Background: We reported previously that α _1B ‐AR (α _1B ‐adrenoceptor) and AVPR1A (arginine vasopressin receptor 1A) heteromerize with CCR1 (C‐C motif [chemokine] receptor 1) in human monocytes, through which CCR1 is controlled. Whether CCR1 affects α _1B ‐AR and AVPR1A signaling and whether such complexes are detectable in human vascular smooth muscle cells (hVSMCs) is unknown. Methods and Results: Bioluminescence resonance energy transfer suggested that the receptors can form hetero‐oligomeric complexes. Activation of CCR1 with CCL23 (chemokine [C‐C motif] ligand 23) increased the efficacy of aVP (arginine vasopressin)‐stimulated AVPR1A and reduced the efficacy of phenylephrine‐stimulated α _1b ‐AR to activate guanine nucleotide‐binding protein G(q) subunit alpha (Gαq) in cells coexpressing all 3 receptors. Although CCL23 increased the efficacy of aVP and phenylephrine to recruit β‐arrestin to AVPR1A and α _1b ‐AR, respectively, when CCR1 is coexpressed, CCL23 did not affect β‐arrestin recruitment to agonist‐stimulated AVPR1A and α _1b ‐AR when all 3 receptors are present. Proximity ligation assays suggested that such receptor complexes are expressed in hVSMCs. Proximity ligation assays after small interfering RNA knockdown of each receptor showed that interactions between CCR1 and AVPR1A depend on the presence of α _1B ‐AR, whereas interactions between CCR1 and α _1B ‐AR and between α _1B ‐AR and AVPR1A are not affected by the presence of the third receptor partner. CCL23 increased IP3 (inositol trisphosphate) production and gel contraction of hVSMCs upon aVP stimulation and inhibited IP3 production and gel contraction of hVSMCs upon phenylephrine stimulation. Conclusions: Our findings suggest that CCR1 within functional heteromeric complexes with α _1B ‐AR and AVPR1A modulates the efficacy of α _1B ‐AR and AVPR1A in hVSMCs to activate downstream signaling cascades that mediate vasoconstriction and control vascular tone.

Background/Objectives: We reported previously that antagonists at chemokine receptors CCR2 and CCR3 have fluid-sparing effects during resuscitation from hemorrhagic shock. Because CCR1 shares several chemokine ligands with CCR2/3, we tested whether the CCR1 antagonist BX471 also reduces fluid requirements to maintain hemodynamics. Methods: Sprague Dawley rats were hemorrhaged for 30 min, followed by fluid resuscitation to maintain blood pressure for 60 min (series 1) and 180 min (series 2). Series 1: Animals received vehicle (n = 5), 0.05 μmol/kg (n = 5), or 0.5 μmol/kg (n = 4) BX471 at t = 30 min. Series 2: Animals received vehicle (n = 8) or 0.5 μmol/kg (n = 7) BX471 at t = 30 min. Hemodynamics, fluid requirements, blood gases, and lactate were monitored. Serum concentrations of CCR1 ligands (CCL3/4/5/7) were determined at baseline and at the conclusion of the experiments. Tissue (small/large intestine, lung) wet/dry (W/D) weight ratios, lung myeloperoxidase activity, and a panel of inflammation markers in tissue extracts were measured. Results: All animals could be resuscitated to target blood pressures. Series 1: A total of 0.5 μmol/kg BX471 reduced fluid requirements by more than 60% (p < 0.05 vs. vehicle and 0.05 μmol/kg BX471). Series 2: Systemic CCL3/5/7 levels increased during the experiment (p < 0.05). BX471-treatment reduced fluid requirements by more than 60% (p < 0.05) and prevented increases in CCL3/7. W/D ratios of large intestine and of the sum of all tissues were lower with BX471 treatment (p < 0.05). BX471-treatment reduced TNFα and IL6 concentrations in large intestine extracts (p < 0.05). Conclusions: Our findings suggest CCR1 as a new therapeutic target to reduce fluid requirements during resuscitation from hemorrhagic shock.