Estrogen protects against hypertension in the spontaneously hypertensive rat, but its protective mechanism is unrelated to impaired arterial muscle relaxation.
OBJECTIVE
To determine if estrogen acutely and directly alters arterial muscle relaxation, if estrogen is responsible for gender dichotomy in hypertension, and if arterial muscle from female spontaneously hypertensive rats (SHR) is slow to relax as is muscle from male SHR compared with arterial muscle of normotensive Wistar-Kyoto rats (WKY).


METHODS
Relaxation rates of isometrically contracted arterial muscle from male rats were measured before and after addition of beta-estradiol. Blood pressure (BP) was monitored in intact male and female SHR and WKY and in ovariectomized and estrone-treated ovariectomized SHR and WKY. Relaxation rates of maximum isometric contractions of arterial muscle excised from male SHR and WKY and female SHR and WKY with varying chronic estrogen status were measured.


RESULTS
Beta-estradiol had no direct, acute effect on arterial muscle force or relaxation. Intact and estrone-implanted SHR females had significantly lower BP than males. Ovariectomized SHR developed high BP equivalent to that of males. Arterial relaxation was slower in both male and female SHR compared with WKY.


CONCLUSIONS
Estrogen lowers BP in female SHR. Strain differences in relaxation rates are independent of gender and estrogen status. Estrogen has no effect on arterial muscle relaxation, suggesting another mechanism for the protective effect of estrogen in hypertension.
Packer
C S
CS
Indiana University School of Medicine, Department of Physiology/Biophysics, 635 Barnhill Dr, Indianapolis, IN 46202-5120, USA.
Pelaez
N J
NJ
Kramer
J A
JA
D000704:Analysis of Variance; D000818:Animals; D004195:Disease Models, Animal; D004343:Drug Implants; D004558:Electric Stimulation; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D006973:Hypertension / Q000517:prevention & control*; D008297:Male; D009126:Muscle Relaxation / Q000187:drug effects*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D010052:Ovariectomy; D051381:Rats; D011921:Rats, Inbred WKY; D017207:Rats, Sprague-Dawley; D014626:Vaginal Smears
D004343:Drug Implants; D004958:Estradiol