On electrolyte determinations in the pituitary and pineal gland: is there a diurnal rhythm?

At four different times during the day determinations of the electrolyte content of the anterior and posterior pituitary as well as of the pineal had been carried out by means of atomic absorption spectroscopy. There are significant differences in the sodium and potassium content between these organs. There are also distinct changes in the adenohypophysial Na+, K+ and Mg++ content between the light and the dark period. Values are low over the day and high during the night. In the light period there is also a significant higher sodium concentration in the neurohypophysis and a greater potassium concentration of the pineal tissue. Despite a similar phylogenetic development the neurohypophysis reveals a considerably less amount of univalent cations than the pineal gland. Data from the literature, however, let suggest that there are no greater differences in the water content of neurohypophysis and pineal. The possibly resulting "hypotonicity" of neurohypophysial tissue and its possible implications for the mode of the release of hormonal substances from the neurohypophysis are discussed.