Digestive Physiology and Nutrition of Marsupials

Hume, I. D.

doi:10.2307/20094706

Cited by 66 publications

(93 citation statements)

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“…The intestines of herbivores are much larger than the intestines of carnivores (Hume 1982). The pools for lipid-soluble compounds are larger in the herbivore than in the carnivore intestinal tract.…”

Section: Evolution Of the Tissue Pattern Of Ttr Gene Expressionmentioning

confidence: 99%

The evolutionary and integrative roles of transthyretin in thyroid hormone homeostasis

Schreiber

2002

Journal of Endocrinology

132

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In larger mammals, thyroid hormone-binding plasma proteins are albumin, transthyretin (TTR) and thyroxine (T4)-binding globulin. They differ characteristically in affinities and release rates for T4 and triiodothyronine (T3). Together, they form a 'buffering' system counteracting thyroid hormone permeation from aqueous to lipid phases. Evolution led to important differences in the expression pattern of these three proteins in tissues. In adult liver, TTR is only made in eutherians and herbivorous marsupials. During development, it is also made in tadpole and fish liver. More intense TTR synthesis than in liver is found in the choroid plexus of reptilians, birds and mammals, but none in the choroid plexus of amphibians and fish, i.e. species without a neocortex. All brainmade TTR is secreted into the cerebrospinal fluid, where it becomes the major thyroid hormone-binding protein.During ontogeny, the maximum TTR synthesis in the choroid plexus precedes that of the growth rate of the brain and occurs during the period of maximum neuroblast replication. TTR is only one component in a network of factors determining thyroid hormone distribution. This explains why, under laboratory conditions, TTR-knockout mice show no major abnormalities. The ratio of TTR affinity for T4 over affinity for T3 is higher in eutherians than in reptiles and birds. This favors T4 transport from blood to brain providing more substrate for conversion of the biologically less active T4 into the biologically more active T3 by the tissue-specific brain deiodinases. The change in affinity of TTR during evolution involves a shortening and an increase in the hydrophilicity of the N-terminal regions of the TTR subunits. The molecular mechanism for this change is a stepwise shift of the splice site at the intron 1/exon 2 border of the TTR gene. The shift probably results from a sequence of single base mutations. Thus, TTR evolution provides an example for a molecular mechanism of positive Darwinian evolution. The amino acid sequences of fish and amphibian TTRs are very similar to those in mammals, suggesting that substantial TTR evolution occurred before the vertebrate stage. Open reading frames for TTR-like sequences already exist in Caenorhabditis elegans, yeast and Escherichia coli genomes.

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Section: Evolution Of the Tissue Pattern Of Ttr Gene Expressionmentioning

confidence: 99%

The evolutionary and integrative roles of transthyretin in thyroid hormone homeostasis

Schreiber

2002

Journal of Endocrinology

132

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“…In ruminants, inoculation of feed particles may be largely through rumination (Leng 2011). Although contraction and some regurgitation (termed merycism) occurs in the forestomach of macropods, this is a sporadic event (Hume 1982) and inoculation of feed with microbes may be facilitated by the blind sac -a pouch formed at the junction of the oesophagus and the forestomach. This pouch may provide a reservoir of microbes similar to that in the vermiform appendix of the large bowl of humans.…”

Section: Reductive Acetogenesismentioning

confidence: 99%

Interactions between microbial consortia in biofilms: a paradigm shift in rumen microbial ecology and enteric methane mitigation

Leng¹

2014

Anim. Prod. Sci.

133

105

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Abstract. Minimising enteric CH 4 emissions from ruminants is a current research priority because CH 4 contributes to global warming. The most effective mitigation strategy is to adjust the animal's diet to complement locally available feed resources so that optimal production is gained from a minimum of animals. This essay concentrates on a second strategy -the use of feed additives that are toxic to methanogens or that redirect H 2 (and electrons) to inhibit enteric CH 4 emissions from individual animals. Much of the published research in this area is contradictory and may be explained when the microbial ecology of the rumen is considered.Rumen microbes mostly exist in organised consortia within biofilms composed of self-secreted extracellular polymeric substances attached to or within feed particles. In these biofilms, individual colonies are positioned to optimise their use of preferred intermediates from an overall process of organic matter fermentation that generates end-products the animal can utilise. Synthesis of CH 4 within biofilms prevents a rise in the partial pressure of H 2 (pH 2 ) to levels that inhibit bacterial dehydrogenases, and so reduce fermentation rate, feed intake and digestibility. In this context, hypotheses are advanced to explain changes in hydrogen disposal from the biofilms in the rumen resulting from use of anti-methanogenic feed additives as follows.Nitrate acts as an alternative electron sink when it is reduced via NO 2 -to NH 3 and CH 4 synthesis is reduced. However, efficiency of CH 4 mitigation is always lower than that predicted and decreases as NO 3 -ingestion increases. Suggested reasons include (1) variable levels of absorption of NO 3 -or NO 2 -from the rumen and (2) increases in H 2 production. One suggestion is that NO 3 -reduction may lower pH 2 at the surface of biofilms, thereby creating an ecological niche for growth of syntrophic bacteria that oxidise propionate and/or butyrate to acetate with release of H 2 .Chlorinated hydrocarbons also inhibit CH 4 synthesis and increase H 2 and formate production by some rumen methanogens. Formate diffuses from the biofilm and is converted to HCO 3 -and H 2 in rumen fluid and is then excreted via the breath. Short-chain nitro-compounds inhibit both CH 4 and formate synthesis when added to ruminal fluid but have little or no effect in redirecting H 2 to other sinks, so the pH 2 within biofilms may increase to levels that support reductive acetogenesis. Biochar or activated charcoal may also alter biofilm activity and reduce net CH 4 synthesis; direct electron transfer between microbes within biofilms may also be involved. A final suggestion is that, during their sessile life stage, protozoa interact with biofilm communities and help maintain pH 2 in the biofilm, supporting methanogenesis.

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“…Accordingly, the secretion of HCO 3 -by the possum ileum may be unique to the ileum and be associated with a specific function of the ileum, possibly related to the fermentation of food material in R. Bartolo and others pNBC MEDEAVLDRGASFLKHVCDEEEVEGHHTIYIGVHVPKSYRRRRRHKRKAGHREKKEKERN 60 Human MEDEAVLDRGASFLKHVCDEEEVEGHHTIYIGVHVPKSYRRRRRHKRKTGHKEKKEKERI 60 ************************************************:**:****** the caecum and proximal colon. The possum is a hindgut fermenter (Hume, 1982), and microbial fermentation in the hindgut requires a suitable environment for microbial growth and absorption of short chain fatty acids that result from the fermentation process. This includes a fluid medium and sufficient buffering capacity to maintain pH within a favourable range (Rechkemmer et al, 1988).…”

Section: Electrogenic CLmentioning

confidence: 99%

Secretagogues stimulate electrogenic HCO3–secretion in the ileum of the brushtail possum,Trichosurus vulpecula:evidence for the role of a Na+/HCO3– cotransporter

Bartolo

Harfoot

Gill

et al. 2009

Journal of Experimental Biology

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SUMMARY Fluid secretion is essential for intestinal function and, in eutherian mammals, is driven by electrogenic Cl-transport, which is dependent upon a bumetanide-sensitive, basolateral Na-cotransporter, NKCC1. However, ileal secretion in the brushtail possum, a marsupial, involves a fundamentally different process, since NKCC1 expression is low in this tissue and the secretagogue-induced short circuit current (I sc ) is insensitive to bumetanide. In view of these differences we have investigated the basis of the secretory response of the possum ileum. In the Ussing chamber the secretory I sc is independent of Cl -but dependent upon Na

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Digestive Physiology and Nutrition of Marsupials

Cited by 66 publications

References 0 publications

The evolutionary and integrative roles of transthyretin in thyroid hormone homeostasis

The evolutionary and integrative roles of transthyretin in thyroid hormone homeostasis

Interactions between microbial consortia in biofilms: a paradigm shift in rumen microbial ecology and enteric methane mitigation

Secretagogues stimulate electrogenic HCO3–secretion in the ileum of the brushtail possum,Trichosurus vulpecula:evidence for the role of a Na+/HCO3– cotransporter

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