In the pase decade, several experimental models of acute renal failure (ARF) have been evaluated with micropuncture and hemodynamic techniques. Five of these models have been most extensively studied: glycerol injection, renal artery clamping, intrarenal norepinephrine infusion, uranyl nitrate, and mercuric chloride administration. In the first three models, renal ischemia is the initiating insult, whereas in the two nephrotoxic models a direct effect of the agent on cellular integrity is also seemingly operative. In all of these models, renal blood flow 24--48 h after the initial insult either spontaneously returns to normal or can be elevated to this level with volume expansion but without restoration of the glomerular filtration rate. Therefore, the maintenance of ARF in these various models is due to other factors, which include tubular obstruction, leakage of filtrate across damaged tubular epithelium, and a decrease in the glomerular capillary ultrafiltration coefficient. In a given model, one or all three of these alterations may be present. Although these various models may not be completely analogous to the clinical setting, they have provided powerful tools for the study of ARF and their use has greatly increased our knowledge in this field.

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Deterrence theories purport to supply the auxiliary assumptions rational choice theories need to predict rational strategic behavior. They generally assume that would-be initiators are (i) instrumentally rational; (2) risk-prone gain-maximizers; (3) free of domestic constraints; and (4) able to identify themselves correctly as defenders or challengers. These assumptions are contradicted by empirical studies that indicate that risk-prone, gain-maximizing initiators are relatively uncommon; that leaders at times calculate as deterrence theories expect, but behave contrary to their predictions; and that the calculus of initiators generally depends on factors other than those identified by deterrence theories. Deductive theories of deterrence are also inadequate because they do not define their scope conditions. Nor can they accommodate deviation by initiators from processes of rational calculation. Rational deterrence theories are poorly specified theories about nonexistent decision makers operating in nonexistent environments.

A B S T R A C T In a previous study we have found that acetylcholine, a renal vasodilator, inhibits fractional and absolute reabsorption of sodium in the proximal tubule of the dog. To delineate whether this effect on proximal tubular sodium reabsorption was related to alterations in renal hemodynamics or to a direct tubular action of the drug, free-flow micropuncture studies were performed in the dog in which the tubular fluid to plasma inulin ratio and nephron filtration rate were determined before and during the administration of a structurally different renal vasodilator, bradykinin. This agent increased sodium excretion from 12 to 96 *Eq/cnin and decreased total kidney filtration fraction from 0.35 to 0.25. However, sodium reabsorption in the proximal tubule of the superficial nephrons was unchanged during bradykinin 'administration.Since it has been shown that a decrease in filtration fraction and presumably peritubular capillary protein concentration will decrease proximal tubular sodium reabsorption, studies were performed to determine whether the fall in total kidney filtration fraction seen with both vasodilators is paralleled by a similar change in the circulation of superficial nephrons. The results of these studies indicate that neither agent altered superficial nephron capillary protein concentration, hematocrit, or filtration fraction.