A Phase 4 interventional study of Phenylephrine Hydrochloride and Isoproterenol Hydrochloride in Vasoconstriction and Vasodilation, sponsored by University of Alberta. Recruiting at 1 site in Canada. Open to participants aged 18 Years to 40 Years, including healthy volunteers. Per ClinicalTrials.gov, last updated 2026-01-08.
Sponsored by University of Alberta · Phase 4, Interventional, and Basic science
The main purpose of this interventional study is to examine differences in resting blood pressure control between healthy males and females. The main questions it aims to answer are:
Participants will complete one study visit of approximately 3 hours where they will:
Blood pressure is in part regulated by activity of your sympathetic nervous system (also known as your "fight or flight" response). Sympathetic nerve activity affects the size of your blood vessels, which in turn will affect your blood pressure. This communication between sympathetic impulses and the resulting change in vascular resistance is termed "sympathetic neurovascular transduction". In other words, transduction represents the reactivity of the blood vessels in response to individual sympathetic bursts of activity.
Males and females regulate their blood pressure in different ways; for example, females tend to have lower blood pressure and sympathetic nerve activity than males. Females also appear to have less constriction of their blood vessels in response to stress. This may be due to differences in the receptors which are activated by the sympathetic nervous system. These receptors are called α and β-adrenergic receptors and are located on vascular smooth muscle cells. They respond to sympathetic neurotransmitters such as norepinephrine in opposite directions: α-adrenoreceptors cause vasoconstriction (and an increase in vascular resistance), and β-adrenoreceptors cause vasodilation (and a decrease in vascular resistance) in part through the endothelium-dependent nitric oxide pathway.
Current evidence suggests that β-adrenergic receptors are more sensitive in females and contribute to paradoxical vasodilation when α-adrenergic receptors are stimulated by norepinephrine from sympathetic bursts. It has also been suggested that estrogen interacts with adrenergic receptors, contributing to this sex difference. This study will contribute to the understanding of sex differences in cardiovascular physiology and may have implications for clinical cardiovascular conditions.
381 studies on the registry are indexed under Aneurysm; 78 are open to participants now.
This study's planned enrollment of 30 is below the median of 46 across 235 interventional studies indexed under Aneurysm.
Browse Aneurysm studies →University of Alberta is the lead sponsor of 823 studies on the registry; 169 are open to participants now.
Of its 5 completed or terminated interventional studies of FDA-regulated products, 3 (60%) have results posted.
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Go through the criteria one by one — yes, no or not sure — and take the list to your doctor or the study team. Kept in this browser only.
Exclusion Criteria:
Underlined terms in the criteria open these too. Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Periods have stopped for good: usually no period for 12 months in a row without another medical reason, sometimes confirmed by a blood test (FSH).
Weight in kilograms divided by height in metres squared. Example: 70 kg and 1.75 m gives 70 ÷ (1.75 × 1.75) ≈ 22.9.
What counts as overweight or obesity differs between countries (some use lower cut-offs), so go by the range the study states.
A reason a treatment, test or procedure should not be given to a particular person, such as an allergy, another illness or a medicine they take.
Postmenopausal
Periods have stopped for good: usually no period for 12 months in a row without another medical reason, sometimes confirmed by a blood test (FSH).
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
BMI (body mass index)
Weight in kilograms divided by height in metres squared. Example: 70 kg and 1.75 m gives 70 ÷ (1.75 × 1.75) ≈ 22.9.
What counts as overweight or obesity differs between countries (some use lower cut-offs), so go by the range the study states.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Contraindication
A reason a treatment, test or procedure should not be given to a particular person, such as an allergy, another illness or a medicine they take.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Normal saline will be infused through the brachial artery catheter at the same calculated rate as propranolol + phentolamine in the α+β-blockade condition to control for volumetric effects.
Drug: Phenylephrine Hydrochloride · Drug: Isoproterenol Hydrochloride · Drug: Norepinephrine Bitartrate
β-adrenoreceptors will be blocked locally in the forearm using propranolol. Normal saline will be co-infused at the calculated rate of phentolamine in the α+β-blockade condition to control for volumetric effects.
Drug: Norepinephrine Bitartrate · Drug: Propranolol Hydrochloride
α-adrenoreceptors will be blocked locally in the forearm using phentolamine. Propranolol will be co-infused to maintain β-blockade.
Drug: Phentolamine Mesylate · Drug: Phenylephrine Hydrochloride · Drug: Isoproterenol Hydrochloride · Drug: Propranolol Hydrochloride
Participants will receive three incremental doses via the brachial artery catheter to assess α1-adrenoreceptor mediated vasoconstriction.
Participants will receive four incremental doses via the brachial artery catheter to assess β-adrenoreceptor mediated vasodilation.
Participants will receive three incremental doses via the brachial artery catheter to assess nonspecific adrenoreceptor activation.
Propranolol will be continuously infused through the brachial artery catheter to induce β-adrenergic blockade locally in the forearm.
Phentolamine will be continuously infused through the brachial artery catheter to induce α-adrenergic blockade locally in the forearm.
Participants will receive one dose via the brachial artery catheter to evaluate the effectiveness of the α-adrenergic blockade.
Participants will receive one dose via the brachial artery catheter to evaluate the effectiveness of the β-adrenergic blockade.
Propranolol will be continuously co-infused with phentolamine to maintain the β-adrenergic blockade.
Forearm blood flow
Measured during resting baseline; changes during phenylephrine, isoproterenol, and norepinephrine infusion to determine agonist sensitivity.
Time frame: 10 minutes per condition + 2 minutes per agonist dose = 60 minutes
Forearm vascular resistance
Measured during resting baseline; changes during phenylephrine, isoproterenol, and norepinephrine infusion to determine agonist sensitivity.
Time frame: 10 minutes per condition + 2 minutes per agonist dose = 60 minutes
Forearm vascular conductance
Measured during resting baseline; changes during phenylephrine, isoproterenol, and norepinephrine infusion to determine agonist sensitivity.
Time frame: 10 minutes per condition + 2 minutes per agonist dose = 60 minutes
Arterial blood pressure
Measured during resting baseline; changes during phenylephrine, isoproterenol, and norepinephrine infusion to determine agonist sensitivity.
Time frame: 10 minutes per condition + 2 minutes per agonist dose = 60 minutes
Muscle sympathetic nerve activity
Resting baseline
Time frame: 10 minutes per condition = 30 minutes
Circulating sex hormone concentrations
Blood samples
Time frame: 2 minutes
Circulating sympathetic neurotransmitter concentrations
Blood sample
Time frame: 2 minutes
Arterial-venous blood gas concentrations
Blood sample during each condition
Time frame: 2 minutes per sample = 6 minutes
Started Oct 2023 (actual). Primary completion is estimated for Dec 2027, 49 months after the start.
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Studies of the drugs tested here: Phenylephrine · Isoproterenol · Norepinephrine · Propranolol · Phentolamine