AJP - Regulatory, Integrative and Comparative Physiology, Vol 246, Issue 5 693-R697, Copyright © 1984 by American Physiological Society
Transient response of the calcium homeostatic system: effect of calcitonin
G. G. Jaros, P. C. Belonje, R. van Hoorn-Hickman and E. Newman
With the use of an intravenous step load of calcium, a rapid (less than 30
min) process that helps regulate plasma calcium has been identified in
pigs. The process appears to be calcitonin dependent, may not involve
simple equilibration, and varies inversely with age, as it is virtually
absent in old sheep compared with its intensity in young sheep. Based on
these findings and a general model of calcium homeostasis, five classes of
regulatory processes are proposed. Grade I (half time, t1/2, congruent to
15 min) is a transient and saturable response present only in young
individuals and is calcitonin dependent. Grade II (1/2 congruent to 60-90
min) is parathyroid hormone and possibly calcitonin dependent. Grade III
(t1/2 = 3-4 h) is parathyroid hormone dependent and probably renal in
nature. Grade IV (t1/2, several hours) is vitamin D dependent and
intestinal in nature. Grade V (t1/2, hours or days) is parathyroid hormone
and calcitonin dependent and skeletal in nature.
