Phosphaturic effect of parathyroid hormone in the spontaneously hypertensive rat

M. J. Onsgard-Meyer, T. J. Berndt, A. A. Khraibi, F. G. Knox

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Abstract

The Okamoto spontaneously hypertensive rat (SHR) has been reported to have altered phosphate metabolism. Hypophosphaturia in the presence of increased serum parathyroid hormone (PTH) levels has been reported in the SHR. Therefore it has been postulated that the SHR may be hyporesponsive to the phosphaturic effect of endogenous PTH. In addition, the SHR exhibits enhanced renal sympathetic nerve activity. Recent studies demonstrated that stimulation of the renal adrenoreceptors decreases the phosphaturic response to PTH infusion. Thus a hyporesponsiveness to PTH in the SHR may be due in part to higher renal sympathetic tone. The present study determined the phosphaturic effect of a pharmacological dose of PTH (33 U/kg bolus and 1 U · kg-1 · min-1 infusion) in the thyroparathyroidectomized SHR compared with its normotensive control, the Wistar Kyoto (WKY) rat. Three groups of clearance experiments were performed on male 10- to 14-wk-old SHR and WKY rats. In the first group of rats, the fractional excretion of phosphate (FE(P(i))) in response to PTH infusion was 35.4 ± 4.2% in the SHR (n = 6) and 26.2 ± 3.0% in the WKY rat (n = 6), NS. In the second group, all animals underwent acute unilateral renal denervation (DNX). The FE(P(i)) in response to PTH was 35.3 ± 1.5% in the innervated (INN) kidney of the SHR (n = 10) compared with 27.9 ± 2.5% in the INN kidney of the WKY rat (n = 11), and 39.1 ± 1.9% in the DNX kidney of the SHR compared with 30.5 ± 2.0% in the DNX kidney of the WKY rat. FE(P(i)) in the SHR was significantly greater than that in the WKY rat (P < 0.05). In the third group of experiments, acutely reducing renal perfusion pressure (RPP) to the normotensive range in the SHR did not alter the phosphaturic effect of PTH, 39.6 ± 9.9% (n = 6). In conclusion, the present study demonstrates that the SHR is not hyporesponsive to the phosphaturic effects of PTH infusion but rather exhibits an intact phosphaturic response to exogenous PTH that is not affected by renal DNX or RPP.

Original languageBritish English
Pages (from-to)R78-R83
JournalAmerican Journal of Physiology - Regulatory Integrative and Comparative Physiology
Volume267
Issue number1 36-1
DOIs
StatePublished - 1994

Keywords

  • parathyroid hormone
  • phosphate
  • renal nerves
  • Wistar-Kyoto rat

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