Some effects of DDT, toxaphene and polychlorinated biphenyl on thyroid function in Bobwhite quail

Effects of continuous feeding of toxaphene to white leghorn layers

Graded levels of toxaphene 0, 0.5, 5.0, 50 and 100 ppm were added to the diets of female white leghorn chicks from one day of age. Each treatment consisted of 90 randomly selected birds divided into three replicates of 30 birds each. Birds fed the 5, 50, and 100 ppm level of toxaphene exhibited osteomalacia manifested by sternal deformities and extremely friable ribs. A decrease in egg shell strength was found in chickens eating feed containing 5 ppm level of toxaphene. Toxaphene did not significantly alter egg production, hatchability or fertility in this trial.

The effect of flight, fasting and p,p'-DDT on thyroid hormones and corticosterone in Gambel's white-crowned sparrow, Zonotrichia leucophrys gambelli

This study examined the effects of p,p'-dichlorodiphenyltrichloroethane (p,p'-DDT), fasting and flight on thyroid hormones and corticosterone in Gambel's White-crowned Sparrows (Zonotrichia leucophrys gambelli). Female sparrows were dosed daily with either 5 mg p,p'-DDT per kg body mass or corn oil vehicle over 3 days. On the fifth day the sparrows were divided into 3 groups: (1) unstressed - non-stressed control sparrows; (2) fasted - sparrows fasted for intervals ranging from 20 min to 9 h; or (3) flown - sparrows flown in a wind tunnel for intervals between 20 min and 2.5 h while fasting. Half the sparrows from each group received DDT (DDT-dosed sparrows) and the other half corn oil vehicle only (vehicle sparrows). Trunk blood plasma was analyzed for thyroxine, triiodothyronine and corticosterone using radioimmunoassay. In the flown group, corticosterone was elevated (DDT-dosed 35.52 ng/ml, P < or = 0.05), and thyroxine was depressed (DDT-dosed 4.09 ng/ml, P < or = 0.05; vehicle 4.33 ng/ml, P < or = 0.05). Elevated corticosterone likely decreased thyroid hormone production through a negative feedback mechanism originating at the hypothalamus. Mean triiodothyronine concentrations did not differ among any of the test groups. Relative to time fasted and flown, thyroxine decreased in flown birds dosed with DDT (P < 0.001) and triiodothyronine decreased in fasted birds dosed with DDT (P = 0.004). The increased rate of hormone diminution may be a result of the ability of DDT to induce microsomal enzyme production.

Effects of environmental synthetic chemicals on thyroid function

Synthetic chemicals are released into the environment by design (pesticides) or as a result of industrial activity. It is well known that natural environmental chemicals can cause goiter or thyroid imbalance. However, the effects of synthetic chemicals on thyroid function have received little attention, and there is much controversy over their potential clinical impact, because few studies have been conducted in humans. This article reviews the literature on possible thyroid disruption in wildlife, humans, and experimental animals and focuses on the most studied chemicals: the pesticides DDT, amitrole, and the thiocarbamate family, including ethylenethiourea, and the industrial chemicals polyhalogenated hydrocarbons, phenol derivatives, and phthalates. Wildlife observations in polluted areas clearly demonstrate a significant incidence of goiter and/or thyroid imbalance in several species. Experimental evidence in rodents, fish, and primates confirms the potentiality for thyroid disruption of several chemicals and illustrates the mechanisms involved. In adult humans, however, exposure to background levels of chemicals does not seem to have a significant negative effect on thyroid function, while exposure at higher levels, occupational or accidental, may produce mild thyroid changes. The impact of transgenerational, background exposure in utero on fetal neurodevelopment and later childhood cognitive function is now under scrutiny. There are several studies linking a lack of optimal neurological function in infants and children with high background levels of exposure to polychlorinated biphenyls (PCBs), dioxins, and/or co-contaminants, but it is unclear if the effects are caused by thyroid disruption in utero or direct neurotoxicity.

Interactions of halogenated industrial chemicals with transthyretin and effects on thyroid hormone levels in vivo

Previous results in experimental systems have suggested that hydroxylated PCBs may decrease thyroid hormone levels through associative interaction with transthyretin. In the present paper it was investigated whether this property was also shared by various industrial chemicals, mainly pesticides. In total, 65 compounds from 12 chemical groups were analyzed for direct interference with the T4 binding site of transthyretin using a competitive binding assay. Sixty per cent of the compounds were competitive at a concentration level of 100 microM. Relatively strong interactions were observed by several chlorophenols, chlorophenoxy acids and nitrophenols, as well as by individual compounds such as hexachlorobenzene, dicofol, bromoxynil and tetrachlorohydroquinone. Examples from these chemical groups, e.g. pentachlorophenol, 2,4-dichlorophenoxybutyric acid, dinoseb and bromoxynil, also reduced plasma TT4 levels in rats. In addition, bromoxynil decreased plasma TT3 levels. The results suggest the existence of a number of halogenated industrial chemicals with a potential for lowering plasma thyroid hormone levels through interference with hormone transport carriers.

Interaction of chlorinated phenols with thyroxine binding sites of human transthyretin, albumin and thyroid binding globulin

Previous results (Brouwer and van den Berg, Toxicol. Appl. Pharmacol., 85 (1986) 301) indicated preferential binding of a hydroxylated metabolite of tetrachlorobiphenyl to transthyretin (TTR) a carrier of thyroxine (T4). In the present study it was investigated whether the T4 binding site of TTR could be occupied specifically by hydroxylated chlorinated aromatic compounds using chlorinated phenol congeners as model compounds in a competition assay with [125I]T4. Chlorinated aromatics such as 2,3-dichlorobenzene and 3,4,3',4'-tetrachlorobiphenyl, and phenols such as 4-hydroxybiphenyl and phenol were inefficient competitors. All chlorinated phenols tested were competitors for the T4 binding site of TTR. The ranking in competition was pentachlorophenol (PCP) greater than trichlorophenols greater than dichlorophenols greater than monochlorophenols. Structures with chlorine in both ortho positions to the hydroxyl group were more efficient competitors. The relative affinity of binding of pentachlorophenol (PCP) to TTR was about twice that of T4. Scatchard analysis showed that PCP mainly decreased the affinity constant K11 while the binding capacity R1 was not altered, indicating a competitive type of inhibition. PCP was also able to compete with T4 sites on albumin with a relative affinity of 0.25. T4 binding to thyroid binding globulin (TBG) was much less affected by interference of PCP (relative affinity 0.001). The results indicate a specific interaction of chlorophenols with the T4 binding site of TTR.

Studies on the tissue disposition and fate of [14C]toxaphene in Japanese quail

The disposition and the fate of a [14C]toxaphene preparation was studied in adult and juvenile female Japanese quail. The distribution of [14C]toxaphene in the body is dominated by high concentrations of radioactivity in the adipose tissue and the egg yolk, and, especially in juvenile birds, in the bone marrow. The [14C]toxaphene compounds present in the fat tend to be less polar than the parent [14C]toxaphene. More than half of the radioactive dose is excreted via the droppings, eggs, and preen gland within a few days, with biliary excretion playing a major role. The main part of the radioactivity in feces and urine consists of water soluble compounds, a part of which is indicated to be glucuronide and sulfate conjugates, but other metabolites are probably also present. A possible connection between the toxaphene residues in the bone and the known toxaphene induced osteomalacia in birds is discussed.

World PCBs map: storage and effects in man and his biologic environment in the 1970s

PCB residues are found in biota all over the world. A biologic magnification of PCBs has been demonstrated in the food chain: plankton-fish-fish eating birds. A world map of the PCBs residues in biota and some of their biologic effects are given in this study. The biologic effects of PCBs are varied and may generally be explained by the induction or inhibition of the activity of a large number of enzymes, which upsets quantitatively, normal biochemical processes. Harm to reproduction, growth, development, defense systems, tissues, and organs appeared in susceptible organisms as a result of such changes or as a chain reaction to heterostases. The adverse health effects, observed in persons occupationally exposed and in those accidentally poisoned, point to the risk for the general population of an ever-increasing environmental pollution by PCBs. There is need for an integrated approach, consisting of epidemiologic studies on high risk groups in the general population and in persons occupationally exposed, as well as periodic assessment of PCB residues in man, his food, and feed supplies.

Ninety-day toxicity of photomirex in the male rat

Photomirex (8-monohydromirex) is a demonstrated environmental contaminant and was observed in previous short-term studies to produce lesions in the liver, thyroid and testes of male rats. The present study was undertaken to confirm those observations and to determine the effects after a longer period of exposure. Male rats were fed photomirex for 13 weeks at levels of 0.20, 1.0, 5.0, 25 and 125 ppm in the diet. Deaths were observed in animals receiving the highest dose. Decreased body weight gain and food intake were also observed in that group. Liver weights were increased at 5.0 ppm photomirex and higher. Photomirex caused changes in several biochemical parameters including serum sorbitol dehydrogenase and hepatic aniline hydroxylase activities. Dose-related histological abnormalities were observed in the thyroid and liver starting at the lowest dose level. These results confirm earlier findings and show that photomirex is a potent hepato- and thyrotoxin.

Effect of toxaphene on the performance of White Leghorn layers and their progeny

An experiment involving 48 white leghorn layers fed 0, 10 and 100 p.p.m. of toxaphene has been conducted. Except for a slight decrease in egg production, no adverse effects on various performance parameters including fertility, hatchability and survival of progeny were observed. A significant increase (P less than .05) in average 7-day weights of progeny was noted.

[Effects of DDT and lindane on thyroid function in the rat]

Using the previously described test method, the authors studied with the aid of iodine-131 labelled NaI the effects of daily doses of 30 and 75 mg DDT/kg of body weight, and of 12 and 36 mg of lindane/kg of body weight on the iodine and hormone metabolism in the rat. With DDT, the authors observed a marked increase of the thyroid mass and of the thyroid tri-iodothyronine and thyroxin levels and a simultaneous decrease of the thyroid iodine level. The values for serum iodine and protein-bound iodine were reduced. Serum thyroxin was slightly increased. Serum tri-iodothyronine was markedly increased, which was also true of the iodine fractions in the liver. Lindane was considerably less effective. Only the decrease of thyroid tri-iodothyronine and the simultaneous increase of thyroid thyroxin were striking. In the serum, both hormones remained unchanged. The values for the urine fractions of both the active principles were indicative of a hypofunction. The causes of the changes observed were discussed with regard to the findings of other authors. The present results permit the conclusion that the effects of the pesticides tested are obviously complex by nature.