[Agmatine inhibits the afferent activity of carotid baroreceptor in rats]

The effect of agmatine (Agm) on the carotid baroreceptor activity was examined in 24 anesthetized rats with perfused isolated carotid sinus by recording sinus nerve afferent discharges. The results are as follows. (1) By perfusing with 1 mmol/L Agm, the functional curve for the intrasinus pressure (ISP)-integral of sinus nerve activity (ISNA) relation was shifted to the right and downward with decreases in peak slope (PS) and peak integral value of carotid sinus afferent discharge (PIV). By perfusing with high concentrations of Agm (5 and 10 mmol/L), the curves were shifted to the right and downward further with marked decreases of PS and PIV. These results showed that Agm exerted an inhibitory action on the baroreceptor activity in a dose-dependent manner. (2) The Agm-induced decrease in sinus nerve afferent activity was eliminated by pretreatment with IR and alpha 2-AR blocker idazoxan (0.1 mmol/L). (3) Selective alpha 2-AR blocker yohimbine (15 mumol/L) partly abolished the inhibitory effect of Agm on baroreceptor. (4) Preperfusing with Bay K 8644 (500 nmol/L), an agonist of calcium channels, also eliminated the effect of Agm on carotid baroreceptor activity. These results indicate that Agm exerts an inhibitory action on carotid baroreceptor and such an action may be attributed to the reduction in calcium influx in carotid baroreceptor, which is mediated by IR and alpha 2-AR.