Renal alterations induced by osmotic stress and metabolic acidosis inXenopus laevis

✍ Scribed by Stetson, David L.

• Book ID: 102893528
• Publisher: John Wiley and Sons
• Year: 1978
• Tongue: English
• Weight: 818 KB
• Volume: 206
• Category: Article
• ISSN: 0022-104X
• DOI: 10.1002/jez.1402060205

✦ Synopsis

Abstract

Xenopus has unusual flask cells within the intermediate segment of the renal nephron. These cells respond to osmotic stress by losing the glycosaminoglycan (GAG) contents from their central cavities. Because of this it has been argued that flask cells participate in osmoregulation. The present work was designed to investigate changes in morphology of the flask cells and to determine whether such changes could be related to simultaneous changes in nitrogen excretion rather than osmotic stress.

In animals exposed to 21 days of osmotic stress, total nitrogen excretion doubled relative to controls and urea comprised 85% of waste nitrogen. The activity of phosphate dependent glutaminase (PDG), a renal ammonia‐producing enzyme, did not decrease even though ammonia excretion decreased by more than 50% in experimental animals. Structurally, flask cells had shrunken and contained little GAG. The average number of distended flask cells within profiles of intermediate segments dropped from about 2 in control animals to 0.60 in animals stressed for 14 days.

Acidosis was induced in Xenopus by injecting a single dose of 2.5 mM HCl per kg body weight. In these animals, ammonia excretion increased 160% over controls and PDG activity increased 30%. The number of flask cells in intermediate segment profiles increased from 2.02 in controls to 4.16 in experimental animals.

These results demonstrate that the number of distended flask cells and their morphology are altered by conditions which change patterns of nitrogen excretion; therefore, the flask cells may be directly involved with ammonia excretion.