorelaxation in isolated blood vessels in vitro. However, the contribution of TRPV(1) receptors to the in vivo hypotensive effect of anandamide is equivocal. We compared the cardiac performance of anaesthetized TRPV(1) knockout (TRPV(1)(-/-)) mice and their wild-type (TRPV(1)(+/+)) littermates and analysed in detail the haemodynamic effects of anandamide using the Millar pressure-volume conductance catheter system. Baseline cardiovascular parameters and systolic and diastolic function at different preloads were similar in TRPV(1)(-/-) and TRPV(1)(+/+) mice. The predominant hypotensive response to bolus intravenous injections of anandamide and the associated decrease in cardiac contractility and total peripheral resistance (TPR) were similar in TRPV(1)(+/+) and TRPV(1)(-/-) mice, as was the ability of the CB(1) receptor antagonist SR141716 to completely block these effects. In TRPV(1)(+/+) mice, this hypotensive response was preceded by a transient, profound drop in cardiac contractility and heart rate and an increase in TPR, followed by a brief pressor response, effects which were unaffected by SR141716 and were absent in TRPV(1)(-/-) mice. These results indicate that mice lacking TRPV(1) receptors have a normal cardiovascular profile and their predominant cardiovascular depressor response to anandamide is mediated through CB(1) receptors. The role of TRPV(1) receptors is limited to the transient activation of the Bezold-Jarisch reflex by very high initial plasma concentrations of anandamide.

Figure 1. Representative pressure–volume relations following vena cava inferior occlusions in TRPV₁^+/+ and TRPV₁^−/− mice

Note that the slope of systolic and diastolic pressure–volume relations (ESPVR and EDPVR) are similar in both mouse strains.

Figure 2. Haemodynamic effects of anandamide in anaesthetized TRPV₁^+/+ (A) and TRPV₁^−/− (B)

Representative recordings of the effect of intravenous injection of anandamide (20 mg kg⁻¹, AEA) on mean arterial pressure (MAP, top panel) and cardiac contractility (LVSP and dP/dt; middle panel) and pressure–volume relations (bottom panel) in anaesthetized TRPV₁^+/+ (A) and TRPV₁^−/− (B) mice. The five parts of the middle and bottom panels represent baseline conditions (Bl), phase I, phase II, and phase III of the anandamide response and conditions 10 min after injection (10 min). The arrows indicate the injection of the drug.

Figure 3. Haemodynamic effects of anandamide (AEA) in TRPV₁^+/+ (•) and in TRPV₁^−/− mice (○)

Values are mean ± s.e.m. (n = 6 for each condition). *P < 0.05, versus baseline of TRPV₁^+/+; #P < 0.05, versus baseline of TRPV₁^−/−; †P < 0.05, TRPV₁^+/+ versus TRPV₁^−/−. Arrow indicates anandamide injection (0 min).

Figure 4. Inhibition of CB1 receptor prevents major haemodynamic effects of anandamide (phase III) in both TRPV₁^+/+ (A) and TRPV₁^−/− (B) mice

Representative recordings of the effects of anandamide (20 mg kg⁻¹ i.v., AEA) after pretreatment with SR141716 (3 mg kg⁻¹, i.v.) on mean arterial pressure (MAP, top panel) and cardiac contractility (LVSP and dP/dt; middle panel) and pressure–volume relations (bottom panel) in anaesthetized TRPV₁^+/+ (A) and TRPV₁^−/− mice (B). The five parts of the middle and bottom panels represent the same five stages as described in the legend for Fig. 2. The arrows indicate the injection of the drugs.

Figure 5. Peak haemodynamic changes in phases I, II and III of the anandamide response (20 mg kg⁻¹, i.v.) in TRPV₁^+/+ (black and dark grey columns) and TRPV₁^−/− mice (open and light grey columns) pretreated with vehicle or SR141716 (grey)

Values are means ± s.e.m. and are expressed as percentage change from baseline; *P < 0.05, versus baseline values; #P < 0.05, TRPV₁^+/+ versus TRPV₁^−/− (n = 6 for each condition).

Figure 6. Representative tracings of MAP illustrate the effect of i.v. capsaicin injections in TRPV₁^+/+ (top) and TRPV₁^−/− mice (bottom)

Capsaicin doses: left, 10 μg kg⁻¹; right, 100 μg kg⁻¹. Similar response was seen in 4 experiments. The arrows indicate the injection of the drug.