The effect of estrogen on renal phosphorus handling in the rat

Background/Aims: Phosphorus reabsorption in the kidney is regulated by para thyroid action on the sodium phosphorus cotransporter (Na-Pi cotransporter) . There is some evidence that estrogen may also regulate renal phosphorus h andling but it is not known if this is an effect of estrogen on filtered ph osphorus load. Methods: This study examined the effect of estrogen on renal phosphorus handling during infusion with calcium or EDTA. Six month old Sp rague Dawley rats were bilaterally oophorectomized (OOX) or underwent a sha m operation under ether anaesthesia 6 weeks before undergoing infusion with calcium chloride or EDTA. A second study examined renal phosphorus handlin g after estrogen replacement in the COX rat injected with 20 mug estradiol valerate, or vehicle alone, prior to calcium infusion. Results: A compariso n of filtered phosphorus load with renal phosphorus excretion indicated tha t the estrogen replete rat had a higher renal excretion of phosphorus when infused with both calcium (p = 0.004) and EDTA (p = 0.037) at all filtered phosphorus loads. A similar analysis in calcium infused, estrogen replaced, COX rats indicated an effect of estrogen to increase renal phosphorus excr etion (p = 0.007) at all filtered phosphorus loads. COX resulted in a mild metabolic alkalosis, an effect not reversed by estrogen administration, tha t was not related to renal phosphorus excretion. OOX decreased renal sodium excretion and uncoupled the relation between renal phosphorus and sodium e xcretion, an effect reversed by estrogen replacement. Conclusion: Ovarian h ormone deficiency in the rat results in a decrease in renal phosphorus excr etion. This finding is comparable to effects of the menopause and hormone r eplacement therapy in postmenopausal women. Copyright (C) 2001 S. Karger AG , Basel.