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H Hörnicke

Publications and source records attributed to H Hörnicke.

At least 19 recordsLinked to original sources
PubMed1989

Problems in estimating the extent of coprophagy in the rat.

The quantity of re-ingested faeces was calculated by comparing faecal dry matter of unrestricted rats and coprophagy-restricted rats after correcting for differences in food intake. Due to high day-to-day variations of produced and re-ingested faeces it was not possible to calculate precisely the extent of coprophagy of an individual rat at a particular day with this difference method. Reliable quantitative estimates require at least two rats and a collection period of 7 d. When fed on a nutritionally complete diet, rats re-ingested 0-11% of their faeces. When fed on low-protein diets (66 g egg albumin/kg) or diets diluted with 200 g cellulose/kg, coprophagy was not significantly increased. A high re-ingestion rate (6-25%) was observed with thiamin and pantothenic acid deficiencies. After re-ingestion of faeces had been prevented for 1 week, the amount of faeces re-ingested during the subsequent week without tail-cups was increased twofold. It is concluded that rats are able to regulate the amount of faeces eaten precisely according to their requirements.

Animals↗
PubMed1989

Ion transport and electrophysiology in rabbit cecum.

We investigated the basic bioelectrical properties and the transport of Na+, Rb+, and Cl- in the isolated cecal epithelium of the rabbit. Intracellular microelectrode recordings provided first estimates of the individual membrane potentials and resistances. The cecal epithelium was found to be a moderately tight epithelium with a high transepithelial potential and a relative high paracellular resistance. It has, however, a low transepithelial resistance caused by a high rate of transcellular ion transport and a high transcellular conductance. Under short-circuit conditions Na+ and Cl- are absorbed, whereas Rb+ is secreted. Na+ absorption seems to be mediated via an electrogenic mechanism with low amiloride sensitivity and is partially linked to Cl- transport. Cl- absorption is not influenced by secretagogues, and Rb+ secretion occurs via a transcellular route. A basolateral K+ conductance was also found. The results show rabbit cecum as an epithelium with a high electrolyte transport capacity, distinctly different from the neighboring proximal colon, and suited to absorb the large quantities of electrolytes that are present in the luminal liquid.

Animals↗
PubMed1988

Circadian rhythm of apical Na-channels and Na-transport in rabbit distal colon.

In vivo and in vitro studies showed that electrogenic sodium transport in rabbit distal colon is modulated by aldosterone. It varies in a circadian rhythm; the external synchronizer is the light-dark cycle. The site of regulation was found to be in the apical membrane of colonic epithelial cells, in which the number of conducting sodium-channels is increased by aldosterone.

Aldosterone↗
PubMed1988

Regional differences in hindgut structure and function in the nutria, Myocastor coypus.

Morphologically the large intestine of the nutria resembles that of other caviomorphs, notably the guinea pig. The cecum is voluminous: it contributes 8.6% of the total intestinal length and 12.7% of the total intestinal surface area (considering the surface enlargement factor). It contains 27-32% of the wet ingesta and 20-23% of the dry matter in the gastrointestinal tract. In the colon the corresponding figures are: 21.8% of length, 12.6% of surface area, 16-21% of wet ingesta, and 16-40% of dry matter. The colon can be subdivided both structurally and functionally into two sections, the proximal and the distal colon, the border between the two being the apical flexure of a long parallel loop. The proximal colon (42% of colonic length) displays on the mucosal surface of its mesenterial side a narrow furrow bordered by ridges, which is absent in the distal colon. The ridges contain subepithelial accumulations of coiled tubuloalveolar mucoid glands, entwined by bundles of muscle fibers. Determinations of nitrogen in the contents near the furrow suggest a concentration of bacteria in this part of the lumen. It is hypothesized that the structural differentiations of the proximal colon provide mechanisms for the transport of bacteria from the proximal colon back into the cecum to maintain the fermentation function. The slopes of the longitudinal profiles for dry matter and for concentrations of sodium, potassium and calcium in the luminal contents change at the tip of the parallel loop. The electrical potential difference "intestinal lumen - blood" is particularly large in the proximal colon, indicating active electrogenic ion transport in this region.

Animal Nutritional Physiological Phenomena↗
PubMed1987

Circadian rhythms of rabbits during restrictive feeding.

Without a zeitgeber the circadian rhythms of five physiological functions free-ran with a period length greater than 24 h. Restricted feeding time (RF) masked the free-running rhythms. In addition to masking, entrainment with RF occurred. This process was most evident in locomotor activity and visits to the food box. RF thus had zeitgeber properties in these rabbits. However, in most rabbits the RF zeitgeber was not strong enough to entrain the circadian rhythm completely. A small component free-ran during RF. Following return to continuous food access the whole circadian rhythm resumed to free-run again. In some animals its phase was determined by the RF zeitgeber and in others by the small free-running fraction present during RF. The results suggest that in addition to the light-dark-entrainable circadian oscillator system a feeding-entrainable oscillator exists that takes over phase control of the majority of the rhythm during RF.

Animals↗
PubMed1985

Segmental differences in electrical properties and Na-transport of rabbit caecum, proximal and distal colon in vitro.

Electrical potential difference, short circuit current, tissue conductance, and unidirectional Na-fluxes were measured in four segments of the rabbit large intestine in vitro. Compared to the relatively tight, low conductance distal colon, caecum and proximal parts of the colon are leaky epithelia with high conductances. Net Na-absorption was highest in caecum, and then decreased gradually towards the distal colon, whereas potential and short circuit current where high in the caecum and proximal colon, low in the middle part of the colon, and high again in the distal colon. Unidirectional Na-fluxes of all four segments were different. The discrepancy between the short circuit current and net Na-absorption in the two segments of the proximal colon indicates electrogenic transport of other ions. 0.1 mM ouabain virtually abolished short circuit current and Na-absorption in all segments, whereas 0.1 mM amiloride was not effective in the caecum and the proximal colonic parts. The present study focuses on the comparative aspects of Na-transport. It demonstrates the marked segmental heterogeneity of the basic electrical properties and suggests four different segmental organizations of large intestinal electrolyte transport.

Amiloride↗
PubMed1985

Effects of aldosterone and dexamethasone on apical membrane properties and Na-transport of rabbit distal colon in vitro.

The effects of pre-treatment in vivo with aldosterone and dexamethasone were investigated on rabbit distal colon. Apical Na-permeability and net sodium transport were measured in vitro. In this epithelium, Na-transport is entirely electrogenic. It can therefore be measured electrically as the fraction of short circuit current which is blockable by amiloride. The epithelia were studied in an Ussing chamber and the electrical values recorded by a computerized digital voltage clamp. Transepithelial parameters, and the transapical membrane parameters (in preparations depolarized from the serosal side) were investigated after treatment with the two hormones. Under transepithelial conditions, aldosterone and dexamethasone stimulated the short circuit current (Isc) from control (17.4 microA/cm2) to a similar degree (86.6 and 93.8 microA/cm2). However, whereas aldosterone did not alter the transepithelial resistance (RT) significantly, dexamethasone reduced RT from 357 to 167 omega X cm2. The stimulation of the potential difference (VT) under control condition (6.6 mV) was therefore significantly different between aldosterone (28.7 mV) and dexamethasone (16 mV). Mucosal amiloride (0.1 mM) inhibited Isc and VT completely under all conditions. Steady state current-voltage relations were obtained by voltage clamping the tissues in "staircase" increments before and after mucosal treatment with amiloride. As measured by the difference between these two states, Na-currents were calculated both for the transepithelial and the transapical condition. Intracellular Na-activity and apical Na-permeability were then calculated by the Nernst and Goldman-Hodgkin-Katz equations. These values were found to be increased after treatment with both hormones. Dexamethasone was a more potent stimulator of both values.(ABSTRACT TRUNCATED AT 250 WORDS)

Aldosterone↗
PubMed1985

Electrolyte transport across rabbit late proximal colon in vitro.

The second part of rabbit proximal colon was investigated in vitro under short circuit conditions. Unidirectional sodium and chloride fluxes were measured during the soft faeces period and during the hard faeces period. Rabbit late proximal colon has a potential difference (psi mS) of 4 mV, a tissue conductance (GT) of 10-11 mS/cm2 and a short circuit current (Isc) of 1.5 mueq/cm2 X hr. Under control conditions sodium (2.65 mueq/cm2 X hr) and chloride (0.67 mueq/cm2 X hr) are absorbed. Ouabain abolished psi ms,Isc and the net sodium flux totally, whereas 0.1 mM amiloride only slightly decreased the net sodium flux. No differences in electrical properties and Na,Cl-fluxes were found between the faeces periods. Removal of sodium abolished psi ms and Isc totally, and a high potassium solution depolarized the preparation (psi ms = 0). A linear current-voltage relation characterizes the tissue as an ohmic resistor between -40 and +50 mV, and reveals a slope conductance of 14 mS/cm2 under KCl conditions. We conclude that the transport functions under in vitro conditions differ markedly from the in vivo situation, and that the diurnal differences of electrolyte transport in vivo occur mainly by the involvement of ionic gradients.

Amiloride↗
PubMed1984

Segmental differences in K-transport across rabbit proximal and distal colon in vivo and in vitro.

Net K-transport was investigated in three different segments of rabbit proximal and distal colon. In vivo studies used a dialysis method, and in vitro studies an everted sac preparation. Results from both methods are in good agreement and show net K-absorption in the two segments of the proximal colon, and net K-secretion in the distal colon. K-absorption in the proximal colon seems to be an active mechanism, because K is transported against an electrical potential gradient. The present study is a comparative approach to demonstrate the heterogeneity of an organ function, and represents the first direct comparison of K-transport in various segments of rabbit colon under in vitro and in vivo conditions.

Animals↗
PubMed1984

Cationophore properties of the new polyether antibiotic Salinomycin investigated in distal rabbit colon in vivo and in vitro.

The distal rabbit colon was used as a model to investigate the influence of the cationophore Salinomycin in vivo with a single-pass perfusion, and in vitro with a modified Ussing chamber technique. For in vivo experiments with labelled 14C-PEG as a volume marker in the perfusate, a dose of 10E-4 mol/l Salinomycin was used. Net water (53 microliters/h/cm), net chloride (3 mumol/h/cm) and net sodium (3.6 mumol/h/cm) absorption was not significantly influenced, but net potassium secretion (-3 mumol/h/cm) was decreased to zero and transepithelial potential (PD) reduced from -45 mV to -33 mV. 10E-4 mol/l Salinomycin, applied in vitro on the muscosal side, decreased PD in 80 min and 10E-3 mol/l in 30 min from 18 mV to zero. Both concentrations decreased the short-circuit current (Isc = 77 microA/cm2) in 60 min, respectively 30 min to 40 microA/cm2. After 60 min mucosal 10E-4 mol/l Salinomycin the Isc increased, resulting from a transepithelial conductance (Gt) increase from 3 to 40 mS/cm2. A dose-related effect was present on PD, Isc and Gt at concentrations between 10E-7 and 10E-6 mol/l. The unidirectional 22Na fluxes were increased to 20 times the control values and net Na transport disappeared. We conclude that Salinomycin when applied in usual doses (10E-4 mol/l) as a coccidiostatic feed additive, profoundly affects colonic electrolyte transport.

Animals↗
PubMed1984

Phase relationship of the circadian rhythms of feed intake, caecal motility and production of soft and hard faeces in domestic rabbits.

In rabbits kept under 12:12 h light conditions, caecal contractions were recorded by implanted strain gauges or induction coils. In animals fed ad libitum caecal contraction frequency varied cyclically in phase with the circadian rhythm of feed intake. Both had their minimum during the time of soft faeces production. Thus all 3 functions seem to depend on the same circadian clock. The close link between caecotrophy and caecal contractions can, however, be upset by either time-restricted feeding or by fasting.

Animals↗
PubMed1982

Structural and functional differences in various divisions of the rabbit colon.

The rabbit colon displays a diversity of form and function along its proximo-distal axis. Morphologically, four regions can be discerned based on macroscopic and microscopic criteria: 1) the initial portion of the colon immediately distal to the cecum (P1), in which wart-like protrusions characterize the surface topography, is 10 cm in length and endowed with three teniae. 2) The adjoining portion of the colon (P2) possesses one tenia, is about 20cm in length and also displays the wart-like protrusions in slightly less prominent form. 3) Fusus coli, a short segment approximately 4 cm in length, is free of teniae, but exhibits longitudinal folds on its inner aspect. Electron microscopically, it shows a paucity of microvilli in direct contrast to the two afore-mentioned regions. These three portions together constitute the proximal colon. 4) The fourth region of the colon, the distal colon, reaches a length of 80-100 cm and shows no obvious second-order enlargements of its surface, displaying scanning electron microscopically ridges in looped configurations. Physiological parameters also showed differences depending on the region of the colon observed. Water content of the ingesta increases slightly during passage of the proximal colon, decreasing in the fucus coli and distal colon. Na concentration was highest in the area P1-P2, decreasing distally. K was low in area P2 and then rose toward the fusus, only to fall again distally. Nitrogen values decrease considerably during passage of P2 but only slightly distally. Transmural electrical potential differences also exhibit a characteristic, discontinuous gradient.

Animals↗
PubMed1982

Influence of osmolality, short chain fatty acids and deoxycholic acid on mucus secretion in the rat colon.

Mucus secretion into the rat colon has been measured in situ using a single perfusion technique. Protein, sialic acid and hexose concentrations in the perfusion solution were found to give reliable estimates of mucus output if samples were homogenized prior to analysis. Mucus output as indicated by an increase in the concentration of mucus constituents was higher when the solution was hypotonic (270 mosm . kg-1) or hypertonic (370 mosm . kg-1) than when isotonic solutions (320 mosm . kg-1) were used. The proportion of hexoses and sialic acid to protein was 23 and 14% at low, 23 and 11% at high osmolality, and 21 and 13% when isotonic solutions were used. Deoxycholic acid (DCA, 4 mmol . 1(-1)) increased the net secretion of mucus constituents 3 fold, whereas short chain fatty acids (SCFA) had no effect. Mucus composition during all treatments did not change significantly, even when stimulated with DCA. When mucus was released from the epithelial surface by previous perfusion with a DCA containing solution, net water and SCFA absorption rates and mucus output were significantly lowered for 2 to 3 h. However, no correlation between mucus secretion and SCFA absorption was found, indicating that a role for mucus as a diffusion barrier to SCFA is unlikely. Mucus output, which indicates the amount of mucus released from the epithelial surface, probably depends on the direction of net water movement, which follows the osmotic gradient between colon lumen and blood.

Animals↗
PubMed1977

Effect of exercise on systemic blood pressure and heart rate in horses.

Carotid loops were prepared in 3 horses several months prior to the experiments. Systemic blood pressure was recorded at rest and during exercise by insertion of a plastic cannula into the carotid artery. The pressure transducer was fixed at the neck of the animal. The blood pressure signal was transmitted by telemetry. When the horses were standing under the rider, the following results were obtained: heart rate 38 +/- 5 beats-min-1, systolic pressure 115 +/- 15, disstolic pressure 83 +/- 10, mean pressure 97 +/- 12, and pulse pressure 32 +/- 9 mm Hg. During steady gallop at a mean speed of 548 +/- 90 m-min-1, heart rate rose to 184 +/- 23 beats-min-1, systolic pressure to 205 +/- 23, diastolic pressure to 116 +/- 12, mean pressure to 160 +/- 20 and pulse pressure to 89 +/- 19 mm Hg. These values remained stable throughout the exercise period of 5-6 min. When the horses were exercised at stepwise increasing speed from walk through trot to gallop, both the mean arterial blood pressure and the pulse pressure rose in proportion to the running speed.

Animals↗