Evidence for pteridine regulation of lead-mediated inhibition of uroporphyrinogen and heme formation in rat bone marrow

Uroporphyrin I (URO I) accumulation has been reported in the bone marrow of rats exposed to lead, suggesting a sensitivity of uroporphyrinogen III cosynthase (COSYN) to this heavy metal. Furthermore, it has been reported that a polyglutamated folate derivative may serve as a coenzyme for the catalytic action of hepatic uroporphyrinogen III cosynthase. These findings raised the question of whether depletion of polyglutamated folate could enhance the susceptibility of bone marrow COSYN to lead and potentially interfere with the formation of heme. Nitrous oxide, an anesthetic agent capable of causing bone marrow tetrahydrofolate deficiency, depressed total bone marrow polyglutamated folate content by 42% with significant reductions in all three chain lengths (5-7) identified in the bone marrow during an exposure period of 7 days at 4 hr/day. Lead acetate (15 mg/kg) administered by ip injection at Days 0 and 2 during a 7-day exposure to nitrous oxide resulted in an 84% increase of bone marrow URO I content, which was markedly higher than the increases of 22 and 38% seen with sole administration of lead or nitrous oxide, respectively. The combination of agents also produced a 48% rise in COPRO I, a 39 and 43% decrease in COPRO III and protoporphyrin, respectively, and a 42% decline in the activity of microsomal 7-ethoxycoumarin O-deethylase, which is hemoprotein, cytochrome P-450 mediated. Heme oxygenase activity was not altered by nitrous oxide, lead, or their combination. These results suggest that bone marrow folate deficiency may render COSYN more sensitive to lead as characterized by increased uroporphyrin I and coproporphyrin I isomer content, decreased coproporphyrin III and protoporphyrin content, and depressed microsomal hemoprotein, cytochrome P-450-mediated drug-metabolizing capability.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30170/1/0000555.pd

Tetrachlorodibenzo-p-dioxin alters rat hypothalamic endorphin and mu opioid receptors

The present study was undertaken to assess if hypothalamic [beta]-endorphin ([beta]E) and/or brain mu opioid receptors are associated with 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD) (50 [mu]g/kg)-induced hypophagia and body weight decline in rats. Hypothalamic [beta]E concentrations were initially increased to 166% of controls on day 1, and then were depressed to 39% and 49% of control values on days 2 and 3, respectively. Brain mu opioid receptor number was increased 60% in TCDD-treated rats at day 3 without a change in the binding affinity. Food-restricted rats did not exhibit changes in hypothalamic [beta]E concentrations or brain mu opioid receptor number. These results indicate that TCDD causes early perturbations in hypothalamic [beta]E concentrations and brain mu receptor number, which may contribute to the mechanisms by which TCDD leads to decreased food intake and progressive weight loss.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29160/1/0000205.pd

Stimulation by voluntary exercise of adrenal glucocorticoid secretion in mature female hamsters

The possibility that habitual voluntary running induces a chronic change in adrenal glucocorticoid synthesis and secretion was examined in freely running mature female hamsters, in whom this behavior accelerates growth, reduces body fat levels, and elevates core temperature. Hamsters were free to run on horizontal discs or in vertical wheels between 32 and 80 days, in 14L:10D or in 10L:14D photoperiods, and at the end of this period, corticosterone and cortisol steroidogenesis and serial plasma corticosterone concentrations during day and night were used as measures of the chronic stimulation of adrenal cortical activity. Habitual voluntary running significantly increased steroidogenesis of both glucocorticoids and plasma corticosterone concentrations and alone accounted for all the variance in enhanced synthesis and secretion of corticosterone. Acute exercise and/or the nocturnal phase of circadian period enhanced the chronic stimulatory effects of exercise on cortiol. Despite its voluntary and apparently stress-free nature, running induces chronic increases in basal glucocorticoid secretion in mature female hamsters. Putative oversecretion of corticotropin releasing factor in freely running hamsters could account for increased steriodogenesis, acceleration of growth, reduced body fat levels, and core temperature elevation.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30139/1/0000516.pd

Chronic ethanol consumption depresses hypothalamic-pituitary-adrenal function in aged rats

In separate experiments, nine (n=20) and fifteen (n=12) month old rats were treated with either 6% ethanol or 12% sucrose (to balance caloric intake) in the drinking water to examine the effect of chronic ethanol consumption on the hypothalamic-pituitary-adrenal axis of aged rats. Rats were maintained on these treatment regimens for thirty days and were killed by decapitation. Blood was collected and plasma concentrations of adrenocorticotropin (ACTH) and corticosterone were determined by radioimmunoassay. Adrenal glands were cleaned, quartered and used to test in vitro responsiveness to ACTH. Anterior pituitary glands from all 15 month old rats and one half of the nine month old rats were collected, frozen and extracted for measurement of tissue ACTH concentration. The remaining anterior pituitary glands from the nine month old rats were challenged with corticotropin releasing hormone (CRH) to test in vitro responsiveness. In nine month old rats, chronic ethanol consumption decreased plasma ACTH and corticosterone (P In vitro responsiveness of the adrenal gland to ACTH in nine month old rats consuming ethanol was unchanged (P > 0.05). Plasma ACTH and corticosterone concentrations were also decreased in 15 month old rats chronically consuming ethanol (P 0.05). The results of these experiments indicate that chronic ethanol consumption decreases hypothalamic-pituitary-adrenal function in aged rats.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29673/1/0000762.pd

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) interference of the synthesis and/or secretion of the anterior pituitary hormone adrenocorticotropin (ACTH).

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a toxic, undesired by-product formed during incineration, paper pulp bleaching and synthesis of chlorinated phenoxyacetic acid herbicides. Both humans and animals exhibit anorexia, progressive weight loss, mobilization of adipose tissue stores, and hypoglycemia after exposure to TCDD suggesting adrenal insufficiency. Adrenal steroidogenesis is regulated by the anterior pituitary hormone adrenocorticotropin (ACTH). TCDD treated rats exhibit elevated plasma ACTH concentrations, but plasma corticosterone (predominant corticosteroid in rat) levels are depressed. The research tested the hypothesis that TCDD interferes with anterior pituitary function by compromising ACTH synthesis and/or secretion thereby impairing adrenal steroidogenesis. TCDD (10\sp{-9}-10\sp{-13} M) caused an early (6 hour) and persistent (10 day) increase in basal levels of ACTH in primary cultures of rat anterior pituitary cells. However, pituitary responsiveness to corticotropin releasing hormone (CRH) and vasopressin was decreased. Adenosine 3\sp\prime,5\sp\prime-monophosphate (cAMP) stimulation increased secretion of ACTH after TCDD exposure suggesting that TCDD acts before cAMP formation. The increased basal ACTH concentrations appear to be mediated through the Aryl hydrocarbon receptor (Ah receptor) since: (1) the Ah receptor antagonist $\alpha$-naphthoflavone (ANF) blocks the stimulatory effect of TCDD on basal ACTH concentrations; (2) the Ah receptor agonist $\beta$-naphthoflavone (BNF) mimics the ACTH increases observed with TCDD exposure; (3) another halogenated aromatic hydrocarbon, 3,3\sp\prime,4,4\sp\prime,5-pentachlorobiphenyl (PCB), binds the Ah receptor and increases basal ACTH levels similarly to TCDD and (4) the halogenated aromatic hydrocarbon, 2,2\sp\prime,4,4\sp\prime,5,5\sp\prime-hexachlorobiphenyl (HCB), with no affinity for the Ah receptor, had no effect on basal ACTH concentrations. ACTH isolated from basal or CRH-stimulated media from pituitary cells exposed to TCDD did not stimulate corticosterone secretion from adrenal cell cultures as well as ACTH purchased from a commercial supplier suggesting that TCDD exposure alters the bioactivity of this peptide hormone. Understanding the regulation of ACTH secretion may lead to using its measurement and monitoring to assess exposure and risk of humans exposed to TCDD and other chlorinated hydrocarbons.Ph.D.ToxicologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/103371/1/9319490.pdfDescription of 9319490.pdf : Restricted to UM users only

Molecular cloning of Brevundimonas diminuta for efficacy assessment of reverse osmosis devices

Brevundimonas diminuta is the test organism specified in the United States Environmental Protection Agency\u27s (USEPA) reverse osmosis (RO) treatment device verification protocol. As non-selective growth medium is employed, enumeration of B. diminuta may be impaired due to interference by indigenous heterotrophic bacteria. Thus the microbial removal capability of the filtration system may be incorrectly assessed. As these treatment devices are used in emergency situations, the health of the public could be compromised. The objective of this study was to develop selective approaches for enumerating viable B. diminuta in test water. Two molecular approaches were investigated: expression of a kanamycin resistance gene and expression of a fluorescent protein gene. The USEPA protocol specifies a 0.3 μm cell size, so the expression of the selective markers were assessed following growth on media designed to induce this small cell diameter. The kanR strain was demonstrated to be equivalent to the wild type in cell dimension and survival following exposure to the test water. The kanR strain showed equivalent performance to the wild type in the RO protocol indicating that it is a viable alternative surrogate. By utilizing this strain, a more accurate validation of the RO system can be achieved. © IWA Publishing 2012