AJP - Renal Physiology, Vol 251, Issue 2 278-F282, Copyright © 1986 by American Physiological Society
Ca fluxes across duodenum and colon of spontaneously hypertensive rats: effect of 1,25(OH)2D3
U. Gafter, S. Kathpalia, D. Zikos and K. Lau
Calcium absorption by spontaneously hypertensive rats (SHR) was variably
reported to be different from normotensive Wistar-Kyoto (WKY) controls.
Furthermore, blunted responsiveness to the intestinal effects of
1,25-dihydroxyvitamin D3 [1,25(OH)2D3] has also been postulated. To
evaluate this hypothesis, calcium fluxes were measured by the Ussing
technique across duodenum and descending colon with or without prior
1,25(OH)2D3 treatment. Duodenal mucosal-to-serosal calcium flux (Jm----s)
(44.9 vs. 52.4 nmol X cm-2 X h-1), serosal-to-mucosal flux (Js----m) (25.6
vs. 28.4 nmol X cm-2 X h-1), and net flux (Jnet) were comparable.
1,25(OH)2D3 increased duodenal Jm----s in both SHR and WKY groups (95.2 and
86.8 nmol X cm-2 X h-1). Js----m was lower in SHR (26.1 vs. 35.6 nmol X
cm-2 X h-1, P less than 0.01), although the tendency for a higher Jnet in
SHR (68.6 vs. 51.2 nmoles X cm-2 X h-1) was statistically insignificant.
Short-circuit current was higher in the colon of SHR, both before and after
1,25(OH)2D3, suggesting increased sodium transport. Basal colonic Jnet was
virtually zero in both groups but comparably increased by 1,25(OH)2D3
because of stimulation in only Jm----s. Prevention of hypertension by
hydralazine since the 4th wk of age did not alter the findings compared
with the hypertensive SHR, suggesting calcium transport rates were
unaffected by hypertension. These data indicate that in vitro, duodenal,
and colonic active calcium transport by the SHR is similar to WKY. Their
normal responses to 1,25(OH)2D3 do not support the hypothesis of intestinal
resistance.
