Transport of calcium by duodenum of spontaneously hypertensive rat.

The absorption of calcium by segments of duodenum obtained from spontaneously hypertensive (SH) rats and normotensive Wistar-Kyoto (WKy) rats was measured before and after the development of hypertension. The systolic blood pressure (SBP) of 5-wk-old SH rats (116 +/- 4 Torr) was significantly elevated above that of age-matched WKy rats (103 +/- 3 Torr) but was not at a level generally considered to be hypertensive. Values obtained for calcium transport [ratio of serosal-to-mucosal fluid 45Ca2+ concn (S/M ratio)] from everted duodenal sacs were similar between the two groups at this age. At 12 wk of age, SH rats exhibited a SBP (153 +/- 4 Torr) well above that of WKy controls (127 +/- 3 Torr), and calcium S/M ratios for duodenal sacs were significantly greater than the WKy control values. Similarly, the in vivo uptake of calcium in duodenal segments was significantly elevated in 12-wk-old SH rats compared with WKy controls. The administration of vitamin D3 or its metabolite, 25-hydroxycholecalciferol, had no detectable effect on duodenal transport of calcium in 12-wk-old SH or WKy rats. By comparison, 1,25-dihydroxycholecalciferol produced a significant increase in duodenal calcium transport both in vitro and in vivo in WKy but not in SH rats. The results indicate a distinct abnormality in the transport of calcium in the duodenum of SH rats, suggesting that the decrease in duodenal uptake of calcium that normally occurs with maturation is slow to develop in this rat strain.