Role of endothelin in noradrenaline-induced hypertension in rats.
OBJECTIVE
To investigate the role of endothelin in noradrenaline-induced hypertension in rats.


METHODS
The dose-response relationship of chronic noradrenaline infusion on arterial pressure was characterized to identify a dose that would produce sustained hypertension, and the effect of combined endothelin ETA and ETB receptor blockade (TAK-044) on the response to this dose was then examined.


RESULTS
Noradrenaline (or vehicle) was infused intravenously at 1 (subpressor acutely), 24 or 48 microg/kg per h (acute pressor response of 9 +/- 1 and 11 +/- 1 mmHg, respectively) for a 14-day infusion, and blood pressure was measured by radiotelemetry. Noradrenaline infusion at 1 microg/kg per h did not produce a 'slow pressor' rise in blood pressure. During noradrenaline infusions at 24 and 48 microg/kg per h, mean arterial pressure peaked initially on days 2-3 (+10 +/- 1 and 14 +/- 2 mmHg, respectively; P < 0.01), fell towards basal levels after day 3, and then began to rise again at days 5-6 only with 48 microg/kg per h, being 10 +/- 1 mmHg above control levels at days 13-14 (P < 0.05). TAK-044 treatment did not alter the magnitude of the initial (13 +/- 1 mmHg) or eventual (12 +/- 2 mmHg) rise in blood pressure achieved in response to 14 days' infusion of noradrenaline at 48 microg/kg per h, but abolished the transient fall.


CONCLUSIONS
Chronic noradrenaline infusion at acutely pressor doses leads either to a transient blood pressure elevation at a moderate dose, or to a triphasic but sustained hypertension at a higher dose, with a temporary escape from the hypertension apparently mediated by endothelin.
Boesen
Erika I
EI
Department of Physiology, Monash University, Victoria 3800, Australia.
Anderson
Warwick P
WP
Kett
Michelle M
MM
D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D016232:Endothelins / Q000502:physiology*; D006339:Heart Rate / Q000187:drug effects; D006973:Hypertension / Q000139:chemically induced*; D008297:Male; D009638:Norepinephrine / Q000494:pharmacology*; D010456:Peptides, Cyclic / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D044023:Receptor, Endothelin B / Q000502:physiology
D016232:Endothelins; D010456:Peptides, Cyclic; D044023:Receptor, Endothelin B; C088196:TAK 044; D009638:Norepinephrine