CB(1) cannabinoid receptor antagonism promotes remodeling and cannabinoid treatment prevents endothelial dysfunction and hypotension in rats with myocardial infarction

Abstract

1. To study the long-term effects of altered cannabinoid receptor activity on myocardial and vascular function, Wistar rats were treated with the selective CB(1) antagonist AM-251 (0.5 mg kg(-1) d(-1)), the potent synthetic cannabinoid HU-210 (50 micro g kg(-1) d(-1)) or vehicle for 12 weeks after coronary artery ligation or sham operation. 2. AM-251 further reduced the pressure-generating capacity, shifted the pressure volume curve to the right (P<0.05) and increased the left-ventricular operating volume (AM-251: 930+/-40 micro l vs control: 820+/-40 micro l vs HU-210: 790+/-50 micro l; P<0.05) in rats with large myocardial infarction (MI). 3. Left-ventricular CB(1) immunoactivity in rats 12 weeks after large MI was unaltered as compared with noninfarcted hearts. 4. Cannabinoid receptor activation through HU-210, a cannabinoid that alters cardiovascular parameters via CB(1) receptors, increased the left-ventricular end-diastolic pressure (LVEDP, P<0.05). However, it prevented the drop in left-ventricular systolic pressure (HU-210: 142+/-5 mm Hg; P<0.05 vs control: 124+/-3 mm Hg; and P<0.001 vs AM-251: 114+/-3 mm Hg) and prevented endothelial dysfunction (ED) in aortic rings of rats with large MI (P<0.05). 5. Compared with AM-251, HU-210 prevented the decline in the maximal rate of rise of left-ventricular pressure and the maximum pressure-generating ability (P<0.05). In rats with small MI, HU-210 increased cardiac index (P<0.01) and lowered the total peripheral resistance (P<0.05). 6. The study shows that during the development of congestive heart failure post-large MI, cannabinoid treatment increases LVEDP and prevents hypotension and ED. Presumed CB(1) antagonism promotes remodeling despite unchanged myocardial CB(1) expression.

Figure 1

The Kaplan–Meier curve of overall survival shows no significant difference for rats treated with vehicle (n=50), AM-251 (n=50) or HU-210 (n=40).

Figure 2

Passive pressure–volume curves in sham-operated rats (a) and in rats with small (b) or large (c) MI. Vertical bars represent SEM. ^*P<0.05 AM-251 vs other groups.

Figure 3

Relaxations induced by acetylcholine (upper panel) and SNP (lower panel) in phenylephrine-preconstricted aortic rings from rats 12 weeks after large MI (filled symbols), as compared to sham-operated rats (open symbols). There was no difference among sham-operated rats treated with either AM-251, HU-210 (both not shown), or vehicle. Vertical bars represent SEM, n=6–10. ^*P<0.05 HU-210 vs vehicle post-large MI.

Figure 4

(a) Western Blot analysis with antibodies specific for the CB₁ cannabinoid receptor (CB1), actin, and glyceraldehyde-3 phosphodehydrogenase (GAPDH). For each lane, 18 μg of protein from vital left-ventricular myocardium after sham operation (control, lanes 1–3) or 12 weeks after MI (lanes 4–6) were loaded. For additional loading control, the same blots were probed for actin and GAPDH. (b) Average Western Blot signal intensity of CB₁ and GAPDH from five control (Ctrl.) and five infarcted animals (MI) were quantified as described in the Methods section. Molecular weight of the protein is shown in kilo Dalton (kD) on the right of the figure.