Abstract
Contraction of the frog's gall bladder can be readily demonstrated by the intracardiac injection of crude secretin. The frog's gall bladder is usually bluish green, moderately full of bile, pear-shaped, flabby, and is easily observed when the abdomen is opened. After the intracardiac injection of a dilute secretin preparation, there is a latent period of 15 to 100 seconds; the gall bladder then changes to a rounded spherical form, and the organ develops a slight or marked opalescence; the surface may also show a slight or marked puckering; blood vessels over the surface may become tortuous; apparent volume changes may at times be noted. After 2–10 minutes, the surface again becomes smooth, opalescence disappears, and the bladder becomes flabby.
The ease with which the above could be duplicated suggested its use as an assay method for substances contracting the gall bladder.
A number of preparations have been compared using the following procedures as standard. Active dark colored male frogs weighing 25–35 g were selected; the cerebra were crushed, the cords pithed, and the animals pinned out on frog boards the feet of the frogs were elevated 1–2 inches above the heads and the gall bladders were exposed; the blood flow to the gall bladder was directly observed microscopically and only preparations were used which showed a good circulation.
Secretin powder S I, (Ivy) which is relatively stable, was used as a standard.
A unit has been arbitrarily defined as the amount of gall bladder contracting material present in 0.2 cc of solution which, when injected intracardially into 30 g frogs, brings about contraction in 50% of 30 experiments.
The activities of 3 crude secretin preparations from dog duodena and a powdered cholecystokinin, prepared according to Ivy's pH 1802 method, have been compared to the standard SI powder.
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