Ultrafine carbon black attenuates the antihypertensive effect of captopril in spontaneously hypertensive rats

Particulate matter (PM) has been associated with increased blood pressure (BP) by affecting renin-angiotensin system (RAS) on a systemic level in spontaneously hypertensive rats (SHR). RAS in SHR is also an important target for the angiotensin converting enzyme (ACE) inhibitors such as captopril. We aimed to determine if ultrafine carbon black (UCB) could affect antihypertensive effect of captopril in SHR. The rats were randomly divided into six groups. Group 1 did not receive intratracheal instillation; group 2 received saline instillation plus captopril administration; groups 3, 4 and 5 received 0.15 mg/kg, 0.45 mg/kg and 1.35 mg/kg UCB per instillation plus captopril administration, respectively; group 6 received 1.35 mg/kg UCB instillation only. Rats in the above groups were intratracheally instilled with saline or UCB once every two days for three times and captopril was administered to group 2-5 after the final UCB treatment, once a day for one week. The BP was measured 24 h after each intratracheal instillation. During captopril administration and 24 h after last captopril administration, we measured BP every two days for four times. Our results showed that UCB at the dose of 1.35 mg/kg induced pulmonary and systemic inflammation in SHR. Captopril reduced BP in rats exposed to 0, 0.15 and 0.45 mg/kg UCB seven and eleven days after the first UCB instillation, and had no effect on BP in rats exposed to 1.35 mg/kg UCB. Captopril also reduced angiotensin II (AngII) in rats exposed to saline. The reduction, however, was attenuated with increasing doses of UCB. We conclude that UCB attenuated the antihypertensive effect of captopril in SHR, and the effect was accompanied by a systemic increase in the concentration of AngII.