The phosphaturic effect of parathyroid hormone (PTH), cyclic adenosine monophosphate (cAMP), acetazolamide (Az) and HCO3 loading was studied in normal, thyroparathyroidectomized (TPTX), and Li treated dogs. PTH administration to normal animals markedly increased fractional excretion (F) of PO4 but had a blunted effect on F(po4) in the Li treated animals. Cyclic AMP likewise markedly increased F(po4) in the normal animals but had a markedly blunted effect in the Li treated animals. Az led to a significant increase in F(na), F(hco3), and F(po4) in the normal animals. In the Li treated dogs, Az induced a significant natriuresis and bicarbonaturia but failed to increase phosphaturia. HCO2 loading in normal dogs caused a significant phosphaturia while having little effect on F(po4) in Li treated dogs. HCO3 loading to TPTX dogs was associated with a lower F(po4) as compared to normal HCO3 loaded animals. These data suggest that Li administration not only blocks the adenyl cyclase cAMP system in the renal cortex, but it may also interfere with a step distal to the formation of cAMP, since the phosphaturic effect of both PTH and cAMP was markedly diminished in Li treated animals.
ASJC Scopus subject areas
- Physiology (medical)