[Influence of estrogens on the impedance of cerebral blood vessels].
OBJECTIVE
Recent experimental research has demonstrated the neuroprotective effect of estrogen on the ischemic brain. There is, however, little data available concerning the effects of estrogen on cerebral circulation in humans. In this contribution we studied the influence of endogenous estrogen on the flow in the carotid arteries and on the cerebrovascular impedance.


METHODS
The plasma concentration of 17-beta-estradiol was measured in 19 healthy, young women over 10 days of the menstrual cycle (days 3, 6, 10, 13-17, 20 and 24). Ultrasound examination of the carotid arteries was performed on the same days using a Toshiba Aplio ultrasound system endowed with a 7.5 MHz linear transducer. Impedance indices based on the recorded systolic, mean and end-diastolic blood flow velocities were calculated for the internal, common and external carotid arteries.


RESULTS
During the follicular phase of the menstrual cycle, blood flow in the internal carotid artery increased considerably in all subjects along with increasing plasma concentrations of estrogen. The end-diastolic blood flow velocity increased most significantly, on average by 16% and by up to 24% in individual cases. At the same time, the impedance indices (resistance index--RI and pulsatility index--PI) decreased significantly from their base values. Blood flow velocity in the common carotid artery, the caliber of this vessel, pulse rate and blood pressure remained stable during the entire follicular phase of the cycle. Nevertheless, the flow velocity in the external carotid artery decreased. This suggests that an increase in the cerebral blood flow, promoted by decreasing cerebro-vascular impedance in the follicular phase of the cycle, occurs at the expense of blood "stolen" from the external carotid artery.


CONCLUSIONS
Estrogen increases blood flow in the internal carotid artery by decreasing the impedance of cerebral microcirculation.
Klinika Neurochirurgii, Akademia Medyczna w Białymstoku. kochanowicz@vp.pl
Jan
J
Kochanowicz
Jarosław
J
Krejza
Olga
O
Koroza
Zenon
Z
Mariak
D000328:Adult; D000704:Analysis of Variance; D001783:Blood Flow Velocity / Q000187:drug effects* / Q000502:physiology; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D002339:Carotid Arteries / Q000000981:diagnostic imaging / Q000187:drug effects* / Q000502:physiology; D002560:Cerebrovascular Circulation / Q000502:physiology; D004958:Estradiol / Q000097:blood*; D004967:Estrogens / Q000097:blood / Q000494:pharmacology / Q000502:physiology*; D005260:Female; D005498:Follicular Phase / Q000502:physiology; D006400:Hematocrit; D006454:Hemoglobins / Q000032:analysis; D006801:Humans; D008183:Luteal Phase / Q000502:physiology; D008597:Menstrual Cycle / Q000097:blood* / Q000502:physiology; D011374:Progesterone / Q000097:blood; D011446:Prospective Studies; D012016:Reference Values; D018616:Ultrasonography, Doppler, Duplex; D014655:Vascular Resistance / Q000187:drug effects / Q000502:physiology
D004967:Estrogens; D006454:Hemoglobins; D011374:Progesterone; D004958:Estradiol