Nonvolatile acid-base loads (dietary or injected) are excreted by grasshoppers allowed to feed; while the respiratory system has no direct role in compensation for nonvolatile acid or base loads. In this study we attempted to discover where, within the digestive and renal system, the regulation of acid-base excretion occurs in response to: (a) variation in feeding state, and (b) injection of HCl into the hemocoel. Grasshoppers fed lettuce excrete base, while un fed grasshoppers excrete acid. Using a glass micro-eleclrode, we measured the luminal pH of the crop, midgut, point of Malpighian tubule after the acidbase challenge. Fluid movement rate through the gut was estimated from the passage rate of cobalt-EDTA, and solid movement rate from the transit of chromic oxide. Change in titratable acid excretion by each gut segment in response to the acid-base challenge was calculated from the difference in luminal pH between conditions, the luminal nonbicarbonate buffer capacity, and the content passage rates. Midgut luminal pH is unaffected by feeding state or injection of HCl into the hemocoel. When feeding state changes, variation in acid-base excretion is accomplished by changes in the acid-base excretion of the Malpighian tubules, ileum, and rectum. The site of regulation with HCl injection is condition-dependent. In unfed animals, the acid is transferred to the lumens of the midgut and crop and retained; in fed grasshoppers, the ileum and rectum are the sites of regulation and the acid load is excreted.
|Original language||English (US)|
|State||Published - Dec 1 1997|
ASJC Scopus subject areas
- Molecular Biology