Graduation date: 1995

Thesis (Ph. D.)--University of Wisconsin--Madison, 1984. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Graduation date: 1998

Monocrotaline (MCT) is a member of a class of naturally occurring phytotoxins known as pyrrolizidine alkaloids (PAs). Exposure to PAs can result in liver and cardiopulmonary lesions as well as lymphoid organ atrophy. In the present study C57BI/6 (B6) mice received MCT (0-150 mg/kg/day, po) for 14 days. Overt toxicity was minimal and observed only at highly immunosuppressive doses. Following MCT exposure, significant dose-dependent suppressions were observed in the following immune responses: numbers of antibody producing cells, cytotoxic T- lymphocyte activity, and NK cell cytotoxicity. The antibody responses to the T cell-dependent antigen, SRBC, and the T cell-independent (TI) antigens, DNP-Ficoll and TNP-LPS, were decreased with identical dose response curves. This, along with data showing MCT decreased blastogenesis of B cells more than T cells at the lowest dose level, and that high doses induced significant decreases in the total number of B cells only, suggest that the B cell may be more sensitive than T cells, NK cells , or macrophages. The liver and lung toxicity of MCT is believed to be mediated through its metabolism by mixed function oxidase (MFO) enzymes to reactive pyrroles (monocrotaline pyrrole, MCTP; and dihydropyrrolizine, DHP). Accordingly, it was our hypothesis that the immunotoxicity could be modulated by altering MFO activity. To test this, mice were given a single dose of MCT (100 or 200 mg/kg, po) after MFO induction with phenobarbital; in other experiments mice received the MFO inhibitor chloramphenicol immediately before and 3 hrs after a single exposure to MCT (300 mg/kg, po). However, neither MFO induction nor inhibition significantly altered the immunosuppressive potency of MCT. The antibody and blastogenic responses of splenic lymphocytes directly exposed to MCT (1-3 mM) or MCTP (1-8 μM) in culture were inhibited in a concentration-dependent manner, indicating that both parent and metabolite were immunotoxic. However, the inability to alter the in vivo immunotoxicity by altering MFO activity questions the role this metabolite may play in vivo. In conclusion, the immune system in B6 mice is a sensitive target of MCT toxicity. Inhibition of blastogenesis appears to be one mechanism of MCT-induced immunosuppression. In contrast to other toxic effects of MCT, our results suggest that the parent compound itself plays a significant role in the immunotoxicity. / Graduation date: 1992

The plant Senecio jacobaea (tansy ragwort) produces several macrocyclic pyrrolizidine alkaloids which cause irreversible liver cirrhosis. All of the pyrrolizidine alkaloids in Senecio jacobaea are macrocyclic diesters of the necine base retronecine, with the two most predominant being seneciphylline and jacobine. Unlike horses and cattle, sheep and goats are generally resistant to chronic pyrrolizidine alkaloid toxicosis due to metabolism of the toxic pyrrolizidine alkaloids by ruminal bacteria. In this study, metabolism of jacobine and seneciphylline by ruminal bacteria was investigated, focusing on two possible metabolic pathways. One pathway involved hydrolysis of jacobine and seneciphylline and the subsequent production of the necine base retronecine. For use in these studies, retronecine was isolated and labeled with deuterium. A method was developed for the determination of retronecine to 0.02 μg /mL. Significant hydrolysis of jacobine and seneciphylline was not observed in either ovine whole rumen fluid or with a mixed culture of anaerobic microbes derived from ovine rumen fluid which metabolizes jacobine and seneciphylline. Direct metabolism of retronecine independent of the macrocyclic pyrrolizidine alkaloids was also not observed. The second metabolic pathway studied involved the production of the necine base modified by the conversion of the 1,2-double bond to an external methylene group. Previously this conversion has been observed during metabolism of pyrrolizidine alkaloids by the organism Peptostreptococcus heliotrinreducens. In this study, P. heliotrinreducens was used to convert the pyrrolizidine alkaloids heliotrine and lasiocarpine to the known 1-methylene-pyrrolizidines. The mixed culture of ovine anaerobic microbes also metabolized heliotrine and lasiocarpine rapidly to identical methylene products. This mixed culture metabolized jacobine and seneciphylline rapidly with production of very low levels of the corresponding 1-methylene compounds. In contrast, metabolism of jacobine or seneciphylline by P. heliotrinreducens was not observed. The mixed culture has demonstrated the ability to metabolize a greater variety of pyrrolizidine alkaloids than P. heliotrinreducens. Although the metabolites of jacobine and seneciphylline were not conclusively identified, it was determined that hydrolysis of jacobine and seneciphylline is not occurring. The second pathway studied appears to be more probable, with the production of 1-methylene compounds as intermediates, although not as end-products. / Graduation date: 1998

No description available.

No description available.

Graduation date: 1998

Objectives of this study were to examine effects of dietary pyrrolizidine alkaloids (PA) on copper and vitamin A metabolism in the chicken which are very susceptible to the hepatoxic effects of PA and Japanese quail which are highly resistant to PA. Also, the possible interaction between copper and vitamin A in the two species and effect of PA on retention of previously stored vitamin A in the chicken were investigated. Three experiments were designed. Experiment 1 was to examine the effect of feeding the PA-containing plant tansy ragwort (TR)(Senecio jacobaea) on tissue levels of copper and vitamin A in the chicken. Experiment 2 was to investigate if dietary PA affected the retention of previously stored vitamin A in the chicken. Experiment 3 was to determine if hepatoxic effects of PA are necessary to influence copper and vitamin A metabolism in Japanese quail. In experiment 1, a 2x2x2 factorial design with dietary 0 and 5% TR, 0 and 250 ppm copper, and 0 and 25,000 IU/kg diet vitamin A was used. The results showed that body weight gain was reduced (P < 0.01) in birds fed TR. Both serum and liver copper concentrations were markedly increased (P <0.01) in the TR-fed group with 250 ppm copper supplement. Zinc concentrations in the serum and liver were significantly decreased (P <0.05) in the TR-fed groups compared to TR-free groups. Liver iron was increased (P <0.05) in the TR-fed birds. The serum vitamin A levels were significantly decreased (P < 0.01) in all TR-fed groups. The ranges of decrease were from 62 to 72 % in four TR -fed groups. The liver vitamin A concentrations were also significantly decreased (P <0.05) in TR-fed groups without vitamin A supplement. The effects of PA on liver and blood vitamin A concentration may reflect PA inhibition of synthesis of retinol-binding proteins, or impaired vitamin A absorption from reduced biliary excretion. There was no interaction between dietary copper and vitamin A levels and tissue concentrations of these nutrients. In experiment 2, a two period experiment was carried out. In the first period, two groups of chicks were fed a diet containing 25,000 IU vitamin A/kg diet for two weeks followed by a control or TR-containing diet for four weeks. Blood samples were taken at 4 day intervals for 24 days. It was found that by day 8, serum vitamin A levels were significantly depressed (P <0.05). After 24 days of PA exposure, serum vitamin A levels were reduced by 55 % and 8.5% in the TR-fed group and the control group, respectively. Liver concentration of vitamin A was increased (P < 0.05) at day 24 of TR feeding, while liver vitamin A concentration in birds fed the control diet was decreased by 13% over the same period. The results indicate that PA inhibit the mobilization of previously stored vitamin A from the liver, probably by inhibiting hepatic synthesis of retinol-binding proteins. Experiment 3 was a 2x2x2 factorial design with added 0 and 5% tansy ragwort, 0 and 250 ppm copper, and 0 and 25,000 IU/kg diet vitamin A. The results showed that consumption of TR did not affect the growth rate of Japanese quail. There were no significant differences in the serum copper concentrations among all treatment groups. Liver copper levels were decreased with TR feeding (P <0.05). The concentrations of zinc and iron in the serum and liver were normal in TR-fed groups compared to the controls. There was no significant effect (P >0.05) on the serum vitamin A concentration. The liver vitamin A concentrations were also not significantly different with the exception of the basal TR group. Copper supplementation of the diet increased serum vitamin A levels (P <0.05). The results suggest that hepatotoxicity is necessary to induce the changes in tissue levels of copper and vitamin A seen in PA-susceptible species. / Graduation date: 1991

No description available.