As bstract. Serum ionized calcium levels are lower and immunoreactive parathyroid hormone levels are higher in the spontaneously hypertensive (SH) rat than in the normotensive Wistar-Kyoto (WKy) control.We postulated that there is either a defect in the regulation ofvitamin D metabolism by parathyroid hormone or that the gut target organ for vitamin D in the SH rat is unresponsive. To test these hypotheses we measured serum concentrations of vitamin D metabolites and intestinal transport of calcium and sodium. Compared with that of WKy controls, in vitro calcium transport by duodenal sacs of the SH rat was decreased (P < 0.001) at 5 wk, before the development of hypertension, and at 12 wk, after hypertension was well established. When measured in vivo in the most proximal 20 cm of small intestine, maximum velocity (Vmax) for calcium transport was decreased (P < 0.05) and net absorption of sodium and water was increased (P < 0.05) in SH rats as compared with WKy rats. Vmax for calcium transport was also decreased (P < 0.05) in the most distal 20 cm of small intestine of SH rats, but net sodium and water transport were the same in SH and WKy rats. At 12 wk, serum concentration of 1 ,25-dihydroxycholecalciferol [1,2D3] was the same in both SH and Wry groups, but its precursor, 25-hydroxycholecalciferol, was increased (P < 0.05) in the SH rat. We conclude that in the SH rat: (a) the concentration of 1,25-(OH)2D3 is inappro-

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An echelle spectrometer has been constructed, which is optimized for use with a charge-coupled array detector, with dispersion and resolution appropriate for elemental analysis and plasma diagnostics. Design considerations, characterization, software, and initial experimental data are reported.