Prolactin content in rat pituitary gland. RIA of prolactin after different extraction procedures.

The prolactin content of rat pituitary varies considerably when determined by RIA, due to incomplete solubilization of prolactin secretory granules with standard procedures for tissue homogenization and centrifugation. Freezing and thawing, Triton X-100 and ultrasonic treatments increased the yield of prolactin significantly but electron microscopy of pellets revealed numerous unmodified secretory granules. Addition of 2.5 M urea produced complete extraction of tissue prolactin confirmed by RIA of supernatants and electron microscopy of pellets.