Increased plasma calcitonin levels in young spontaneously hypertensive rats: role in disturbed phosphate homeostasis.

In young spontaneously hypertensive rats (SHR) and in normotensive Wistar-Kyoto controls (WKY) several parameters of phosphate and calcium homeostasis were determined. At 6 and 8 weeks, blood analysis revealed a significant hypophosphatemia (p less than 0.001) in SHR and twice as high plasma calcitonin levels in SHR than in WKY controls. At 8 weeks, 1,25-dihydroxycholecalciferol concentration was 20% higher in SHR (p less than 0.02) while 25-hydroxycholecalciferol was unaltered (p greater than 0.51). In addition total immunoreactive PTH, iPTH, was slightly increased (p less than 0.07) but intact PTH (1-84) (p greater than 0.90) was not significantly different from age matched WKY controls. Also at 8 weeks, a slightly reduced serum ionized Ca2+ concentration (p less than 0.001) with no change in total serum calcium was found in SHR (p greater than 0.39). Balance studies at 6 and 8 weeks of age revealed no significantly different balances for phosphate (F = 2.5, p greater than 0.10) and for calcium (F = 2.6, p greater than 0.09), although a tendency for slightly more positive balances existed in SHR when compared to WKY. However, SHR excreted significantly less phosphate in the urine than WKY control (F = 0.2, p less than 0.0009). Bone analysis was performed on femora of SHR and WKY of 6 weeks of age. Femora were significantly shorter in SHR (20.54 +/- 0.35 vs. 21.50 +/- 0.05 mm in WKY), whereas bone dry weight (127 +/- 6 vs. 107 +/- 2 mg).(ABSTRACT TRUNCATED AT 250 WORDS)