Cytological and physiological activity of the ultimobranchial glands in the premetamorphic anuran Rana catesbeiana

Abstract

The physiological influence of ultimobranchial glands as a source of calcitonin in larvae of Rana catesbeiana was investigated by ultimobranchialectomy (UBX) and by the cytological response of glands and larvae under conditions of a low (3 meq/l) or high (15 mEq/l) calcium environment. Normal glands from stages III–XVIII generally consist of a single follicle composed of pseudostratified epithelium with a small central cavity. Glands examined from larvae (Stages III–XVIII) kept in high calcium (15 mEq/l) exhibited an increase in secondary follicle formation after 6 weeks' treatment. Cytoplasmic secretory material in secretory cells could be increased after 3 weeds in high calcium at all stages and was associated with secondary follicle formation. In addition, there was an increase in contents in the central cavity. Ultimobranchialectomy at Stages III–XIX followed by maintenance in low calcium environment resulted in decreased calcium uptake by paravertebral lime sacs and poorly ossified metamorphosed adults. Ultimobranchialectomized larvae kept in high calcium also were unable to accumulate calcium in the lime sacs until stage XVIII. At stage XVIII (metamorphosis) UBX larvae accumulated calcium in lime sacs in amounts greater than controls and skeleton was ossified to the extent seen in intact animals kept in low calcium. The cytological alterations suggest that ultimobranchial glands can undergo precocious hyperactivity with high calcium challenge prior to metamorphosis. The presence of the ultimobranchial glands influences accretion of calcium into lime sacs during larval development, apparently to ensure maximal accretion of calcium into bone during metamorphosis.