Effects of estrogen and progestin on hypothalamic blood flow autoregulation.
OBJECTIVE
The consequences of female sex hormone deficiency and the effects of hormone replacement therapy are controversial because individual hormones and their derivates can result in partially antagonistic activities. This intricate system involving cerebral autoregulatory mechanisms caused by ovariectomy and female sex hormone replacement was studied in rats.


METHODS
The lower limit of cerebral blood flow autoregulation was determined by stepwise reduction of systemic arterial pressure while simultaneously measuring the changes of the hypothalamic blood flow (HBF) using the hydrogen gas-clearance method.


RESULTS
In ovariectomized rats resting HBF decreased substantially and the threshold of cerebrovascular autoregulation decreased to 40 mm Hg. Estrogen replacement prevents the former change and shifts the latter upwards. Similarly, progestin replacement restores autoregulation to the physiological levels found in control animals, whereas it has no influence on the ovariectomy-induced reduction of resting blood flow.


CONCLUSIONS
Steady-state HBF and compensatory changes of regional cerebral vascular autoregulation are altered significantly following ovariectomy. Estrogen or progestin replacement has an opposite effect on these cerebral circulatory parameters. Our observations highlight the essential role of female sex hormones in hypothalamic autoregulation during hypotensive stress.
Szelke
Emese
E
Institute of Human Physiology and Experimental Research, Faculty of Medicine, Semmelweis University, Budapest, Hungary.
Varbiro
Szabolcs
S
Mersich
Tamas
T
Banhidy
Ferenc
F
Szekacs
Bela
B
Sandor
Peter
P
Komjati
Katalin
K
D000818:Animals; D001794:Blood Pressure; D001810:Blood Volume / Q000502:physiology; D001835:Body Weight; D002245:Carbon Dioxide / Q000097:blood; D002560:Cerebrovascular Circulation / Q000187:drug effects*; D003271:Contraceptive Agents, Female / Q000494:pharmacology*; D004958:Estradiol / Q000031:analogs & derivatives* / Q000494:pharmacology; D005260:Female; D006706:Homeostasis / Q000187:drug effects; D007031:Hypothalamus / Q000098:blood supply*; D017258:Medroxyprogesterone Acetate / Q000494:pharmacology*; D010052:Ovariectomy; D010100:Oxygen / Q000097:blood; D051381:Rats; D017207:Rats, Sprague-Dawley
D003271:Contraceptive Agents, Female; D002245:Carbon Dioxide; D004958:Estradiol; D017258:Medroxyprogesterone Acetate; C023482:estradiol dipropionate; D010100:Oxygen