Foetal hypothalamic and pituitary expression of gonadotrophin-releasing hormone and galanin systems is disturbed by exposure to sewage sludge chemicals via maternal ingestion

Abstract

Animals and humans are chronically exposed to endocrine disrupting chemicals (EDCs) that are ubiquitous in the environment. There are strong circumstantial links between environmental EDC exposure and both declining human/wildlife reproductive health and the increasing incidence of reproductive system abnormalities. The verification of such links, however, is difficult and requires animal models exposed to 'real life', environmentally relevant concentrations/mixtures of environmental contaminants (ECs), particularly in utero, when sensitivity to EC exposure is high. The present study aimed to determine whether the foetal sheep reproductive neuroendocrine axis, particularly gondotrophin-releasing hormone (GnRH) and galaninergic systems, were affected by maternal exposure to a complex mixture of chemicals, applied to pasture, in the form of sewage sludge. Sewage sludge contains high concentrations of a spectrum of EDCs and other pollutants, relative to environmental concentrations, but is frequently recycled to land as a fertiliser. We found that foetuses exposed to the EDC mixture in utero through their mothers had lower GnRH mRNA expression in the hypothalamus and lower GnRH receptor (GnRHR) and galanin receptor (GALR) mRNA expression in the hypothalamus and pituitary gland. Strikingly, this, treatment had no significant effect on maternal GnRH or GnRHR mRNA expression, although GALR mRNA expression within the maternal hypothalamus and pituitary gland was reduced. The present study clearly demonstrates that the developing foetal neuroendocrine axis is sensitive to real-world mixtures of environmental chemicals. Given the important role of GnRH and GnRHR in the regulation of reproductive function, its known role programming role in utero, and the role of galanin in the regulation of many physiological/neuroendocrine systems, in utero changes in the activity of these systems are likely to have long-term consequences in adulthood and represent a novel pathway through which EC mixtures could perturb normal reproductive function.

Fig. 1

mRNA expression of galanin receptors 1, 2 and 3 relative to β-actin in maternal (A) hypothalamus and (B) pituitary gland and in foetal C) hypothalamus and D) pituitary gland following in-utero exposure to sewage sludge chemicals (Exposed). *P<0.05 in comparison with respective control value.

Fig. 2

Maternal and foetal hypothalamic galanin mRNA expression following in-utero exposure to sewage sludge chemicals (Exposed).

Fig. 3

mRNA expression of (A) GnRH and (B) GnRHR relative to β-actin in foetal hypothalamus following in-utero exposure to sewage sludge chemicals (Exposed). **P<0.01 in comparison with respective control value.