Appearance of a cardiodepressant factor in the medium incubating in situ the posterior pituitary lobe of the rat. I. Isolation of active compound.

The experiments were carried out with 2 groups of male rats under urethane-chloralose anaesthesia. In the 1st group the anterior pituitary lobe was removed and the posterior one was incubated in situ in McIlwain's solution. The incubating fluid was collected with methanol, centrifuged, and the supernatant was lyophilized. The lyophilized fluid incubating the posterior pituitary lobe in situ was filtered on a Sephadex G-15 column and fractions with cardiodepressant activity were passed through a SP Sephadex C-25 column. The cardiodepressant activity was tested on an isolated auricle of the right atrium of a two-day-old rat. The cardiodepressant activity of the fractions was evaluated. The fluid incubating the posterior pituitary lobe was found to contain a factor reducing the contraction rate of the isolated auricle. In the control group the sphenoid bone was exposed and bathed in McIlwain's solution, in the same approach as the posterior pituitary lobe. The fluid bathing the sphenoid bone in situ was filtered on a Sephadex G-15 column. No cardiodepressant activity was found in the fractions.