[Role of the hypophysis, hormonal growth inducers and physical exercises in the regulation of function of thyrocytes, C-cells and parathyrocytes in rats during simulated weightlessness].

Immunohistochemistry and histomorphometry were employed to assay thyroid and parathyroid glands in hypophysectomized rats following a10-day tail suspension in head-down position and daily injection of either physiological solution or growth hormone or insulin-like growth factor 1 on the background of physical exercise, i.e. ascent up a 1 m high staircase with a load fastened to the tail. Hypophysectomy was found to cause atrophic/sclerotic changes in the thyroid and parathyroid glands, and dramatically suppress the functional activity of thyrocytes, C-cells (calcitonin producers) and parathyrocytes (parathormone producers). Assumingly, the impairing effect of hypophysectomy on C-cells and parathyrocytes is consequent to the reduced production of thyroid hormones and concomitant moderation of metabolism. The suspension by tail added somewhat to the severity of changes in thyroid and parathyroid glands under the effect of hypophysectomy, whereas the injection of growth hormone or insulin-like growth factor 1 slightly stimulated thyrocytes, C-cells, and parathyrocytes activities; however, it failed to offset the hypophysectomy-provoked developments. Although the activities of thyrocytes, C-cells or parathyrocytes were not affected by physical exercise, there was a mild C-cell proliferation.