© 1986 by The Society for Integrative and Comparative Biology
Hormones and Calcium Regulation in Fundulus heteroclitus1
Department of Pharmacology, Texas Tech University Health Sciences Center Lubbock, Texas 79430
For the past 20 years, our laboratory has been involved in studying the endocrine control of calcium balance in the killifish, Fundulus heteroclitus. We have surveyed almost all endocrine systems and discovered two main ones directly involved in plasma calcium regulation. They are the pituitary gland and the corpuscles of Stannius. When fish adapted to low-calcium seawater were hypophysectomized, hypocalcemia and tetany were observed. When fish adapted to high-calcium seawater were Stanniectomized, hypercalcemia was seen. In both cases, other electrolytes were unaffected and replacement therapy corrected the plasma calcium changes. We have tried to characterize the active principles in both glands. We discovered that prolactin is hyperacalcemic. The pituitary gland also seems to contain a second hypercalcemic factor which may be located in the PAS-positive pars intermedia cells. For the Stannius corpuscle factors, we developed a bioassay and named the active substance(s) hypocalcin. In collaboration with Dr. Hirofumi Sokabe at Jichi Medical School, Japan, we showed that the Stannius corpuscles also contain a renin-like substance capable of generating a hypocalcemic angiotensin-like substance. The exact chemical nature of the hypocalcemic substance is being investigated. Calcium balance in the whole fish was also studied with 47-calcium. These studies were carried out in collaboration with Dr. Nicole Mayer-Gostan at Villefranche-sur-Mer, France. We discovered that killifish depend on the environment rather than bone as a calcium reservoir. Hormones may be involved in the exchanges with the environment.