Heterogeneous luteinizing hormone and follicle-stimulating hormone storage patterns in subtypes of gonadotropes separated by centrifugal elutriation

The application of centrifugal elutriation to the separation of pituitary cells has produced a fraction that is enriched with LH and FSH gonadotropes. In this study, stains were performed on serial sections of fractions taken from six elutriation experiments with 1:10,000-1:30,000 anti-bLH beta or 1:2,000-1:8,000 anti-hFSH beta and the avidin-biotin-peroxidase complex technique. Over 900 serially sectioned gonadotropes were analyzed. In the initial cell suspensions, 59.6% of the gonadotropes contained both LH and FSH; 18% contained LH, and 23% contained FSH. Fewer than 3% contained ACTH. The elutriation fractions contained several subtypes of gonadotropes. A few small (8 micron), poorly granulated LH or FSH cells were eluted with the smallest cells (10-12%) at flow rates of 15.7 ml/min. Medium sized gonadotropes (10-10.5 micron) that eluted at flow rates of 19.8-30.5 ml/min were infrequent (3-6%) and resembled the larger gonadotrope. An analysis of serially sectioned fields showed that only 15.2%-22% of the small and medium sized gonadotropes contained both LH and FSH, whereas 30-40% contained only LH and 46-50% stored only FSH. The gonadotrope-enriched fraction was eluted at 37-39.5 ml/min; 78% of these gonadotropes (diameter, 14-15 micron) contained both LH and FSH, 10% contained only LH, and 12% contained FSH. Finally, large cells (diameter, 15-16 micron) that contained FSH only were found in the Wash fraction. These studies demonstrate that smaller gonadotropes tend to store only one of the hormones whereas most of the larger cells either store LH and FSH together or FSH alone. These heterogeneous storage patterns may correlate with studies by others who measured different responses to GnRH in gonadotropes separated by size on a unit gravity sedimentation gradient. They may also reflect different secretory phases of gonadotropes from the mixed group of cycling female rats.