Intestinal calcium transport in the spontaneously hypertensive rat: response to calcium depletion
Schedl, H.P.; Miller, D.L.; Horst, R.L.; Wilson, H.D.; Natarajan, K.; Conway, T.
American Journal of Physiology 250(4 Pt 1): G412-G419
1986
ISSN/ISBN: 0002-9513 PMID: 3963190 Document Number: 278052
We previously found intestinal Ca2+ transport to be lower in the spontaneously hypertensive (SH) as compared with the Wistar-Kyoto control (WKY) rat. These animals were fed a relatively high (1%) Ca2+ diet, and the concentration of 1.alpha.,25-dihydroxycholecalciferol [1.alpha.,25(OH)2D3] in serum was the same in both groups. In the present experiment we tested the possibility that the lower Ca2+ transport in the SH rat was the result of unresponsiveness to 1.alpha.,25(OH)2D3. We fed diets high and low in Ca2+ and measured serum 1.alpha.,25(OH)2D3. We fed diets high and low in Ca2+ and measured serum 1.alpha.,25(OH)2D3 and Ca2+ transport. Serum 1.alpha.,25(OH)2D3 increased in response to Ca2+ depletion at both 5 and 12 wk in both the WKY and SH rat. With high-Ca2+ diet, Ca2+ transport was lower in SH than in WKY when studied (1) in vitro in duodenum at 5 wk of age, and (2) in vivo in proximal and distal small intestine at 12 wk of age. Ca2+ transport increased in SH in response to Ca2+ depletion, but not in WKY, except in distal small intestine in vivo at 12 wk. In summary, although Ca2+ transport is lower in the SH as compared with the WKY rat when vitamin D activity is basal through feeding a high-Ca2+ diet, Ca2+ transport increases in the SH rat in response to the increase in 1.alpha.,25(OH)2D3 produced by feeding a low-Ca2+ diet. We conclude that (1) the vitamin D-regulated component of mediated Ca2+ transport is intact in the SH rat and is unrelated to hypertension, and (2) mediated Ca2+ transport under basal conditions, i.e., nonvitamin D-regulated, differs in the SH and WKY rats and may be related to hypertension.