Effects of central Substance P on baroreflex regulation

Abstract

The effects of intracerebroventricularly (i.c.v.) administered Substance P (100 pg, 1 μg, 10μg) on mean blood pressure (MBP), inter-beat interval (IBI) and the baroreceptor heart reflex (BHR) were studied in conscious Wistar rats. The BHR was induced by intravenous injection of both phenylephrine (1 μg) and sodium nitroprusside (5 μg) before and after SP administration (3 and 15 min). The dose of 100 pg SP was without effect on the resting values of both MBP and IBI but enhanced the BHR sensitivity by about + 0.5 ms/mm Hg in the phenylephrine test 3 min after i.c.v. SP. 1 μg and 10 μg SP caused a long-lasting dose dependent increase in MBP and changed the IBI. In contrast to the results obtained with 100 pg, the BHR sensitivity was impaired-1μg SP:−0.2 ms/mm Hg (phenylephrine) and −0.45 ms/mm Hg (nitroprusside), 10 μg SP: −0.35 ms/mm Hg (phenylephrine). These changes in BHR sensitivity were only recognised 3 min, but not 15 min, after i.c.v. treatment even though changes in the resting values of MBP and IBI were still present at 15 min. These data suggest that SP through the cerebrospinal fluid may participate in central cardiovascular control and, moreover, it may influence the baroreflex regulation.