Rat ovarian subcellular compartmentalization of luteinizing hormone

To determine if human luteinizing hormone (hLH) follows the same subcellular route in the pseudo-pregnant rat ovary as human chorionic gonadotropin (hCG), the distribution of immunoreactive and bioactive hLH within cytosol, lysosomes, and a combined plasma membrane/prelysosomal vesicle fraction was examined. Immunoreactive levels were determined using a specific radioimmunoassay and bioactive levels were determined in an in vitro Leydig cell bioassay. Low cytosolic hLH levels were apparent the first few hours after hLH administration and may reflect at least some contamination by serum and interstitial fluid. Plasma membrane/prelysosomal vesicles attained the highest hLH concentration 1 h after hLH injection, after which hLH levels declined rapidly until barely detectable levels were observed at 18 h. The hormone in this fraction was receptor bound and exhibited the highest bioactivity of the three fractions examined. Lysosomal hLH concentrations were highest at 12 after hLH injection and were maintained at high levels through 18 h. Substantial amounts of lysosomal hLH appeared to be receptor bound but this hormone was not bioactive. In situ degradation of the oligosaccharides may have occurred while lysosomal hLH was receptor bound. Lysosomal degradation is the major pathway for hLH inactivation as has been described for hCG. However, hLH may be degraded within lysosomes more quickly than hCG. The differential subcellular distribution of immunoreactive and bioactive hLH provides strong support for hLH internalization and degradation within ovarian luteal cells.