Do adolescent smokers experience withdrawal effects when deprived of nicotine?

This is the first controlled prospective study of the effects of nicotine deprivation in adolescent smokers. Heart rate and subjective withdrawal symptoms were measured over an 8-hr period while participants smoked normally. Seven days later, participants were randomized to wear a 15-mg (16-hr) nicotine patch or a placebo patch for 8 hr, and they refrained from smoking during the session. Those wearing the placebo experienced a decrease in heart rate across sessions and an increase in subjective measures of nicotine withdrawal. Those wearing the active patch also reported significant increases for some subjective symptoms. Expectancy effects were also observed. The findings indicate that adolescent smokers experience subjective and objective changes when deprived of nicotine. As in previous research with adults, expectancies concerning the effects of nicotine replacement also influenced perceptions of withdrawal.

Functional preference of the constituent amino acid residues in a phage-library-based nonphosphorylated inhibitor of the Grb2-SH2 domain.

A nonphosphorylated disulfide-bridged peptide, cyclo(Cys-Glu1-Leu-Tyr-Glu-Asn-Val-Gly-Met-Tyr9-Cys)-amide (termed G1) has been identified, by phage library, that binds to the Grb2-SH2 domain but not the src SH2 domain. Synthetic G1 blocks the Grb2-SH2 domain association (IC50 of 15.5 microM) with natural phosphopeptide ligands. As a new structural motif that binds to the Grb2-SH2 domain in a pTyr-independent manner, the binding affinity of G1 is contributed by the highly favored interactions of its structural elements interacting with the binding pocket of the protein. These interactions involve side-chains of amino acids Glu1, Tyr3, Glu4, Asn5, and Met8. Also a specific conformation is required for the cyclic peptide when bound to the protein. Ala scanning within G1 and molecular modeling analysis suggest a promising model in which G1 peptide binds in the phosphotyrosine binding site of the Grb2-SH2 domain in a beta-turn-like conformation. Replacement of Tyr3 or Asn5 with Ala abrogates the inhibitory activity of the peptide, indicating that G1 requires a Y-X-N consensus sequence similar to that found in natural pTyr-containing ligands, but without Tyr phosphorylation. Significantly, the Ala mutant of Glu1, i.e. the amino acid N-terminal to Y3, remarkably reduces the binding affinity. The position of the Glu1 side-chain is confirmed to provide a complementary role for pTyr3, as demonstrated by the low micromolar inhibitory activity (IC50 = 1.02 microM) of the nonphosphorylated peptide 11, G1(Gla1), in which Glu1 was replaced by gamma-carboxy-glutamic acid (Gla).

Structural basis of binding of high-affinity ligands to protein kinase C: prediction of the binding modes through a new molecular dynamics method and evaluation by site-directed mutagenesis.

The structural basis of protein kinase C (PKC) binding to several classes of high-affinity ligands has been investigated through complementary computational and experimental methods. Employing a recently developed q-jumping molecular dynamics (MD) simulation method, which allows us to consider the flexibility of both the ligands and the receptor in docking studies, we predicted the binding models of phorbol-13-acetate, phorbol-12,13-dibutyrate (PDBu), indolactam V (ILV), ingenol-3-benzoate, and thymeleatoxin to PKC. The "predicted" binding model for phorbol-13-acetate is virtually identical to the experimentally determined binding model for this ligand. The predicted binding model for PDBU is the same as that for phorbol-13-acetate in terms of the hydrogen-bonding network and hydrophobic contacts. The predicted binding model for ILV is the same as that obtained in a previous docking study using a Monte Carlo method and is consistent with the structure-activity relationships for this class of ligands. Together with the X-ray structure of phorbol-13-acetate in complex with PKCdelta C1b, the predicted binding models of PDBu, ILV, ingenol-3-benzoate, and thymeleatoxin in complex with PKC showed that the binding of these ligands to PKC is governed by a combination of several highly specific and optimal hydrogen bonds and hydrophobic contacts. However, the hydrogen-bonding network for each class of ligand is somewhat different and the number of hydrogen bonds formed between PKC and these ligands has no correlation with their binding affinities. To provide a direct and quantitative assessment of the contributions of several conserved residues around the binding site to PKC-ligand binding, we have made 11 mutations and measured the binding affinities of the high-affinity PKC ligands to these mutants. The results obtained through site-directed mutagenic analysis support our predicted binding models for these ligands and provide new insights into PKC-ligand binding. Although all the ligands have high affinity for the wild-type PKCdelta C1b, our site-directed mutagenic results showed that ILV is the ligand most sensitive to structural perturbations of the binding site while ingenol-3-benzoate is the least sensitive among the four classes of ligands examined here. Finally, we have employed conventional MD simulations to investigate the structural perturbations caused by each mutation to further examine the role played by each individual residue in PKC-ligand binding. MD simulations revealed that several mutations, including Pro11 --> Gly, Leu21 --> Gly, Leu24 --> Gly, and Gln27 --> Gly, cause a rather large conformational alteration to the PKC binding site and, in some cases, to the overall structure of the protein. The complete abolishment or the significant reduction in PKC-ligand binding observed for these mutants thus reflects the loss of certain direct contacts between the side chain of the mutated residue in PKC and ligands as well as the large conformational alteration to the binding site caused by the mutation.

Molecular dynamics simulations of beta-hairpin folding.

Molecular dynamics simulations of beta-hairpin folding have been carried out with a solvent-referenced potential at 274 K. The model peptide V4DPGV4 formed stable beta-hairpin conformations and the beta-hairpin ratio calculated by the DSSP algorithm was about 56% in the 50-ns simulation. Folding into beta-hairpin conformations is independent of the initial conformations. The simulations provided insights into the folding mechanism. The hydrogen bond often formed in a beta-turn first, and then propagated by forming more hydrogen bonds along the strands. Unfolding and refolding occurred repeatedly during the simulations. Both the hydrogen bonding and the hydrophobic interaction played important roles in forming the ordered structure. Without the hydrophobic effect, stable beta-hairpin conformations did not form in the simulations. With the same energy functions, the alanine-based peptide (AAQAA)3Y folded into helical conformations, in agreement with experiments. Folding into an alpha-helix or a beta-hairpin is amino acid sequence-dependent.

Erectile response to transurethral alprostadil, prazosin and alprostadil-prazosin combinations.

PURPOSE: Transurethral alprostadil has been shown to be efficacious in many men with erectile dysfunction. We compared transurethral alprostadil and prazosin alone, and in combination to treat this disorder. MATERIALS AND METHODS: In this double-blind, placebo controlled study the erectile responses to transurethral alprostadil, prazosin and alprostadil-prazosin combinations were assessed in 234 men 26.8 to 81.5 years old with complete organic erectile dysfunction. Patients self-administered a random sequence of 7 doses in the clinic in 4 weeks. The erectile response was assessed using categorical and visual analog scales. RESULTS: Full penile enlargement or rigidity was achieved by 165 of the 234 men (70.5%) after at least 1 active dose of medication. The most effective alprostadil dose (500 microg.) resulted in full penile enlargement or rigidity in 51.8% of administrations, whereas the most effective prazosin dose (2,000 microg.) and placebo resulted in a similar response in 12.7 and 2.7%, respectively (p <0.001). The 500/2,000 microg. alprostadil/prazosin combination, which resulted in full enlargement or rigidity in 58.9% of doses, was only slightly better than the most effective dose of alprostadil alone (500 microg.). However, combinations of 125/500 and 250/500 microg. alprostadil/prazosin were more effective (p <0.01) than 125 and 250 microg. alprostadil given alone, respectively. The most common side effect of therapy was penile pain, which rarely led to study discontinuation. Hypotension most commonly developed at the higher alprostadil-prazosin combination. CONCLUSIONS: Transurethral alprostadil and alprostadil-prazosin combinations produced erections in men with complete organic erectile dysfunction. This combination therapy may be an option in patients who do not respond to transurethral alprostadil alone.

Effects of alprostadil and prazosin on motility, viability and membrane integrity of human sperm.

PURPOSE: We evaluated the effects of alprostadil, prazosin hydrochloride, and alprostadil/prazosin hydrochloride, agents used in the clinical treatment of male erectile dysfunction, on the motility, viability and membrane integrity of human sperm. MATERIALS AND METHODS: Ten healthy volunteers provided semen samples that were incubated with 0.4 mg./ml. alprostadil, 0.1 and 0.2 mg./ml. prazosin hydrochloride and 0.4 mg./ml. alprostadil plus 0.1 mg./ml. prazosin hydrochloride for 2 hours. Control incubations included polyethylene glycol 1450, the formulation vehicle for the clinical use of alprostadil and prazosin, and Ham's F-10 buffer. Serial evaluations of percent sperm motility, percent viability, membrane function (by hypo-osmotic swelling test) and several computer generated measurements of sperm motion, including straight line velocity, curvilinear velocity, linearity and amplitude of lateral head displacement, were made. RESULTS: None of the agents had a significant impact on the percentage of motile or viable sperm or on sperm membrane function. Incubation with 0.2 mg./ml. prazosin reduced straight line velocity and curvilinear velocity significantly compared with the other agents. These changes were most likely a direct result of the viscosity of the 0.2 mg./ml. prazosin solution and not a cellular or metabolic effect on the sperm. CONCLUSIONS: Alprostadil and prazosin hydrochloride at doses used in transurethral therapy for erectile dysfunction have no effect on the motility, viability and membrane integrity of human sperm.

[Uptake of amino acids in the rumen epithelium in sheep]. / Zadrzanie amínokyseliny v bachorovom epiteli oviec.

By the modification of the methods which are used for determination of amino acid uptake in the mammary gland and in the small intestine the uptake of 14C-lysine was measured in two parts of the sheep rumen epithelium in vitro. Three various lysine concentrations were used (0.95; 4.95 and 9.95 mM/l). Duration of the incubation was 15, 30 or 60 minutes. Comparison of the lysine distribution ratios as depending upon the duration of incubation period in the dorsal rumen sac at 9.95 mM/l concentration revealed significant differences between at the 15 min and 60 min incubation (0.952 +/- 0.089 vs 1.931 +/- 0.108; P < 0.05, respectively) and between 30 min and 60 min incubation (1.165 +/- 0.138 vs 1.931 +/- 0.108, P < 0.05, respectively)-Fig. 1. Comparison of the lysine distribution ratios as depending upon the duration of incubation period in the ventral rumen sac at 4.95 mM/l concentration revealed significant differences between the incubations of 15 and 30 min (1.182 +/- 0.131 vs 1.742 +/- 0.113; P < 0.05, respectively) and between the incubations of 15 and 60 min (1.182 +/- 0.131 vs 2.10 +/- 0.204; P < 0.05, respectively)-Fig. 2. Comparison of the lysine distribution ratios in both the dorsal and ventral sac as depending upon the duration of incubation period after 15 min incubation revealed a significant difference at the 4.95 mM/l concentration 1.619 +/- 0.078 vs 1.182 +/- 0.131; P < 0.05, respectively)-Fig. 3. Our results showed that the lysine uptake in the dorsal and ventral sheep rumen epithelium is dependent on the incubation duration only under certain concentrations of lysine. Differences in absorption of lysine between dorsal and ventral rumen epithelium are not mostly significant.

The effect of a single whole-body irradiation with a lethal dose on catecholamine levels in the pineal glands of rats.

Male Wistar rats adapted to light-dark cycle (LD) 12:12 h were exposed in the darkness to a lethal single dose of 14.35 Gy gamma-rays on the whole body. Irradiation, sham-irradiation and decapitation 30, 60, 120 min after the exposure, were performed between 2000 h and 0100 h in the darkness. The changes in the concentrations of catecholamines (CA) were determined by the radioenzymatic method in the pineal gland of rats. Results were evaluated in comparison with those of the sham-irradiated (30, 60, 120 min) control groups of rats. From the results it follows that the concentration of dopamine (DA) and norepinephrine (NE) in the rat pineal gland significantly decreased 30 and 120 minutes after irradiation (p < 0.01). At min 60 of the postirradiation period it was possible to observe a tendency to recovery of the levels of DA and NE to control values. Epinephrine (EPI) exhibited a significant (p < 0.05) decrease at min 60 and 120 of postirradiation (by 61.8% and 62.8%, respectively).

A double-blind, placebo-controlled evaluation of the erectile response to transurethral alprostadil.

OBJECTIVES: Previous studies have indicated that the urethra may provide an effective route for administering vasoactive medication for the treatment of erectile dysfunction. We evaluated the safety and efficacy of alprostadil administered intraurethrally at home for the treatment of this disorder. METHODS: This prospective, multicenter, double-blind, placebo-controlled study evaluated the erectile response to randomly assigned doses of transurethral alprostadil at home in 68 men with long-standing (mean 41 months) erectile dysfunction of primarily organic etiology. Patients completing the study each administered a random sequence of four different doses (125, 250, 500, and 1000 micrograms) and placebo over a 2 to 4-week period. Assessments included the couples' ability to have intercourse, patient ratings of erectile response by both categorical and visual analogue scales, penile volume measurements, and overall assessments of comfort and ease of administration. RESULTS: Overall, 75.4% (49 of 65) of study patients achieved full enlargement of the penis and 49.2% (32 of 65) achieved an erection judged by the patient to be sufficient for intercourse. In addition, 63.6% (42 of 66) of patients reported intercourse. Efficacy was similar across etiologies. The most common side effect was penile pain, which occurred in association with 9.1% to 18.3% of alprostadil administrations, depending on dose. Mean comfort ratings ranged from 79 to 87, depending on dose, where 0 = severe discomfort and 100 = comfortable; ease of administration scores were above 90 for each dose, where 0 = difficult and 100 = easy. There were no episodes of priapism in this study. CONCLUSIONS: Short-term treatment with transurethral alprostadil produced erections resulting in sexual intercourse in most patients with chronic erectile dysfunction. This therapy may be a useful treatment option for patients with erectile dysfunction.

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).

The effect of hormonal superovulatory preparation FSH on the levels of catecholamines in the blood plasma of sheep.

The effect of hormonal stimulation with FSH injection in the doses of 18 mg (360 IU) and 24 mg (480 IU FSH) on the levels of plasma catecholamines (dopamine, norepinephrine and epinephrine) was studied by radioenzymatic methods during synchronized oestrous cycles of the sheep. Catecholamines were determined in the blood plasma before and 24, 48, 96 and 120 hours after application of FSH. It follows from the results that the levels of plasma dopamine increased significantly (p<0.001) 24 and 48 hours after FSH application. Furthermore, the levels of dopamine (DA) during the other time intervals observed, compared with those of controls before hormonal stimulation, remained at a higher level. A lower dose of the hormone (18 mg) had a more pronounced effect on changes in the levels of plasma dopamine. Norepinephrine (NE) did not exhibit any significant changes in comparison with the plasma levels of dopamine in the sheep after hormonal stimulation with FSH. A statistically significant increase in plasma norepinephrine was recorded 24 hours after administration of 18 or 24 mg FSH. During the other time intervals observed, its levels did not differ from the control values. Plasma epinephrine (E) showed a significant increase 24 and 48 hours after FSH application but not later. The effect of FSH on plasma catecholamine levels was not dose-dependent and their increase was pronounced especially in the period of ovulation.

Catecholamine levels and activity of monoamine oxidase in some hypothalamic structures and in the pineal gland of sheep after administration of FSH.

The influence of hormonal preparations of FSH in a dose of 24 mg (480 IU) on levels of catecholamine (dopamine, norepinephrine and epinephrine) and the activity of their degradation enzyme monoamine oxidase (MAO) in the hypothalamic regions regulating the reproductive system of sheep (area preoptica, eminentia mediana, corpus mamillare) and pineal gland were investigated in the oestrous period employing radiochemical methods. The administration of FSH resulted in significant (p<0.001) increases of dopamine levels in the area preoptica and corpus mamillare of the hypothalamus of sheep as compared to control groups with synchronized oestrus. Hormonal stimulation with FSH increased the levels of hypothalamic norepinephrine in the areas studied and these differences were significant in the eminentia mediana (p<0.05) and corpus mamillare (p<0.05). Significant (p<0.001) changes in epinephrine levels were found in the corpus mamillare and area preoptica (p<0.05). Our results indicate that the administration of FSH caused the most pronounced decrease of MAO activity in corpus mamillare (p<0.001). The pineal gland reacted to the hormonal preparation by decreased levels of norepinephrine and dopamine (p<0.001) and by an increase in MAO activity (p<0.01). We suggest that FSH administration affects catecholamine levels and the activity of monoamine oxidase in the studied areas of the brain of sheep by means of a feedback mechanism.

[Transfer of amino acids across the rumen epithelium in sheep: interaction between leucine and lysine]. / Prestup aminokyselín cez bachorový epitel oviec: interakcie medzi leucínom a lyzínom.

Experiments were conducted on six head of sheep of the Slovak Merino breed with average live weight of 40 kg. The sheep received 0.4 kg of industrially produced molasses feed M and 1 kg of meadow hay once a day. The feed ration for a head of sheep per day contained: 1177.58 g dry matter, 89 g digestible crude protein (SNL), 0.554 starch units. The animals had free choice of water. Rumen epithelium with submucosa was used in the experiment. Amino acid transfer was measured in a mucosa-serosa direction. Amino acids were dissolved in Thyrode's solution with pH value 6.9 on the mucosa side and 7.4 on the serosa side. A constant temperature of 39 degrees C was maintained during the experiment. The epithelium area was 13.2 cm2 for either part of the experiment. Lysine and leucine were incubated separately in the first part of experiment. These concentrations were used: 5, 25, 50 and 75 mumol/l. The values of lysine and leucine readings are denoted as control lysine (lysine K) and control leucine (leucine K) in the result section. Lysine and leucine were incubated simultaneously in the second part of experiment: Lys 5 mumol/l-Leu 5 mumol/l; Lys 5 mumol/l--Leu 15 mumol/l; Lys 5 mumol/l--Leu 20 mumol/l; Lys 25 mumol/l--Leu 25 mumol/l; Lys 25 mumol/l--Leu 75 mumol/l. The values of lysine readings on the other part of experiment are denoted as experimental lysine (lysine P). Figs. 1 and 2 show transfer of control lysine and leucine through the rumen epithelium as depending upon their concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

[Catecholamine blood levels in sheep during superovulation in estrus]. / Hladiny katecholamínov v krvnej plazme oviec v estrickom období pocas superovulácie.

The effects of a serum gonadotropin (SG) superovulation hormonal preparation were investigated on catecholamine levels (norepinephrine, dopamine and epinephrine) in the blood plasma of ewes with synchronized oestrus in the oestrus period. In this trial the blood plasma of eleven ewes of the Slovak Merino breed was analyzed to detect catecholamines in the oestrus period. Superovulation was induced by an i.m. administration of 1500 IU SG as soon as oestrus synchronization with Agelin vaginal tampons finished (20 mg chlorsuperlutin) which lasted for 10 days. Catecholamines were detected in the blood plasma before synchronization, on the day of Agelin vaginal tampons application, and in 48 and 72 hours after the hormone administration--on the days of the expected ovulation. Catecholamine concentrations in the blood plasma were determined by a radioenzymatic assay using a Catechola test (Praha). The results indicate that synchronization and hormonal stimulation influence plasma catecholamine levels. The norepinephrine (NE) concentration in the blood plasma of the control samples has the value of 8.31 +/- 0.732 pmol/ml. An insignificant increase in the NE levels (13.12 +/- 0.120 pmol/ml; Fig. 1) was recorded on day 1 of the trial, after the start of synchronization. On the day of the expected ovulation the NE concentrations rose to 17.12 +/- 1.289 pmol/ml (P less than 0.001) and they remained significantly increased (P less than 0.01) at the level of 12.89 +/- 1.020 pmol/ml on the following day of the experiment. The dopamine level (DA) in the plasma of a control sample is 6.42 +/- 0.350 pmol/ml (Fig. 2).(ABSTRACT TRUNCATED AT 250 WORDS)

[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)

Elevated catecholamine levels and mono aminooxidase activity in the hypophysis of EWES following hormonal stimulation with serum gonadotropin.

The effect of hormonal stimulation on catecholamine levels and activity of its degradation enzyme monoaminooxidase in the hypophysis of ewes in the estric period was studied by the radioenzymatic method. The estrus of ewes was synchronised with Agelin sponges (Agelin, Spofa) containing 20 ug chlorosuperlutin. After completed synchronisation we induced superovulation in the experimental group by means of 2000 IU serum gonadotropin. Catecholamines were determined radioenzymatically using the Catechola test. Monoaminooxidase activity was determined radiochemically. The results indicate that hormonal serum gonadotropin stimulation increases significantly (P < 0.01) pituitary dopamine and epinephrine levels in ewes. In comparison with the control group norepinephrine concentration did not change in this tissue. MAO activity in the hypophysis decreased significantly to almost one half in comparison to control values (P < 0.001). According to our results serum gonadotropin in combination with hyperestrogenisation influences selectively dopamine and norepinephrine metabolism in the hypophysis of hormonally stimulated ewes and reduces monoaminooxidase activity.

The use of a 51Cr technique to detect gastrointestinal microbleeding associated with nonsteroidal antiinflammatory drugs.

Of techniques used to evaluate gastrointestinal (GI) bleeding, use of radiochromium (51Cr)-tagged erythrocytes is the most quantitative and scientifically acceptable method. The value of this technique as well as systematic errors possible with its use are discussed. The medical literature concerning 51Cr evaluation of GI microbleeding with naproxen therapy is critically reviewed. We suggest that future studies using this technique be parallel, randomized, double-blind, and include a 1-week placebo baseline phase for all subjects. Treatment with nonsteroidal antiinflammatory drugs (NSAIDs) should last 3 to 4 weeks. A parallel group of subjects should receive placebo throughout the study. For valid statistical analyses, randomization must achieve baseline comparability of weight, height, age, and sex in the treatment groups. Data transformations may be necessary to satisfy the assumptions of the statistical model. Following these guidelines will enable investigators to better evaluate GI microbleeding during treatment with naproxen or other NSAIDs, and, hopefully, to establish the safety profiles of these drugs.

[The effect of water depletion on renal excretion of urea and electrolytes in sheep]. / Vplyv vodnej deplécie na renálnu exkréciu mocoviny a elektrolytov u oviec.

Experiments were conducted with the sheep of Merino breed given water only at a rate corresponding to 0.5% of their live weight for three days. The animals were given feed ad libitum and during the control measurements water was also available to them ad lib. The fourth day the sheep were given no water and no feed and their renal functions were measured by the standard clearance technique. In the water-depleted sheep the diuresis was naturally reduced and the glomerular filtration rate (GFR) was also observed to have decreased from 77.6 +/- 5.3 to 62.2 +/- 4.2 ml X min-1, P less than 0.05. A small, though significant, decrease was also recorded in plasma urea concentration as a result of the reduced intake of food. The amount of excreted urea decreased by 41% (from 354.0 +/- 41.6 to 208.5 +/- 25.5 mumol X min-1, P less than 0.01) without significant changes in fractional excretion and tubular reabsorption of urea. After three days of water depletion the sheep exhibited a tendency of slight natriuresis whereas the excretion of potassium was reduced. Water depletion was also accompanied by a significant increase in the osmolality of plasma (from 298.0 +/- 1.3 to 317.0 +/- 1.8 mosmol X kg-1 H2O, P less than 0.001) and urine from 789.0 +/- 95.0 to 1547.0 +/- 53.0 mosmol X kg-1 H2O, P less than 0.001), without changes in the clearance of free water. On the other hand, the osmotic clearance was reduced as a result of suppressed excretion of urea and potassium (from 2.33 +/- 0.21 to 1.61 +/- 0.17 ml X min-1, P less than 0.02).(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.