Effect of hypoglycemic stress on the pars intermedia of the mouse pituitary gland: an ultrastructural analysis.

The present study was made to clarify the relationship between functions of the pars intermedia of the mouse pituitary gland and hypoglycemic stress. Morphometrical analysis of the ultrastructures of the pars intermedia cells showed (1) a rise in the percentage volume of rough endoplasmic reticulum (r-ER) indicative of an increase in protein synthesis, (2) an increase in the number of Golgi granules per unit Golgi area showing an induction of granule-forming activity and (3) a decrease in the numerical density of secretory granules reflecting a release of the secretory granules. These findings suggest that hypoglycemic stress induced by daily treatment with insulin or restriction of food intake was able to elicit heightened secretory activity of the pars intermedia cells of the mouse pituitary gland. However, acute hypoglycemic stress induced by food deprivation did not cytologically affect the pars intermedia. These observations suggest that repeated hypoglycemic stress, rather than acute hypoglycemic stress, may be a natural physiological stimulus of the pars intermedia of the mouse pituitary gland.