Tissue-specific effects of estrogen on monoamine oxidase A and B in the rat.
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.
Dept. of Psychiatry and the Biobehavioral Sciences, School of Medicine, University of Southern California, Los Angeles, USA.
D P
DP
Holschneider
T
T
Kumazawa
K
K
Chen
J C
JC
Shih
D000818:Animals; D004305:Dose-Response Relationship, Drug; D004967:Estrogens / Q000008:administration & dosage / Q000494:pharmacology*; D005260:Female; D008995:Monoamine Oxidase / Q000378:metabolism*; D008996:Monoamine Oxidase Inhibitors / Q000494:pharmacology*; D010052:Ovariectomy; D010919:Placebos; D051381:Rats; D017207:Rats, Sprague-Dawley
D004967:Estrogens; D008996:Monoamine Oxidase Inhibitors; D010919:Placebos; D008995:Monoamine Oxidase