Effects of parathyroid hormone and urinary phosphate on collecting duct hydrogen secretion.
Urine-minus-blood PCO2 (U - B PCO2) during alkaline diuresis (urinary pH greater than 7.8) was determined in paired experiments using bicarbonate-loaded rats to assess the effects of parathyroid hormone (PTH) and urinary phosphate concentration [( Pi]u) on collecting duct H+ secretion. U-B PCO2 was higher for any value of urinary bicarbonate concentration ([HCO3]u) in the presence of PTH [intact rats and thyroparathyroidectomized (TPTX) PTH-infused rats] than in its absence (calcium-infused intact rats and TPTX rats). However, when [Pi]u was maintained constant by prior phosphate infusion, PTH administration in TPTX rats failed to elevate U-B PCO2. When PTH was infused in TPTX rats to maintain constant the plasma PTH level, subsequent phosphate infusion increased [Pi]u and elevated U-B PCO2 for any value of [HCO3]u. Moreover, when the data were pooled, there was a positive linear relationship between U-B PCO2 factored for [HCO3]u and [Pi]u (P less than 0.001). In all experiments, other factors that may affect U-B PCO2, such as plasma acid-base status, urinary osmolality, and extracellular fluid volume, did not vary. We conclude that PTH stimulates collecting duct H+ secretion indirectly via the increase in [Pi]u.
D000818:Animals; D001639:Bicarbonates / Q000652:urine; D002245:Carbon Dioxide / Q000097:blood / Q000652:urine; D004231:Diuresis; D004573:Electrolytes / Q000097:blood; D005919:Glomerular Filtration Rate; D006859:Hydrogen / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007684:Kidney Tubules / Q000378:metabolism*; D007685:Kidney Tubules, Collecting / Q000378:metabolism*; D008297:Male; D009994:Osmolar Concentration; D010281:Parathyroid Hormone / Q000494:pharmacology*; D010313:Partial Pressure; D010710:Phosphates / Q000652:urine*; D051381:Rats; D011919:Rats, Inbred Strains
D001639:Bicarbonates; D004573:Electrolytes; D010281:Parathyroid Hormone; D010710:Phosphates; D002245:Carbon Dioxide; D006859:Hydrogen