Gut Fluid Research Articles

Sarcotaces sp., a Parasitic Copepod Infection in two Deep-Sea Fishes, Lepidion Eques and Coelorhynchus Occa

This paper describes the incidence and pathology of a copepod parasite (Sarcotaces sp.) in two species of deep-sea bottom-living fish. The fish Lepidion eques (Moridae) and Coelorynchus occa (Macrouridae) are common on the continental slope to the west of the British Isles at depths from about 400 to 1300 m and 700 and 2000 m respectively.In both species the parasite was located beneath the skin. In L. eques it was found primarily on the head, whereas in C. occa it was present on the mid to lower flank, often close to the anal vent. Excision of the parasite from the host tissue showed it to consist of a pyriform sac filled with inky black fluid. Detailed histological investigations revealed the parasite wall to be a highly complex structure. Within the gut fluid shown to be of haematogenous origin, numerous copepod nauplii were often observed.

Bacteria—food or food competitors of silver carp, Hypophthalmichthys molitrix Val.?

The role of bacteria in the nutrition of silver carp was studied by in‐vitro tests, which confirmed earlier results that the potentially important source of nitrogen in bacteria is not utilized by the fish. Cultures of aerobic and anaerobic bacteria, recovered from a fish pond, were incubated with digestive fluids from the gut contents and from tissues surrounding the alimentary tract (Organ of Leydig) respectively. Growth of aerobic isolates was not affected by the digestive fluids whereas growth of all anaerobes was inhibited. A susceptibility test revealed a bacteriostatic rather than bactericidal effect of the digestive fluid on the bacteria. During 42 h incubation at approximately 20°C of gut fluid, trypsin activity decreased between 14% (in fore‐gut fluid) and 62% (in mid‐gut fluid). The addition of aerobic bacteria (to the mid‐gut fluid) or anaerobic bacteria (to the fore‐gut fluid) did not accelerate the degradation of trypsin.

The effect of acquired microbial enzymes on assimilation efficiency in the common woodlouse, Tracheoniscus rathkei.

The digestive tract of the common woodlouse, Tracheoniscus rathkei Brandt (Isopoda: Oniscoidea), contains digestive enzymes active against α-1,4-glucans, which are the chief storage polysaccharides of vascular plants, algae, fungi, and animals, and β-1,3-glucans, which are present in algae and fungi. Digestive tract extracts also exhibit significant activity toward xylan and carboxymethyl-cellulose but negligible activity toward microcrystalline cellulose, substrates representative of the major structural polysaccharides of vascular plants. Low activity was detected toward pectin, and no activity was detected toward chitin. Activity toward xylan is due in part to microbial enzymes acquired from the leaf litter which was the isopod's normal food. Although ingested microbial xylanases are stable and active in the gut fluid, they do not make a quantitatively significant contribution to the isopod's ability to assimilate the hemicellulosic component of its diet. However, the assimilation of carbon from labeled plant fiber is enhanced in isopods which have acquired a cellulase by ingestion of leaf litter amended with a commercial preparation of the cellulase complex from the fungus, Penicillium funiculosum. This result demonstrates the potential contribution of acquired enzymes to the digestion of plant fiber in terrestrial detritivores. We urge caution, however, in assigning an important digestive function to ingested enzymes on the basis of evidence that only indicates that such enzymes are present in the gut fluid without additional evidence that their presence results in an enhancement of digestive efficiency.

Diurnal potassium excretory cycles in the rat

Diurnal potassium cycles (DPC) were measured in unanesthetized undisturbed rats fed a liquid diet and maintained in a 12-h light-dark environment. A fourfold step increase in diet potassium content increased DPC amplitude without altering phase. After presentation of the high-potassium diet, the initial adaptive increase in excretion occurred within 1.5 h (diet given during dark phase) and within 6 h (diet given during light phase). On a day when food was withheld (no potassium intake), DPC were present but with a lowered amplitude. The amount of potassium excreted on a fasting day exceeded gut and extracellular fluid potassium content and was only modestly increased when rats were previously fed a high-potassium diet. In adrenalectomized rats that received no steroid replacement or received constant infusions of low levels of aldosterone, dexamethasone, or aldosterone plus dexamethasone, potassium balance and DPC were normal. It is concluded that the amplitude of DPC in the rat is determined in part by the availability of potassium from both intracellular and extracellular potassium pools; mechanisms independent of potassium intake can generate the DPC; and the presence or the cyclic secretion of adrenal steroids is not necessary for the generation of DPC in the rat.

Inhibition of Metarhizium anisopliae by the gut bacterial flora of the desert locust, Schistocerca gregaria: Evidence for an antifungal toxin

A study has been made on the effects of the gut of the desert locust, Schistocerca gregaria, on germination and viability of conidia of the entomopathogenic fungus Metarhizium anisopliae. Germination in the gut of conventional insects in vivo and in conventional gut fluid in vitro was poor. In addition gut-passage through conventional insects reduced viability by over 50%. Adverse pH or osmotic pressure, dietary chemicals, oxygen or nutrient deficiency, fungal cell-wall degrading enzymes, and competition for nutrients with the microflora could not account for the inhibitory properties of the locust gut. Fungitoxicity was, however, dependent on the presence of the gut bacterial flora. Since there was no apparent difference in gut or whole animal physiology between axenic and conventional (nonparasitized) locusts, the hypothesis was made that an antifungal toxin, produced by the gut bacterial flora, was responsible for the above observations. The results are discussed in the light of this possibility.

Digestive Enzymes and Feeding Strategies of Three Stream Invertebrates

Gut pH and ability to digest protein and carbohydrates were studied in three steam-dwelling detritivores (Gammarus tigrinus, Hydropsyche betteni and Tipula caloptera). In animals freshly collected from slightly acid streams, gut pH was close to neutrality in Gammarus and Hydropsyche, and moderately alkaline in Tipula. After three weeks in alkaline laboratory water (pH=8.5), gut pH increased significantly in all three invertebrates. Maximum proteinase activity toward Azocoll occurred at a pH higher than that found in freshly collected animals. Only Tipula was able to hydrolyze proteins of unconditioned maple leaves. Ability to digest major plant polysaccharides and to release sugars from unconditioned maple leaves was restricted to Gammarus. All three animals could digest starch and laminarin. Enzymes capable of breaking glycosidic linkages in small molecules, similar to those that might be released during microbial breakdown of leaf polysaccharides, were present in the gut fluids of all three animals. Fungal carbohydrases, ingested with maple leaves, remained active in the guts of Gammarus and Hydropsyche but not in Tipula.

Tandem Recruitment and Trail Laying in the Ponerine Ant Diacamma rugosum: Signal Analysis1

AbstractDuring nest emigration, Diacamma rugosum scouts recruit female nestmates to the new nest site by tandem running. ♂♂, brood and prey objects are carried.The tandem leaders stimulate their nestmates to follow them by pushing or, more rarely, pulling them with the mandibles.The signals releasing the following behaviour are mainly chemical. Only 15–30% of motivated followers react positively to an odourless paper or wax dummy. The ♀♀ follow cut‐off thoraces, legs and gasters plugged at the end or without hind gut and sting apparatus, just as well as a leading ant. The ants even follow a dummy consisting of body parts if they are not in direct mechanical contact with it. The leading effect of the body surface is not reduced by intensive cleaning with water or by extraction in solvents of different polarity. Only maceration in potash lye eliminates the leading effectiveness of the cuticula. None of the secretions of the tested abdominal glands release following behavior. Only the hind gut fluid possesses leading signal qualities. No distribution of faeces over the bodies of the leading ants can be observed before or during tandem running. The faecal pheromone responsible for this leading effect does not seep into the superficial layer of a leader dummy made from bee wax but it can be washed off with water. These results show that the actual signal releasing tandem following is an unspecific odour substance of the cuticula surface. The presence of the hind gut fluid is not necessary for the tandem following response. It may be an additional signal. During nest emigration the hind gut fluid is scattered patchily in the form of small droplets by the nest finders on their way to the new nest. No increased deposition of faecal droplets could be observed on the way to repeatedly visited rich food sources.The hind gut fluid serves as a long lasting trail substance and has an exclusively orienting effect. The secretions of the other abdominal glands are not trail pheromones. The nest entrance is marked colony‐specifically.

Effects of surfactants, pH, and certain cations on precipitation of proteins by tannins

Tannic acid and pin oak tannins precipitate large amounts of the abundant leaf protein, ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPC), over a wide pH range (6.15-9.30) in the presence of sodium, potassium, magnesium, and calcium ions at concentrations comparable to those reported in the gut fluids of lepidopteran herbivores. The presence of lysolecithin, a surfactant known to be present in the gut fluids of some insects, significantly reduces the amount of RuBPC precipitated under these conditions. We conclude that high detergency is far more effective than high alkalinity in countering the potential protein-precipitating properties of tannins. We further conclude that tannins do not deserve the status they were once accorded as general, all-purpose, dose-dependent, antidigestive defensive chemicals. We also describe the application of the Schaffner-Weissman protein assay for studying the protein-precipitating capacity of plant extracts. This method is far superior to the one we have used in our earlier studies.

Conditions de digestion et activité de quelques polysaccharidases dans le tube digestif de l'oursin Paracentrotus lividus (Echinodermata)

The pH level of the gut fluid of the echinoid P. lividus is slightly acidic and its oxygen content is low (from 5 to 8%). An amylase and a cellulase-like enzyme are secreted by the echinoid stomach. Amylolytic activities have been detected also in food pellets from the stomach and from the posterior part of the intestine. This activity of intestinal pellets could be of microbial origin.

X-ray microanalysis of elements in frozen-hydrated sections of an electrogenic K+ transport system: the posterior midgut of tobacco hornworm (Manduca sexta) in vivo and in vitro.

The lepidopteran midgut is a model for the oxygen-dependent, electrogenic K+ transport found in both alimentary and sensory tissues of many economically important insects. Structural and biochemical evidence places the K+ pump on the portasome-studded apical plasma membrane which borders the extracellular goblet cavity. However, electrochemical evidence implies that the goblet cell K+ concentration is less than 50 mM. We used electron probe X-ray microanalysis of frozen-hydrated cryosections to measure the concentration of Na, Mg, P, S, Cl, K, Ca and H2O in several subcellular sites in the larval midgut of Manduca sexta under several experimental regimes. Na is undetectable at any site. K is at least 100 mM in the cytoplasm of all cells. Typical in vivo values (mM) for K were: blood, 25; goblet and columnar cytoplasm, 120; goblet cavity, 190; and gut lumen, 180. The high K concentration in the apically located goblet cavity declined by 100 mM under anoxia. Both cavity and gut fluid are Cl deficient, but fixed negative charges may be present in the cavity. We conclude that the K+ pump is sited on the goblet cell apical membrane and that K+ follows a nonmixing pathway via only part of the goblet cell cytoplasm. The cavity appears to be electrically isolated in alimentary tissues, as it is in sensory sensilla, thereby allowing a PD exceeding 180 mV (lumen positive) to develop across the apical plasma membrane. This PD appears to couple K+ pump energy to nutrient absorption and pH regulation.

Phytoplanktivorous or omnivorous fish? Digestibility of zooplankton by silvercarp, Hypophthalmichthys molitrix (Val.)

Small zooplankton, rotatoria and nauplii decomposed rapidly during in-vitro incubation in the gut fluid of silvercarp. Algae remained unchanged. Gut content analysis, therefore, erroneously suggests a phytoplanktivorous strategy, whereas omnivorous feeding may actually be required for maintaining a positive energy balance in these stomachless fish.

Surfactants: their role in preventing the precipitation of proteins by tannins in insect guts.

Much more tannic acid or pin oak tannin is required to precipitate the abundant leaf protein, ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPC), from Manduca sexta gut fluid adjusted to pH 6.5 than is required to precipitate this protein from an aqueous buffer at the same pH. This finding demonstrates that some characteristic of M. sexta gut fluid, in addition to its basicity, counteracts the potential of tannins to precipitate ingested proteins. Gut fluid of M. sexta has a surface tension of 36-39 dynes/cm, indicating the presence of surfactants. Lysolecithin and linoleoylglycine, surfactants known to be present in insect gut fluids, also interfere with the precipitation of RuBPC by tannins at pH 6.5. It is concluded that detergency is a widespread property of insect gut fluids that counteracts the potential of tannins to precipitate die ary proteins, and it is argued that there is no longer any justification for continuing to refer to tannins as digestibility-reducing-substances. Finding that there has been no formidable barrier to the evolution of mechanisms that counter a generalized antidigestive action by tannins is difficult to reconcile with the idea that reduced digestibility is an evolved anti-herbivore adaptation of apparent plants.

Campylobacter jejuni diarrhea model in infant chickens.

To study the pathogenic mechanisms of Campylobacter jejuni infection, 36- to 72-h-old chickens were fed 10(3) to 10(6) live cells, using strains isolated from 40 patients with watery diarrhea and 6 with bloody mucoid diarrhea from whom no other known enteropathogen was detected. Chickens of Starbro strain were more likely to develop C. jejuni-induced diarrhea than were White Leghorn chickens. Diarrhea was defined on the basis of amounts of gut fluid in 288 chicks fed with live C. jejuni versus 183 saline-fed control as an accumulation greater than or equal to 0.4 ml of fluid in the guts (excluding ceca) of chickens. Twenty-five percent of the chickens developed diarrhea on day 2, 49% on day 4, and 81% on day 5. The intestines, including ceca, were distended with watery fluid. The majority of the strains, irrespective of whether they were isolated from watery or bloody mucoid enteritis patients, caused watery diarrhea in chickens, and a few caused mucoid diarrhea. No correlation was observed between the source of a strain and the outcome in the experimental model. Bloody diarrhea was never observed in chickens. The peak incidence of diarrhea on day 5 coincided with the mean of maximum fluid accumulation. The organisms multiplied by 3 to 4 logs in all parts of the intestine, with a steady increase in number until day 5. Systemic invasion occurred frequently: C. jejuni could be recovered from the spleen in 47% of the chickens on day 5, in 25% from the liver on day 6, and in 11% from heart blood on day 4. Histopathological examination of gut tissue of the chickens having watery diarrhea did not reveal any abnormality except slight submucosal edema. However, in chickens with mucoid diarrhea, the organisms were found to adhere to brush borders and penetrate into the epithelial cells with formation of a breach in continuity of the brush border lining. The electrolyte composition of the intestinal fluid from chickens infected with C. jejuni and from saline-fed controls did not show significant differences, except for depletion of K+ in the test group. The results obtained in this highly reproducible chicken diarrhea model indicate that (i) most chickens develop nonexudative watery diarrhea 2 to 5 days after oral feeding of 10(3) to 10(6) live cells of C. jejuni; (ii) the organism multiples in all parts of a chicken intestine, (iii) systemic invasion is common, and (iv) local invasion is sometimes observed.

Alkaline proteases from the gut fluids of detritus-feeding larvae of the crane fly, Tipula abdominalis (say) (diptera, tipulidae)

The high level of proteolytic activity present in the midgut fluids of the detritus-feeding larvae of the crane fly, Tipula abdominalis, is due to a mixture of enzymes, consisting largely of serine proteases with trypsin- or chymotrypsin-like substrate specificities. These enzymes have high alkaline pH optima ( pH > 11 ) and high stability at pH values of 8.5–11.5 at 15°C, properties that enable them to function effectively in the highly alkaline gut fluids (pH 9.5–11.5) of an insect that feeds and grows in cold water (0–25°C). The enzymes also have very low isoelectric points (pH < 6), resulting in their having a high negative charge in vivo. Possibly their anionic character prevents their inactivation through adsorption on ingested lignin, humic acid or clay. These serine enzymes arise from the midgut epithelial cells, and not from microbes residing in the gut or from ingested detrital food. The digestive system of T. abdominalis larvae is adapted for the efficient utilization of the limited quantities of dietary protein present in detrital food.

Spiroplasmas from coleopterous insects: New ecological dimensions

The genusSpiroplasma (helical wall-less prokaryotes) is a recently described group of microorganisms that cause disease in plants, arthropods, and experimentally, in vertebrates. Two spiroplasmas from beetles have now been discovered in a search for microorganisms suitable for biological control of economically important coleopterous insects. Colorado potato beetles (CPB) infected with spiroplasma were commonly found on potato and other solanaceous plants in Maryland. Although this spiroplasma occurred in high concentration in gut fluids and sputum, it could not be cultivated in conventional spiroplasma media. However, another spiroplasma (CN-5 and related strains) reported here to occur commonly in association with larvae and adults of the green June beetle,Cotinus nitida, could be cultivated readily in the SM-1 formulation and several other conventional spiroplasma media. The CN-5 spiroplasma was serologically distinct from representative members of all 8 major groups now recognized. Thus, it represents a ninth major spiroplasma serogroup (IX), and can be considered to be an unnamed species. The CPB spiroplasma is apparently maintained in plant surface-insect gut cycles, but details of maintenance of the CN-5 spiroplasma are incompletely understood. Isolation of CN-5 spiroplasma from soil in which host larvae had fed suggests that transmission of this agent may occur in the soil. Both CN-5 and CPB spiroplasmas exhibited unusually active translational motility in natural fluids, and CN-5 organisms exhibited such motility in culture media. Although we have no evidence that either spiroplasma is pathogenic to its usual host, the pathogenicity of spiroplasmas to many hosts, including the beetle,Melolontha melolontha, suggests possible application for biological control.

Uptake and intracellular disposition of IgA by rat hepatocytes in monoalyer culture.

It is well documented that the liver provides an important source of secretory immunoglobulin A (sIgA) in the gut fluid. In the rat, liver parenchymal cells can actively sequester the dimeric form of IgA (dIgA) from plasma and transfer it attached to its receptor, secretory component (SC), via vesicles into the bile. In the present investigation, isolated rat hepatocytes in monolayer culture were studied using quantitative electron microscopic autoradiography to determine if the previous reported specific binding of dIgA by isolated cells would result in internalization of the ligand and, if so, whether its distribution within the cultured hepatocytes would be similar to that found in vivo. The specificity of the process for receptor (SC) availability was evaluated utilizing sIgA and by blocking the receptor with rabbit IgG anti–rat SC antibody. For these studies, purified dIgA and sIgA were iodinated with [125I] and added to fresh culture medium 24 hr following the isolation of the hepatocytes. After 3, 30, and 60 min of incubation with the isotope, the cells were washed, fixed, and processed for light and electron microscopic autoradiography. Binding of dlgA to the cells occurred by 3 min, and the number of autoradiographic grains per unit membrane length remained constant throughout the 60–min time period. With time, there was a progressive increase in the per cent of internalized grains. As in the previous in vivo studies, the majority of these internalized grains were localized to vesicles and smooth surface endoplasmic reticulum. There was no evidence of binding or uptake of sIgA at any time period and pretreatment with anti–SC reduced binding and internalization of dIgA to 16% of the control value. These data provide new evidence that isolated hepatocytes in monolayer culture appear functionally intact with regard to dIgA uptake and demonstrate their usefulness as an in vitro system for future studies of IgA metabolism.

Freezing-tolerant insects with low supercooling points

1. 1. Pytho deplanatus [Coleoptera: Pythidae (Salpingidae)] is an alpine species that overwinters as a larva under the bark of fallen spruce in the Rocky Mountains. It belongs to a small group of insects which not only is tolerant of freezing but also develops the capacity to supercool to low sub-zero temperatures (−54°C), indeed in this case the lowest ever recorded for this category. 2. 2. The freezing tolerance profile of P. deplunatus is similar to that of many other insects in that glycerol is accumulated to moderately high levels during low temperature acclimation, while water content and glycogen concentrations are considerably reduced. Blood sugar levels, mainly trehalose. also accumulate during this period. 3. 3. The most feasible explanation for the co-existence of freezing tolerance and low supercooling points is that P. deplanatus is physiologically incapable of synthesizing haemolymph nucleating agents and that nucleators in the gut and other fluid compartments are absent in the overwintering larvae. The adaptive advantage of this strategy is that larvae would normally overwinter in a supercooled state, but if freezing did occur (e.g. by inoculation from contact water in the hibernaculum) then the antifreeze function of glycerol and blood sugars would assume a cryoprotective role. 4. 4. The freezing tolerance mechanisms of P. deplanatus larvae are compared and contrasted with those of (a) the congeneric P. americanus which also overwinters under the bark of fallen trees but has both an alpine and arctic distribution, and (b) Xylophagus sp. (Diptera: Xylophagidae) which has a different phylogenetic background but occupies a similar niche in the Arctic.

Protein digestion and proteolytic activity in the digestive tract of an omnivorous cyprinid

1. 1. In adult and juvenile roach ( Rutilus rutilus) feeding on meal worms or grass and acclimated to temperatures between 6 and 20 C the following variables were determined: pH, protein and protelytic activity of gut fluid and faeces, food consumption, duration of gut passage and efficiency of protein assimilation. 2. 2. Proteolytic enzymes of fish are very stable against autolysis but they disappear in posterior portions of the intestine, suggesting the existence of a pinocytotic process. 3. 3. In herbivorous roach as well as in adult carnivorous roach feeding at 20 C this results in very low proteolytic activities in the faeces, whereas in juvenile fish and in adults feeding on meal worms at lower temperatures, the process of reabsorption seems to be less efficient. 4. 4. Daily production of proteases as well as “daily proteolytic duration” are higher in herbivorous than in carnivorous roach. 5. 5. For the same amount of protein consumed, fish feeding on grass require 10 times higher proteolytic activities than fish feeding on meal worms.

The osmoregulatory role of the filter‐chamber in relation to phloem‐feeding in Eurymela distincta (Cicadelloidea, Homoptera)

ABSTRACT. The cicadelloid leaf‐hoppers, Eurymela distincta (Signoret) and Eurymela fenestrata (Le Pelletier &amp; Serville), feed on the phloem sap of Eucalyptus spp. The osmotic pressure profile of haemolymph and gut fluids is consistent with a filtration mechanism based on passive osmosis. This is responsible for shunting water rapidly from foregut to hindgut in the relatively simple filter chamber. The osmotic gradient which drives the system is probably produced by active secretion of sodium and potassium into the Malpighian tubules and posterior midgut. Although the osmotic pressures in all parts of the system are higher, the mechanism is probably similar to that previously described for xylem‐feeding cicadas.The major haemolymph cations are sodium and magnesium and the concentrations of sodium and magnesium in the urine are higher than potassium. A variety of storage granules in the midgut contain calcium, phosphorus (as phosphate), ferric iron, zinc, magnesium, manganese and copper.

The effect on salt appetite and the renin—aldosterone system on replacing the depleted ions to sodium‐deficient cattle

1. Sodium depletion which occurred in cattle following exteriorization of a parotid duct produced depression of both plasma and salivary sodium, acidosis, elevated plasma aldosterone and renin activity. Increased sodium appetite, characteristic of sodium depletion, was assessed by operant behaviour where scoring of panel pressing for NaHCO(3) rewards showed change in sodium appetite.2. Sodium-depleted calves readily drank the calculated ionic deficit as a hypertonic solution (4 l.) in a few minutes, or as an isotonic solution (16 l.) usually within 30 min.3. When the ionic deficit was restored by either i.v. infusion or drinking, sodium appetite was reduced significantly. The suppression of sodium appetite was more rapid when the depleted ions were replaced by drinking (30 min) than by i.v. infusion (2 hr) but in both circumstances the effect was short lived since sodium appetite redeveloped within 3 hr.4. The rapid return of sodium appetite following restoration of the ionic deficit occurred even when the plasma sodium level was normal. Other biochemical changes resulting from sodium depletion, such as acidosis and reduced salivary sodium, could not be correlated with variation in sodium appetite.5. Rapid infusion of Ringer saline (4 l.) did not inhibit the sodium appetite, which suggests that neither vascular volume changes per se nor vascular baroreceptors control sodium appetite in sodium-deficient calves.Plasma aldosterone fell rapidly following infusion of the hypertonic solution but only slightly with the isotonic infusion. The change in plasma hormone level was not related to changes in sodium appetite.6. Drinking the hypertonic solution produced a marked reduction in panel pressing for NaHCO(3) with a rapid rise in plasma sodium. Consumption of the larger volume of isotonic solution also inhibited sodium intake but plasma sodium remained low. A secondary increase in plasma renin activity (p.r.a.) occurred following ingestion of the hypertonic solution, but both p.r.a. and aldosterone fell to normal levels over the next 6 hr when the cattle again showed marked sodium appetite. It is possible that these effects may be due to ion and fluid movement between gut and extracellular fluid and reflect osmolality changes or tissue dehydration.7. It is concluded that the sodium appetite of sodium deficient cattle is only temporarily alleviated by restoration of the depleted ionic loss, and that the behavioural response to seek sodium rewards is independent of plasma sodium, p.r.a., aldosterone and volume changes in the gut and vascular system.8. Recent reports suggest that sodium appetite may be controlled by receptors in the hypothalamus or by angiotensin II in the brain. In cattle the capacious gut may also be involved, since sodium appetite is inhibited more rapidly when the depleted ions are taken orally than by i.v. infusion.