Inhibition of carotid sinus baroreflex in neonatal rats exposed to chronic intermittent hypobaric hypoxia.

Chronic intermittent hypobaric hypoxia (CIHH) facilitates carotid sinus baroreflex (CSB) in adult rats, but the effect of CIHH on CSB in young rats is not known. The purpose of present study was to investigate the effect of CIHH on CSB in the young rat treated with CIHH from neonatal age, and the role of nitric oxide (NO) and Ca²⁺ in the effect of CIHH. Neonatal male Sprague-Dawley rats were randomly divided into three groups: 42-day CIHH treatment group (CIHH42), 56-day CIHH treatment group (CIHH56), and an age-matched control group (control). CIHH neonatal rats with the maternal rats were exposed to a simulated high-altitude hypoxia in a hypobaric chamber mimicking 5,000-m altitude (O₂ at 11.1%) for 42 or 56 days, 6 h per day, respectively. Isolated carotid sinus perfusion technique was used to test CSB of the rats. After 42-day and 56-day CIHH exposure, the CSB of the rats was inhibited significantly, manifesting as decrease of peak slope (PS) and reflex decrease (RD), and increase of threshold pressure (TP), equilibrium pressure (EP) and saturation pressure (SP). This inhibitory effect was canceled by L-type calcium channel activator Bay K 8644, but not by nitric oxide synthase (NOS) inhibitor NG-nitro-L-arginine methyl ester (L-NAME). The data showed that CIHH inhibited CSB in anesthetized young rats through blocking L-type calcium channels in carotid sinus baroreceptor.