AJP - Endocrinology and Metabolism, Vol 247, Issue 5 625-E633, Copyright © 1984 by American Physiological Society
Evidence for an intestinal mechanism in hypercalciuria of spontaneously hypertensive rats
K. Lau, D. Zikos, J. Spirnak and B. Eby
To define the mechanism for the hypercalciuria in spontaneously
hypertensive rats (SHR), Ca clearance was evaluated in fasted 23-wk-old SHR
and normotensive Wistar Kyoto (WKy) controls. There was no exaggerated
calciuria before or after parathyroidectomy. Ca balance was therefore
measured in the nonfasted animals, which revealed hyperabsorption in SHR of
both sexes with increments 10-fold that of Ca excretion, supporting the
primacy of intestinal hyperabsorption. In situ duodenal Ca uptake was also
increased in the SHR. Parathyroidectomy did not affect the hyperabsorption.
Hypercalcemia (total and ionized) and hypercalciuria in SHR associated with
reduced adenosine 3',5'-cyclic monophosphate excretion, were abolished by
fasting. Correction of hypertension for 6 mo failed to abolish the
hypercalciuria. Bone Ca deposits were increased in 1-yr-old SHR.
Ten-week-old SHR, in contrast, displayed mild malabsorption. Our data do
not support the "renal leak" hypothesis. Instead, the adult SHR is
characterized by increased Ca retention due to primary hyperabsorption,
absorptive hypercalciuria, and increased bone Ca deposition. These
phenomena are independent of sex, parathyroid hormone, and treatment of the
established hypertension.
