Tissue and whole-body extracellular, red blood cell and albumin spaces in the rainbow trout as a function of time: A reappraisal of the volume of the secondary circulation

摘要

Co-58]EDTA, [Cr-51]RBC and [I-125]albumin spaces in the whole body and 28 tissue samples were examined at timed intervals over 16 h in rainbow trout Oncorhynchus mykiss. [Co-58]EDTA space (which approximates extracellular fluid volume; ECF) in fins, skin, gallbladder and eye are reported for the first time. After a 16 h equilibration, ECF volume was large (376-726 mu l g(-1) wet tissue mass) in kidney, swimbladder, skin and fins, moderate (219-313 mu l g(-1) wet tissue mass) in stomach, skull, spleen, liver, intestine, gills, eye and cecum, and small (53-181 mu l g(-1) wet tissue mass) in red muscle, fat, brain, gallbladder and white muscle. Whole-body ECF was 387+/-10.6 mu l g(-1) (mean +/- S.E.M.; N=11). [Cr-51]RBC space relative to [Co-58]EDTA space was large in spleen, liver, intestine and gill, and low in skin, fins, stomach and skull. Whole-body [Cr-51]RBC space was 9.9+/-0.6 mu l g(-1) body mass (N=17). Blood volume calculated from [Cr-51]RBC space at 16 h and a dorsal aortic hematocrit of 24.5% was 40.4 mu l g(-1) body mass. Whole-body [I-125]albumin space at 16 h was 118.0+/-7.4 mu l g(-1) body mass (N=6), which resulted in an estimated blood volume of 156.6 mu l g(-1) body mass, nearly four times that estimated from the [Cr-51]RBC space. Tissue hematocrits, calculated from [I-125]albumin and [Cr-51]RBC spaces, were significantly lower than dorsal aortic hematocrit in all tissues except spleen, kidney and liver. [Co-58]EDTA and [Cr-51]RBC spaces reached equilibrium in nearly all tissues within Ih, whereas [I-125]albumin continued to accumulate in many tissues up 24 h. The disparity between [I-125]albumin distribution kinetics compared with the kinetics of [Co-58]EDTA and [Cr-51]RBC distribution, as well as the accumulation of [I-125]albumin in tissues not known to have a secondary circulation, indicates that [I-125]albumin is a poor marker of plasma volume in trout and that previous studies based on [I-125]albumin clearance from the plasma have overestimated both the volume and the turnover rate of the secondary system. Revised estimates of secondary circulation volume, based on [Co-58]EDTA distribution rate, indicate that it is no more than 10-20% of the volume of the primary circulation. [References: 26