AJP - Endocrinology and Metabolism, Vol 244, Issue 4 313-E316, Copyright © 1983 by American Physiological Society
Nature of calcemic effect of 1,25-dihydroxyvitamin D3 in experimental hypoparathyroidism
E. Hefti, U. Trechsel, H. Fleisch and J. P. Bonjour
The influence of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] treatment on the
daily fluctuation of plasma calcium concentration ( [Ca]P1) in relation to
the feeding-fasting alternation has been studied in vitamin D-replete
sham-operated (sham) and thyroparathyroidectomized (TPTX) rats fed a normal
Ca diet. 1,25(OH)2D3 was given (26 or 39 pmol/day) intraperitoneally either
by single injection or constant infusion using osmotic minipumps. After 7
days of treatment [Ca]P1 was measured at 4-h intervals for 24 h. Pair-fed,
sham and TPTX animals received the solvent vehicle intraperitoneally. The
results show that in sham rats the very moderate daily fluctuation of
[Ca]P1 was not accentuated by 1,25(OH)2D3. A marked fluctuation of [Ca]P1
in relation to the food intake was observed in untreated TPTX as compared
with sham rats. In TPTX rats 1,25(OH)2D3 increased the fasting [Ca]P1. In
contrast the rise in [Ca]P1 during feeding was not significantly
accentuated by 1,25(OH)2D3. The daily fluctuation of [Ca]P1 was the same
whether the dose of 1,25(OH)2D3 was given in one single injection or by
constant infusion, suggesting that this hormone is not involved in the
hour-to-hour regulation of [Ca]P1. In conclusion, in the absence of
parathyroid glands, 1,25(OH)2D3 given in doses that stimulate intestinal
calcium absorption has a much more pronounced effect on the fasting
calcemia than on the rise in calcemia observed during the feeding period.
These results suggest that the mobilization of calcium from bone could play
an important role in the calcemic effect of 1,25(OH)2D3 when given in the
hypoparathyroid state.
