Prolactin was isolated from frozen goat pituitary glands by a simple procedure involving gel filtration and chromatography on DEAE-cellulose. The major product (yield, 2·5 mg/g pituitary tissue) had high pigeon crop sac-stimulating activity (27 i.u./mg) and was free of growth hormone and other pituitary hormones. The molecular weight was similar to that of ovine prolactin.
Caprine prolactin was immunologically indistinguishable from ovine prolactin in radioimmunoassays, in which ovine prolactin antiserum and either ovine or caprine prolactin labelled with 125I were used.
The results indicate that caprine and ovine prolactin are closely related and that radioimmunoassay for ovine prolactin may be used to estimate caprine prolactin in serum.