Diuresis from left atrial receptors: effect of plasma on the secretion of the Malpighian tubules of Rhodnius prolixus.

1. Stimulation of left atrial receptors by distension of a balloon in the lumen of the left atrium of anaesthetized dogs was shown to result in an increase in urine flow. Plasma samples obtained from these dogs during control periods and during periods of stimulation were applied to the Malpighian tubules of Rhodnius prolixus. 2. It was found that the tubules suspended in test plasma secreted at a significantly lower rate than those suspended in control plasma. 3. These differences were also evident in extracts of plasma prepared using the solvent n-butanol. 4. Cutting or cooling the cervical vagi abolished these differences along with the increase in urine flow. It is argued that this preparation of the Malpighian tubule of Rhodnius prolixus could be used as a means of detecting the diuretic agent responsible for the increase in urine flow.