Arterial blood pressure response in conscious rabbits to administration of C-terminal fragment of substance P into the cerebral ventricles, intravenously and intragastrically.

The blood pressure was measured in the common carotid artery in a cutaneous bridge in conscious rabbits. The synthetic hexapeptide SP6-11 of C-terminal fragment of Arg-Pro-Lys-Pro-Gln-Gln-Phe-Phe-Gly-Leu-Met-NH2 (Substance P) was administered to animals accustomed to the experimental environment in three separate trials: into the cerebral ventricles, intravenously and intragastrically. Introduction of 2 nmol/kg hexapeptide into the cerebral ventricles via a chronically implanted cannula in the lateral ventricle caused an increase in the blood pressure, reaching a peak 10 min after administration. This maximum increase averaged 34.5 mmHg. Intravenous injection of 2 nmol/kg caused after 1 min a rapid fall in the blood pressure, the decrease averaging 42.7 mmHg at this time. Administration of 2 mg/kg into the stomach caused a slight decrease in blood pressure. Although the decrease was only slight it was statistically significant after 10 min.