Haemodynamic mechanisms of corticotropin (ACTH)-induced hypertension in the rat.
OBJECTIVE
To investigate the roles of cardiac output and systemic and regional resistances in corticotropin (ACTH)-induced hypertension in the rat


METHODS
This study consisted of three series of experiments with eight groups of male Sprague-Dawley rats (n = 132). Series 1 comprised groups 1-4, where group 1 = sham (0.9% NaCl, subcutaneous (s.c.) injection); group 2 = ACTH (0.5 mg/kg per day, s.c.); group 3 = atenolol + sham; group 4 = atenolol + ACTH treatments. Series 2 comprised groups 5 and 6, where group 5 = minoxidil + sham and group 6 = minoxidil + ACTH treatments. Series 3 comprised groups 7 and 8, where group 7 = ramipril + sham and group 8 = ramipril + ACTH treatments. Systolic blood pressure, water and food intakes, urine volume, and body weight were measured every second day. After 10 days of treatment, mean arterial blood pressure was measured by intra-arterial cannulation, and cardiac output (CO), and renal, mesenteric and hindquarter blood flows (RBF, MBF and HBF) determined using transonic small animal flowmeters.


RESULTS
ACTH treatment increased blood pressure (P < 0.001) with a rise in CO (P < 0.01) and renal vascular resistance (RVR, P < 0.05), but did not affect total peripheral resistance (TPR). Atenolol blocked the rise in CO without affecting the rise in blood pressure produced by ACTH treatment Minoxidil lowered TPR, but did not prevent the rise in blood pressure or renal vascular resistance. Ramipril blunted the rise in RVR and blood pressure without significantly affecting TPR.


CONCLUSIONS
Neither preventing rise in CO nor lowering TPR altered the ACTH-induced rise in blood pressure in the rat However, both the hypertension and rise in RVR were prevented by ramipril. These data suggest that increase in RVR may play a role in the pathogenesis of ACTH-induced hypertension in the rat.
Wen
C
C
Department of Medicine, The St George Hospital, University of New South Wales, Sydney, Australia.
Fraser
T
T
Li
M
M
Turner
S W
SW
Whitworth
J A
JA
D000324:Adrenocorticotropic Hormone / Q000009:adverse effects*; D000818:Animals; D000959:Antihypertensive Agents / Q000494:pharmacology; D001262:Atenolol / Q000494:pharmacology; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology*; D002302:Cardiac Output / Q000187:drug effects / Q000502:physiology*; D004734:Energy Metabolism / Q000187:drug effects; D006977:Hypertension, Renal / Q000139:chemically induced* / Q000188:drug therapy / Q000503:physiopathology*; D008297:Male; D009929:Organ Size; D017257:Ramipril / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012079:Renal Circulation / Q000187:drug effects / Q000502:physiology; D013152:Splanchnic Circulation / Q000187:drug effects / Q000502:physiology; D014655:Vascular Resistance / Q000187:drug effects / Q000502:physiology
D000959:Antihypertensive Agents; D001262:Atenolol; D000324:Adrenocorticotropic Hormone; D017257:Ramipril