The effects of experimental anaemia on CO2 excretionin vitro in rainbow trout,Oncorhynchus mykiss

SUMMARYAntarctic icefishes possess several cardiovascular characteristics that enable them to deliver oxygen adequately in the absence of hemoglobin (Hb). To gain insight into mechanisms driving development of these cardiovascular characteristics of icefish, we chemically induced severe anemia in a red-blooded notothenioid, Notothenia coriiceps. After 10 days of treatment with phenylhydrazine HCl, the hematocrit and Hb concentration of N. coriiceps decreased by >90% and >70%, respectively. Anemic fish exhibited a significantly higher concentration of nitric oxide (NO) metabolites in their plasma compared with that of control animals, indicating that corporeal levels of NO are higher in anemic animals than in control fish. The activity of nitric oxide synthase (NOS) was measured in brain, retina, pectoral muscle and ventricle of control and anemic animals. With the exception of retina, no significant differences in NOS activities were observed, indicating that the increase in plasma NO metabolites is due to loss of Hb, which normally plays a major role in the degradation of NO, and not due to an overall increase in the capacity for NO production. To determine whether loss of Hb can stimulate remodeling of the cardiovascular system, we measured expression of HIF-1a, PHD2 and VEGF mRNA in retinae of control and anemic fish. Expression of all three genes was higher in anemic animals compared with control N. coriiceps, suggesting a causative relationship between loss of Hb and induction of angiogenesis that probably is mediated through nitric oxide signaling.

Section: Phenylhydrazine Treatment Results In Increased Levels Of Nitmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

Phenylhydrazine-induced anemia causes nitric-oxide-mediated upregulation of the angiogenic pathway in Notothenia coriiceps

Borley

Beers

Sidell

2010

“…SMR was comparable between the two treatments, implying that within the anaemic treatment group remaining erythrocytes in circulation are sufficient to support standard metabolic function, but all other measures of aerobic potential showed marked differences. Haemolytic anaemia has been widely employed in other studies on fish to address the consequences of reduced O 2 -carrying capacities (Smith et al, 1971;Houston et al, 1988;Gallaugher et al, 1995;Gilmour and Perry, 1996). Of these, the study of Gallaugher and colleagues (Gallaugher et al, 1995) investigated changes in respiratory character, and showed an approximate 70% drop in maximum rate of O 2 uptake (V O2,max ) when anaemic (10% Hct) and normocythaemic (30% Hct) rainbow trout were compared under normoxic conditions.…”

Section: Discussion Effects Of Anaemia On Aerobic Physiology and Avoimentioning

confidence: 99%

“…Fish were kept for a minimum of 6 weeks before experimentation and fed with a diet of frozen squid and pilchard. Prior to experimentation, anaemia was induced using a haemolytic agent (Gilmour and Perry, 1996). Briefly, fish were transferred to an anaesthetic tank containing 22p.p.m.…”

Section: Fish Handling and Anaemia Inductionmentioning

confidence: 99%

Anaemia adjusts the aerobic physiology of snapper (Pagrus auratus) and modulates hypoxia avoidance behaviour during oxygen choice presentations

Cook

Wells

Herbert

2011

SUMMARYThe effect of altered oxygen transport potential on behavioural responses to environmental hypoxia was tested experimentally in snapper, Pagrus auratus, treated with a haemolytic agent (phenylhydrazine) or a sham protocol. Standard metabolic rate was not different between anaemic and normocythaemic snapper (Hct6.7 and 25.7gdl -1 , respectively), whereas maximum metabolic rate, and hence aerobic scope (AS), was consistently reduced in anaemic groups at all levels of water P O2 investigated (P<0.01). This reduction of AS conferred a higher critical oxygen limit (P crit ) to anaemic fish (8.6±0.6kPa) compared with normocythaemic fish (5.3±0.4kPa), thus demonstrating reduced hypoxic tolerance in anaemic groups. In behavioural choice experiments, the critical avoidance P O2 in anaemic fish was 6.6±2.5kPa compared with 2.9±0.5kPa for controls (P<0.01). Behavioural avoidance was not associated with modulation of swimming speed. Despite differences in physiological and behavioural parameters, both groups avoided low P O2 just below their P crit , indicating that avoidance was triggered consistently when AS limits were reached and anaerobic metabolism was unavoidable. This was confirmed by high levels of plasma lactate in both treatments at the point of avoidance. This is the first experimental demonstration of avoidance behaviour being modulated by internal physiological state. From an ecological perspective, fish with disturbed oxygen delivery potential arising from anaemia, pollution or stress are likely to avoid environmental hypoxia at a higher P O2 than normal fish.

“…RBC CA plays a key role in CO 2 excretion by catalyzing the hydration of CO 2 to HCO 3 -to load CO 2 into the blood in the tissues, and by catalyzing the reverse process in the gills, where HCO 3 -is dehydrated to CO 2 that then diffuses out of the blood and into the ventilatory water (see Perry, 1986;Tufts and Perry, 1998;Perry and Gilmour, 2006) (reviewed by Esbaugh and Tufts, 2006). When the availability of RBC CA is reduced, through either severe anaemia (Wood et al, 1982;Gilmour and Perry, 1996;Gilmour and MacNeill, 2003) or treatment with a permeant CA inhibitor such as acetazolamide (e.g. Hoffert and Fromm, 1973;Gilmour et al, 2001), CO 2 excretion is impaired as evidenced by increases in the partial pressure of CO 2 (P CO2 ) in the arterial blood and the appearance of a respiratory acidosis.…”

Section: Introductionmentioning

confidence: 99%

Carbonic anhydrase expression and CO2 excretion during early development in zebrafishDanio rerio

Gilmour

Thomas

Esbaugh

et al. 2009

SUMMARYCarbonic anhydrase (CA) is critical for CO 2 excretion in adult fish, but little is known of the expression or function of CA during early development. The present study examined the hypothesis that, as rates of CO 2 production increased during early development in zebrafish (Danio rerio), CA would become necessary for effective CO 2 excretion, and that the pattern of CA expression during early development would reflect this transition. Real-time RT-PCR was used to examine the mRNA expression of the two main intracellular CA isoforms over a time course of early development ranging from 0 to 120h post fertilization (h.p.f.). The mRNA expression of zCAb was generally higher than that of zCAc, particularly during the earliest stages of development. Rates of CO 2 excretion increased approximately 15-fold from 24 to 48h.p.f. whereas rates of O 2 uptake increased only 6.7-fold over the same period, indicating a relative stimulation of CO 2 excretion over O 2 uptake. Treatment of 48h.p.f. larvae with the CA inhibitor acetazolamide resulted in CO 2 excretion rates that were 52% of the value in control larvae, a significant difference that occurred in the absence of any effect on O 2 uptake. Antisense morpholino oligonucleotides were used to selectively knock down one or both of the main intracellular CA isoforms. Subsequent measurement of gas transfer rates at 48h.p.f. indicated that CA knockdown caused a significant relative inhibition of CO 2 excretion over O 2 uptake, regardless of which cytosolic CA isoform was targeted for knockdown. 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 CO 2 excretion.