HYPOPHYSE UND HORMONELLES CALCIUM-REGULATIONSSYSTEM

ABSTRACT A survey of the literature of the last fifty years relating to our topic indicates that the sentence from Copp (1969) »there is no evidence that the anterior pituitary or the central nervous system has any direct effect on the secretion of parathormone or calcitonin« is not based upon concrete experimental data. This is particularly evident from a morphological aspect, since considerable variations in the parathyroids have been repeately observed as the result of both hypophysectomy and the application of hypophyseal extracts. Experimental evidence has contributed little material relevant to a possible hypophyseal control of the parathyroids with the exception of the observation that after hypophysectomy the plasma calcium level remains unchanged. Contrary to this, up to now no positive morphological changes in the C-cells of the thyroid have been determined, although experimental evidence suggests a certain hypophyseal control upon the secretion of calcitonin. All the results of our own experiments in parathyroid morphology suggest significant alterations in the glands subsequent to hypophysectomy. A histological survey shows a considerable reduction in the size of the entire organ and an increase in the connective tissue of the gland. Karyometric tests reveal a reduction of the small diameter of the nuclei of 13.5%, a quantity which corresponds to that found in the nuclei of the adrenal cortex and the follicular cells of the thyroid after the same operation. As a result of hypophysectomy it is possible under the electron microscope to distinguish alterations in the secretory structures of the parenchyma cells of the parathyroid that may indicate restricted parathormone synthesis. In order to exclude the possibility that these changes may have been conditioned by a cessation of adrenal activity, the parathyroid morphology was analyzed also after adrenalectomy. The results obtained in this way differ fundamentally from those produced by hypophysectomy. Morphometrical investigation of the C-cell population of the thyroid after hypophysectomy show a significant reduction in the size of the nuclei of 13.6 % and, under the electron microscope, a reduction of the cytoplasm as well as an increase in the number of calcitonin granula. Two further test series have shown that in hypophysectomized but otherwise untreated animals the plasma calcium level is within the normal range. On the other hand the normal ability to counteract hyper- or hypocalcaemia was found to be lacking to a great extent. All the results obtained suggest the existence of some hypophyseal influence upon the hormonal calcium regulation system. A hypothesis is framed to the effect that the feedback: plasma calcium – parathormone and calcitonin serves, above all, the purpose of compensating an alimentary over- and under-supply of calcium, whereas the hypophyseal regulatory cycle serves to meet the endogenic calcium requirements of the organism under special circumstances, as for instance growth or lactation.