Tamm-Horsfall glycoprotein in streptozotocin diabetic rats: a study of kidney in situ hybridization, immunohistochemistry, and urinary excretion.

Tamm-Horsfall glycoprotein, present only in the kidney thick ascending limb of Henle's loop, was studied here in streptozotocin diabetic rats. Tamm-Horsfall glycoprotein mRNA in situ hybridization was performed on snap-frozen left kidneys; the right kidneys were perfusion-fixed with 4% paraformaldehyde and embedded either in paraffin, for Tamm-Horsfall glycoprotein immunohistochemistry, or in Epon for stereologic measurements. The length of the thick ascending limb of Henle's loop and the amount of glycogen were measured and the ultrastructure of the cells was evaluated. Urinary excretion of Tamm-Horsfall glycoprotein, calcium, magnesium and albumin was measured. After 10 and 50 days' duration of diabetes, kidney weight increased 20 and 41%, respectively and the length of the thick ascending limb of Henle's loop increased 28 and 56%, respectively, compared with controls. Substantial glycogen accumulations were present in the thick ascending limb of Henle's loop, and electron microscopy revealed a significant decrease in organelles and basolateral membranes. After 10 and 50 days' duration of diabetes, in situ hybridization of Tamm-Horsfall glycoprotein mRNA revealed a fourfold decrease, and the immunostaining for Tamm-Horsfall glycoprotein showed a threefold decrease as measured by densitometry. However, urinary Tamm-Horsfall glycoprotein excretion rate was increased fivefold and urinary concentration about twofold. Urinary calcium excretion increased three-fold and magnesium twofold, but urinary albumin excretion was not significantly increased. The increased amount of Tamm-Horsfall glycoprotein, calcium and magnesium in the urine in diabetes occurs here concomitant with severe cellular damage in the thick ascending limb of Henle's loop.