The absorption and distribution of metals via the gut of fish is not well known.
Consequently, the aim of the present study was to describe the movement of metals along
the gut, their absorption and binding to gut tissues, and their distribution to the internal
tissues following model dietary exposure. Two different approaches were employed, an
in vivo gastric dosing procedure, and an in vitro gut bag protocol and two different metals
were studied: an essential metal, zinc, and a non-essential (and more toxic) metal,
cadmium.
The dietary uptake and distribution of zinc and cadmium to 0.3 kg rainbow trout
(Oncorhynchus mykiss) was examined at l5°C at 1, 2, 3, or 7 days following a single
bolus dose to the stomach of 0.5 mM of radio labelled metaL After exposure, all internal
organs and the remaining carcass were individually counted for radioactivity. Uptake,
distribution and excretion of both zinc and cadmium was rapid, occurring largely within
the first 24 h of exposure. By 24 h, fish exposed to Zn had absorbed 20.0% of the dose,
21.0% was bound in the gastrointestinal tissues and the remainder was either excreted
(38.1 %) or was present in the gut lumen (20.9%). Cadmium showed a much different
pattern of uptake, with only 2.9% of the dose absorbed after 24 h, and the remainder
found either in the gut tissue (30.2%) and the lumen (19.0%) or excreted (47.9%). Over
the following six days, very little uptake and internal metal redistribution occurred.When exposed to higher doses of metal in vivo (0.5 - 50 mM), there were distinct
differences in the handling of the two metals. Zinc concentrations in the gut tissues
continued to rise at higher doses until apparent saturation. In contrast, gut tissues were
saturated with cadmium at the lowest dose employed (0.5 mM). Both metals bound most
avidly to the distal intestine but all gut tissues had a higher binding capacity for zinc, as
compared to cadmium. Target tissues (liver, gills, kidney) all saturated with zinc at high
doses. In contrast, cadmium concentrations in these tissues continued to rise in a linear
fashion with increasing dose.
In vitro studies revealed that the most important region of the gut for metal uptake
in rainbow trout was the mid-intestine. Studies using the metabolic uncoupler, 2,4-DNP,
suggested that the transfer of both zinc and cadmium across intestinal cells was passive at
the brush border membrane, but was at least partly dependent on A TP for movement
across the basolateral membrane. Furthermore, this transport mechanism was not shared
by calcium, as the presence of calcium had no inhibitory effect on the transport of either
metal.
Mucus within the intestinal lumen appears to have a higher binding affinity but
lower capacity for cadmium than zinc. Calcium did not displace cadmium from the
mucus layer. In contrast, zinc was displaced by an equimolar exposure to calcium in the
medium. Gut mucus apparently impedes the movement of metals along the intestine
with the extent of the delay likely being related to the binding affinity of the metal. The
impediment was greatest for cadmium, as 10% of the metal remained in the lumen of fish exposed in vivo, after a period of7 days. In contrast, only 2% ofthe original dose of zinc
remained in the gut lumen after only 3 days. / Thesis / Master of Science (MSc)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/22710 |
| Date | 09 1900 |
| Creators | Baskin, Shawn |
| Contributors | McDonald, D. Gordon, Biology |
| Source Sets | McMaster University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis |
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