Cardiovascular responses to centrally applied sodium chloride solution

Area of Science:

• Cardiovascular physiology
• Neuroscience
• Renal and electrolyte balance

Background:

• The baroreceptor heart reflex (BHR) is crucial for maintaining blood pressure homeostasis.
• Cerebrospinal fluid (CSF) composition can influence central cardiovascular regulation.
• Understanding how CSF osmolarity affects BHR is vital for cardiovascular health.

Purpose of the Study:

• To investigate the impact of intracerebroventricular (i.c.v.) administration of hypertonic NaCl solutions on BHR sensitivity in conscious and anesthetized rats.
• To compare the effects of different i.c.v. solutions, including isotonic NaCl, hypertonic NaCl, artificial cerebrospinal fluid (aCSF), and mannitol, on BHR.

Main Methods:

• The BHR was assessed in conscious and anesthetized rats by measuring the alteration in inter-beat interval (IBI) in response to induced blood pressure (BP) changes via phenylephrine or sodium nitroprusside injections.
• Reflex sensitivity was quantified using the slope of the correlation function between BP and IBI.
• Various solutions (isotonic NaCl, 0.6 M and 1.0 M NaCl, aCSF, 1.0 M mannitol) were administered i.c.v.

Main Results:

• In anesthetized rats, i.c.v. 1.0 M NaCl impaired BHR sensitivity by 0.23 ms/mm Hg.
• In conscious rats, i.c.v. hypertonic NaCl increased BP and prolonged IBI, reducing BHR sensitivity by approximately 0.6 ms/mm Hg.
• Isotonic NaCl, aCSF, and mannitol had no significant effect on BHR in either conscious or anesthetized rats.

Conclusions:

• Intracerebroventricular administration of hypertonic NaCl solution significantly impairs baroreceptor heart reflex sensitivity in rats.
• The effect of hypertonic NaCl on BHR is more pronounced in conscious rats compared to anesthetized rats.
• These findings highlight the sensitivity of central cardiovascular regulatory mechanisms to changes in cerebrospinal fluid osmolarity.