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|Title:||The effect of modification of mixed function oxidases and inhibition of enterohepatic circulation on concentration of estrogens in plasma in laying hens (Gallus domesticus)|
|Doctoral Committee Chair(s):||Dziuk, Philip J.|
|Department / Program:||Animal Sciences|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Subject(s):||Health Sciences, Toxicology
Biology, Animal Physiology
|Abstract:||The rate of metabolism and recirculation contributes to the rate of excretion and to concentration in the circulation. Steroids are substrates for mixed function oxidases (MFO). Enterohepatic circulation (EHC) of estrogens prolongs the half life of estrogens. Thus, the amount of recirculation and the extent of inactivation of estrogens by MFO can influence the peripheral concentration of estrogens. The objective of this thesis was to determine the influence of altering MFO by xenobiotics and inhibition of EHC on the peripheral concentration of estrogens and on estrogen dependent functions in laying hens (Gallus domesticus).
The first objective was to investigate the extent of EHC on peripheral concentration of estrogen in laying hens. Analysis of bile from hens, showed that more than 95% of estrogen are conjugates indicating that the excretion of estrogen conjugates in the bile and indicates the possibility of EHC of estrogen. Sequestering of free estrogens in the gut by oral charcoal leading to fecal excretion or inhibition of bacterial deconjugating enzymes in the gut by antibiotics would reduce reabsorption and recirculation. Oral antibiotics reduced the concentration of estrone (E1) and estradiol glucuronide in the hepatic portal vein. Hen treated with charcoal also had lower concentration of E1 in the hepatic portal vein, and higher circulating concentration of E2 than control hens. Hens treated with charcoal and antibiotics laid more eggs than control hens. The second objective was to investigate the effect of modification of metabolizing enzymes on the peripheral concentration of estrogens in laying hens. Phenobarbital (PB) increased MFO thereby depressing concentration of E2 and E1 but not estrogen conjugates. Treatment with PB increased MFO, decreased E2 and total blood calcium in a dose dependent manner. Depressing MFO by administration of carbon tetrachloride increased the concentration of E2. The third objective was to examine the hypothesis that a change in estrogen in laying hens might detect reproductive toxicants. Aroclor 1254 (PCBs) and Dichlorodiphenyl-trichloroethane (DDT) are reported to have profound effects on avian reproduction, and both caused depression of circulating E2, whereas benzpyrene has been found not to have an affect on reproduction and did not affect E2. High doses of PCBs and PB not only decreased E2 but also depressed reproductive functions such as egg lay, eggshell thickness and total plasma calcium.
These results indicate that effect of diet on reproduction might be due to modification of MFO or inhibition of EHC, and consequent reproduction. It also helped to explain that eggshell thinning and reproductive failure caused by toxicants might be due to change of MFO.
|Rights Information:||Copyright 1992 Chen, Shu-Wen|
|Date Available in IDEALS:||2011-05-07|
|Identifier in Online Catalog:||AAI9215790|