Reduced α-adrenoceptor responsiveness and enhanced baroreflex sensitivity in Cry-deficient mice lacking a biological clock

To reveal the role of clock genes in generating the circadian rhythm of baroreflexes, we continuously measured mean arterial pressure and baroreflex sensitivity in free-moving normal wild-type mice, and in Cry-deficient mice which lack a circadian rhythm, in constant darkness for 24 h. In wild-type mice the mean arterial pressure was higher at night than during the day, and was accompanied by a significantly enhanced baroreflex sensitivity of -13.6 +/- 0.8 at night compared with -9.7 +/- 0.7 beats min(-1) mmHg(-1) during the day (P < 0.001). On the other hand, diurnal changes in arterial pressure disappeared in Cry-deficient mice with remarkably enhanced baroreflex sensitivity compared with wild-type mice (P < 0.001): -21.9 +/- 1.6 at night and -23.1 +/- 2.1 beats min(-1) mmHg(-1) during the day. Moreover, the mean arterial pressure response to 10 mu g kg(-1) of phenylephrine, an alpha(1)-adrenoceptor agonist, was severely suppressed in Cry-deficient mice regardless of time, while that for the wild-type mice was 10.1 +/- 1.9 mmHg in the night, significantly lower than 22.0 +/- 3.5 mmHg in the day (P < 0.01). These results suggest that CRY genes are involved in generating the circadian rhythm of baroreflex sensitivity, partially by regulating alpha(1)-adrenoceptor-mediated vasoconstriction in peripheral vessels.