A laminar flow superfusion technique with much increased sensitivity for the detection of smooth muscle-stimulating substances.

The classical superfusion technique was modified by immersing the isolated assay tissues in mineral oil, making it possible to superfuse the preparations through the oil with a drip of Krebs solution at very low flow rates (0.1 - 0.2 ml/min). In this way the sensitivity of the preparation for the detection and quantitation of endogenous biologically active substances was extended to the picogram level.