A Phase 1 interventional study of Phentolamine and Saline in Insulin Resistance, Healthy and Obesity, sponsored by Vanderbilt University Medical Center. Active, not recruiting at 1 site in United States. Open to participants aged 18 Years to 60 Years, including healthy volunteers. Per ClinicalTrials.gov, last updated 2026-03-02.
Sponsored by Vanderbilt University Medical Center · Phase 1, Interventional, and Basic science
Among 12 studies in Insulin Resistance by Vanderbilt University Medical Center — 2 open to participants now, 3 under way, none of them phase 3. Insulin Resistance · Vanderbilt University Medical Center.
Among the 12 studies in Insulin Resistance by Vanderbilt University Medical Center, this one is the 3rd largest by planned enrollment of the 11 interventional ones that give a count, is one of 4 that started in 2017, is one of 7 in phase 1, and was the 8th registered.
2,969 studies on the registry are indexed under Insulin Resistance; 338 are open to participants now.
This study's planned enrollment of 36 is close to the median of 40 across 2,369 interventional studies indexed under Insulin Resistance.
Browse Insulin Resistance studies →2 of the 12 studies in Insulin Resistance by Vanderbilt University Medical Center are open now, in 1 country. Each count lists the studies.
Of the 244 Insulin Resistance studies recruiting now, 54 (22%) set no upper age limit and 158 (65%) stop at 75 or younger; 30 take children under 18; 113 take healthy volunteers.
This study: 18 Years to 60 Years · all sexes · healthy volunteers too.
The full table on the hub →12 studies; the count open now beside each. This study's row is marked.
A study in two phases is counted once above. Listed by phase, each with its combined phases: Phase 1 8 · Phase 2 3
First in 2010; this study’s year is marked. 4 started in 2017.
Median enrollment 20 across the 11 interventional studies, 500 across the 1 observational. Of the 6 that completed or were terminated, 4 (67%) have results posted.
Vanderbilt University Medical Center is the lead sponsor of 833 studies on the registry; 155 are open to participants now.
Of its 125 completed or terminated interventional studies of FDA-regulated products, 92 (74%) have results posted.
2 of the studies in Insulin Resistance by Vanderbilt University Medical Center that are under way reach primary completion within a year, 0 of them phase 3. Phase 3 first, then by date:
| Study | Primary completion |
|---|---|
| NCT03318094Vanderbilt University Medical CenterRole of Sympathetic Vasoconstriction on Insulin-Mediated Microvascular Recruitment and Glucose Uptake in Obesity | 2026-11-30 |
| NCT06609356Vanderbilt University Medical CenterCardiometabolic Benefit of Reducing Iatrogenic Hyperinsulinemia Using Insulin Adjunctive Therapy in Type 1 Diabetes | 2027-07 |
Among the 12 studies in Insulin Resistance by Vanderbilt University Medical Center, from their registry updates:
Nothing recorded among them since 2026-09-25.
The purpose of this study is to better understand the contribution of sympathetic vasoconstriction to impaired insulin-mediated vasodilation and subsequently insulin-mediated glucose uptake. The investigators will test the hypothesis that removal of sympathetic vasoconstriction can result in improvement in insulin-mediated vasodilation and subsequently sensitivity to insulin-mediated glucose uptake.
Several studies have shown that obese subjects have impaired Nitric Oxide (NO)-mediated dilation; and those who develop insulin resistance tend to be more obese, have higher insulin levels and greater sympathetic activity. Furthermore, we have made the novel observation that autonomic blockade improves glucose utilization in obese subjects with insulin resistance, providing a causal relation between sympathetic activation and insulin resistance. The autonomic blockade also improved NO-mediated dilation in obese subjects, which may improve glucose uptake by promoting glucose delivery.
The investigators will enroll obese insulin-resistant subjects and in parallel experiments two comparator groups: obese insulin sensitive subjects, and healthy lean control subjects. We will assess the effects of insulin (hyperinsulinemic euglycemic clamp) on microvascular recruitment, and forearm glucose uptake on two separate occasions randomly assigned and at least one month apart, during an intrabrachial infusion of the alpha-adrenergic blocker phentolamine (blocked day) or saline control (Control day).
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.
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.
Before you join, the study team explains what taking part involves — its purpose, what happens, the risks and possible benefits — and answers your questions, so you can decide freely. Consent is usually recorded on a form (the informed consent form, ICF) signed by you or, where the law allows, by someone legally authorised to decide for you.
You can keep asking questions during the study, you are told of new information that matters, and you can choose to leave at any time.
A “mini-stroke”: temporary stroke-like symptoms caused by reduced blood flow to part of the brain, spinal cord or eye, without signs of a new stroke on a scan.
Stroke symptoms need emergency care at once, even if they go away.
Two enzymes measured in a routine blood test of the liver. Higher levels can mean the liver is under strain or damaged. SGPT and SGOT are older names for ALT and AST.
Criteria usually give a limit as a multiple of the upper limit of normal (ULN), often higher when cancer has spread to the liver.
The top of the normal range for a blood test, as set by the laboratory that runs it. Each lab prints its own range next to your result.
“≤ 2.5 × ULN” means the result can be up to two and a half times that top value.
The protein in red blood cells that carries oxygen. A low level is anaemia, which can cause tiredness and breathlessness. Measured in g/dL or g/L (9 g/dL is 90 g/L).
Anti-inflammatory medicines such as prednisone, prednisolone and dexamethasone — not the anabolic steroids used for muscle.
Studies differ in what they allow: check which steroid medicines, routes (tablets, injections, creams, inhalers, eye drops) and doses this study accepts.
A drug or device being studied in a clinical trial.
It may be new, or already approved and being studied for another use, dose or form. Criteria often leave out people who took part in another study of one within a recent period, commonly 30 days or five half-lives.
Judged by the study doctor to matter for your health or for the study. It is a doctor’s decision, so ask the study team if you are unsure whether something counts.
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.
Informed consent
Before you join, the study team explains what taking part involves — its purpose, what happens, the risks and possible benefits — and answers your questions, so you can decide freely. Consent is usually recorded on a form (the informed consent form, ICF) signed by you or, where the law allows, by someone legally authorised to decide for you.
You can keep asking questions during the study, you are told of new information that matters, and you can choose to leave at any time.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
TIA (transient ischaemic attack)
A “mini-stroke”: temporary stroke-like symptoms caused by reduced blood flow to part of the brain, spinal cord or eye, without signs of a new stroke on a scan.
Stroke symptoms need emergency care at once, even if they go away.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
ALT and AST (liver enzymes)
Two enzymes measured in a routine blood test of the liver. Higher levels can mean the liver is under strain or damaged. SGPT and SGOT are older names for ALT and AST.
Criteria usually give a limit as a multiple of the upper limit of normal (ULN), often higher when cancer has spread to the liver.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
ULN (upper limit of normal)
The top of the normal range for a blood test, as set by the laboratory that runs it. Each lab prints its own range next to your result.
“≤ 2.5 × ULN” means the result can be up to two and a half times that top value.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Hemoglobin (Hb)
The protein in red blood cells that carries oxygen. A low level is anaemia, which can cause tiredness and breathlessness. Measured in g/dL or g/L (9 g/dL is 90 g/L).
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Corticosteroids (steroids)
Anti-inflammatory medicines such as prednisone, prednisolone and dexamethasone — not the anabolic steroids used for muscle.
Studies differ in what they allow: check which steroid medicines, routes (tablets, injections, creams, inhalers, eye drops) and doses this study accepts.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Investigational drug or device
A drug or device being studied in a clinical trial.
It may be new, or already approved and being studied for another use, dose or form. Criteria often leave out people who took part in another study of one within a recent period, commonly 30 days or five half-lives.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Clinically significant
Judged by the study doctor to matter for your health or for the study. It is a doctor’s decision, so ask the study team if you are unsure whether something counts.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Saline
Other: Saline
Phentolamine
Drug: Phentolamine
Sodium Nitroprusside
Drug: Sodium Nitroprusside
Intrabrachial phentolamine will be given on the blocked day
Also known as: alpha-adrenergic blocker
Intrabrachial saline will be given this day
Intrabrachial sodium nitroprusside will be given this day to compare with phentolamine
Also known as: Active comparison
Contrast Enhanced-Ultrasonography (CEU)
The Primary Outcome will be the change in CEU induced by insulin during hyperinsulinemic clamp compared to baseline. To test the null hypothesis that insulin will not produce any changes in microvascular blood volume using CEU in response to α-adrenergic blockade (phentolamine) in the isolated forearm model.
Time frame: Before clamp and 15 minutes after clamp
Started Oct 2017 (actual). Primary completion is estimated for Nov 2026, 109 months after the start.
Of 51 non-industry phase 1 interventional studies under Insulin Resistance, half reached primary completion within 26 months of starting (the median), counting those still running; a quarter within 14 and three quarters within 80. This study's planned 109 months is above that.
Counting every sponsor, half of 65 studies reached it within 24 months; a quarter within 13 and three quarters within 67.
How these figures are worked out, and which studies are left out of them.
This study is active, not recruiting, as verified in Feb 2026. You cannot join it, but the record below documents what was studied.
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Studies of the drug tested here: Phentolamine
Vanderbilt University Medical Center →