A new method for inducing copious drinking and the accompanying stimulation on the pars intermedia of the mouse pituitary gland.

A new method for causing excessive liquid intake was developed as the condition opposite to dehydration, and the effect of this copious drinking for 2, 4 and 6 days on the pars intermedia of the hypophysis was evaluated by quantitative electron microscopy in mice. Free access to 5% glucose solution and concurrent food deprivation resulted in the development of polydipsic mice. Drinking volume was 18.9 +/- 1.1 ml/10 g BW on day 2, 20.8 +/- 1.2 on day 4 and 24.1 +/- 1.3 on day 6, respectively, while remaining at 2.2 +/- 0.2 ml/10g BW in the control. Copious drinking was found to elicit secretory activity of the pars intermedia cells. The cytoplasmic volume percentage of rough endoplasmic reticulum (rER) and the numerical density of Golgi granules increased significantly on day 2 reaching a peak on day 4. Contrarily, secretory granules decreased in number, indicating that the granule release exceeded the activated granule formation. The rise in the activity of the gland was followed by a slight fall after 6 days, which was probably due to a malnutritional condition by food deprivation. Neither 20% glucose drinking nor food deprivation for 4 days enhanced the pars intermedia cells. Thus, excessive water intake seems to be a plausible reason for stimulating secretory activity in cells of the pars intermedia of the hypophysis in mice.