Thesis (Ph. D.)--University of Texas at Austin, 2002. / Vita. Includes bibliographical references. Available also from UMI Company.

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Thesis (Ph. D.)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references (leaves 114-131). Available also in a digital version from Dissertation Abstracts.

Thesis (Ph. D.)--University of Texas at Austin, 2002. / Vita. Includes bibliographical references (leaves 125-138). Available also in a digital version from Dissertation Abstracts.

Thesis (Ph. D.)--University of Texas at Austin, 2002. / Vita. Includes bibliographical references. Available also from UMI Company.

Not available / text

Thesis (Ph. D.)--University of Texas at Austin, 2004. / Vita. Includes bibliographical references.

Many studies in animals and humans have demonstrated that exposure topolychlorinated biphenyls (PCBs) can interfere with the normal function of the thyroid system. In this study, Atlantic croaker (Micropogonias undulatus) were exposed to a PCB mixture (Aroclor 1254) or one of three individual congeners (ortho-PCB 153, ortho-PCB 47 or planar PCB 77) in the diet for 30 days to investigate the effects of PCBs on thyroidal status. Thyroid hormones, thyroxine (T4) and triiodothyronine (T3) were extracted from plasma samples and measured with an enzyme-linked immunosorbent assay. Both male and female croaker exposed to the PCB mixture Aroclor 1254 (0.2 and 1.0 mg/kg body wt/day) had decreased plasma levels of total T3 when compared to the parallel control groups, but the effects on total T4 levels were inconsistent. Exposure to PCB 153 (0.1 and 1.0 mg/kg body wt /day) significantly lowered both T4 and T3, while PCB 47 at the same doses had no effect on thyroid hormone levels. Fish exposed to PCB 77 had no effect on T4 or T3 levels except an increase in T4 levels at the highest dose employed (0.1 mg/kg body weight/day). However, this dose of PCB 77 caused partial loss of appetite and may be too high to be relevant for the effects observed after exposure to Aroclor 1254 considering the fact that it constitutes only 0.31% of the PCB mixture. The results of the present study demonstrate that exposure to synthetic endocrine disrupting chemicals, such as PCBs at the higher end of environmentally realistic concentrations can have profound effects on the thyroidal status of Atlantic croaker. The ability of Aroclor 1254, as well as ortho-PCB 153, to consistently disrupt the natural homeostasis of the thyroid system in croaker is an important finding that contributes to a better understanding of PCB endocrine toxicity in teleosts.

The goal of this research was to examine the role of the novel membrane progestin receptor alpha (mPR[alpha]) in the stimulation of sperm hypermotility by the progestin 17,20[beta],21-trihydroxy-4-pregnen-3-one (20[beta]-S) in two teleosts; the Atlantic croaker (Micropogonias undulatus) and the southern flounder (Platylicthys lethigstomata). In croaker, the expression, localization and hormonal regulation of mPR[alpha] in testis and sperm were investigated, as were the intracellular signaling pathways activated by 20[beta]-S and mPR[alpha] to induce croaker sperm hypermotility. In flounder, stimulation of sperm hypermotility by 20[beta]-S and binding of this steroid to flounder sperm membranes were examined. Finally, expression of mPR[alpha] was investigated in flounder testes and the expression and localization of this receptor in flounder testis and sperm was examined. In croaker sperm, mPR[alpha] was expressed on the plasma membrane and localized to the midpiece. Expression of mPR[alpha] was also shown to be associated with high sperm motility and regulated by gonadotropin. The signaling pathways activated by 20[beta]-S in croaker sperm were shown to involve activation of olfactory G-proteins (Golf). Subsequent activation of membrane adenylyl cyclases was also demonstrated and shown to be necessary for 20[beta]-S-stimulated cAMP production and 20[beta]-S-induction of sperm hypermotility. Furthermore, co-immunoprecipitation studies show mPR[alpha] and Golf physically associate with one another, establishing mPR[alpha] as the mediator of 20[beta]-S actions in croaker sperm. Finally, evidence was obtained for progestin-stimulation of sperm hypermotility and the presence of mPR[alpha] on sperm membranes in another marine teleost species belonging to a different family, the southern flounder. In addition, mPR[alpha] was shown to be expressed on flounder sperm membranes and also localized to the sperm midpiece. Results from the following studies support the hypothesis that mPR[alpha] is the mediator of 20[beta]S-stimulated sperm hypermotility in croaker and is a likely intermediary in southern flounder. Furthermore, these data provide a plausible mechanism by which 20[beta]-S and mPR[alpha] stimulate croaker sperm hypermotility. In addition, these results provide the first evidence of hormonal activation of Golf proteins for any species. Finally, mPR[alpha]-mediated mechanisms to increase sperm motility are suggested to be evolutionarily conserved in teleosts since they also likely exist in a non-sciaenid species, the southern flounder.

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