Effects of PTH, ADH, and cyclic AMP on distal tubular Ca and Na reabsorption.

Tubular microperfusion experiments were performed in rats to examine the effects of thyroparathyroidectomy (TPTX), parathyroid hormone (PTH), antidiuretic hormone (ADH), and cyclic AMP (cAMP) on distal tubular Ca, Na, and water reabsorption. TPTX caused a significant decrease in the Ca reabsorptive rate as compared to intact animals. PTH (5 U/kg; 2 U x kg-1 x h-1) replacement in TPTX animals restored Ca transport to control levels. Application of either cAMP (10(-3) M) or 8-(p-chlorophenylthio)-cyclic 3',5'-adenosine monophosphate (10(-5) M) to the surface of the kidney caused a stimulation of Ca reabsorption similar to that produced by PTH. Neither TPTX nor PTH changed Na or water reabsorption significantly, whereas the cyclic nucleotides increased both of these parameters. These later actions of cAMP duplicated effects of ADH observed in these distal tubules.