THE DIRECT ACTION OF 17-BETA-ESTRADIOL IN ISOLATED OMENTAL ARTERY FROM NONPREGNANT AND PREGNANT-WOMEN IS RELATED TO CALCIUM ANTAGONISM

OBJECTIVE: Our purpose was to study the mechanism by which 17 beta-est radiol modulates contractile activity in isolated rings of omental art ery from nonpregnant and pregnant patients. STUDY DESIGN: Rings of ome ntal artery with intact endothelium from nonpregnant and pregnant wome n were mounted in organ chambers for isometric tension recording. The concentration-relaxation relationship to 17 beta-estradiol (10(-7) mol /L to 3 x 10(-5) mol/L) was studied in rings contracted with 60 mmol/L potassium chloride (in both the absence and the presence of tamoxifen , 10(-6) mol/L). The effect of 17 beta-estradiol (10(-5) mol/L) on the contraction induced by 60 mmol/L potassium chloride and on the concen tration-contraction relationships to both norepinephrine (10(-9) mol/L to 10(-5) mol/L) and calcium ion (0.05 mmol/L to 2.5 mmol/L in calciu m-free depolarizing solution) were studied in the presence and absence of tamoxifen (10(-6) mol/L). The maximal contraction, negative logari thm of the concentration producing 50% relaxation or 50% contraction t o the reference 60 mmol/L potassium chloride contraction, and the area under the curve were calculated. Data analysis was by one-way analysi s of variance, Newman-Keuls test, and two-sample tests as appropriate. Probability values less than 0.05 in a two-tailed test were considere d statistically significant. RESULTS: 17 beta-Estradiol relaxed omenta l arteries contracted with 60 mmol/L potassium chloride, and this effe ct was potentiated by tamoxifen in both groups. Incubation of the omen tal arteries with 17 beta-estradiol inhibited contractions induced by 60 mmol/L potassium chloride in rings from both groups of patients, an d tamoxifen did not antagonize this effect in either group. Rings of o mental artery from the nonpregnant patients (expressed as percentage o f the reference potassium chloride contraction) showed greater contrac tion than rings from the pregnant women when exposed to norepinephrine , a statistically significant difference. 17 beta-Estradiol decreased the norepinephrine-induced contraction in omental arteries from nonpre gnant but not pregnant women in a statistically significant way. Tamox ifen did not influence the effect of norepinephrine for either group. 17 beta-Estradiol inhibited calcium ion-induced contraction similarly in rings of omental artery from both nonpregnant and pregnant patients . Tamoxifen potentiated estradiol-induced inhibition in arteries from pregnant patients. CONCLUSIONS: 17 beta-Estradiol inhibits norepinephr ine-induced contractions in omental arteries from nonpregnant but not pregnant patients. The inhibition of the tension developed after expos ure to potassium chloride, norepinephrine, and calcium ion is caused b y a calcium channel blocking action.