Hepatic indices of thyroid status in rats treated with hexachlorobenzene

Abstract

The functional thyroid status of hexachlorobenzene (HCB)-treated rats was studied. HCB caused a depletion of serum thyroxine (T4), but did not change L-3,5,3'-triiodothyronine (T3) levels in serum of rats. The activities of the thyroid regulated mitochondrial enzyme L-glycerolphosphate dehydrogenase (LGPD) and cytosolic enzymes, malic enzyme (ME), glucose-6-phosphate dehydrogenase (G6PD) and 6-phosphogluconate dehydrogenase (6PGD) were assayed in livers of normal and HCB (100 mg/100 g bw) treated Wistar rats. Mitochondrial LGPD activity did not change significantly, however ME, 6GPD and G6PD were induced by HCB only in non-thyroidectomized animals. The absence of cytosolic enzymes induction in thyroidectomized rats treated with HCB indicates that HCB is not intrinsically thyromimetic. The induction of hepatic ME, G6PD and 6PGD activities in HCB thyroidectomized rats was dependent on the presence of thyroid hormone. The unchanged activity of mitochondrial LGPD in contrast to the increased activities of the cytosolic enzymes ME, G6PD and 6PGD is not consistent with a shift in functional thyroid status following HCB treatment.

The role of type I and type II 5′ deiodinases on hexachlorobenzene-induced alteration of the hormonal thyroid status

“…The present results showing that thyroid hormones concentrations were not modified by HCB treatment in the liver, are in agreement with a previous report from our laboratory showing that the pattern of thyroid-responsive enzyme activities in livers of rats treated with HCB was not compatible with a functional shift in hepatic thyroid status (Kleiman de Pisarev et al, 1995).…”

“…Our data indicate that the mechanism of action of HCB on thyroid homeostasis is complex and tissue-specific, leading to different effects in the studied tissues. In this respect, we have previously demonstrated that HCB increases malic enzyme activity in rat liver, but decreases this enzyme activity in BAT (Alvarez et al, 2000;Kleiman de Pisarev et al, 1995).…”

Relationship of Thyroid Hormone Levels to Levels of Polychlorinated Biphenyls, Lead, p,p ′ - DDE, and Other Toxicants in Akwesasne Mohawk Youth

“…The negative association of HCB with T 4 levels among Akwesasne adolescents is consistent with the literature. Numerous animal studies have demonstrated HCB-induced hypothyroidism, with T 4 levels being particularly sensitive in rats (Alvarez et al 2005; Foster et al 1993; Kleiman de Pisarev et al 1990, 1995; Rozman et al 1986; van Raaij et al 1993). Lower T 4 levels associated with HCB exposure may be attributed to peripheral disposition of T 4 (Kleiman de Pisarev et al 1989) or increased hepatic T 4 metabolism (Kleiman de Pisarev et al 1990).…”

Reproductive effects of hexachlorobenzene in female rats

“…The increase in those parameters is a well-characterized effect of HCB under the current experimental conditions. 19 However, during the time of the experiment, mean body, ovarian and uterine weights of the treatment group were not significantly altered by HCB ( Table 1). The external aspect of the uterus and oviducts from treated rats was of less irrigation and colour.…”

“…This dose was previously used in our and other's laboratories to induce hepatic porphyria and liver lipogenic enzymes and to study thyroid status. 18,19 Treatment with HCB had no effect on the general health of the animals, as shown by the healthy appearance of the rats, and no effect on body weight or water and food consumption. After 2 weeks of HCB administration, the cycles were observed again until the day of sacrifice, i.e.…”