MP13 Aquatic Ecotoxicology
Monday, 14 November 2005: 8:00 AM - 6:30 PM in Exhibit Hall

(WAT-1117-840572) Computational Model of the Hypothalamic-Pituitary-Gonadal Axis in Female Fathead Minnows: Baseline state of unexposed fish.

Watanabe, K¹, Jensen, K², Villenueve, D², Ankley, G², Orlando, E³, Sepulveda, M⁴, Bencic, D⁵, Whitehead, T⁶, Miller, D⁷, Denslow, N⁸, ¹ Oregon Health & Science University, Beaverton, OR, USA² U.S. EPA, ORD, NHEERL, MED, Duluth, MN, USA³ Florida Atlantic University, Boca Raton, FL, USA⁴ Purdue University, West Lafayette, IN, USA⁵ U.S. EPA, ORD, NERL, EERD, Cincinnati, OH, USA⁶ U.S. EPA, ORD, NERL, ERD, Athens, GA, USA⁷ U.S. EPA, ORD, NHEERL, MED, Grosse Ile, MI, USA⁸ University of Florida, Gainesville, FL, USA

ABSTRACT- The fathead minnow (FHM, Pimephales promelas) has a widespread distribution throughout the United States, and has been identified by the U.S. Environmental Protection Agency as an excellent model for evaluating the effects of several endocrine disrupting chemicals. The normal reproductive biology of FHM has been investigated by Jensen et al. (Comp Biochem Physiol C, 128(1): 127-141.); however, there is very little known about the neuroendocrine regulation of reproduction in this species. To better understand the reproductive system of this species, we developed a physiologically based model of the hypothalamic-pituitary-gonadal axis in female FHM. The model structure included compartments representing the gill, brain, gonad, liver and other tissues. Within these compartments, more detailed biochemical processes were included such as steroidogenesis in the gonad, the formation of vitellogenin in the liver, and regulatory signaling in the control of reproduction in the brain. Measurements of the number of eggs spawned, and plasma concentrations of 17- estradiol, testosterone, and vitellogenin from 113 unexposed, control fish were used to calibrate the model. These fish were used in experiments conducted in the laboratories of the Mid-Continent Ecology Division (MED), U.S. Environmental Protection Agency. A hierarchical statistical model and Markov Chain Monte Carlo simulations were used to estimate the unknown model parameters.

Key words: Pimephales promelas, HPG axis, physiological model, reproduction