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Life Sci. 1998;63(3):155-60.

Tissue-specific effects of estrogen on monoamine oxidase A and B in the rat.

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  • 1Dept. of Psychiatry and the Biobehavioral Sciences, School of Medicine, University of Southern California, Los Angeles, USA.


Estrogen replacement therapy is widely used in postmenopausal women. The current study examines the effect of varying concentrations of estrogen on the levels of activity of monoamine oxidase A and -B in brain and in other tissues. Adult female rats were ovariectomized and randomized to receive a subcutaneous, slow-release preparation of either placebo or one of three doses of 17-beta-estradiol (0.05, 0.5, or 5.0 mg/pellet, estimated serum levels of 20-25 pg/ml, 100-600 pg/ml, and 1-2 ng/ml, respectively). Animals were sacrificed at 3 weeks and MAO-A and -B activity was assessed in homogenates of heart, liver, lung, uterus, kidney, adrenal and small intestine using 5-hydroxytryptamine and phenylethylamine as substrates. Cortex, amygdala and hypothalamus were microdissected from frozen sections of the brain and were also assayed for MAO-A and -B activity. High dose estrogen (5 mg/pellet) significantly decreased MAO-B activity and resulted in lesser or insignificant changes in MAO-A activity, respectively in liver (-30%, +1%), kidney (-22%, -11%), and uterus (-57%, -35%) (p < 0.05). No significant changes in enzyme activity were observed in heart, adrenal, lung and small intestine. In brain, estrogen (5 mg/pellet) decreased MAO-A activity in the hypothalamus (-28%) and amygdala (-21%), with no significant change seen in MAO-B. Our results suggest that estrogen exerts a tissue-specific, differential regulation of MAO-A and -B activity.

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