Central Sodium Sensing: Implications for Blood Pressure Regulation

The ability of the brain to sense changing sodium levels in the blood is critical in mediating the neurohumoral responses to hypernatremia, however, the mechanisms underlying sodium sensing in humans is poorly understood. The purpose of this study is to identify key sodium-sensing regions of the human brain in older adults and determine if the Na-K-2Cl co-transporter mediates the neurohumoral response to acute hypernatremia. Completion of this project will increase our understanding of blood pressure regulation, which has major public health implications.

Study Overview

• Status: Recruiting
• Conditions: Salt Sensitivity of Blood Pressure
• Intervention / Treatment: Other: Dietary Intervention; Other: Hypertonic Saline

Detailed Description

The prevalence of hypertension is very high in older adults, and a major factor in hypertension is salt sensitivity of blood pressure (BP) and elevated sympathetic nerve activity (SNA). However, we know very little about how the human brain 'senses' sodium, and what molecular mechanisms are involved. Rodent studies have identified specialized sodium chloride (NaCl)-sensing neurons in the circumventricular organs (CVOs), which mediate NaCl-induced changes in SNA, arginine vasopressin (AVP), and BP. Recent data suggest the Na-K- 2Cl co-transporter (NKCC2) is not kidney specific but is also expressed in brain regions that regulate whole body NaCl and water homeostasis. In addition, NKCC2 is accessible by drugs in the circulation since the CVOs lack a complete blood brain barrier. The objective of this R21 is to identify key NaCl-sensing regions of the brain in older adults and determine if NKCC2 mediates the neurohumoral response to acute hypernatremia. We seek to translate the prior rodent findings to humans by assessing neuronal activation (using blood oxygen level dependent functional magnetic resonance imaging, BOLD fMRI) as well as thirst, AVP, SNA and BP during an acute hypernatremic stimulus, with and without an NKCC2 antagonist (furosemide). This will enable us to assess the role of NKCC2 in NaCl sensing. The overall hypothesis is that acute hypernatremia will elicit detectable changes in the BOLD fMRI signal and increase thirst, AVP, SNA, and BP largely through NKCC2 in healthy older adults. Accordingly, the first specific aim is to identify the areas of the human brain that respond to acute hypernatremia and determine the role of NKCC2 in central NaCl- sensing. Acute hypernatremia will be induced with a 30-minute infusion of 3% NaCl delivered intravenously. Brain activity during the hypertonic saline infusion will be measured in regions such as the organum vasculosum laminae terminalis, subfornical organ, anterior cingulate cortex, hypothalamus, and insular cortex. The second specific aim is to determine the effect of acute hypernatremia on thirst, AVP, SNA, and BP, and determine the role of NKCC2 in mediating these responses. Salt sensitivity of BP will be individually assessed and comparisons will be made between those with a salt resistant and salt sensitive phenotype; we anticipate that acute hypernatremia will elicit changes in the BOLD fMRI signal and SNA & AVP in all subjects, but the responses will be greater in those who are classified as salt sensitive. This would represent the first trial in healthy human subjects to identify a putative brain NaCl-sensing co-transporter, and we think the scope and innovative approaches are ideal for the R21 funding mechanism. Older adults are prone to hypertension, so it is critically important to understand how normotensive older adults centrally sense sodium, to provide a needed foundation for exploring the mechanistic underpinning of salt sensitive hypertension.

• Study Type: Interventional
• Enrollment (Estimated): 40
• Phase: Not Applicable

Contacts and Locations

• Study Contact: Name: William B Farquhar, PhD; Phone Number: 302-831-6178; Email: wbf@udel.edu
• Study Contact Backup: Name: Joseph M Stock, PhD; Phone Number: 610-331-6553; Email: jmstock@udel.edu

Study Locations

• United States
  • Delaware
    • Newark, Delaware, United States, 19713
      • Recruiting
      • William B Farquhar
      • Contact: William B Farquhar, PhD; Phone Number: 302-831-6178; Email: wbf@udel.edu
      • Contact: Joseph M Stock, PhD; Phone Number: 610-331-6553; Email: jmstock@udel.edu

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: 18 years to 45 years (Adult)
• Accepts Healthy Volunteers: Yes

Description

Inclusion Criteria:

• Age: 18 - 45 years
• Blood pressure: >100/60 mmHg and <130/80 mmHg
• BMI: 18.5 kg/m2 - 30 kg/m2
• Serum potassium: 3.5 mmol/L - 5.5 mmol/L

Exclusion Criteria:

• Age: < 18 years or > 45 years
• Blood pressure: < 100/60 mmHg or > 130/80 mmHg
• BMI: < 18.5 kg/m2 or > 30 kg/m2
• Serum potassium: < 3.5 mmol/L or > 5.5 mmol/L
• Abnormal ECG
• History of - cardiovascular, cancer, metabolic, respiratory, renal disease
• Hormone replacement therapy
• Current tobacco or nicotine use
• Pregnant or nursing mothers
• Major brain injury (concussions do not count)
• Clinically diagnosed psychiatric or neurological disorder
• Clinically diagnosed anxiety or depression
• Psychiatric, neurological, anxiety or depression medications
• Hypertension medications
• Sulfonamide drug allergy

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Basic Science
• Allocation: Randomized
• Interventional Model: Crossover Assignment
• Masking: Double

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Salt Sensitivity Assessment; 1 week high salt diet and 1 week low salt diet	Other: Dietary Intervention; Subjects will consume a low salt diet for 1 week and a high salt diet for 1 week to determine sodium sensitivity
Experimental: Functional Magnetic Resonance Imaging; Hypertonic saline infusion perturbation with and without NKCC2 antagonism (furosemide) to examine sodium sensing mechanisms	Other: Hypertonic Saline; Subjects will undergo MRI with a hypertonic saline infusion with and without NKCC2 antagonism (furosemide)

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
fMRI to assess SFO-OLVT functional connectivity (z-score)	Functional connectivity between sodium sensing regions the brain (subfornical organ and organum vasculosum of the lamina terminalis)	1 hour
Plasma arginine vasopressin concentration (pg/mL)	hormone circulating in the blood	1 hour

Collaborators and Investigators

• Sponsor: University of Delaware

Study record dates

Study Major Dates

• Study Start (Actual): June 1, 2022
• Primary Completion (Estimated): January 31, 2025
• Study Completion (Estimated): January 31, 2025

Study Registration Dates

• First Submitted: July 27, 2022
• First Submitted That Met QC Criteria: July 27, 2022
• First Posted (Actual): July 29, 2022

Study Record Updates

• Last Update Posted (Estimated): December 14, 2023
• Last Update Submitted That Met QC Criteria: December 7, 2023
• Last Verified: December 1, 2023

More Information

Terms related to this study

• Additional Relevant MeSH Terms: Immune System Diseases; Hypersensitivity
• Other Study ID Numbers: 1808532

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: UNDECIDED

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No
• product manufactured in and exported from the U.S.: Yes