Human Cerebral Blood Flow Regulation (Gas Challenge)

Human Cerebral Blood Flow Regulation: Sex, Mechanism, and Stress Differences

To determine cerebrovascular control mechanisms in humans and provide mechanistic knowledge to offer new sex-specific therapeutic options for cerebrovascular diseases. The current objective is to determine how sex and sex hormones influence CBF control in healthy young adults without confounds of age or disease. The central hypothesis is men exhibit reduced cerebral vasodilator function due in part to differences in COX signaling compared to women. Comprehensive CBF data from multi-modal MRI indicate the magnitude of sex differences-as well as the vasodilator mechanisms-are regionally distinct. Research confounding variables like aging and disease will be mitigated by comparing younger adults (18-40 years old).

Study Overview

• Status: Completed
• Conditions: Cerebral Arterial Diseases
• Intervention / Treatment: Drug: Indomethacin 25 MG/50 MG; Drug: Placebo - Lactose

Detailed Description

Cerebrovascular disease is the third leading killer in the U.S. and contributes to decreased quality of life and increased long-term care spending. The risk of cerebrovascular disease is inversely associated with resting cerebral blood flow (CBF). Men exhibit a lower resting CBF and have twice the risk of cerebrovascular disease when compared to premenopausal women. The ability of cerebral vessels to respond to challenges is also inversely related to disease risk, and may be useful in identifying at-risk patients pre-clinically. However, these studies are often confounded by aging and/or comorbidities, and the associations provide little insight into physiologic mechanisms responsible for sexually dimorphic cerebrovascular disease risk. Conversely, animal studies use supraphysiologic levels of hormone treatment in primarily young animals, which limits the translational relevance of animal CBF mechanisms. While there is general agreement that estrogen is protective in healthy adults, the basic impact of sex, and physiologic fluctuations in sex hormones, on mechanisms of CBF control remains unclear.

The overall goal of this research program is to investigate the mechanisms which actively control cerebral blood flow (CBF) in humans, particularly how men and women differ in control mechanisms on a regional basis throughout the brain circulation. The investigators propose to study CBF control mechanisms in healthy younger (18-40 yrs) adult men and women. The overall hypothesis is that female sex and sex hormones contribute to larger stress-induced increases in CBF, due to greater prostanoid (COX) and nitric oxide (NOS) dilation.

A key technological innovation of this proposal derives from multi-mode, high-resolution, flow sensitive MRI to quantify CBF at macrovascular and microvascular levels, at rest, and in response to environmental challenges (stress test for the brain). Additionally, the research design allows for quantification of sex differences in two vascular control mechanisms across all brain regions. Preliminary data demonstrate: hypoxic cerebral vasodilation is 60-100% higher in women compared to men, COX inhibition reduces dilation in women but not men, NOS inhibition reduces vasodilation more in women. Those concepts will be tested in Aims 1-2 of the grant in this current proposal, covered in Phase 1 using technical innovative MRI and pharmacologic tools to test potential sex specific mechanisms of CBF control. The conceptual innovation is planned in Aim 3 of the grant (or Phase 2). Participants must complete Phase 1 studies to continue to Phase 2. Study procedures in Phase 1 and 2 are identical, but the investigators conduct them twice: once in the context of sex hormone suppression, and a second time during a single hormone replacement (during suppression), to study the independent impact of testosterone (men) and estrogen (women) on CBF control mechanisms.

Substantial preliminary findings support these hypotheses, and integrated physiologic, pharmacologic, and MRI approaches are available to test them. This state-of-the-art approach will yield previously unattainable insight into not only maintaining basal CBF, but actively controlling it during physiologic demands for increased flow. These novel, high resolution, regionally-specific, sex-specific, and mechanism-specific findings will serve as a knowledge platform, for designing sex-specific CBF studies in high risk disease populations (e.g. diabetes, hypertension, Alzheimer's) which exhibit strong sex-specific etiology and important vascular contributions.

Three Specific Aims will be addressed in this study:

Aim 1: Test the hypothesis that healthy males exhibit reduced cerebral vasodilation compared to healthy females despite exhibiting similar vasodilation to hypercapnia.

Aim 1A: Vasodilation to hypoxia will be markedly lower in males. Aim 1B: Vasodilation to hypercapnia will be lower in males.

Aim 2: Test the hypothesis that acute inhibition of COX will explain sex differences in hypoxia-mediated cerebral vasodilation.

Aim 2A: COX-signaling mediating hypoxic vasodilation is greater in females. Aim 2B: COX-signaling mediating hypercapnic vasodilation is greater in females.

Updated Protocol (CP011):

Fifty-four (54) otherwise healthy adults between 18-40 years of age inclusive composed of 27 males and 27 females. These 54 participants will complete both Aims 1 and 2 (both Aims completed in 2 study visits).

Updated Protocol (CP017):

Fifty-seven (57) otherwise healthy adults between 18-40 years of age inclusive composed of 30 males and 27 females. These 57 participants will complete both Aims 1 and 2 (both Aims completed in 2 study visits). The number of male participants was increased by 3 to meet the recruitment requirements of the Phase 2 (2023-0548) study. Completion of Phase 1 (2020-0336) is required to participate in Phase 2. No females were added as the recruitment for Phase 2 females will fall within the 27 females who will have completed Phase 1 (2020-0336).

• Study Type: Interventional
• Enrollment (Actual): 42
• Phase: Early Phase 1

Contacts and Locations

Study Locations

• United States
  • Wisconsin
    • Madison, Wisconsin, United States, 53706
      • University of Wisconsin, Madison

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: 18 years to 40 years (Adult)
• Accepts Healthy Volunteers: Yes

Description

Inclusion Criteria:

• All participants will be healthy adults between 18-40 years old, matched for age and aerobic fitness
• Participants will be non-hypertensive (<125/80mm Hg)
• Participants will be non-obese (BMI 19-25 kg/m2)
• Participants will have normal blood glucose (<100 g/dl)
• Participants will have normal lipids (LDL cholesterol <130 mg/dl, triglycerides <150 mg/dl)
• Women must have a natural regular menstrual cycle

Exclusion Criteria:

• Participants with a history of:

  • peripheral vascular disease
  • hepatic disease
  • renal disease
  • hematologic disease
  • stroke
  • obesity
  • prediabetes
  • diabetes
  • sleep apnea
• Participants with current BP>130/85 mmHg
• Regular smokers
• Taking cardiovascular medications
• Women who take hormonal birth control
• Women who are pregnant or have polycystic ovarian syndrome [Hormonal birth control will not be allowed in women]
• Contradictions to MRI
• Lactose intolerance

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Basic Science
• Allocation: Non-Randomized
• Interventional Model: Parallel Assignment
• Masking: None (Open Label)

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Male; Males visit MRI twice. Once for indomethacin visit (hypoxia + hypercapnia), and once for placebo visit (hypoxia + hypercapnia). These 2 MRI visits are conducted in a double-blind placebo controlled design. CBF measured via MRI sequences, and hemodynamics monitored for safety/research.	Drug: Indomethacin 25 MG/50 MG; Indomethacin is a nonsteroidal anti-inflammatory drug commonly used to reduce fever, pain, stiffness, and swelling from inflammation. It prevents the production of prostaglandins, endogenous signaling molecules known to cause symptoms from inflammation. Indomethacin is used to test COX as a potential mechanism explaining sex differences in CBF control. Indomethacin usage is IND exempt.; Drug: Placebo - Lactose; Participants will be screened for lactose intolerance. Total dosing will be calculated to match the mg needed for the indomethacin study visit. Placebo usage is IND exempt.
Experimental: Female; Females visit MRI twice. Once for indomethacin visit (hypoxia + hypercapnia), and once for placebo visit (hypoxia + hypercapnia). These 2 MRI visits are conducted in a double-blind placebo controlled design. CBF measured via MRI sequences, and hemodynamics monitored for safety/research.	Drug: Indomethacin 25 MG/50 MG; Indomethacin is a nonsteroidal anti-inflammatory drug commonly used to reduce fever, pain, stiffness, and swelling from inflammation. It prevents the production of prostaglandins, endogenous signaling molecules known to cause symptoms from inflammation. Indomethacin is used to test COX as a potential mechanism explaining sex differences in CBF control. Indomethacin usage is IND exempt.; Drug: Placebo - Lactose; Participants will be screened for lactose intolerance. Total dosing will be calculated to match the mg needed for the indomethacin study visit. Placebo usage is IND exempt.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Cerebrovascular Conductance (CVC) in Response to Hypoxia, Male vs Female	CVC is the ratio between Cerebral Blood Flow (CBF) and blood pressure (BP). Change in CVC in response to hypoxia between male and female groups, where baseline CVC is subtracted from hypoxia CVC. Hypoxia typically lasts about 20 minutes. The hypothesis is that women will exhibit 50-60% more vasodilation in response to hypoxia [Aim 1].	up to 75 minutes for entire visit, but hypoxia lasts about 20 minutes
CVC in Response to Hypercapnia, Male vs Female	CVC is the ratio between Cerebral Blood Flow (CBF) and blood pressure (BP). Change in CVC in response to hypercapnia between male and female groups, where CBF is normalized for BP. Baseline CVC will be subtracted from hypercapnia CVC. Hypercapnia typically lasts about 10-15 minutes.The hypothesis is that hypercapnic vasodilation will be similar between groups [Aim 1B].	up to 75 minutes for entire visit, but hypercapnia lasts about 10-15 minutes

Collaborators and Investigators

• Sponsor: University of Wisconsin, Madison
• Collaborators: National Heart, Lung, and Blood Institute (NHLBI)
• Investigators: Principal Investigator: William Schrage, PhD, University of Wisconsin, Madison

Publications and helpful links

Helpful Links

• HYPEROXIA Responses and ROS
• Brain Blood Flow Responses to Stress: Sex Differences

Study record dates

Study Major Dates

• Study Start (Actual): April 12, 2021
• Primary Completion (Actual): March 31, 2025
• Study Completion (Actual): May 31, 2025

Study Registration Dates

• First Submitted: February 7, 2020
• First Submitted That Met QC Criteria: February 7, 2020
• First Posted (Actual): February 11, 2020

Study Record Updates

• Last Update Posted (Actual): June 12, 2026
• Last Update Submitted That Met QC Criteria: May 18, 2026
• Last Verified: May 1, 2026

More Information

Terms related to this study

• Additional Relevant MeSH Terms: Cerebrovascular Disorders; Brain Diseases; Central Nervous System Diseases; Nervous System Diseases; Vascular Diseases; Cardiovascular Diseases; Intracranial Arterial Diseases; Cerebral Arterial Diseases; Heterocyclic Compounds; Heterocyclic Compounds, 2-Ring; Heterocyclic Compounds, Fused-Ring; Indoles; Indomethacin
• Other Study ID Numbers: 2020-0336; A176000 (Other Identifier: UW Madison); EDUC/KINESIOLOGY/KINESIOLOG (Other Identifier: University of Wisconsin, Madison); 1R01HL150361-01 (U.S. NIH Grant/Contract); 21-TRISH PD21-0012 (Other Grant/Funding Number: NASA, HEADQUARTERS (HQ)); Protocol Version 1, 06/05/2024 (Other Identifier: UW Madison)

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO

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.: No