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Uterine Blood Flow Response to Alpha-Adrenergic Blockade in Nulligravid Women of Reproductive Age

Department of OB-GYN, Deaconess Billings Clinic, 2800 10th Avenue North, Billings, MY 59107-7000 dpdamron{at}byu.net

Ira M. Bernstein, MD

Robert E. Shapiro, MD

Adrienne Schonberg, RN

Departments of Obstetrics-Gyencology and Neurology, University of Vermont College of Medicine, Burlington, Vermont

Objective: Elevated uterine artery resistance has been associated with the development of preeclampsia. We sought to determine if the human uterine arterial circulation was more sensitive to alpha-adrenergic blockade than a control vascular bed.

Methods: We studied 38 healthy nulliparous women during the follicular phase of the menstrual cycle. Arteriolized venous blood was measured for plasma epinephrine and norepinephrine. Doppler ultrasound of the uterine and upper extremity radial artery was performed before and after intravenous administration of phentolamine. Heart rate and volumetric flow were calculated. Data are presented as means ± SD.

Results: Mean heart rate before and after administration of phentolamine was 63 ± 11 and 68 ± 12 beats per minute (7.5% increase, P < .001). Mean radial artery blood flow before and after administration of phentolamine was 4.6 ± 4.7 mL/min and 5.8 ± 5.9 mL/min (19.9% increase, P = .071). Mean uterine blood flow before and administraiton of phentolamine was 15.4 ± 10.1 mL/min and 27.3 ± 17.5 mL/min (43.7% increase, P < .001). The uterine response (43.7% increase) and radial response (19.9% increase) were significantly different (P < .001). The increase in uterine blood flow after phentolamine administration was linked with resting norepinephrine (r = 0.394, P = .063).

Conclusion: We found evidence that uterine alpha-adrenergic tone is more sensitive to blockade by phentolamine than upper extremity radial circulation. This provides evidence for a differential responsiveness and sensitivity to alpha-adrenergic blockade in different vascular beds. We theorize that the increased adrenergic tone associated with preeclampsia may contribute disproportionately to decreased uterine blood flow.

Key Words: Phentolamine • preeclampsia • alpha-adrenergic tone

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