Fractionation of the rat ventral prostate with respect to isolation and exocytosis of the prostatic secretion protein

Abstract

The ventral prostate was fractionated into one mitochondrial and three microsomal fractions. The different fractions were characterized morphologically and chemically. An interesting finding was that upon homogenization the endoplasmic reticulum membranes often turned 'inside-out' giving rise to microsomes with ribosomes attached to the inside of the vesicles. The secretion of the prostatic secretion protein was studied by means of isotopic pulse labeling using radioactive leucine. Peak radioactivity in the microsomal fraction was obtained at 2 h after injection with a relatively rapid fall. The radioactivity in the secretory fluid displayed a continuous increase up to 8 h followed by a plateau. When prostatic secretion protein was purified from secretory fluid and microsomes using a Con A-Sepharose column it showed a typical precursor-product relationship with an early peak at 60 min in microsomal prostatic secretion protein followed by a peak in secretory fluid at 4 h. Vinblastine blocked the release of labeled secretion protein into the secretory fluid, a phenomenon characteristic for secretory proteins which are exocytosed by means of fusion between secretory granules and the plasma membrane. Following intravenous injection of [3H]estramustine, accumulation was seen in the secretory fluid. Some estramustine probably binds to newly synthesized prostatic secretion protein and follows the same route of intracellular transport and extracellular discharge as does prostatic secretion protein.