In higher vertebrates, normal digestion and absorption by the
gastrointestinal tract are dependent on the orderly and controlled
transit of intraluminal contents. A relationship between fluid
passage through the gut and absorption from the gut has yet to be
examined in fish. In marine teleosts, the osmolality and ion concentration
of the ingested seawater (SW) must be lowered before
water absorption is initiated. By assuming that these processes are
related to fluid transit, it is likely that alterations in these
processes as well as in the water-electrolyte balance (WEB) of the
animal would result with changes in the transit of intraluminal fluid.
I hypothesized that marine teleosts regulate gut motility to achieve
essential water absorption and thereby maintain the WEB. To test
this, the gut of a marine teleost, the buffalo sculpin (Enophrys
bison G.), was challenged in situ with forced drinking (continuous
perfusion) at rates above and below that of the measured drinking
rate (DR).
Initially, the sensitivity of the WEB of the sculpin to
preparatory manipulations that were essential for testing the above
proposal was determined. The WEB was monitored before, during and
after manipulation that included handling, containment, benzocaine-induced
anesthesia, arterial and esophageal cannulation and serial
sampling of blood. To monitor the WEB, indicators of the osmotic
status and the intravascular volume were measured. Within one to
three hours after surgery, a hyper-osmotic hemodilution resulted from
an influx of hyper-osmotic fluid. Blood volume increased about 18%
after surgery. The osmotic imbalance was corrected within 24 hours
after surgery, whereas, the volume disturbance persisted. The occurrence
of plasma hyper-osmolality after surgery was inhibited with
esophageal occlusion. This implicated the gut as the origin of the
osmotic and volume disturbances. Further data evaluation suggested
that the surgery-induced WEB disturbance was a resultant of enhanced
ion and water absorption in the upper and lower gut.
Next, the DR and drinking behavior of the buffalo sculpin were
determined. Also assessed was the influence of the manner of SW
ingestion (ab libitum drinking or forced drinking) and of the rate
of ingestion on SW modification by the gut. DR was variable within
as well as among experimental groups. DR appeared to increase with
the animal's capture duration suggesting that water permeability of
the sculpin was gradually increasing after capture. The fluid
volume and resident duration, and water modification in the upper gut
and lower gut were consistent over a broad range of DRs. This demonstrated
that the sculpin were ingesting SW frequently, perhaps in a
manner similar to sipping. In respect to estimates made in sculpin
allowed to drink ab libitum, forced drinking had a negative effect
on desalting.
Finally, a relationship was looked for between gut motility and
the WEB of the sculpin. Several indicators of gut motility, water
absorption, and the WEB were monitored while the gut was perfused at
several different rates. If gut motility is regulated to achieve
essential water absorption, then changes in gut motility would result
in response to alterations in the forced drinking rate, so that
adequate water modification and absorption would be accomplished
and the WEB maintained. Over the levels of perfusion administered,
the WEB was not maintained. With the elevation in perfusion rate,
the intravascular volume increased and yet intestinal water absorption
was maintained or gradually increased. It appears that under the
circumstance of enhanced SW ingestion, the mechanisms regulating gut
motility and water absorption are not integrated with mechanisms
maintaining the WEB of the buffalo sculpin. It remains unclear if,
without SW ingestion, gut motility and the WEB are actively related. / Graduation date: 1982
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/37144 |
| Date | 15 June 1981 |
| Creators | Sleet, Randolph Bullock |
| Contributors | Weber, Lavern J. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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