AJP - Renal Physiology, Vol 237, Issue 3 175-F181, Copyright © 1979 by American Physiological Society
Resistance to the phosphaturic effect of parathyroid hormone in the hamster
C. A. Harris and J. F. Seely
The renal effects of parathyroid hormone (PTH) and dibutyryl 3'5'-cyclic
AMP (DBcAMP) were studied in thyroparathyroidectomized hamsters. The
hamsters were permitted free access to food and water or fasted for 16 h.
PTH caused a phosphaturia in the fed hamster (fractional excretion of
phosphate (FEPO4) increased from 5.8 +/- 1.3 to 27.4 +/- 4.6%, P less than
0.001) but not in the fasted hamster (from 9.9 +/- 2.5 to 12.4 +/- 2.5%,
NS), whereas calcium excretion decreased significantly in both groups.
There was no significant difference in blood acid-base or phosphate levels
between the two groups. Insulin did not restore the phosphaturic response
to PTH (FEPO4 from 7.7 +/- 2.6 to 5.3 +/- 1.7%), whereas phosphate or NH4Cl
infusion did, FEPO4 increasing from 20.9 +/- 3.1 to 38.1 +/- 5.4% (P less
than 0.02) and from 19.5 +/- 3.8 to 39.0 +/- 7.5%, respectively. DBcAMP
caused a phosphaturia both in the fasted (from 9.6 +/- 2.7 to 20.1 +/-
4.5%, P less than 0.01) and fed (from 2.5 +/- 0.5 to 10.7 +/- 1.5%, P less
than 0.02) hamster. A fasting state of up to 64 h did not produce
resistance to PTH in the rat. It is concluded that fasting produces
resistance to the phosphaturic but not the calcium-retaining effects of PTH
in the hamster. The resistance may occur, at least partly, prior to the
production of cAMP within the renal tubular cell.
