Effects of experimental hypo- or hypernatremia on the fine structure of the pars intermedia of the murine pituitary. A morphometric study.

Quantified ultrastructural observations of the pars intermedia (PI) of the murine hypophysis enable evaluation and kinetic study of relatively fine secretory changes in the gland. Changes in volume of rER and newly formed dense secretory granules (Golgi granules) appear to best translate functional variations in the PI, as shown by the morphological effects of drugs affecting the dopaminergic control of the gland. Our morphometric results show that the PI is stimulated, but only briefly (no longer than 8-12 days), by both salt-loading and Na deprivation. However, the PI displays different secretory patterns in salt-loaded and Na-deprived mice; moreover, bromocriptine, which abolishes PI stimulation in Na-deprived mice, has only a slight inhibitory effect in salt-treated animals. Thus, it appears that the stimulation of the PI under both experimental conditions is triggered by different mechanisms. These results underline the plurifactorial control of the PI and show that the gland may have complex effects on hydromineral regulation.