SECRETORY DISORDERS IN PITUITARY THYROTROPES OF STREPTOZOCIN-DIABETICMALE-RATS

Pituitary cells transport secretory products from deep cytoplasmic por tions towards the subplasmalemmal region (SPL) by two mechanisms: (a) the regulated, secretagogue-dependent and (b) the secretagogue-indepen dent constitutive pathway. Since thyrotropin (TSH) secretion is impair ed in diabetes, we studied both pathways in the thyrotropes of control and streptozocin (STZ)-treated male rats. By electron microscopy, we measured the nucleus and cytoplasm area and counted the secretory gran ules. In 4 selected SPL (500 nm deep) areas per cell we also counted t he marginated secretory granules and measured their area. Moreover, af ter TSH indirect immunogold labelling we counted immunogold particles on (a) the secretory granules of the SPL and (b) the intergranular SPL cytoplasm. To check the background staining we also counted immunogol d particles on nonthyrotropic cells. In diabetic compared with control thyrotropes we found: (a) cytoplasmic atrophy and increased number of secretory granules per cytoplasm unit area, (b) reduced number of sec retory granules in the SPL (blunted regulated secretion), (c) larger s ecretory granules in the SPL (abnormal secretory granule maturation), (d) decreased immunogold labelling of secretory granules in the SPL (r educed TSH transported by each secretory granule towards the cell memb rane) and (e) decreased immunogold labelling of the intergranular SPL cytoplasm (blunted constitutive secretion). Our data suggest reduced r egulated and constitutive TSH secretion and may thus contribute to a b etter understanding of the hypothyroidism in STZ-diabetic rats.