Variability in Adrenergic Response

Not Applicable

Completed

Brief Summary: The goal of this project is to determine the genetic factors contributing to interindividual differences in response to physiological and pharmacological vasoconstrictors and vasodilators.

Detailed Description: The dorsal hand vein model is a relatively non-invasive and robust experimental model to examine the local in vivo effect of vasoactive drugs without elucidating systemic counterregulatory reflexes. Infusion of incremental low doses of phenylephrine into a dorsal hand vein results in increasing local venoconstriction, without systemic effects. Similarly, infusion of incremental low doses of nitroglycerin into a preconstricted dorsal hand vein results in increasing local venodilation, without systemic effects. Systemic vascular responses can be measured by the cold pressor test (CPT),that leads to increase in blood pressure and heart rate , or mental stress that is also known to stimulate cardiovascular responses. Individuals vary in their local and systemic vascular responses but the genetic determinants of these are not clear.

Recruitment & Eligibility

Inclusion Criteria

Age between 18 and 40 years, inclusive.
Subject must be willing to give written informed consent and be able to adhere to diet and study schedules.
Subjects must be free of any clinically significant disease that requires a physician's care and/or would interfere with the study evaluations.
Subjects must have a normal or clinically acceptable physical examination and ECG.
Clinical laboratory tests (CBC, blood chemistries, and urinalysis) must be within normal limits or clinically acceptable to the investigator.

Exclusion Criteria

Any subject who has taken any prescription or over-the-counter drugs, other than oral contraception if female, within two weeks prior to study drug administration.
Subjects who are presently, or were formerly, narcotic addicts or alcoholics.
Subjects who have a clinically significant allergy/intolerance to phenylephrine.
Females with a positive serum/urine pregnancy test at screening.
Females who are nursing.
Subject using sildenafil or other phosphodiesterase inhibitors.

Arm && Interventions

Group	Intervention	Description
African Americans	Phenylephrine	Subjects' hand veins will be measured for maximum constriction while being infused with phenylephrine, and then mental stress and cold pressor testing
Caucasians	Phenylephrine	Subjects' hand veins will be measured for maximum constriction while being infused with phenylephrine, and then mental stress and cold pressor testing

Primary Outcome Measures

Name	Time	Method
ED50 After Phenylephrine	70 minutes	ED50 is a measurement of vein constriction and indicates 50% of maximal constriction after being given medication phenylephrine, representing sensitivity to the drug. Phenylephrine was infused at increasing dose rates, ranging from 12-9600 ng/min. The infusion at each dose rate lasted 7 minutes, with the vein diameter measured during the last 2 minutes of the infusion. The number represents the ng/ml of phenylephrine needed to reach 50% of maximal vein constriction. ED50 values were not normally distributed and were log-transformed for analysis and expressed as geometric means.

Secondary Outcome Measures

Name	Time	Method
Change in Blood Pressure	baseline to 2 minutes	change in systolic and diastolic blood pressure, comparing before and after cold pressor test. A subset of 57 participants (of the 106) who were in the primary outcome measure also participated in the cold pressor test.