More than twenty years ago it was found that the renal medullary interstitium of the mammals contained abundant amounts of glycosaminoglycans (GAG) and that the urine of hydropenic animals had a high hyaluronidase activity. Histochemical and physiological observations led to the hypothesis that passage of water out of the renal collecting duct following antidiuretic hormone (ADH) might be facilitated by the release of hyaluronidase with subsequent depolymerization of GAG in the interstitiurn.' But the literature contains contradictory reports as to the influence of ADH on the GAG of the renal medullary interstitiurn," and up to now the effect of ADH on the interstitial structures, which, as supposed, plays an important role in the urinary concentration, remains disputablc. The homozygous Brattleboro rats with diabetes insipidus seemed to offer unique advantages for solving this problem. Recently, it has been found that the renal papilla interstitium of homozygous rats contains greatly reduced amounts of GAG when compared with normal or heterozygous ones." We have obtained the same data and undertook a research to investigate the renal enzyme system of hyaluronate hydrolases and GAG in detail.Experiments were carried out on the homozygous (DI) and heterozygous (HZ) Brattleboro rats bred from the stock supplied by the Institute of Physiology of the Czechoslovak Academy of Sciences. The total hyaluronate hydrolases (HH) activity of the renal papilla tissue was determined according to Bollet et al." To investigate the hyaluronidase (Hy) activity, the exohydrolases' effect on the substrate was blocked by muck acid.5 For the evaluation of 8-glucuronidase and N-acetylhexosaminidase activities we used as substrates PNP-fl-D-glucuronide, PNP-2-acetamido-2-deoxy-fl-~-glucopyranos~de, respectively (Koch-Light, England). Urine and plasma osmolality was determined by freezing-point osmometry. For the histochemical study, the kidneys were fixed in the 10% solution of neutral formalin. The slices were stained by several methods for identification of GAG.O To avoid some possible faults when staining, the slices of control and experimental rats were processed simultaneously.The study of H H activity in the papilla tissue showed that the basal level of the total HH activity and the Hy of two exohydrolases were significantly less in DI rats than in HZ ones (TABLE 1 ) ; but the activity was nearly equal to that of Wistar rats.' The treatment of the rats with ADH (Pituitrin P, 500 pU/lOO g b.wt., subcutaneously twice in 30 min) increased the urinary osmolality as well as the HH activity. Although the level of the enzyme activity in the DI rat kidney remained lower than in HZ rat, the percentage of 503 0077-8923/82/0394-0503 $1.7510 0 1982, NYAS
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