Hemodynamic profile, responsiveness to anandamide, and baroreflex sensitivity of mice lacking fatty acid amide hydrolase

Abstract

The endocannabinoid anandamide exerts neurobehavioral, cardiovascular, and immune-regulatory effects through cannabinoid receptors (CB). Fatty acid amide hydrolase (FAAH) is an enzyme responsible for the in vivo degradation of anandamide. Recent experimental studies have suggested that targeting the endocannabinergic system by FAAH inhibitors is a promising novel approach for the treatment of anxiety, inflammation, and hypertension. In this study, we compared the cardiac performance of FAAH knockout (FAAH-/-) mice and their wild-type (FAAH+/+) littermates and analyzed the hemodynamic effects of anandamide using the Millar pressure-volume conductance catheter system. Baseline cardiovascular parameters, systolic and diastolic function at different preloads, and baroreflex sensitivity were similar in FAAH-/- and FAAH+/+ mice. FAAH-/- mice displayed increased sensitivity to anandamide-induced, CB1-mediated hypotension and decreased cardiac contractility compared with FAAH(+/+) littermates. In contrast, the hypotensive potency of synthetic CB1 agonist HU-210 and the level of expression of myocardial CB1 were similar in the two strains. The myocardial levels of anandamide and oleoylethanolamide, but not 2-arachidonylglycerol, were increased in FAAH-/- mice compared with FAAH+/+ mice. These results indicate that mice lacking FAAH have a normal hemodynamic profile, and their increased responsiveness to anandamide-induced hypotension and cardiodepression is due to the decreased degradation of anandamide rather than an increase in target organ sensitivity to CB1 agonists.

Fig. 1

Representative pressure-volume relations following inferior vena cava occlusions in FAAH^+/+ and FAAH^−/− mice. Note that the slopes of end-systolic and end-diastolic pressure-volume (P-V) relations (ESPVR and ED-PVR), indicators of left ventricular (LV) contractility and stiffness, respectively, are similar in the two strains.

Fig. 2

Hemodynamic effects of anandamide (AEA) in FAAH^+/+ (A) and FAAH^−/− (B) mice. Representative recordings of the effect of intravenous injection of AEA (20 mg/kg) on mean arterial pressure (MAP, top), cardiac contractility [LV systolic pressure (LVSP) and pressure change over time (dP/dt); middle], and P-V relations (bottom) in an anesthetized FAAH^+/+ (A) and FAAH^−/− (B) mouse are shown. The six parts in the middle and bottom represent baseline conditions (Bl) and responses 2, 5, 10, 20, and 30 min after injection of AEA. Arrows indicate the injection of the drug. Note that the hypotensive and cardiodepressant effects of AEA (phase III) last much longer in FAAH^−/−(> 30 min) than in FAAH^+/+ mice (<10 min).

Fig. 3

Phase III hemodynamic effects of AEA are mediated by cannabinoid type 1 (CB₁) receptors in both FAAH^+/+ (A) and FAAH^−/− (B) mice. Representative recordings of the effects of AEA (20 mg/kg iv) after pretreatment with the CB₁ antagonist AM-251 (3 mg/kg iv) on MAP (top), cardiac contractility (LVSP and dP/dt; middle), and P-V relations (bottom) in a FAAH^+/+ (A) and a FAAH^−/− mouse (B) are shown. The six parts in the middle and bottom panels represent baseline conditions and responses 2, 5, 10, 20, and 30 min after injection of AEA. Arrows indicate the injection of the drugs.

Fig. 4

A: dose-dependent effects of HU-210 on MAP and heart rate (HR) in FAAH^+/+ (●) and FAAH^−/− mice (○). Note that the effects of HU-210 are similar in the two strains. Values are means ± SE; n = 6 mice for each condition. B: dose-dependent effects of AEA on MAP and HR in FAAH^+/+ (●) and FAAH^−/− mice (○). Note the increased sensitivity of FAAH^−/− mice to the effects of AEA. Values are means ± SE; n = 4 –7 mice for each condition. Student’s t-test was used for pairwise comparisons. *P < 0.05, FAAH^−/− vs. FAAH^+/+. C and D: detection of cardiac CB₁ receptors by Western blot analysis(C) or RT-PCR (D) in FAAH^+/+ and FAAH^−/− mice. Optical density (OD) values for Western blot analyses are means ± SE from 5 separate experiments and have been corrected for loading. AU, arbitrary units.

Fig. 5

Hemodynamic effects of AEA in FAAH^+/+ (solid symbols) and FAAH^−/− mice (open symbols) after vehicle (circles) or AM-251 treatment (squares). Values are means ± SE; n = 5–7 mice for each condition. AEA was injected at 0 min, as indicated by arrow. Note that AM-251 blocks the major hemodynamic effects of AEA in both strains. Strain- and time-dependent differences were analyzed by two-way ANOVA. Student’s t-test was used after ANOVA for pairwise comparisons. Significance was assumed if P < 0.05 for FAAH^+/+ pre- vs. posttreatment (*), for FAAH^+/+ pre- vs. posttreatment ($), and for FAAH^−/− vs. FAAH^+/+ (#). LVSP, LV systolic pressure; +dP/dt and −dP/dt, pressure increment and decrement, respectively; CO, cardiac output; TPR, total peripheral resistance.

Fig. 6

Pressor (top) and reflex bradycardic responses to phenylephrine (middle) and baroreflex sensitivity (BRS) (bottom) in anesthetized FAAH^+/+ (●) and FAAH^−/− mice (○). Baroreflex sensitivity was determined as described in METHODS. Values are means ± SE; n = 4 – 6 mice for each condition.