Central cardiovascular action of urotensin II in conscious rats

Objective: To examine the central cardiovascular action of urotensin II in conscious rats. Methods: Intracerebroventricular (ICV) injections of urotensin II (1 and 10 nmol) were carried out in conscious Wistar rats. The effects of intravenous (i.v.) urotensin II (10 nmol) were also determined. Results: The ICV injection of urotensin II at a dose of I nmol did not alter the arterial pressure or heart rate significantly, while 10 nmol urotensin II increased the arterial pressure and heart rate. The mean arterial pressure at 5 min of ICV urotensin II was 121 ± 4 mmHg, which was significantly higher than that obtained by ICV injection of artificial cerebrospinal fluid (107 ± 3 mmHg, P < 0.05). In addition, significant increases in heart rate were observed 5-15 min after ICV urotensin II. Pretreatment with pentolinium (5 mg/kg, i.v.) significantly attenuated the increases in mean arterial pressure (20 ± 3 versus 8 ± 2 mmHg, P < 0.01) and heart rate (78 ± 18 versus 7 ± 5 beats/min, P < 0.05) induced by ICV urotensin II. On the other hand, i.v. injection of urotensin II (10 nmol) elicited a depressor response associated with tachycardia; mean arterial pressure 5 min after injection was significantly lower in the urotensin II-injected rats (89 ± 5 mmHg) than in the control rats (102 ± 2 mmHg, P < 0.05), and the heart rate was significantly higher in the former (402 ± 11 versus 360 ± 9 beats/min, respectively, P < 0.05). Conclusions: Central urotensin II produces pressor and tachycardic responses through sympathetic activation, while peripheral urotensin II exerts a vasodilation-mediated depressor response in conscious rats.