Factors influencing noradrenaline uptake by the perfused spleen of the cat.

1. Noradrenaline was infused intra-arterially at the constant rate of 0.51 mug/min for 22 min into the cat spleen perfused with Krebs saline, and the amount appearing in the perfusate was assayed either chemically or on the blood pressure of the pithed rat.2. In normal animals, 34% of the infused noradrenaline appeared in the perfusate, indicating 66% removal by the spleen.3. Neither removal of calcium from Krebs solution nor perfusion with 25 mM-Ca(2+) Krebs solution had significant effects on noradrenaline recovery.4. In spleens perfused with 0 or 50 mM-K(+) Krebs solution the noradrenaline recoveries were not significantly different from the control recoveries.5. Removal of sodium from Krebs solution increased the recoveries to 92%.6. The effect of interference with energy metabolism on noradrenaline recoveries was investigated. Iodoacetate or dinitrophenol alone increased the recoveries only moderately, but combined treatment with both metabolic inhibitors increased the recoveries to 74%.7. If the temperature of the perfusion fluid was reduced to 15 degrees C, noradrenaline recoveries increased to 96%. At 27 degrees C the recoveries were 48%.8. At pH 5.6, noradrenaline recoveries in the venous effluent increased to 63%. At pH 9.0 the recoveries were not significantly different from the control recoveries.9. When (+)-noradrenaline was infused at 0.51 mug/min into the spleen, 55% of the infused amount was recovered in the venous effluent. This recovery is significantly higher than the 34% for (-)-noradrenaline.10. Ouabain and tetracaine increased the recoveries to over 70%, whereas mercuric chloride and insulin had no effect.11. Neither the flow rate nor the size of the spleen correlated with noradrenaline recovery.12. Our results suggest that uptake of infused noradrenaline is energy dependent and has an absolute requirement for the presence of sodium ions in the perfusion medium.