Effects of Cortisol and Salinity Challenge on Water Balance in Developing Larvae of Tilapia ( Oreochromis mossambicus )

SUMMARY We have explored intestinal function in the euryhaline killifish Fundulus heteroclitus after transfer from brackish water (10%seawater) to fresh water. Plasma Na+ and Cl–concentrations fell at 12 h post-transfer, but recovered by 7 days. Drinking rate decreased substantially at 12 h (32% of control value) and remained suppressed after 3 and 7 days in fresh water (34 and 43%). By contrast, there was a transient increase in the capacity for water absorption measured across isolated intestines in vitro (3.3- and 2.6-fold at 12 h and 3 days),which returned to baseline after 7 days. These changes in water absorption could be entirely accounted for by changes in net ion flux: there was an extremely strong correlation (R2=0.960) between water absorption and the sum of net Na+ and net Cl–fluxes (3.42±0.10 μl water μmol–1 ion). However,enhanced ion transport across the intestine in fresh water would probably not increase water uptake in vivo, because the drinking rate was far less than the capacity for water absorption across the intestine. The increased intestinal ion absorption after freshwater transfer may instead serve to facilitate ion absorption from food when it is present in the gut. Modulation of net ion flux occurred without changes in mRNA levels of many ion transporters (Na+/K+-ATPase α1a,carbonic anhydrase 2, CFTR Cl– channel,Na+/K+/2Cl– cotransporter 2, and the signalling protein 14-3-3a), and before a measured increase in Na+/K+-ATPase activity at 3 days, suggesting that there is some other mechanism responsible for increasing ion transport. Interestingly, net Cl– flux always exceeded net Na+ flux, possibly to help maintain Cl– balance and/or facilitate bicarbonate excretion. Our results suggest that intestinal NaCl absorption from food is important during the period of greatest ionic disturbance after transfer to fresh water, and provide further insight into the mechanisms of euryhalinity in killifish.

Section: Plasticity Of Intestinal Function After Freshwater Transfersupporting

confidence: 92%

Section: Molecular Responses To Transfer To Freshwatermentioning

confidence: 99%

Plasticity of osmoregulatory function in the killifish intestine:drinking rates, salt and water transport, and gene expression after freshwater transfer

Scott

Schulte

Wood

2006

“…Although transfer to higher salinity increases drinking rate, simultaneous addition of cortisol increases drinking rate to an even greater extent in both tilapia larvae (Lin et al, 2000) and juvenile rainbow trout (Fuentes et al, 1996). The estimated drinking rates for cannulated toadfish may thus be higher than those measured in non-cannulated fish due to the combination of high salinity and stress from handling and extensive surgical procedures.…”

Section: Increased Drinking Rate In Elevated Salinitymentioning

confidence: 96%

“…It is known that cortisol, a key stress hormone, has a role in the regulation of drinking rate in teleost fish (Fuentes et al, 1996;Lin et al, 2000). Although transfer to higher salinity increases drinking rate, simultaneous addition of cortisol increases drinking rate to an even greater extent in both tilapia larvae (Lin et al, 2000) and juvenile rainbow trout (Fuentes et al, 1996).…”

Section: Increased Drinking Rate In Elevated Salinitymentioning

confidence: 99%

Effects of salinity on intestinal bicarbonate secretion and compensatory regulation of acid–base balance inOpsanus beta

Genz

Taylor

Grosell

2008

“…Therefore, LPS must have been taken up predominantly by drinking. Indeed, using the freshwater drinking rate described for tilapia larvae by Lin et al (2000), it can be calculated that during the 10·day experimental period our juvenile tilapia have ingested 22·mg·LPS·kg …”

Section: Lps Effects In Juvenile Tilapiamentioning

confidence: 99%

Bacterial lipopolysaccharide (LPS) modulates corticotropin-releasing hormone (CRH) content and release in the brain of juvenile and adult tilapia (Oreochromis mossambicus; Teleostei)

Pepels

Bonga

Balm

2004

SUMMARY Although immune endocrine interactions in teleost fish have been shown to involve adrenocorticotropin hormone (ACTH) and cortisol, the involvement of corticotropin-releasing hormone (CRH) has not been demonstrated. The present study investigates whether treatment with bacterial endotoxin(lipopolysaccharide, LPS) modulates brain CRH contents or in vitroCRH release in tilapia (Oreochromis mossambicus). 10 days LPS(Escherichia coli) exposure of juvenile tilapia (4.5 weeks post hatch) via the ambient water increased brain CRH and α-MSH content,whereas cortisol contents were not increased. This indicates that the elevation of brain CRH levels were not secondary to activation of HPI-axis. Adult tilapia were treated for 6 days with LPS (intraperitoneally) and were sampled before and after 24 h of confinement. Overall LPS pre-treatment modified the reaction of tilapia to the additional stressor of 24 h confinement, as interactions between LPS treatment and confinement were observed at the level of the hypothalamus (diencephalic CRH content), the pituitary (CRH and α-MSH content) and in plasma glucose levels. In vitro, LPS pre-treatment abolished CRH release from telencephalic tissues induced by norepinephrine, one of the CRH secretagogues released during stress in vivo. This effect might be a mechanism of action through which LPS in vivo abolished the up-regulation of telencephalic CRH induced by confinement stress. Our results provide evidence that the role of CRH in immune–endocrine interactions is a phylogenetically old mechanism, and we here demonstrate that LPS molecules are able to locally modulate CRH release in the central nervous system.