Identification of a less immunoreactive form of prolactin in the rat pituitary

Disc electrophoretic analysis of prolactin (PRL) in the rat pituitary is usually performed using a 7.5% concentration of acrylamide gel. Re-electrophoresis of the eluate of the PRL band from such a gel on polyacrylamides of serially increasing concentrations revealed that the PRL band of 7.5% gel actually contains at least two additional proteins. One of these, whose apparent mol. wt. is 31,000, has significant pigeon crop-sac stimulating activity but very little or no cross-reactivity in a RIA for rat PRL. It also has a rapid turnover rate in short-term in vitro incubations. This newly-found protein seems to be a nonimmunoreactive molecular variant of rat PRL.