tokens: The decrease in the heart rate ( HR ) induced by the beta - AR antagonist metoprolol in conscious rats was significantly attenuated in TGR compared with SD rats ( - 9 . 9 + / - 1 . 7 % vs . - 18 . 1 + / - 1 . 5 % ) , whereas the effect of parasympathetic blockade by atropine on HR was similar in both strains .