Endocrine Control of Calcium Metabolism and Parturient Hypocalcemia in Dairy Cattle

Abstract

Calcium plays a key role in many fundamental biologic processes including neuromuscular excitability, membrane permeability and blood coagulation in addition to being an essential structural component of the skeleton. The precise control of calcium ions in extracellular fluids is vital, therefore, to the health of animals and man. To maintain a constant concentration of calcium, despite marked variations in intake and excretion, endocrine control mechanisms have evolved that primarily consist of the interactions of three major hormones. Although the direct roles of parathyroid hormone, calcitonin and vitamin D frequently are emphasized in the control of blood calcium, other hormones such as adrenal corticosteroids, estrogens, thyroxine, somatotrophin and glucagon may contribute to the maintenance of calcium homeostasis under certain conditions. The objectives of this report are: (a) to summarize and illustrate some recent findings on the structure and function of calcium control mechanisms under normal and pathologic conditions; and (b) to relate these findings where indicated to the pathogenic mechanisms of parturient hypocalcemia and paresis in dairy cattle.