17β-Estradiol Reduces Nitric Oxide Production in the Guinea Pig Cochlea

Abstract

In diff erent approaches, it was shown that 17β-estradiol can infl uence NO production differently depending on the tissue. In the endothelium of blood vessels, a 17β-estradiol-dependent increase in the endothelial nitric oxide synthase (eNOS) expression or an upregulation of its activity was detected, both resulting in an increased NO concentration [ 12 ]. On the other hand, a 17β-estradiol-dependent downregulation of nitric oxide synthase activity was identifi ed in the uterus and vagina of rabbits [ 13 ]. At the cellular level, an estrogen-mediated inhibition of Ca 2 + infl ux via L-type Ca 2 + channels was described for murine cardiomyoctes [ 14 ] and this attenuated glutamate-induced cell death in a ventral spinal motoneuron and neuroblastoma hybrid cell line (VSC 4.1) [ 15 ]. Thus, 17β-estradiol was found to fulfi ll multiple tasks in NO-regulated vertebrate physiology including neuroprotection [ 16-19 ]. In addition, clinical and experimental studies have shown that estradiol