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

Objectives Secondary hypertension is often characterized by loss of diurnal blood pressure variability. This study examined circadian (24 h) blood pre ssure variability in adrenocorticotrophin (ACTH)-induced hypertension in th e Sprague-Dawley rat. Methods Male Sprague-Dawley rats were randomly allocated to sham (0.9% sali ne, s.c.), n = (9), ACTH (0.5 mug/kg per day, s.c., n = 8) or ACTH (100 mug /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 i n unrestrained animals over 3 control days (C1-C3) and 10 treatment days (T 1-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 mug/kg per day increased SBP from 124 +/- 2 pooled control (PC) to 134 +/- 2 mmHg (T1 0), 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 bod y 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 mug/kg per day. SBP, MAP, DBP and heart rate were consistently hig her for ACTH 100 mug/kg per day and sham-treated animals during the dark cy cle (1800 h to 0600 h) than the light cycle (0600 h to 1800 h). Conclusions ACTH 100 mug/kg per day raises blood pressure in conscious unre strained Sprague-Dawley rats without any change in normal diurnal rhythm.