Camp. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Bioehem. Physiol. Vol Printed in Great Britain BLOOD VOLUME AND RED CELL SPACE IN TISSUES zyxwvutsrqponmlk 87A. No. 2, pp. 393-398, 1987 03~-9629~87 $3.00 f 0.00 Q 1987 Pergamon JoumaIs Ltd D. w. DUFF,*? D. FITZGERALD,t D. KULLMAN,t D. w. LIPKE,? J. WARD? and K. R. OtsoNt$ *Department of Zoology, Indiana University at South Bend, South Bend, IN 46634, USA; tIndiana University School of Medicine, South Bend Center, University of Notre Dame, Notre Dame, IN 46556, USA (Received 5 August 1986) Abstract-l. Whole body blood volume and red cell space of 22 tissues were measured in unanesthetized rainbow trout at 4, 12, 30,60, I50 and 240 min after dorsal aortic injection of ‘Q-labeled red blood cells. 2. Apparent blood volume decreased during the initial 30 min after injection and increased thereafter. At 240min the blood volume was 33.5 & 3.1 mi/kg body wt. 3. Tissue red cell space varied as a function of the interval between labeled red cell injection and tissue collection. Bed cell space was highest in spleen followed by heart, kidney and liver. Lowest red cell spaces were found in stomach and red and white skeletal muscle. 4. Variability in blood volume and tissue red cell space over time suggests that caution should be exercised in the design of experiments that employ indicator dilution measurements to measure vascular volumes. Techniques that evaluate the accumulation of bio- molecules and xenobiotics by fish tissues have fre- quently been used to examine the selectivity of organs for the material in question (Agarwal and Gupta, 1974; Busacker and Chavin, 1977; Ferguson et ai., 1984; Gluth et al., 1985; Hilton et al., 1979; Nekvasil and Olson, 1986; Olson et al., 1973, 1978, 1986; Primor et al., 1980; Ryo et al., 1974; Somero et al., 1977; Ungell, 1985). From this data the sensitivity of the organ to the compound and/or the physiological response or pathological outcome is often inferred. Commonly, the material is injected intra-arterially or is allowed to enter by diffusion across the gills and after an appropriate distribution or equilibrium time, tissue or organ samples are collected and assayed. The actual amount of material accumulated by various organs depends on several factors including: 1. Selectivity (affinity) of the various organs to the material, 2. Plasma concentration of the material during the exposure period, 3. Duration of exposure, 4. Blood volume and degree of organ perfusion during the exposure period, and 5. The position of the organs in the vascular tree relative to the injection or absorbtion site. Items 4 and 5 (and to some extent 2 and 3) are influenced by the inherent features of the cardiovascular system and must be recognized when such a study is pianned. Ideally, an inert indicator that is neither metabolized nor selectively accumu- lated by tissues should be used in these studies in conjunction with the substance under investigation to compensate for inequities in tissue perfusion or blood distribution (Nekvasil and Olson, 1986; Olson et al., 1986). $To whom all correspondence should be addressed at: Center for Medical Education, Haggar Hall, University of Notre Dame, Notre Dame, IN 46556, USA. Whole-body and intraorgan blood volumes in fish have frequently been measured using standard indicator dilution techniques originally developed for mammals (Conte et al., 1963; Gingerich et al., 1987; Houston and DeWilde, 1969; Huggel et al., 1969; Milhgan and Wood, 1982; Munshi et al., 1975; Nikinmaa et al., 1981; Schiffman and Fromm, 1959; Smith, 1966; Stevens, 1968). As indicated by Ginger- ich et al. (1986) plasma volume markers such as Evans blue dye and radioiodinated albumin are probably not completely confined within the vascular space and may over-estimate both whole body and intraorgan volumes. Red cells tagged with chromium (“Cr) are retained within the vasculature and appear to provide a better index of blood volume (Gingerich et al., 1987). A number of the above studies have used s’Cr tagged cells to measure total blood volume but relatively few (Gingerich et al., 1987) have measured intraorgan vascular space. Both of these measure- ments require that the tagged red cells are uniformly mixed within the vasculature, a parameter that has been examined for whole-body red cell space (Gingerich et al., 1987) but not in reference to distribution of red cells to individual organs. The purpose of the present study was to examine the distribution of Vr labeled red cells to various organs of rainbow trout as a function of time. The results from this study corroborate previous reports on organ vascular space in trout and also demon- strate the relative degree of perfusion of different organs. The intraorgan red cell space appears time sensitive. This sensitivity varies among different tis- sues and must be considered when evaluating tissue accumulation of blood borne molecules. MATEREALS AND METHODS Rainbow trout (.Sulmo gairdneri, 200-4OOg) were pur- chased locally and maintained in 2000-I. fiberglass tanks with continuous through-flowing well water at 14°C. They 393