Baroreceptor-heart Reflex Sensitivity Research Articles

Effects of central Substance P on baroreflex regulation

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.

Cardiovascular Responses to Centrally Applied Sodium Chloride Solution

In conscious and anaesthetized rats the baroreceptor heart reflex (BHR) was checked before and after i.c.v. application of isotonic or hypertonic (0.6 M; 1.0 M) NaCl solution, artificial cerebrospinal fluid (aCSF) and 1.0 M mannitol solution. The BHR was tested by evaluating the alteration of the inter-beat interval (IBI) in response to an artificial BP rise or drop which had been evoked by i.v. bolus injection of either phenylephrine or sodium nitroprusside. The slope of the correlation function was taken to index the reflex sensitivity. In anaesthetized rats the mean sensitivity of the BHR was 0.6 ms/mm Hg (phenylephrine). l.c.v. administration of isotonic NaCl solution did not change BP, IBI or the BHR sensitivity, whilst i.c.v. infusion of hypertonic NaCl solution increased BP and shortened IBI. The BHR sensitivity was impaired only when 1.0 M NaCl solution was i.c.v. infused by 0.23 ms/mm Hg. In conscious rats the mean sensitivity of the BHR was 1.14 ms/mm Hg (phenylephrine) and 1.35 ms/mm Hg (sodium nitroprusside). In the conscious rats i.c.v. bolus injection of hypertonic NaCl solution increased BP as in anaesthetized rats, however, the IBI was prolonged, whilst 1.0 M mannitol solution and aCSF were without any influence on BP, IBI and BHR. l.c.v. administration of hypertonic NaCl solution reduced the BHR sensitivity by approximately 0.6 ms/mm Hg.