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1. Indwelling non-occlusive catheters were placed in the vena porta and inferior vena cava of female rats several days before experimentation. Isotonic saline or isosmotic glucose (2% of body wt.) was infused into one vein followed one to several days later with an identical infusion into the other vein of each conscious animal. 2. Significantly higher urine flow and sodium excretion resulted from infusion of isotonic saline (0.5 ml/min) into the vena porta than into the vena cava. Modest prehydration or section of the hepatic branch of the right vagus did not affect the differential sodium response. Changes in endogenous creatinine clearance and potassium excretion were not significantly different for the two routes. Mean values for net peak sodium excretion and contemporaneous urine flow, urinary sodium concentration, and fractional sodium excretion were significantly higher for the portal than for the caval infusion while differences in glomerular filtration rate and filtered sodium load were insignificant. No significant difference in sodium excretion resulted from infusion of isosmotic glucose by the two routes. 3. Compared to the response promoted by the isotonic saline load infused at 0.5 ml/min, the differential response in sodium excretion was prolonged when the same load was infused at 0.375 ml/min. Sodium excretion was not significantly different for the two routes when the same isotonic saline load was infused at 0.75 ml/min. 4. These experiments provide evidence for participation of the liver in the control of sodium excretion and suggest release of a hepatic humoral factor which may be controlled by the duration of exposure of the hepatic circulation to an adequate load of isotonic saline.

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Zusammenfassung: Es wird ein Durchflußsystem zur NH^-selektiv-enzymatischen Harnstoffbestimmung beschrieben, bei der mit löslicher Urease schwimmend eine Harnstoff Spaltung erfolgt und die NH 4 " h -Freisetzung sekundär mit einer ammoniumselektiven Disk-Elektrode erfaßt wird. Als aktive Komponente für die Elektrodenmembran wurde das Carrier-Antibiotikum Nonactin in eine Polyvinylchlorid-Matrix inkorporiert. A NH^-selective-enzymatic flow-through system. A method for the continuous enzymatic, electrochemical determination of urea, II.Summary: A flow-through system for the measurement of urea concentrations is described, using soluble urease and consecutive determination of liberated ammonium ions by a selective disc-electrode. The active component of the electrode membrane was the carrier-antibiotic nonactin which was incorporated in a Polyvinylchloride matrix. Einleitung

The fluid content of circulating blood was followed continuously by conductometric measurement of large vein hematocrit in the alert rat. Arterial pressure was registered simultaneously. 2.5-23% of the determined blood volume was withdrawn rapidly and the changes of fluid content (delta v) calculated. Determinations of plasma protein showed that calculated delta v(delta vapp) may exceed true delta v due to transvascular fluid inflow by maximally 38%. A very fast phase of fluid inflow into the circulation (delta vfapp, within 1 min) was observed at the beginning, followed by a slow phase (delta vsapp), the magnitude of both being proportional to the concomitant arterial pressure drop (delta p). At delta p = 0, delta vfapp was 20% of the volume of blood withdrawn, total replacement (delta vfapp + delta vsapp = volume withdrawn) being complete in 60 min. At delta p = -20 mm Hg the figures were 40% and 20 min, respectively. Experiments on splenectomized animals showed essentially the same relations, excepting that delta vsapp may have been underestimated in normal rats. An arterial pressure rise after hemorrhage may attenuate complete replacement. The results are discussed in terms of capillary fluid conductivity. Thus CFC may be in the order of 0.029 ml/min x mm Hg x 100 g.

Single injections of noradenaline and adrenalineeeee were made into the v. cava of conscious rats during continuous registration of arterial blood pressure and conductivity (reciprocal hematocrit) in blood from different circulatory areas. The resulting hct and B.P. changes were compared with similar changes elicited by a 3-sec tactile stimulus. Two phases of hct response--the first due to local vascular reactions, the second due to a general vasodilatory reaction--can be distinguished. Whereas adrenalin and noradrenaline show differential effectivity in producing the local reactions (the former more potent as a precapillary vasoconstrictor, promoting hct drop due to fluid inflow in the portal and hepatic vein, the latter more so in the renal vein and the aorta), adrenalin is invariably more effective in producing the second phase dilatory reaction with fluid outflow (hct rise). In the v. cava close to the iliac bifurcation a greater hemoconcentrative potency of adrenalin can be demonstrated, but only by close injections into the aorta. Close injections into the portal vein make postcapillary hepatic reactions more sensitive to adrenalin manifest. The catecholamine dose equivalent to a 3-sec tactile stimulus in the rat is 80-120 ng.