H D Colby

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Experiments were done to determine the actions of ACTH on the morphologic and functional characteristics of the zona fasciculata (ZF) and zona reticularis (ZR) in the guinea pig adrenal cortex. In control guinea pigs, a number of morphologic differences distinguished the ZF from the ZR, including the presence of far more lipid in the ZF than in the ZR.(More)
We have studied the effects of ACTH treatment on steroid hydroxylase activities in the inner (zona reticularis) and outer (zona fasciculata plus zona glomerulosa) zones of the guinea pig adrenal cortex. Animals received 5 or 10 U of ACTH daily for 6 days and enzyme activities were then assessed in isolated microsomal or mitochondrial preparations. In(More)
Recent reports indicate that the cytochrome P450 isozyme, CYP2D16, is expressed at high levels in the inner regions of the guinea pig adrenal cortex and may contribute to xenobiotic and/or steroid metabolism in the gland. In the present studies, immunohistochemical and in situ hybridization techniques were employed to definitively establish the localization(More)
We recently reported that CYP2D16, a xenobiotic-metabolizing P450 isozyme, was expressed at higher levels in adrenal microsomes from inbred Strain 13 guinea pigs than in those from outbred English Short Hair (ESH) animals. Studies were done to determine if there also were strain differences in adrenal microsomal steroid metabolism. In both inner (zona(More)
Prior in vitro investigations demonstrated that the P450 suicide substrate, 1-aminobenzotriazole (ABT), was a potent inhibitor of xenobiotic metabolism but had no effect on steroidogenic enzymes in the guinea pig adrenal cortex. Studies were done to determine if ABT administration of guinea pigs in vivo also selectively inhibited adrenal xenobiotic(More)
Studies were done to determine the effects of age on steroidogenesis in the inner (zona reticularis) and outer (zona fasciculata plus glomerulosa) zones of the guinea pig adrenal cortex. In 35-day-old animals, cortisol production by adrenal outer zone cells was approximately twice as great as that by inner zone cells. With aging, cortisol secretion by inner(More)
Studies were done to determine the role of the 17 alpha-hydroxylase in the conversion of 7 alpha-thiospironolactone (7 alpha-thio-SL) to a reactive metabolite causing the degradation of testicular cytochrome P-450. Incubation of guinea pig testicular microsomes with 7 alpha-thio-SL plus NADPH resulted in an approx. 70% decline in cytochrome P-450 content(More)
Studies were done to determine the mechanism(s) of action of spironolactone (SL) and of its deacetylated metabolite, 7 alpha-thio-SL, to inhibit cortisol secretion by guinea pig adrenocortical cells in vitro. Preincubation of cells at 37 degrees C with SL or with 7 alpha-thio-SL caused a time-dependent decline in subsequent ACTH-stimulated cortisol(More)
Prior studies demonstrated far greater amounts of lipid peroxidation (LP) in mitochondria from the zona reticularis (inner zone) of the guinea pig adrenal cortex than in mitochondria from the outer zone (zona fasciculata + zona glomerulosa) of the gland. alpha-Tocopherol concentrations, by contrast, were greater in the outer zone. To determine if the(More)