Avian Models for Research in Toxicology and Endocrine Disruption

Abstract

There have been significant strides in our knowledge of the effects of toxicants on birds. This communication presents a brief review of avian toxicology with emphasis on effects of common toxicants that disrupt endocrine system function and control of reproduction, growth, development, stress and calcium-phosphorus homeostasis. For those hormonal systems that act through hypothalamic-pituitary axes, we emphasize current knowledge of the axis``level'' at which the toxicants alter endocrine control. The classes of toxicants discussed are acid rain andyor aluminum, organochlorines such as polychlorinated biphenyls (PCBs), fungicides and insecticides, mycotoxins, (PCBs) and petroleum. The use of several types of avian models for endocrine disruption studies is discussed in the context of utility and practicality, developmental modes, species sensitivity and the choice of sentinel species. Promising new approaches for avian toxicological research are considered including shell-less embryos, continuous-flow administration of toxicants to avian embryos, gene microarrays, proteomics and metabolomics.

Comparison of the in vitro effects of TCDD, PCB 126 and PCB 153 on thyroid-restricted gene expression and thyroid hormone secretion by the chicken thyroid gland

“…To our knowledge this is the first in vitro investigation showing a direct influence of TCDD, coplanar PCB 126 and non-coplanar PCB 153 on the expression of thyroid-restricted genes in the adult chicken. Previous studies revealed that TCDD and PCBs may impair thyroid function by changing the activity of the HPT axis (Gould et al, 1999;Scanes and McNabb, 2003). Byrne et al (1987) discovered that PCB exposure diminished thyroidal response to exogenous TSH in rats, which also indicates a direct inhibition of the thyroid gland.…”

The Hypothalamic-Pituitary-Thyroid (HPT) Axis in Birds and Its Role in Bird Development and Reproduction

“…In rats, exposure to PCBs causes marked decreases in plasma T 4 and T 3 (see, e.g., Barter and Klaassen, 1992a, 1992b). In contrast, a variety of laboratory and field studies in birds give much more equivocal and often inconsistent results (review: Scanes and McNabb, 2003). Thus, in many of these studies one cannot 180 F. M. A. McNABB tell whether the chemical is affecting thyroid function or whether the effect is obscured by variability in the circulating hormones.…”

Polychlorinated biphenyl effects on avian hepatic enzyme induction and thyroid function

“…Some of these developmental abnormalities include defects of the central nervous system and skeletal anomalies, such as incomplete skeletal ossification and stunted growth. For instance, embryos of fish-eating birds collected at contaminated sites in the Great Lakes had shorter femur and tarsal lengths than those collected at reference sites (reviews, Fox, 1993;McNabb and Fox, 2003;Scanes and McNabb, 2003).…”

“…These chemicals are lipophilic, so they are stored in body fats and biomagnify up the food chain, increasing exposure in top predators such as fish-eating birds. In addition, female birds deposit these chemicals in their eggs, exposing their young as embryos, when they may be most vulnerable to toxicants (reviews, McNabb and Fox, 2003;Scanes and McNabb, 2003).…”

“…In wildlife such as fish-eating birds, polychlorinated biphenyls (PCBs) have been associated with developmental abnormalities that may be due to altered thyroid function (reviews, Fox, 1993;McNabb and Fox, 2003;Scanes and McNabb, 2003). This has stimulated research on how PCBs affect thyroid function, but most of the research has been done on laboratory mammals.…”