Circadian blood pressure variability in adrenocorticotrophin-induced hypertension in the rat

Abstract

Objectives. Secondary hypertension is often characterized by loss of diurnal blood pressure variability. This study examined circadian (24 h) blood pressure variability in adrenocorticotrophin (ACTH)-induced hypertension in the Sprague-Dawley rat. Methods. Male Sprague-Dawley rats were randomly allocated to sham (0.9% saline, s.c.), n = (9), ACTH (0.5 μg/kg per day, s.c., n = 8) or ACTH (100 μg/kg per day, s.c., n = 7) in a room with a 12 h light/dark cycle (0600 h to 1800 h). A radio telemetry transducer was used to measure blood pressure in unrestrained animals over 3 control days (C1-C3) and 10 treatment days (T1-T10). Heart rate, systolic (SBP), mean arterial (MAP) and diastolic (DBP) blood pressure were continuously recorded. Body weight was measured daily and serum corticosterone concentration ([B]) prior to death. Results. Sham treatment had no effect on any parameters. ACTH 100 μg/kg per day increased SBP from 124 ± 2 pooled control (PC) to 1 34 ± 2 mmHg (T10), MAP from 105 ± 2 to 115 ± 2 mmHg and DBP from 87 ± 1 to 99 ± 2 mmHg and decreased heart rate from 305 ± 6 to 249 ± 5 beats/min and body weight from 299 ± 6 (C3) to 280 ± 8 g (T10) (all P′ < 0.0036). Serum [B] was higher in ACTH- (881 ± 44 ng/ml) than sham-treated rats (384 ± 17 ng/ml, P<0.001). There were no differences between sham treatment and ACTH 0.5 μg/kg per day. SBP, MAP, DBP and heart rate were consistently higher for ACTH 100 μg/kg per day and sham-treated animals during the dark cycle (1800 h to 0600 h) than the light cycle (0600 h to 1800 h). Conclusions. ACTH 100 μg/kg per day raises blood pressure in conscious unrestrained Sprague-Dawley rats without any change in normal diurnal rhythm. Show more