Masahiro Hosono (1), Tohru Hiruma (1), Kiyoshi Watanabe (1), Yutaka Hayashi (1), Haruo Ohnishi (1), Yoshinobu Takata (2) and Hitoshi Kato (2)
(1) Pharmaceutical Research Laboratories, Fujirebio Inc., 51 Komiya-cho, Hachioji, Tokyo 192, Japan
(2) Department of Pharmacology, Faculty of Pharmaceutical Sciences, Teikyo University, Sagamiko, Kanagawa 199-01, Japan
Abstract: We investigated the effect of cilnidipine on cardiovascular and neuroendocrine responses to acute cold stress in conscious and unrestrained or moderately restrained spontaneously hypertensive rats (SHRs). Acute cold stress significantly increased mean blood pressure without marked change in heart rate. The acute cold stress-induced elevation in blood pressure was almost abolished by 1 mg/kg, p.o. of prazosin. The cold stress also elevated plasma norepinephrine and epinephrine levels. Cilnidipine at 3 mg/kg, p.o. significantly inhibited the pressor response to acute cold stress. Although 3 mg/kg, p.o. of nifedipine, nicardipine or manidipine lowered mean blood pressure to a similar extent as cilnidipine, none of these three drugs affected the pressor response. Cilnidipine also reduced the cold stress-induced increment in plasma norepinephrine but not the epinephrine level. These findings suggest that acute cold stress may induce the elevation in blood pressure due to an enhanced activation of the sympathoadrenal system in SHRs and that cilnidipine may suppress the pressor response by inhibiting the sympathetic nerve activity.
Keywords: Cilnidipine, Acute cold stress, Pressor response, Plasma catecholamine level, Spontaneously hypertensive rat