## 1 Introduction  
Contamination from heavy metals has occurred in rivers worldwide, especially during the last decade, with river water and sediments being a major environmental focus [1]. Concerns over heavy metals are due to their profusion, persistence, and toxicity, as reported in several studies [2, 3, 4]. The pollution of aquatic environments is closely associated with human activities, and lakes and rivers can receive heavy metals as a result of discharges of untreated or inadequately treated wastewater from domestic, industrial, and agricultural sources, as well as by natural processes that can contribute to metal contamination. Both natural and anthropogenic activities are largely liable for the heavy metal occurrence in the environment [5, 6, 7, 8]. Heavy metals can be classified in two main groups, as essential and potentially toxic. Iron (Fe), manganese (Mn), cobalt (Co), nickel (Ni), copper (Cu), and zinc (Zn) are believed to be essential, as they form a cofactor for many enzymes, interact in metabolic activities, and are considered to be nutritionally essential for humans. The toxic heavy metals of arsenic (As), cadmium (Cd), lead (Pb), and mercury (Hg) do not show any nutritional or beneficial effects on human health and can have harmful effects, even at low concentrations when ingested over a long period [9]. In recent years, there has been an increase in articles showing that some heavy metals could influence the endocrine system, and Cd, Hg, As, Pb, Ni, Mn, and Zn have been classified as endocrine-disrupting chemicals (EDCs) or metalloestrogens [10; 11]. These heavy metals exert estrogenic effects through the alteration of the gene expression and/or modifying the activity of estrogenic receptors. Their presence in terrestrial and aquatic environments is well documented [12; 13; 14; 15]. Fish populations are repeatedly exposed to heavy metal contamination from different food sources and water conditions, and an understanding of toxicant uptake and responses in fish may therefore have a high ecological relevance. They are also an important link between the environment and human populations through fisheries and consumption by local and other markets [16]. Fish are frequently used in biomonitoring programs as they offer several specific advantages for describing the natural characteristics of aquatic systems and in assessing biological and biochemical responses to environmental contaminants [17; 18]. Thus, they are recognized as bioindicators of chemical pollution [16]. Amongst the fish that are used for biomonitoring aquatic ecosystems, those of the genus Salmo, in particular various species of trout, are commonly employed to monitor loads of organic compounds and heavy metals [19; 20; 21; 22; 23; 24; 25]. Brown trout (_Salmo trutta trutta_) is a fish species native to rivers of the Abruzzi region and is the dominant species in most wild rivers, particularly in the Gran Sasso-Monti della Laga National Park. This park is one of the largest in Italy, and its biodiversity is among Europe's richest. In order to assess exposure to or the effects of environmental pollutants on aquatic environments or ecosystems, several bioassays based on sensitive biomarkers have been developed and VTG has been demonstrated to be a consistent biomarker to evaluate the estrogenic pollution [17; 26]. This study fits into a local biomonitoring plan program carried out from the National Park of Gran Sasso e Monti della Laga office to confirm the wild fish health status living in a protected area, apparently unpolluted. This investigation was conducted to measure the heavy metal contamination in wild brown trout from two different rivers located in the Gran Sasso-Monti della Laga National Park, Abruzzi region (Italy). Furthermore, to assess the potential adverse effects on the endocrine system from low-level environmental exposures to metals, we investigated the VTG pattern in fish.