Publication Date




Embargo Period


Degree Type


Degree Name

Doctor of Philosophy (PHD)


Marine Biology and Fisheries (Marine)

Date of Defense


First Committee Member

Martin Grosell

Second Committee Member

M. Danielle McDonald

Third Committee Member

Majorie F. Oleksiak

Fourth Committee Member

Lynne A. Fieber

Fifth Committee Member

Martin Tresguerres


The findings in the present dissertation describe the regulatory role the guanylin peptides play in seawater teleost intestinal physiology through the use of the model organism, the Gulf toadfish (Opsanus beta). For the majority of the findings, renoguanylin (a guanylin peptide exclusive to teleost fish) is used as an experimental tool and elicits responses in the posterior intestine and rectum of the Gulf toadfish, but does not affect the anterior intestine. Both the posterior intestine and rectum display secretory short-circuit currents, reversed transepithelial potentials, and increased conductance in response to renoguanylin stimulation. These changes are driven primarily by chloride secretion via activation of an apical cystic fibrosis transmembrane conductance regulator (CFTR) chloride PPchannel, and inhibition of the apical absorptive ion transporters, SLC26a6 (a bicarbonate/chloride antiporter) and NKCC2 (SLC12a1). The combined effects of renoguanylin stimulation on the posterior intestine and rectum are inhibited transepithelial salt and water absorption. This is an unexpected response by the intestine of a seawater teleost, given that these fish must continually drink water and absorb it by the intestine to counteract pervasive branchial water loss to their hypertonic environment. Furthermore, the response to renoguanylin is elevated when Gulf toadfish are acclimated to hypersalinity, a situation that increases the formation of carbonate precipitates in the intestine, as part of normal osmoregulatory processes. The tissue response in hypersalinity also coincides with increased gene expression of CFTR and NKCC1 (SLC12a2), which constitute a chloride-secretory pathway that is stimulated by renoguanylin. The above observations suggest that the renoguanylin-stimulated secretory response is, at the very least, important when teleosts encounter hypertonic environments. It is proposed that the secretory response facilitates the removal of solids, such as carbonate precipitates, from the intestinal tract. A secretory response would ensure the availability of fluid in the intestinal lumen for the purposes of increasing the efficiency of peristaltic movement of solids.


guanylin; uroguanylin; renoguanylin; bicarbonate; chlrodie; CFTR; osmoregulation; fluid secretion; hypersalinity; marine teleost