The Use of Chlorisondamine to Assess the Vasomotor Sympathetic Tonus in Normotensive Mice
Authors: Souza Lucas A. C. , Cooper Silvana G. , Worker Caleb J. , Thakore Pratish , Earley Yumei Feng 
Published: April 2020

Chlorisondamine (CSD), a long‐lasting nicotinic receptor antagonist and ganglionic blocker, has been commonly used to assess the sympathetic vasomotor tone in mice. Both cardiac output and peripheral resistance are blood pressure (BP) determinants; however, it is not defined whether the BP reduction observed after the administration of this agent is caused by a decrease in the sympathetic activity solely to the blood vessels (vasomotor tone) or if there is a contribution from the reduction in cardiac output. The aim of this study was to examine the effects of CSD in cardiac output and BP, and to identify an appropriate dose of CSD for the assessment of the sympathetic vasomotor tone in normotensive mice. We used echocardiography to examine the cardiac output (CO) and function, and telemetry system to record BP and heart rate (HR) in response to intraperitoneal (i.p.) injection of CSD.

C57Bl/6J mice (12–14 weeks old) were i.p. injected with series doses of CSD (1, 2, 3, or 6 mg/Kg) and the cardiac function was assessed by Echocardiography (VEVO® 2100, Fujifilm Visualsonics) after 30 minutes of injection. Two‐dimensional M‐mode images of the parasternal long‐axis and the short‐axis of the heart were used to calculate CO, stroke volume (SV), ejection fraction (EF) and fractional shortening (FS). We found that CSD in 1 mg/kg (16.1±1.0 ml/min, n=7, p=0.70) and 2 mg/kg (14.89±0.7 ml/min, n=7, p=0.22) did not affect the CO; while, the doses of 3 mg/Kg (CO: 13.3±0.4 ml/min, n=7, p<0.05) and 6 mg/Kg (CO: 14.3±1.1 ml/min, n=14, p<0.05) of CSD significantly reduced CO when compared to baseline (CO: 18.0±0.8 ml/min, n=21). There was no impact of CSD on stroke volume (SV), ejection fraction (EF) and fractional shortening (FS). The data indicate that a higher dose of CSD reduced CO in mice.

A second set of C57Bl/6J (n=5–7/group) mice were instrumented with radio telemetry transmitters (PA‐C10; Data Science International). After 14 days of recovery, baseline BP and HR were recorded and the mice were i.p. injected with series doses of CSD (1, 2, 3, or 6 mg/Kg) every 48 hours while BP and HR were simultaneously recorded. The trough in mean arterial pressure (MAP) and HR tracings were used to calculate the maximum response to CSD. We found that 1 mg/Kg of CSD did not significantly reduce BP or HR when compared to the i.p. injection of 0.9% saline; whereas, all other doses of CSD significantly reduced BP (ΔMAP) (2 mg/Kg: −25.5±3.3 mmHg; 3 mg/Kg: −31.1±3.4 mmHg, 6 mg/Kg: −31.0±7.0 mmHg, p<0.01), an indicative of sympathetic contribution to the BP. Interestingly, there is no significant difference in reduction in BP among mice that received 2, 3, or 6 mg/kg of CSD. In summary, our data suggest that 2 mg/Kg of CSD is an appropriate dose that can be used to assess the sympathetic vasomotor tone in normotensive mice as the BP reduction observed after the injection of this dose of CSD are not accompanied by changes in cardiac output.

Support or Funding Information

NIH/NHLBI (R01HL122770), American Heart Association ( 17IRG33370128), NIH/NIGMS (1P20GM130459‐5451)