M. Hirabayashi

Chronic intracerebroventricular infusions of endothelin elevate arterial pressure in rats

We investigated the effects of intracerebroventricular infusions of endothelin on cardiovascular and endocrinological responses using conscious, unrestrained rats. Chronic intracerebroventricular infusions of endothelin, 10 pmol/h for 7 days, elevated arterial pressure significantly on days 5, 6 and 7 of the infusion, compared with intracerebroventricular infusions of the vehicle. Heart rate decreased from day 1 of the infusion of endothelin until the end of the experiment. The urinary excretion of norepinephrine increased on day 3 and epinephrine increased on days 3, 4 and 5 of endothelin infusion. The urinary excretion of arginine vasopressin increased on day 5, 6 and 7 of the infusion. These findings suggest that chronic intracerebroventricular infusions of endothelin elicit elevations in arterial pressure and that the initiation of blood pressure rises can be related to sympathetic activation although the actual role for the pressor responses has been played by the released arginine vasopressin.

Serum Calcium Increases the Incidence of Arrhythmias During Acetate Hemodialysis

We investigated the occurrence of arrhythmias during maintenance acetate hemodialysis (HD) using a 24-hour continuous electrocardiogram recording system. Three of 22 patients showed augmented increases in both ventricular premature beats and supraventricular premature beats during HD. When we changed the dialysate from one with a Ca2+ concentration of 1.75 mmol/L (3.5 mEq/L), to one with a Ca2+ concentration of 1.25 mmol/L (2.5 mEq/L), the elevation of serum Ca2+ concentration during HD was abolished and the increases in both ventricular premature beats and supraventricular premature beats were significantly decreased. The elevation of serum Ca2+ concentration during HD might induce either extracellular or intracellular increase in Ca2+ concentration in the heart and elicit either reentry- or triggered-activity types of arrhythmias during HD. The present results indicate that the dialysate with a lower Ca2+ concentration is advisable to use in patients with underlying cardiac diseases.

Effects of long-acting antihypertensive drugs on 24-hour blood pressure

Abstract The effects of various long-acting antihypertensive agents on 24-hour blood pressure were assessed by ambulatory blood pressure monitoring. Blood pressure (BP) was recorded in 56 patients with essential hypertension (34 men and 22 women; mean age, 64 ± 11 years). Each drug was administered once a day for 2 weeks. Beta-blockers (atenolol 50 mg/day and bisoprolol 5 mg/day) significantly reduced both blood pressure and heart rate throughout the 24-hour period, especially during the day. The beta-blockers had a similar hypotensive effect on both high and low BP ranges. An angiotensin converting enzyme inhibitor (enalapril 10 mg/day) significantly reduced both systolic and diastolic BP throughout the day, especially during the daytime, but heart rate was not altered. Cumulative percentage analysis revealed that enalapril decreased BP to a greater degree when baseline BP was higher. Calcium channel blockers (nitrendipine 10 mg/day, nisoldipine 5 mg/day, and manidipine 20 mg/day) significantly reduced blood pressure throughout the 24 hours, especially during the day, but heart rate was unaffected. Calcium channel blockers had a similar hypotensive effect on both the high and low BP ranges. These results show that oncedaily doses of long-acting antihypertensive drugs significantly reduce blood pressure throughout the day, especially in the daytime. Cumulative percentage analysis revealed that the pattern of blood pressure reduction by enalapril was similar to that of spontaneous and physiologic decreases in blood pressure.