REDUCED NUMBER AND LH CONTENT OF MARGINATED SECRETORY GRANULES IN PITUITARY GONADOTROPES OF STREPTOZOCIN-INDUCED DIABETIC MALE-RATS

The transport of secretory granules towards the subplasmalemmal (SPL) region of the luteinizing-hormone (LH) gonadotrope is controlled by th e LH-releasing-hormone-dependent pathway. The SPL granules contain the most readily releasable LH. To test the effect of diabetes on both th e number and LH content of marginated granules, we studied by indirect immunogold-labelling pituitaries from control and streptozocin (STZ)- treated male rats. On electron micrographs we measured the areas of th e gonadotrope nucleus and cytoplasm, counted all secretory granules, a nd counted and measured secretory granules in selected SPL regions. Fu rthermore, we counted gold particles (IG) on (a) the secretory granule s of the SPL regions, (b) the intergranular SPL cytoplasm and (c) the region outside the cell. Finally, in order to evaluate possible diabet es-related changes of the pituicyte cytoskeleton, we measured by densi tometry actin, tubulin, vimentin, and desmin in immunocytochemically s tained pituitary sections. In diabetic compared with control cells of the studied pituitary region, we observed: (a) cytoplasmic atrophy; (b ) the number of secretory granules per unit area increased in the tota l cytoplasm, and decreased in the SPL cytoplasm (lowered regulated sec retion); (c) decreased IG labelling in the SPL granules (reduced amoun t of hormone transported by each granule towards the cell membrane); ( d) decreased IG labelling in the intergranular SPL cytoplasm (reduced constitutive secretion), and (e) strongly increased actin and desmin, yet unchanged tubulin and vimentin immunoreactivity. Our data indicate that both regulated and constitutive secretion are possibly reduced i n gonadotropes of diabetic male rats. The cytoskeletal alterations may also contribute to the reduced regulated secretion.