The aim of the study is to test whether genetic variation in the alpha 2A adrenergic receptor affects diurnal variation in platelet aggregation.

There is a marked diurnal fluctuation in the occurrence of acute myocardial infarction and sudden death, with peak incidences occurring in the early morning. Platelet aggregation has also been shown to increase in the early morning. The investigators will test the hypothesis that alpha 2a-adrenergic receptor (ADRA2A) genetic variation, specifically haplotype 4, affects platelet aggregation. The investigators will compare diurnal platelet aggregation in haplotype 4 subjects with subjects in the other haplotype families. In addition, the investigators will compare platelet aggregation after the cold pressor test in haplotype 4 with the other haplotype families. If there are no differences among haplotypes, then the haplotypes will be combined to analyze.

Inclusion Criteria:

• Men and women aged 18 - 45 years inclusive.
• Women of the above age will be studied between day 1 and day 14 of a normal menstrual cycle.
• Subjects must be willing to give informed consent for the study and able to adhere to the study diet and study procedures.
• Subjects and immediate extended family up till grandparents will be Caucasians or African Americans only.
• Subjects will be free of any clinically significant disease.
• Clinical laboratory test (CBC, blood chemistry) will be within acceptable limits.

Exclusion Criteria:

• Subjects who have taken any antiplatelet, anticoagulant or procoagulant medicines within the last three weeks preceding the study.
• Subjects who have taken medications (including over the counter medications) other than oral contraceptives in the past two weeks.
• Subjects who smoke or have smoked in the past 3 months.
• Subjects who are presently or were formerly a narcotic addict or alcoholic.
• Females with a positive pregnancy test.
• Females who are breast feeding.

Healthy subjects will be recruited by advertisement and word-of-mouth.

all IDP that underlie results in a publication

6 months after publication

Access Criteria:

IPD will be shared on request made to the PI. Criteria: Data is not to be shared. Data should only be used for biomedical research. Researchers requesting access will need appropriate IRB approval and sign a data use agreement.

Adverse event data was collected from the time participant was admitted to the Clinical Research Center the evening before the study, to the end of the study, a 24 hour period.

Healthy young subjects studied, thus findings may not apply to different populations. Plasma catecholamines are an indirect measure of sympathetic activity--norepinephrine spillover would be more precise, but is technically demanding, not feasible.