Chemical suppression of steroidogenesis.

A large number of chemicals are known to interfere with steroidogenesis in the adrenal cortex and other tissues. Many xenobiotics inhibit steroid hormone production as a result of interactions with cytochrome P-450-containing hydroxylases in adrenal mitochondria or microsomes. For example, metyrapone, a compound used clinically in the evaluation of pituitary-adrenocortical function, binds to various cytochromes P-450 in the adrenal, preventing the interactions of steroid substrates with the enzymes and inhibiting steroidogenesis. The mineralocorticoid antagonist, spironolactone, and its major circulating metabolite, canrenone, also competitively interact with adrenal steroid hydroxylases. In addition, spironolactone is converted by adrenal microsomes to an unknown metabolite which promotes the destruction of cytochromes P-450, decreasing the activities of steroid hydroxylases. Carbon tetrachloride is similarly "activated" by adrenal microsomal mixed function oxidases resulting in a decline in steroidogenic enzyme activity. Carbon tetrachloride (in the presence of NADPH) initiates lipid peroxidation in adrenal microsomes but its toxic effects on steroid hydroxylases are fully demonstrable when lipid peroxidation is inhibited by EDTA. A number of heavy metals, including cadmium, also inhibit adrenal steroid hydroxylases. When incubated with adrenal microsomes, cadmium does not affect cytochrome P-450 levels but decreases basal and substrate stimulated NADPH-cytochrome P-450 reductase activity. Although inhibitory effects of many chemicals on steroidogenesis have been described, the toxicological significance as well as definitive mechanisms of action have in most cases yet to be determined

Valuing Private and Public Greenspace Using Remotely Sensed Vegetation Indices

In a typical metropolitan area, greenspace varies substantially in its quality and extent. Remotely sensed vegetation index data is used to characterize the heterogeneity in private and public greenspace (riparian corridors) in metropolitan Tucson, Arizona. This data set enables the researcher to test if: (1) greenness is a significant determinant of house price variation in this desert city; and (2) whether there is an interaction between public and private greenspace. Private greenspace amenities can be endogenously improved by homeowners as a complement or substitute for the greenspace that is publicly provided, whereas public greenspace might be exogenous or endogenous depending on households ability to pressure the local government to protect or restore public greenspace. The results of a Hausman test indicate that endogeneity is a problem in the dataset and therefore an instrumental variable two stage least squares estimation is used. The results of this analysis indicate that homebuyers in the study area have preferences for both greener lots and greener riparian corridors and that private and public greenspace appear to be substitutes. Results are robust across multiple identification strategies designed to address potential endogeneity. The study results could have fundamental implications for the efficient use of limited water supplies in this semi-arid metropolitan area.Resource /Energy Economics and Policy,