Journal of Applied Physiology, Vol 73, Issue 2 169S-173S, Copyright © 1992 by American Physiological Society
Circulating parathyroid hormone and calcitonin in rats after spaceflight
S. B. Arnaud, P. Fung, I. A. Popova, E. R. Morey-Holton and R. E. Grindeland
National Aeronautics and Space Administration Ames Research Center, Moffett Field, California 94035-1000.
Parathyroid hormone and calcitonin, two major calcium-regulating hormones,
were measured in the plasma of five experimental groups of rats to evaluate
postflight calcium homeostasis after the 14-day COSMOS 2044 flight.
Parathyroid hormone values were slightly higher in the flight animals (F)
than in the appropriate cage and diet controls (S) (44 +/- 21 vs. 21 +/- 4
pg/ml, P less than 0.05), but they were the same as in the vivarium
controls (V), which had different housing and feeding schedules. Neither V
nor S showed the increase in plasma creatinine phosphorus and magnesium
found in F, features of early renal insufficiency. F showed the lowest mean
plasma calcitonin that was statistically different from V only. This
difference in F and V (22 +/- 11 vs. 49 +/- 16 pg/ml, P less than 0.05) was
most likely due to failure of circulating calcitonin in F to show the
normal age-dependent increase we demonstrated in age-matched controls in a
separate experiment. Basal values for parathyroid hormone and calcitonin
were unchanged after 2 wk of hindlimb suspension, a flight simulation
model, in age-matched and younger rats. From a time course experiment serum
calcium was higher and parathyroid hormone lower after 4 wk than in
ambulatory controls. Postflight circulating levels of parathyroid hormone
appear to reflect disturbances in calcium homeostasis from impaired renal
function of undetermined cause, whereas levels of calcitonin reflect
depression of a normal growth process.
