Abstract
Elevated serum-P-levels in thyrotoxicosis have been ascribed to increased renal P-reabsorption as a result of suppressed parathyroid activity. In acute experieraents, Beisel found a decrease of TRP under T3 in PTX dogs. In our experiments the longterm effect of experimental hypo- and hyperthyreoidism on renal P-handling in PTX rats was measured. Hypothyroidism (TX): thyroidectomy 3 w. prior to the experiment; hyperthyroidism (Ht): daily i.p. inj. 0,05 mg T4 over 6 days.
Results: Serum-Ca: TXPTX 3,42±0,O6 mEg/l; euthyroid PTX 3,23±0,08; HtPTX 3,13±0,08. Serum-P: EuPTX 14,4±0,276 mg%; TXPTX 12,7±0,325 mg%; HtPTX 15,5±0,255 mg% (p<0,01). No significant difference of TRP in any group. Correlation between filtered load and TRP showed that, - at any given GFR x serum-P, - TRP was higher in thyrotoxicosis.
Conclusion: Hyperphosphatemia was induced by T4 even in PTX rats. Therefore elevated serum-P-levels in thyrotoxicosis are not due to parathyroid suppression but due to parathyroid suppression but due to a renal effect of T4 (increased tubular reabsorption).
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Bommer, J., Ritz, E., Mehls, O. et al. The effect of thyroxine on renal phosphorus handling. Pediatr Res 8, 913 (1974). https://doi.org/10.1203/00006450-197411000-00087
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DOI: https://doi.org/10.1203/00006450-197411000-00087