Isolation and biochemical study of secretory granules from rat pituitary glands.

Secretory granules from anterior pituitary glands of young adult male castrate rats were isolated by differential centrifugation, microfiltration, and discontinuous density gradient centrifugation. The granules were obtained as pellets, sectioned, and studied with the electron microscope. A major part of the gonadotropin and a substantial amount of the TSH were associated with the isolated granules. Negligible amounts of growth hormone and prolactin were present as contaminants. Succinic dehydrogenase, glucose-6-phosphatase, acid protease, and acid and alkaline phosphatases were not found in the granules. Alkaline protease was the only enzyme found to be associated with the granules, and it is suggested, in the light of these results, that the alkaline protease may be involved in the release of the hormones.