7. THE ULTIMOBRANCHIAL GLANDS
391
E. Ultimobranchial Response to Hypercalcemia
Matsuzawa and Kurosumi (1967) observed that many of the secretory
granules in the parafollicular (ultimobranchial) cells of rat thyroid were
discharged 4 hr after injection of 10 mg of calcium per kilogram. Robertson (1968b) also observed increased secretory activity in the ultimobranchial gland of the frog, Rana pipiens, during hypercalcemia. When
these frogs were treated with 200,000 units of vitamin D and maintained
in water containing 0.8% CaCl,, plasma calcium rose to 15 mg f& and the
ultimobranchial glands were grossly hypertrophied after 2 weeks (Robertson, 1968a). After 3 weeks in freshwater, the gland returned to its initial
size.
The original experiments which revealed the existence of calcitonin
(Copp et al., 1962) indicated that hypercalcemia caused release of the
hormone. In elegant experiments in which hog thyroid glands were perfused with blood of varying calcium concentrations, Care et al. (1968)
showed that secretion of calcitonin increased in direct proportion to the
increase in the calcium in the perfusing blood. This suggests a highly
effective negative feedback mechanism.
F. Action in Mammals
As indicated in the reviews quoted above, most of the studies on
calcitonin have been carried out on mammals. In young rats, the most obvious effect was a rapid reduction in plasma calcium and phosphate which
occurred even in the absence of parathyroid or kidney (Hirsch et al.,
1964). This apparently results from inhibition of bone resorption. In organ
cultures of mouse calvaria, addition of calcitonin inhibited bone resorption, particularly when this had been stimulated by the presence in the
medium of parathormone (Aliopoulios et al., 1966) or vitamin A
(Reynolds and Dingle, 1968). The latter found that 20 mU/ml of chicken
calcitonin in the medium was as effective as 500 mU/ml of the porcine
hormone. In intact rats, calcitonin inhibited bone resorption induced by
low calcium peritoneal lavage (Klein et al., 1967) or by administration of
large doses of vitamin A (Foster et al., 1968).
G. Action in Fishes
There is at present very little information on the action of calcitonin
in fishes, although the presence of large ultimobranchial glands and high
concentrations of calcitonin suggest that it must have an important function. Pang and Pickford (1967) failed to obtain any fall in plasma calcium
391
E. Ultimobranchial Response to Hypercalcemia
Matsuzawa and Kurosumi (1967) observed that many of the secretory
granules in the parafollicular (ultimobranchial) cells of rat thyroid were
discharged 4 hr after injection of 10 mg of calcium per kilogram. Robertson (1968b) also observed increased secretory activity in the ultimobranchial gland of the frog, Rana pipiens, during hypercalcemia. When
these frogs were treated with 200,000 units of vitamin D and maintained
in water containing 0.8% CaCl,, plasma calcium rose to 15 mg f& and the
ultimobranchial glands were grossly hypertrophied after 2 weeks (Robertson, 1968a). After 3 weeks in freshwater, the gland returned to its initial
size.
The original experiments which revealed the existence of calcitonin
(Copp et al., 1962) indicated that hypercalcemia caused release of the
hormone. In elegant experiments in which hog thyroid glands were perfused with blood of varying calcium concentrations, Care et al. (1968)
showed that secretion of calcitonin increased in direct proportion to the
increase in the calcium in the perfusing blood. This suggests a highly
effective negative feedback mechanism.
F. Action in Mammals
As indicated in the reviews quoted above, most of the studies on
calcitonin have been carried out on mammals. In young rats, the most obvious effect was a rapid reduction in plasma calcium and phosphate which
occurred even in the absence of parathyroid or kidney (Hirsch et al.,
1964). This apparently results from inhibition of bone resorption. In organ
cultures of mouse calvaria, addition of calcitonin inhibited bone resorption, particularly when this had been stimulated by the presence in the
medium of parathormone (Aliopoulios et al., 1966) or vitamin A
(Reynolds and Dingle, 1968). The latter found that 20 mU/ml of chicken
calcitonin in the medium was as effective as 500 mU/ml of the porcine
hormone. In intact rats, calcitonin inhibited bone resorption induced by
low calcium peritoneal lavage (Klein et al., 1967) or by administration of
large doses of vitamin A (Foster et al., 1968).
G. Action in Fishes
There is at present very little information on the action of calcitonin
in fishes, although the presence of large ultimobranchial glands and high
concentrations of calcitonin suggest that it must have an important function. Pang and Pickford (1967) failed to obtain any fall in plasma calcium