Interactions between cortisol and Rhesus glycoprotein expression in ureogenic toadfish, Opsanus beta

Abstract

SUMMARYIn their native environment, gulf toadfish excrete equal quantities of ammonia and urea. However, upon exposure to stressful conditions in the laboratory (i.e. crowding, confinement or air exposure), toadfish decrease branchial ammonia excretion and become ureotelic. The objective of this study was to determine the influences of cortisol and ammonia on ammonia excretion relative to expression of Rhesus (Rh) glycoproteins and the ammonia-fixing enzyme, glutamine synthetase (GS). In vivo infusions and/or injections were used to manipulate corticosteroid activity and plasma ammonia concentrations in ureotelic toadfish. Metyrapone treatment to lower circulating cortisol levels resulted in a 3.5-fold elevation of ammonia excretion rates, enhanced mRNA expression of two of the toadfish Rh isoforms (Rhcg1 and Rhcg2), and decreased branchial and hepatic GS activity. Correspondingly, cortisol infusion decreased ammonia excretion 2.5-fold, a change that was accompanied by reduced branchial expression of all toadfish Rh isoforms (Rhag, Rhbg, Rhcg1 and Rhcg2) and a twofold increase in hepatic GS activity. In contrast, maintenance of high circulating ammonia levels by ammonia infusion enhanced ammonia excretion and Rh expression (Rhag, Rhbg and Rhcg2). Toadfish treated with cortisol showed an attenuated response to ammonia infusion with no change in Rh mRNA expression or GS activity. In summary, the evidence suggests that ammonia excretion in toadfish is modulated by cortisolinduced changes in both Rh glycoprotein expression and GS activity. Supplementary material available online at

Nitrogenous Waste Handling by Larval ZebrafishDanio rerioin Alkaline Water

“…In addition to those pathways, there is a growing focus on the facilitated diffusion of ammonia (likely in the form of NH 3 ) through a series of strategically positioned isoforms of ammonia-conducting Rh glycoproteins. Rh glycoproteins have been identified in several fish species, and on the basis of gene/protein expression analyses and lossof-function studies, it is clear that Rh glycoproteins constitute an important mechanism for ammonia excretion in fish (Nakada et al 2007a(Nakada et al , 2007bNawata et al 2007;Shih et al 2008;Braun et al 2009a;Braun and Perry 2010;Perry et al 2010;Wu et al 2010;Rodela et al 2012;Bucking et al 2013a; for recent reviews on mechanisms of ammonia excretion, see Wright andWood 2009, 2012). The existence of multiple mechanisms for ammonia excretion highlights the importance of effectively removing ammonia to prevent its toxic effects (Chew et al 2005).…”

Experimental manipulation of perceived predation risk and cortisol generate contrasting trait trajectories in plastic crucian carp

“…Experimental tanks were assigned (random permutation) to one of four treatments: predator absent with sham implant (Sham), predator absent with cortisol implant (CORT), predator present with sham implant (P+Sham) and predator present with metyrapone implant (P+MTP). Metyrapone, here used as a cortisol blocker, acts by inhibiting the synthesis of cortisol from 11-deoxycortisol by 11β-hydroxylase, a biomedical process that has been demonstrated to successfully inhibit cortisol synthesis in teleost fish (Hopkins et al, 1995;Milligan, 2003;Rodela et al, 2012). On 10 December, all fish were weighed (to the nearest 0.1 g) to enable calculation of the total volume of substances needed to produce implants suitable for body mass-specific delivery (see 'Implants', below).…”

Comment: Practices for Drawing Blood Samples from Teleost Fish

“…; Rodela et al. ; Zimmer and Wood ), thus making repeated sampling possible over short sampling intervals. However, applying a “rule” across the board is not helpful, especially considering the great diversity in fish size and physiology.…”

“…The 3-month interval proposed by Duman et al (2019) has no scientific basis: sometimes it may be on the order of minutes or hours, and in other cases it may be weeks or months depending on the nature of the research questions being asked. The effects of repeated blood sampling on parameters such as hematocrit can be offset by re-injecting salinesuspended red cells back into the animal (e.g., Rogers et al 2003;Rodela et al 2012;Zimmer and Wood 2014), thus making repeated sampling possible over short sampling intervals. However, applying a "rule" across the board is not helpful, especially considering the great diversity in fish size and physiology.…”