The level of faunation of rumen in relation to some factors of nitrogen metabolism.

Our experiments on metabolic processes in the rumen were performed on sixteen 5-month-old lambs divided into 4 groups (defaunated - D, totally refaunated - T, partially refaunated - P and intact - I). The absence or presence of protozoa in the rumen did not significantly affect the pH values. The greatest differences in NH3 concentration in the rumen before feeding were found between the T and D group (P<0.05). The animals of the T and I groups had higher NH3 concentrations than the D and P groups 1-5 hours after feeding (P<0.05 to P<0.001). Blood urea concentrations before and after feeding were significantly higher in the group I compared to the other groups (P<0.05 to P<0.001). Significant differences in the total nitrogen in rumen fluid were only found between groups D and I. The values of protozoan nitrogen in the rumen and their mutual relationship among the groups could be expressed by the following ratios: I>T>P>D. Proportions of the values of bacterial nitrogen followed in this order: D>P>T>I. The animals in group D had a significantly higher level of residual nitrogen than those in the other groups (P<0.05).

[In vitro transport of amino acids across the rumen mucosa in sheep]. / Prestup aminokyselín cez bachorovú sliznicu oviec in vitro.

Transfer of six amino acids through rumen epithelium of sheep has been studied on mucous and serous sides. Amino acids were classified into two groups: 1. lysine-arginine-glutamic acid, 2. glycine-alanine-leucine. The transfer of amino acids in triads was measured after 60 min. incubation. To determine amino acids transfer through rumen epithelium, three concentrations of amino acids were used: 1500: 150 and 15 mumol per 50 ml. In the first group of amino acids, the highest transfer of arginine was found in comparison with lysine and glutamic acid in all concentrations. The lowest transfer was found in glutamic acid. It follows from this that initial concentration of amino acids in the first group had no effect on amino acids transfer as far as the transfer of amino acids was as follows in all concentrations: arginine greater than lysine greater than glutamic acid. On the other hand, the composition of amino acids and initial concentration of amino acids in the second group exhibited the marked dependence on the transport of amino acids. The transfer of amino acids at the concentration of 1500 mumol per 50 ml was as follows: the passage of amino acids was the highest while this was lowest in alanine and leucine, at the concentration 150 mumol per 50 ml the highest transfer was found in alanine, it was lower in glycine and lowest in leucine and at the concentration 15 mumol per 50 ml the transfer of glycine was highest, lower in leucine and lowest in alanine.(ABSTRACT TRUNCATED AT 250 WORDS)

[Detection of residues of foreign substances in the tissues of cows and bulls and in bull sperm]. / Detekcia reziduí niektorých cudzorodých látok v tkanivách genitálu býkov a kráv a v sperme býkov.

The presence of residues of some chemical foreign substances in the tissues of cow and bull genitals and in sire sperm was investigated due to frequently occurring reproductive disorders in some large cow herds, mainly with the large-scale rearing system. Negative effects of these substances on the reproductive process of cows and bulls were supposed to be exerted. In keeping with the opinions and data mentioned by some authors in the literature there is a fact that the sperm and tissues of genitals belong to those biological materials which are the first to respond to the toxic effects of different chemicals by disorders of their physiological functions. These disorders, mainly in sperm cells, can be evaluated objectively from the recorded changes in physical and biological characteristics. The chemicals under investigation were residues of hexachlorobenzene (HCB), alpha, beta, gamma hexachlorocyclohexane isomers, sigma DDT and its metabolites and of polychlorinated biphenyls (PCB). The concentrations of the residues of these substances in the examined biological materials were very low, in some cases they were not detected at all. It is therefore supposed that these residues could not exert and significant effects on the physiological functions of examined cows and bulls with respect to their reproductive organs. These examinations should become more extensive and thorough, mainly in the herds and regions exposed to potential contamination; the residues of foreign substances should be investigated in view of ecological conditions. These postulates are very urgent, as illustrated by the literature data: in some cases negative effects of certain foreign substances (PCB) were found out and demonstrated on the reproductive functions of people and farm animals.(ABSTRACT TRUNCATED AT 250 WORDS)

[Endogenous urea in the intestinal tract and its significance in nitrogen metabolism in ruminants]. / Endogénna mocovina v crevnom trakte a jej význam v metabolizme dusíka u prezúvavcov.

In the first series of experiments we studied in wethers the percent involvement of various parts of the intestinal tract (from duodenum to cecum) in the secretion of endogenous urea. We found out the following involvement of the given intestinal parts secreting urea to duodenum during 24 hours: bile 6.33%, pancreatic juice 1.85%, through the wall of the front part of jejunum 55.71%, through the wall of the rear part of jejunum 32.25% and through the cecum wall 3.86% of nitrogen of endogenous urea. The urea secreted to the mentioned parts represents one third of the total amount of endogenous urea transported to the entire gastrointestinal tract. Possibilities of utilizing this endogenous source of nitrogen in the organism of ruminant animals were studied in further experiments where 15N-labelled urea was applied to the cecum. We found out that more than four fifths of endogenous urea secreted to the small intestines returned to the metabolic circulation and that only less than one fifth was excreted, not being utilized anew in the organism.

Utilization of endogenous urea secreted into the gastrointestinal tract of the sheep.

The possibility of the utilization of endogenous urea secreted into the gastrointestinal tract was studied in sheep to which a single dose of 3 g 15N urea (50.4% enrichment) was administered by slow infusion via a permanent surgical cannula into the caecum. During a 7 days' experiment, 31.15 +/- 1.08% of the dose was excreted in the urine and 19.65 +/- 1.08% in the faeces, while 49.20 +/- 1.49% was retained in the organism. The maximum 15N values in blood from the jugular vein were found 10 h after starting the infusion and a high concentration was maintained for a further 24 h; sixty hours after the infusion, no more 15N was found in the blood. The maximum 15N values in the total nitrogen of the rumen contents were observed 24 h after the infusion and low levels could still be detected on the 6th day of the experiment. Evidence that 15N participates in enterohepatic and ruminohepatic circulation, and that it is also utilized, is based on the finding of the total, but mainly the protein nitrogen concentration in the duodenum. The maximum 15N values in the total nitrogen (0.247 +/- 0.041 At % 15N) and protein nitrogen (0.262 +/- 0.023 At % 15N) of the duodenal contents were found 24 h after the infusion and 15N could still be demonstrated there in the nitrogen fractions on the 5th day of the experiment.

[Secretion of endogenous urea into the cecum in sheep]. / Sekrécia endogénnej mocoviny do slepého creva oviec.

In one-hour intervals before feeding and 1, 2, 3, 4 and 5 hours after feeding, three wethers were studied for the quantitative secretion of urea N and ammonia N into the caecum pouch (volume 80 ml). The amount of ammonia N secreted into the caecum ranged from 10.0 +/- 2.8 to 20.0 +/- 3.5 microM/h. The concentration of ammonia N was 271.2 +/- 60.6 microM/l, on the average. The passage of urea N showed no statistically significant differences before and after feeding (37.8 +/- 4.2 - 41.4 +/- 5.0 microM/h). The concentration of urea N in the caecum pouch was from 617.8 +/- 67.8 microM/l to 710.7 +/- 82.1 microM/l. Urea penetrates through the caecum wall into the caecum mostly in the form of a whole molecule, only its small proportion has the form of ammonia, its hydrolysis product.

Mechanism-controlled stereospecificity. Acylation of subtilisin with enantiomeric alkyl and nitrophenyl ester substrates.

The activation parameters of acylation of subtilisin with alkyl and p-nitrophenyl esters of N-acylamino acid enantiomers were determined. It was found that (1) the activation entropy is much higher with the nitrophenyl esters than with the corresponding methyl esters, (2) the difference in rate constants between enantiomers is 10(4)--10(5) with methyl esters whereas it is only of the order of 10 with nitrophenyl esters. The results indicate that the catalytic mechanism is simpler for nitrophenyl esters than for alkyl esters. The simple mechanism requires only general base catalysis, and thus permits more freedom of motion in the transition state, whereas the complex mechanism involves both general base and general acid catalysis. Furthermore, the strikingly low enantiomeric specificity with nitrophenyl esters indicates that not only binding but also the catalytic mechanism is an important factor in determining the stereospecificity of an enzyme. The activation parameters for enantiomeric nitrophenyl ester reactions suggest that structurally related substrates can be transformed by the enzyme in different conformations which may be energetically similar or not. The energetically different conformations may account for the activation enthalpy-entropy compensation.

[Participation of bile and pancreatic juice in the secretion of endogenous nitrogen into the digestive tract of sheep]. / Beteiligung der Galle und des Pankreassaftes an der Sekretion des endogenen Stickstoffs in den Verdauungstrakt von Schafen.

The amount of bile and pancreas juice excreted and the amount of urea-N and total-N discharged by the bile and pancreas juice into the duodenum was established in eight experiments with two full-grown sheep of the merino species and with a live weight of 50 kg. For this purpose they had permanent cannulae for the measuring of the passage of bile and pancreas juice which was carried out at 1-hour intervals in the course of 24 hours beginning at 7 o'clock in the morning. During 24 hours 245.3 +/- 6.3 mg urea and 4,418.1 +/- 85.8 mg total-N were discharged with bile and pancreas juice, of which 186.9 +/- 9.6 mg urea and 2,095.3 +/- 119.7 mg total-N were discharged in the bile and 58.5 mg urea-N and 2322.8 +/- 52.9 mg total-N were discharged in the pancreas juice. The amount of pancreas juice secreted and its nitrogen is constant in the course of the day (between 7 a.m. and 7 p.m.) and of the night (between 7 p.m. and 7 a.m.) In the daytime the secretion of bile and its nitrogen is significantly higher than at night. (p less 0.05). The concentration of urea-N and of total-N remained constant throughout the whole day. The amount of bile and pancreas juice secreted correlated greatly significantly with the amount of nitrogen (urea-N and total-N) discharged in bile and pancreas juice. The results indicate that, within the enterohepatalous circulation of endogenous urea, its secretion in bile and pancreas juice is quantitatively less important. The amount of total-N which gets from the endogenous pool into the duodenum is high and corresponds to approximately one third of the metabolic nitrogen which the animals consume daily with their feed.

Endogenous urea secretion into the sheep gastrointestinal tract.

Urea turnover and the proportion of endogenous urea secreted and excreted in the saliva, the bile, the pancreatic juice and the urine and directly across the wall of the digestive tract was studied in 6 experiments, after a single i.v. dose of labelled 15N, in two adult sheep weighing 49 and 50 kg, with permanent biliary and pancreatic fistulus and with an exteriorized right parotid duct. It was found that, of the total amount of endogenous urea secreted into the animals' digestive tract (0.2694+/-0.0138 mg/min/kg b.w.), 10.27+/-0.94% reached the contents in the saliva, 2.12+/-0.28% in the bile and 0.66+/-0.08% in the pancreatic juice, and that 86.95+/-2.1% was secreted into the gastrointestinal tract, across its wall, from the blood capillaries. Exogenous turnover amounted to 0.3228+/-0.192 mg/min/kg. Of the total amount of 476.6 mg i.v. injected 15N urea, 274.1+/-8.86 mg was excreted in the urine 5.1+/-0.9 mg in the bile, 3.19+/-0.06 mg in the pancreatic juice, 4.96+/-0.76 mg via the right parotid gland and 9.34+/-1.09 mg in the faeces. The results show that the quantitatively most important part of the recirculation of endogenous urea is its passage from the blood across the wall of the gastrointestinal tract into its contents.

[Passage of endogenous urea into a jejunum of sheep]. / Pasáz endogénnej mocoviny do jejuna oviec.

The quantitative passage of urea-N and ammonia N into an isolated jejunum of the merino sheep was studied within one hour before, and 1, 2, 3, 4 and 5 hours after feeding. The total amount of ammonia-N that passes to the isolated jejunum [to both proximal and distal part] within an hour is small [0.28-0.35 mg h-1], without any significant differences in passage prior to and after feeding. However, urea-N secretion is high, especially secretion to the fore part of the jejunum [ 3.35-3.62 mg h-1]. The passage of urea-N to the rear part of the jejunum is about 1/3 lower than passage to the fore part. Urea solution of higher concentration than in peripheral blood was incubated in the isolated jejunum to study an adverse phenomenon: absorption of urea from intestinal lumen to the blood. The levels of urea in peripheralblood and in incubate reached a balance state within one hour after administration. The data obtained testify to the permeability of the wall of the gut for urea in both directions.

Utilization of 15N-urea administered into the sheep small intestine.

The retention and excretion of intrajejunally administered 15N-urea was studied in four experiments on two sheep with a permanently fistulated small intestine. In the first 7 days after the administration of 2 g 15N-urea, 18.26% was excreted in the faeces and 19% in the urine; 62.74% was retained in the organism. Urinary excretion took place mainly on the first day and from the 3rd to the 7th day no 15N was present in the urine. The rate of 15N excretion in the faeces was roughly the same for the first 4 days and then fell; on the 7th day there was no 15N in the faeces. The proportion of 15N-urea retained in the organism and excreted in the urine was 81% showing that urea in the ruminant gastrointestinal tract is largely linked up into metabolic circulation as part of the general exchange of nitrogenous compounds.