An Atlantic cod (Gadus morhua L.) pituitary model system for reproductive and reprotoxic testing in vitro

Due to factors such as overfishing, climate changes and pollution, most fish stocks are in decline. This is also the case for the commercially important marine species, Atlantic cod (Gadus morhua). As a result, the last few decades there has been growing interest to cultivate this species. However, a major set-back in cod aquaculture is precocious sexual maturity in farmed fish, leading to decreased flesh quality and quantity, higher susceptibility to diseases and spread of gametes from the net-pens to the surrounding environment. Sexual maturation in fish, as in other vertebrates, is regulated through the brain-pituitary-gonadal (BPG) axis. The brain produces gonadotropin releasing hormone (Gnrh) which stimulate synthesis and release of follicle-stimulating hormone (Fsh) and luteinizing hormone (Lh) from gonadotrope cells in the pituitary. Fsh and Lh travel through the blood to the gonads, where they initiate gametogenesis and sex steroid production. The BPG axis is modulated through external factors such as temperature and light, and internal factors such as nutritional status. In recent years, endocrine disruptive (ED) properties have been demonstrated in many commercial compounds released into the environment, some of which have the capacity to affect fish development and reproduction. The exact mechanisms behind many of the above-mentioned regulating factors are largely unknown. Therefore, the primary aim of this thesis was to investigate further the reproductive-related regulation of the Atlantic cod pituitary. In order to do so, a primary culture model system using dispersed pituitary cells was developed. The system was optimized to mimic cod physiology and the natural environment, leading to stable, healthy, and physiologically relevant cultures. Once established, the culture system was subsequently used to investigate potential effects from sex steroids, the stress hormone cortisol, and the suspected ED contaminants, bisphenol A (BPA) and tetrabromobisphenol A (TBBPA), on pituitary gene expression and cell viability. By using cod donors at different stages of sexual maturity, potential maturity-dependent effects were also assessed. The results demonstrate that pituitary cultures are receptive to direct mechanisms from both endogenous and exogenous factors and that the Atlantic cod pituitary is a site for direct influence from sex steroids, stress, and pollutants. Dependent on dose and stage of sexual maturity, all tested substances were able to affect cell viability and gene expression and could potentially modulate cod reproductive function. For future work, this model system can be a useful tool for investigating physiological mechanisms in the pituitary and for screening of potential effects from environmental contaminants