K M Gilmour

..07; P > 0.05). The intravenous administration of carbonic anhydrase (CA; 10 mg/kg) before vascular volume loading eliminated the increase in Pa(CO2) with increased Vb that was observed in control fish...

..Furthermore, these results support the hypothesis that distinct glucocorticoid and mineralocorticoid receptor populations are present in teleost fish, despite the apparent absence of the classic mineralocorticoid hormone, aldosterone...

..Thus, unlike in exclusively water-breathing teleosts, P. dolloi would appear to rely solely on internal/airway O2 chemoreceptors for initiating catecholamine secretion and cardiorespiratory responses...

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..These results indicate that extracellular CA contributes substantially to CO(2) excretion in the dogfish, an elasmobranch, and confirm that CA is not available to plasma CO(2) reactions in rainbow trout, a teleost...

..Additionally, the apparent lack of effect of V(b) changes on PCO(2) suggests that, in contrast to teleost fish, CO(2) excretion in dogfish does not behave as a diffusion-limited system...

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..Internally-oriented CO2-sensitive chemoreceptors may also be involved, although evidence on this point remains equivocal. In the present paper, the evidence for a CO2/pH-keyed ventilatory drive in fish will be reviewed...

..Exocytosis of water following the fusion of vesicles with gill cell membranes could explain the significantly elevated 3H2O efflux observed during urea pulses...

..dolloi, and (ii) suggest that CO(2) excretion in Protopterus may be less reliant on carbonic anhydrase than in most other fish species...

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..However, externally oriented carbonic anhydrase (if present in dogfish) plays no role in catalysing the hydration of the excretory CO2 in water flowing over the gills and thus is unlikely to facilitate CO2 excretion...

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..Overall, the data emphasize the coordination of acid-base, osmoregulatory and ionoregulatory processes that occur with salinity transfer in a euryhaline fish...

..Further work is required to determine whether it applies to elasmobranch fish as a group...

..Like fish and amphibians, however, extra-renal routes play a key role in metabolic compensation...

..Aquatic hypercapnia (approximately 37.5 mmHg) increased pulmonary breathing frequency (from 15.3+/-2.3 to 28.7+/-5.4 h(-1)) in free swimming lungfish, whereas aerial hypercapnia was without effect in aquatic or terrestrialized fish...

..Selection for the presence of carbonic anhydrase inhibitors in fish plasma appears to be the result of multiple physiological pressures, including preservation of red cell intracellular pH, ventilatory control, and red cell fragility...

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..The finding is surprising because the cultured epithelium appears to consist entirely of pavement-type cells...

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..These results provide compelling evidence for chemoreceptor-mediated control of breathing in hagfish and suggest that ventilatory responses to environmental hypoxia and hypercapnia in the vertebrates arose in the myxine lineage...

..How this is accomplished and the role it plays in re-establishing acid-base balance are questions that remain to be answered...

..The results of the present study support the widely held premise that branchial intracellular CA activity (tCAc) plays a key role in regulating acid-base balance in freshwater teleost fish...

..In this way, membrane-bound, luminal CA thus promotes the absorption of osmolytes and reduction on luminal osmotic pressure, both of which will serve to enhance osmotic gradients to promote intestinal water absorption...

..These results suggest that between 24 h.p.f. and 48 h.p.f., developing zebrafish begin to rely on CA to meet requirements for increased CO2 excretion...

..The findings have implications for the interpretation of studies that examine correlates of GC concentrations as they suggest consistency in stress responsiveness is influenced by factors such as size and condition...

..Induction of anaemia revealed differential expression of the two isozymes in the red blood cell; whereas TCAc mRNA expression was unaffected, TCAb mRNA expression was significantly increased by 30- to 60-fold in anaemic trout...

..In this review, the CA isoforms that have been identified to date in fish will be discussed together with their tissue localizations and roles in systemic acid-base regulation...

..These responses were not synchronized with or influenced by plasma Cat levels. Thus the acute humoral adrenergic stress response does not appear to stimulate ventilation during acute hypoxia in these tropical species...

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..08 ± 0.09 mL O(2) g(-1) haemoglobin, N = 9). Collectively, these data indicate that chronic social stress impacts the ability of trout to respond to the additional, acute stress of hypoxia...

..Results also bring forth the reality that environmental variables such as temperature must be considered in studies where these factors can vary, such as when sampling wild animals at liberty...

..However, during a hypotensive stress elicited by vascular smooth muscle relaxation. Ang II indirectly contributes to cardiovascular control by dose-dependently stimulating catecholamine release...

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..Collectively, the data suggest that subordinate trout are able to regulate blood pH during a respiratory acidosis...

..Findings show both elevated pre-stress and stress-induced cortisol concentrations at arrival to the spawning grounds to be associated with reduced survival...

..44). These results suggest that subordinate rainbow trout chronically maintain high levels of CRF mRNA during social stress and that NPY may be involved in the control of the stress axis in trout...

..These results suggest that while bullhead RBCs possess a beta-adrenoreceptor linked to cyclic AMP formation, stimulation of this adrenergic receptor does not result in measurable activation of a Na(+)/H(+) exchanger...

..The following review attempts to integrate gas transfer and gas sensing at the fish gill by exploring recent advances in these areas...

..The results indicate that existing respiratory disturbances modulate cardiorespiratory responses to further respiratory challenges reflecting both changes in chemosensitivity and the capacity for further change...

..Unlike skate and ratfish, bullhead exhibited high plasma non-bicarbonate buffering capacity and lacked an endogenous carbonic anhydrase inhibitor in the absence of plasma and gill membrane-bound carbonic anhydrase activities...

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..7%). Thus, the unusually high non-bicarbonate buffer capacity of bullhead plasma appears to stem from the presence in the plasma of a histidine-rich albumin...

..These results suggest that reduced silver bioavailability is the mechanism behind the pattern of peak and decline in gill silver accumulation previously reported for static exposures to silver...

..Our findings suggest that neither the environmental conditions of hypoxia, hyperoxia or hypercapnia, nor direct branchial chemoreceptor activation by NaCN play a major role in the regulation of pulsatile urea excretion in toadfish...

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