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