Partial purification and identification of cardiodepressant factor from the posterior pituitary lobe in rats

It has been demonstrated previously that the cardiodepressant activity is p resent in the bovine hypothalamic extract and in the medium incubating the rat's posterior pituitary lobe "in situ". In this study medium incubating t he posterior pituitary lobe was fractionated by a low pressure gel filtrati on procedure and the cardiodepressant fractions were pooled and further pur ified by the HPLC technique on C-8 and TSK 3000 SW columns. It was shown, o n the basis of mass spectrometry, that cardiodepressant activity is associa ted with substance(s) with molecular mass of about 500 d. Application of th is fraction into the fluid used for incubation of isolated right auricle of the right heart atrium of a two-day-old rat, strongly decreased the freque ncy of spontaneous discharge of the pacemaker tissue.