Arginine vasopressin V1a agonist attenuates methicillin-resistant Staphylococcus aureus-induced vascular leakage by inhibiting bradykinin

Background

Previously, we have shown that methicillin-resistant Staphylococcus aureus (MRSA) sepsis was associated with more severely pronounced vascular leakage compared with Pseudomonas aeruginosa sepsis. We have also demonstrated that the arginine vasopressin V1a receptor (V1aR) agonist significantly attenuated the severity of MRSA-induced vascular leakage [1]. The goal of the present study was to explore mechanistic aspects of V1aR agonist's action.

Materials and methods

Twelve adult female sheep were operatively prepared for chronic study. After 5 days of recovery, tracheostomy was performed under anesthesia and injury was given. The injury consisted of insufflation of cooled cotton smoke (48 breaths) and instillation of 2.5 × 10⁶ CFU MRSA into the lungs by bronchoscope under maintenance isoflurane anesthesia. Following the injury, sheep were awakened, placed on mechanical ventilation and randomly allocated into two groups: control group, saline treated, n = 6; and POV group, treated with intravenous V1aR agonist, Phe2-Orn8-Vasotocin (POV) (Ferring Research Institute, Inc., San Diego, CA, USA), n = 6. The titration of POV was started when mean arterial blood pressure (MAP) dropped by 10 mmHg from the baseline with the initial dose of 30 pmol/minute, which was further adjusted to maintain MAP close to baseline. All sheep were resuscitated with lactated Ringer's solution with initial rate of 2 ml/kg/hour that was further adjusted according to hematocrit. The experiment lasted 24 hours. Plasma levels of nitric oxide (NO; Grease reaction), asymmetric dymethylarginine (ADMA; mass spectrometry) and bradykinin (mass spectrometry) were determined at 0 hours and every 3 hours after the injury.

Results

MRSA-induced plasma levels of NO (nitrite/nitrate) as well as cumulative body fluid were significantly inhibited by V1aR agonist. The treatment with POV also attenuated the MRSA-induced hypotension. The plasma levels of ADMA were higher in the treated group compared with the control at 24 hours after the injury (0.93 ± 0.14 in control, n = 3 vs. 1.23 ± 0.08 in POV, n = 6). In addition, the treatment with POV significantly inhibited the MRSA-induced bradykinin increases at 3 hours after the injury (1.14 ± 0.4 in control vs. 0.52 ± 0.001 in POV, P < 0.05).

Conclusions

Arginine vasopressin V1aR agonist attenuates the severity of MRSA-induced vascular leakage by inhibiting potent permeability factor bradykinin and excessive NO. The V1aR agonist may modulate NO production by promoting the release of endogenous NO synthase inhibitor ADMA.