Impaired Parathyroid Hormone Action on Urinary Phosphorus Excretion in Isolated Perfused Kidney of Streptozotocin-Induced Diabetic Rats

Abstract

To study the effects of diabetes on the renal actions of parathyroid hormone (PTH), we observed urinary excretion of cyclic adenosine monophosphate (cAMP) and phosphorus in isolated perfused rat kidney. Diabetic rats were kept for 7 days after an intraperitoneal injection of 70 mg/kg streptozotocin (STZ). STZ-induced diabetic rats were treated with a daily injection of 20 U/kg lente-type insulin for 7 days. Plasma albumin, calcium, phosphorus, and PTH levels were not different among normal control, diabetic and insulin-treated diabetic groups. In the control rat kidney, the addition of PTH increased urinary cAMP excretion from 8 ± 3 to 190 ± 49 pmol/5 min and urinary phosphorus excretion from 11.3 ± 4.4 to 33.6 ± 10.8 µg/5 min. In the STZ-diabetic rat kidney, basal urinary cAMP was impaired, and PTH altered neither urinary cAMP nor phosphorus excretion (from below 0.7 to below 0.7 pmol/5 min, and from 15.5 ± 4.5 to 13.6 ± 8.1 µg/5 min, respectively). Insulin treatment completely recovered the PTH actions. These results show that insulinopenic diabetes induces PTH resistance in the kidney.

Key words

Streptozotocin Diabetes - Parathyroid Hormone - Cyclic Adenosine Monophosphate - Tubular Reabsorption of Phosphorus