Bradykinin's involvements in physiological phenomena such as blood clotting,vascular smooth muscle contractility, peripheral nocioception, etc. have been extensively studied, however, involvement of this or structurally related kinins in other physiological functions has received little attention. Our recent finding that several kinins, including bradykinin, occur in bovine milk provided chemical evidence to rationalize earlier observations regarding the likely involvement of kininogens and/or kallikreins in postnatal development. Recent efforts to recover milk kininogens have permitted resolution of two soluble forms by isoelectric focusing, the low-pI and high-pI milk kininogens; a third form has also been recognized. The MW of the milk HMW kininogen appears to be around 68,000 and the pI is 4.15 +/- 0.5; by contrast, the MW of bovine plasma HMW kininogen is 76,000 and its pI is 4.6. Methods are being developed to facilitate recovery of pure bovine milk kininogens in order to permit (a) determination of structural difference(s) between milk and plasma kininogens and (b) to ascertain the chemical nature of kinins, other than bradykinin, which may occur in milk. The long-term goals are to develop methods which may be generally applied to isolation of tissue kininogens and to ascertain the potential physiological significance(s) of such molecules.
