Both the endocannabinoid system (ECS) and estrogens have significant roles in cardiovascular control processes. Cannabinoid type 1 receptors (CB₁Rs) mediate acute vasodilator and hypotensive effects, although their role in cardiovascular pathological conditions is still controversial. Estrogens exert cardiovascular protection in females. We aimed to study the impact of ECS on vascular functions. Experiments were performed on CB₁R knockout (CB₁R KO) and wild-type (WT) female mice. Plasma estrogen metabolite levels were determined. Abdominal aortas were isolated for myography and histology. Vascular effects of phenylephrine (Phe), angiotensin II, acetylcholine (Ach) and estradiol (E2) were obtained and repeated with inhibitors of nitric oxide synthase (NOS, Nω-nitro-L-arginine) and of cyclooxygenase (COX, indomethacin). Histological stainings (hematoxylin-eosin, resorcin-fuchsin) and immunostainings for endothelial NOS (eNOS), COX-2, estrogen receptors (ER-α, ER-β) were performed. Conjugated E2 levels were higher in CB₁R KO compared to WT mice. Vasorelaxation responses to Ach and E2 were increased in CB₁R KO mice, attenuated by NOS-inhibition. COX-inhibition decreased Phe-contractions, while it increased Ach-relaxation in the WT group but not in the CB₁R KO. Effects of indomethacin on E2-relaxation in CB₁R KO became opposite to that observed in WT. Histology revealed lower intima/media thickness and COX-2 density, higher eNOS and lower ER-β density in CB₁R KO than in WT mice. CB₁R KO female mice are characterized by increased vasorelaxation associated with increased utilization of endothelial NO and a decreased impact of constrictor prostanoids. Our results indicate that the absence or inhibition of CB₁Rs may have beneficial vascular effects.

Background: Atherosclerosis forms the background of several cardiovascular pathologies. LDL receptor knockout (LDLR-KO) mice kept on a high-fat diet (HFD) develop high cholesterol levels. Previously we found that vasodilation responses in HFD LDLR-KO mice were improved in the absence of type 1 cannabinoid receptors (CB₁Rs). We aimed to reveal the effects of HFD and CB₁Rs on vascular contractile and structural properties. Methods: Experiments were performed on LDLR-CB₁R double knockout and wild type (WT) mice, kept on an HFD or control diet (CD) for 5 months. Thoracic aortas were isolated for Oil Red plaque staining and abdominal aorta segments for myography to obtain phenylephrine (Phe)-induced (100 nM–10 µM) contractile responses. Aorta samples were subjected to histology stainings with hematoxylin–eosin and resorcin–fuchsin (elastin density) and for smooth muscle actin (SMA) immunohistochemistry. Results: Phe-induced contractions significantly increased in HFD groups (p < 0.05) similarly in all genotypes. However, contractions were stronger with CD in CB₁R-KO compared to WT. Plaque areas were increased in LDLR-KO mice compared to WT, significant in HFD groups (p < 0.05). SMA increased to HFD, while elastin density remained similar, with the highest value in double KO-HFD. Intima/media ratio significantly decreased in double KO-HFD vs. CD. Conclusions: Our results indicate that HFD-treated LDLR-KO mice develop atherosclerosis with functional contractile and structural alterations modulated by CB₁Rs: absence of CB₁Rs elicited higher contraction properties with some modification in vascular remodeling indicating contribution of the CB₁R to cellular signalization controlling wall thickness and elasticity in pathological conditions.