Histamines and Central Hemodynamics

The Role of Histamines on Central Hemodynamics

When we exercise, more blood flow goes to our muscles, challenging our blood vessels. Following exercise, blood flow remains elevated and seems to be the reason for many of the positive cardiovascular benefits that occur with exercise. When the actions of histamine, a molecule primarily known for its role in allergies, are blocked, there is an attenuated blood flow response following exercise. However, this effect has never been studied in the blood vessels that supply our lungs. The purpose of this study is to examine the effects of histamines on pulmonary hemodynamics following exercise.

Study Overview

• Status: Recruiting
• Conditions: Exercise; Histamine
• Intervention / Treatment: Other: Placebo; Drug: Diphenhydramine hydrochloride; Other: Exercise Bout

• Study Type: Interventional
• Enrollment (Estimated): 20
• Phase: Not Applicable

Contacts and Locations

• Study Contact: Name: Neil Eves, PhD; Phone Number: (250) 807-9676; Email: neil.eves@ubc.ca
• Study Contact Backup: Name: Cassidy Williams, BHK; Phone Number: (250) 807-9676; Email: cwilli08@student.ubc.ca

Study Locations

• Canada
  • British Columbia
    • Kelowna, British Columbia, Canada, V1V2L2
      • Recruiting
      • University of British Columbia
      • Contact: Neil Eves, PhD; Phone Number: (250) 807-9676; Email: neil.eves@ubc.ca

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult
• Accepts Healthy Volunteers: Yes

Description

Inclusion Criteria:

1. Age: 19 - 39.
2. Willing to visit the lab on 3 separate occasions.

Exclusion Criteria:

1. Previously diagnosed heart condition,
2. Previously diagnosed lung condition (including asthma),
3. Previously diagnosed metabolic condition,
4. Currently smokers (cigarettes, electronic cigarettes, cannabis) or who have smoked within the last 3 months,
5. Resting blood pressure >140/90 mmHg,
6. Unable to obtain appropriate quality ultrasound images of the heart.,
7. Individuals without tricuspid regurgitation at rest to allow assessment of the primary outcome,
8. Pregnant or trying to become pregnant,
9. Breastfeeding,
10. Chronically take antihistamines (i.e. daily),
11. History of adverse reactions to antihistamines,
12. Never taken antihistamines previously,
13. Currently taking any medications (including oral contraceptives).

Study Plan

How is the study designed?

Design Details

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

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Blockade + Exercise Bout; Participants will ingest histamine H1 receptor blockade before performing an exercise bout.	Drug: Diphenhydramine hydrochloride; H1 receptor antagonist: 50mg Diphenhydramine Hydrochloride; Other: Exercise Bout; Participants will complete a total of three 5-minute high intensity exercise intervals, interspersed with 5-minute lower intensity exercise bouts (4 total), for a total of 35 minutes.
Placebo Comparator: Placebo + Exercise Bout; Participants will ingest a placebo before an exercise bout.	Other: Placebo; Placebo; Other: Exercise Bout; Participants will complete a total of three 5-minute high intensity exercise intervals, interspersed with 5-minute lower intensity exercise bouts (4 total), for a total of 35 minutes.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Systolic pulmonary artery pressure	The difference in systolic pulmonary artery pressure (measured as tricuspid regurgitation velocity using echocardiography) between the H1 blockade condition and the placebo condition.	Pre-exercise and 10, 20, and 30-minutes post-exercise.

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Tricuspid annular plane systolic displacement	The difference in tricuspid annular plane systolic displacement between the H1 receptor blockade condition and the placebo condition.	Pre-exercise and 0, 10, 20, 30, 45, and 60 minutes post-exercise.
Right ventricular stroke volume	The difference in right ventricular stroke volume (measured using pulsed wave velocity of the right ventricular outflow tract velocity time integral) between the H1 receptor blockade condition and the placebo condition.	Pre-exercise and 0, 10, 20, 30, 45, and 60-minutes post-exercise.
Femoral artery blood flow	The difference in femoral artery blood flow between the H1 receptor blockade condition and the placebo condition.	Pre-exercise and 0, 10, 20, 30, 45, and 60-minutes post-exercise.
Mean arterial systemic pressure	The difference in mean arterial systemic pressure between the H1 receptor blockade condition and the placebo condition.	Pre-exercise and 0, 10, 20, 30, 45, and 60-minutes post-exercise.

Collaborators and Investigators

• Sponsor: University of British Columbia

Study record dates

Study Major Dates

• Study Start (Estimated): December 1, 2025
• Primary Completion (Estimated): August 1, 2026
• Study Completion (Estimated): August 1, 2026

Study Registration Dates

• First Submitted: December 3, 2025
• First Submitted That Met QC Criteria: December 3, 2025
• First Posted (Estimated): December 16, 2025

Study Record Updates

• Last Update Posted (Actual): December 23, 2025
• Last Update Submitted That Met QC Criteria: December 16, 2025
• Last Verified: December 1, 2025

More Information

Terms related to this study

• Keywords: exercise; pulmonary function; histamine; pulmonary blood flow; femoral blood flow
• Additional Relevant MeSH Terms: Behavior; Motor Activity; Organic Chemicals; Hydrocarbons; Hydrocarbons, Cyclic; Hydrocarbons, Aromatic; Amines; Benzene Derivatives; Ethylamines; Benzhydryl Compounds; Diphenhydramine
• Other Study ID Numbers: H25-01909

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