Regulation of gonadotropin secretion in the anterior pituitary

Studies on the regulation of gonadotropin secretion in dissociated pituitary cell cultures are described. Initial studies employing a ferritin-labelled analogue of gonadotropin hormone releasing hormone (GnRH) to localize its receptor sites on the gonadotropin cell surface that while these receptor sites initially have a random monodisperse distribution, binding of the ligand causes coarse aggregation and internalization of the GnRH receptor. These events are not due to the multivalency of the ligand and probably reflect redistributive events in vivo. By using an octapeptide analogue GnRH that binds to the GnRH receptor but lacks gonadotropin releasing activity in conjunction with sequence-specific antisera it is shown that antibodies that bind the octapeptide can induce the octapeptide to release gonadotropin. These data suggest that receptor aggregation is important in GnRH stimulation. Finally immunocytochemical studies are described in which golg-protein-A-antibody complexes are used to identify gonadotropins on ultrathin frozen sections of porcine pituitary cells. These studies indicate that in porcine gonadotropin cells the majority of the secretory granules contain both luteinizing hormone and follicle-stimulating hormone.     

Filament-containing chromophobe in anterior pituitary of the guinea-pig

Numerous 95 ± 5 Å filaments have been observed in a chromophobe within the anterior pituitary gland of the guinea-pig. The cytoplasm of the chromophobe is somewhat electron lucid and long processes of the cell extend between granulated parenchymal cells. A basement membrane borders the plasma membrane of chromophobes facing the pericapillary space. Adjacent chromophobes are connected by maculae adherentes (desmosomes) and zonula adherens and often form a lumen; microvilli project into the lumen from the chromophobes.