The influence of the thyroid and parathyroid glands on the variations in magnesemia in fed and fasted rats.

Rats fed and libitum were adapted to alternating 12 hr periods of light and dark. A number of animals were parathyroidectomized (PTX) or thyroparathyroidectomized (TPTX) and then supplemented with thyroxine. The PTX and TPTX animals showed hypomagnesemia. If food was not supplied during darkness, the normal feeding period, hypermagnesemia was found in normal rat after 12 hr fasting but not in PTX animals. In normally fed rats the level of magnesium increased during darkness and then dropped significantly at the end of the night. In contrast in TPTX animals the magnesemia continued to rise significantly after the end of the dark period. In rats lack of parathormone or of calcitonin modifed the variations in magnesemia during the night or after a short period of fasting. These hormones may thus play a physiological role in the regulation of magnesemia.