Abstract. The blood clearance of 51Cr-labelled heat-killed Salmonella pullorurn was biphasic and exponential for each phase. This pattern was the same for all three concentrations of bacteria used. The initial more rapid phase lasted for approximately 15 minutes when roughly 90% of the bacteria had been cleared. The second slower phase started 25 to 30 minutes post-inoculation and lasted for approximately 25 to 30 minutes. The tissue distribution of bacteria showed that in both absolute and relative terms, the kidney was the most important organ, accounting for more than 70% uptake of the bacteria.These kinetics demonstrate that rainbow trout at 8°C are able to clear their bloodstream of Salmonella very efficiently, in a fashion very similar to mammals. It is not known, however, which of the various possible clearance mechanisms dominates each phase.Fish are becoming increasingly important both in terms of their farming potential (aquaculture) and the possibility of their use as sentinels for detecting environmental pollution. Many of the more economically serious diseases of fish are bacterial, and yet little is known about the in vivo fate of su:h pathogens.Many workers have emphasized the efficiency of the reticuloendothelial system in clearing the bloodstream [27] and the kinetics of the clearance of particulate matter (both inert colloids and bacteria) usually has been accepted as a direct measure of this phagocytic efficiency [29]. Despite substantial work on reticuloendothelial kinetics in mammals, there is little knowledge of the subject in teleost fish, or ectothermic vertebrates in general. Indeed, we can find only one report describing in vivo rates of reticuloendothelial clearance in fish-in the goldfish (Curussius uurutus), lamprey (PetromyconJluviutiZis)7 and dogfish (Scylliorhinus caniculus) [25].The histological and ultrastructural location and distribution of intravenously and intraperitoneally injected vital dyes and other particles have been studied in several fish species [lo, 11, 17,23, 24,3 I]. These studies represent in broad terms a "mapping outy7 of the fish reticuloendothelial system in both fresh and saltwater species, ranging from primitive to advanced members of the group.Briefly, these studies (largely using colloidal carbon) showed that in teleosts, the spleen and kidney (both anterior and posterior) were important reticuloendothelial 687

Oxytetracycline pharmacokinetics and tissue distribution were studied in rainbow trout following bolus i.v. administration at 5 mg/kg. The mean serum (log) drug concentration data were plotted against time (linear). The decay curve was described by a three-component exponential decay function and a three-compartment model. The t1/2 of rapid distribution was 0.9 h, the t1/2 of the slow distribution was 5.9 h and the t1/2 elimination was 81.5 h. Clearance was 25.4 ml/kg/h and Vd(area) 2988 ml/kg. Regression analysis of the serum levels for the three intervals, 0.5-2.0 h, 6.0-18.0 h, and 24-96 h, indicated that the rates of decay for each interval were 0.6151 h-1, 0.0564 h-1 and 0.0088 h-1 respectively. Rates of equilibration between tissues and serum were determined. Kidney equilibrated the fastest with t1/2 to equilibration of 1.1 h for H (anterior) kidney and 1.98 h for P (posterior) kidney. The highest drug levels were found in the liver and the lowest were in the brain.

The blood clearance of 51Cr-labeled heat-killed Salmonella pullorum was generally biphasic and exponential for each phase. Starvation had little significant effect on this pattern, although the rate of first phase clearance was probably slower. Raising the water temperature from 8 degrees C to 18 degrees C enhanced the rate of clearance of the second phase to almost exactly double that at 8 degrees C. At 18 hr postinoculation, the spleen contained much more radioactivity per gm than any other tissue. This finding is in marked contrast to earlier work that showed that at 1 hr postinoculation, the kidney contained the most, and it suggests that redistribution of bacteria occurred. The most distinct effect of temperature stress on tissue localization of bacteria was in the heart: A rising temperature stress caused increased numbers of bacteria to localize within the heart. Less clear-cut changes were also seen in other tissues with different treatments. With the possible exception of starvation effecting a slower first phase clearance rate, we have been unable to demonstrate that the vascular clearance mechanisms, including the reticuloendothelial system, are significantly compromised by raising the water temperature or by starvation.

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