Influence of dietary protein on blood cholesterol and related metabolites of growing calves

Forty male, Holstein calves were utilized to evaluate effects of either low (12%) or high (25%) dietary protein on growth and serum metabolites, with a particular concern for serum cholesterol. All diets contained 19% acid detergent fiber and consisted of corn silage, alfalfa hay and grain mixtures. Average concentration of total serum cholesterol was depressed (P = .001) for calves on the high-protein diets (58.8 mg/dl) as compared with their low-protein counterparts (67.9 mg/dl). Calves fed the high-protein diet had lower (P = .002) free serum cholesterol but elevated high-density lipoprotein cholesterol as a percentage of total cholesterol. Calves receiving the high-protein diets showed increases (P = .206) in lecithin cholesterol acyltransferase activity compared with low-protein counterparts. Serum urea nitrogen was increased (P = .001) for calves fed high-protein diets, while serum protein and glucose remained unchanged. Calves fed the high-protein diets consumed less dry matter with improved (P = .09) growth efficiency (gain/feed).

Relationships among dietary lipid intake, serum cholesterol and ovarian function in Holstein heifers

Experiments were performed to determine whether serum concentrations of total cholesterol (TC) undergo cyclic changes during the estrous cycle of dairy heifers and to assess the relationship between serum concentrations of TC and ovarian steroid hormones. The effects of a hypercholesterolemic diet upon luteal progesterone secretion also were determined. Experiment 1 involved five dairy heifers exhibiting normal estrous cycles. Serum concentrations of TC, progesterone, testosterone and estradiol-17 beta were determined in blood samples collected throughout a complete estrous cycle. A transient decline in TC was observed during the luteal phase of all heifers beginning on d 2 and reached a nadir 6 d after estrus. Highest mean concentrations of TC occurred between d -2 and +2 (96.3 +/- 8.2 mg/dl), which were markedly higher (P less than .05) than the lowest mean concentrations (76.3 +/- 10.3 mg/dl) observed on d 6. Concentrations of serum TC were negatively correlated (r = -.40; P less than .01) with progesterone between d 2 and 9. Serum TC was not correlated with testosterone or estradiol-17 beta. In Exp. 2, seven cycling Holstein heifers were fed a control diet for 70 d (Stage I), a diet containing 15% whole sunflower seed as a source of supplemental dietary lipid for 70 d (Stage II) and then the control diet for 70 d (Stage III). Diets were isocaloric and isonitrogenous. All heifers were synchronized with prostaglandin F2 alpha after wk 5 in each of the three feeding stages.(ABSTRACT TRUNCATED AT 250 WORDS)

Dual action of aldosterone on toad bladder: Na+ permeability and Na+ pump modulation

The effects of aldosterone on the functional characteristics of the Na+ entry step across the apical membrane and on the Na+ exit step across the basolateral membrane of the urinary bladder of toads were examined using amiloride and ouabain as probes of the respective surfaces of the cell. Aldosterone stimulated Na+ transport with a concurrent increase in the transepithelial electrical conductance as did two other agents, vasopressin (ADH) and p-chloromercuriphenylsulfonate (PCMPS), primarily active on the apical membrane. Unlike the effects of ADH and PCMPS, however, the effect of aldosterone on Na+ conductance was blocked by actinomycin D and was associated with a decreased sensitivity of the apical Na+ channel to amiloride. In addition, aldosterone increased the sensitivity of the Na+ pump on the basolateral side to ouabain, an effect that was dependent on the metabolic state of the urinary bladder. These results support the inference of coordinate effects on Na+ permeability of the apical membrane and the Na+ pump of the basolateral membrane. Both effects of aldosterone appear to be dependent on the metabolic state of the transporting epithelium.

Effect of aldosterone on abundance and phosphorylation kinetics of Na-K-ATPase of toad urinary bladder

The possibility was explored that aldosterone-dependent modulation of either the abundance or the kinetic properties of the Na+ pump (Na-K-ATPase) is involved in the mechanism of natriferic action on toad urinary bladder. Cell membranes from the epithelium of urinary bladders of toads were prepared by a sucrose-Ficoll step gradient method, which yielded a 10-fold increase in specific activity of plasma membrane marker enzymes and only minor contamination with other subcellular fractions. Phosphorylation of Na-K-ATPase by gamma-PO4 of [gamma-32P]ATP in the presence of Mg2+ was Na+ dependent, whereas dephosphorylation was K+ dependent. Km for phosphorylation by ATP was 3 X 10(-8) M and K1/2 (half-maximal stimulation) for Na+ was 13 +/- 2 mM. Pretreatment of cell membranes with sodium deoxycholate (DOC) increased the maximal extent of phosphorylation (Nmax) about threefold without changing the Km for ATP. Aldosterone (5 X 10(-8) M) stimulated transepithelial Na+ transport two- to threefold in 5 h but had no significant effect on Km for ATP in the phosphorylation reaction (with or without activation by DOC) or on the abundance of the enzyme inferred from Nmax of phosphorylation in the absence of activation by DOC. After pretreatment with DOC, average Nmax was 13% greater in the aldosterone-treated population. Regression analysis of these responses revealed no significant correlation between increments in short-circuit currents and Nmax values of phosphorylation with or without pretreatment with DOC.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of carboxyl group in Na+-entry step at apical membrane of toad urinary bladder

Mucosal addition of N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) and some lipid-soluble carbodiimides, agents which are selective for carboxyl groups, irreversibly inhibited Na+ transport as measured by short-circuit current (SCC) in the urinary bladder of the toad. The inhibition of Na+ transport by EEDQ had the following characteristics: 1) the inhibition was accompanied by a significant increase in the transepithelial electrical resistance; 2) the decrease in SCC was accounted for by a comparable decrease in 22Na+ influx without effect on Na+ efflux; 3) amphotericin B produced complete recovery of SCC inhibited with EEDQ but not with antimycin A or ouabain; 4) mucosal EEDQ decreased the amiloride-sensitive reversal of Na+ current that is induced by serosal nystatin in the absence of mucosal Na+; 5) vasopressin and acid mucosal pH caused an increase in SCC in proportion to the SCC remaining after EEDQ inhibition; and 6) Vmax of the SCC was decreased without alteration in the apparent Km for Na+. Based on these characteristics of EEDQ inhibition of Na+ transport, we infer that a carboxyl group of the Na+ channel is involved in the Na+-entry step across the apical membrane of "tight" epithelia. The inhibition of Na+ transport with EEDQ most likely involves closing the Na+ channel through a chemical reaction involving a carboxyl group of the channel.

Modification of carboxyl of Na+ channel inhibits aldosterone action on Na+ transport

We investigated the effect of the carboxyl-selective reagent N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) on aldosterone stimulation of Na+ transport in the urinary bladder of the toad. Na+ transport, measured as the short-circuit current (SCC), was irreversibly inhibited by EEDQ in a dose- and time-dependent manner prior to addition of aldosterone. The greater the percentage inhibition by EEDQ (X), the smaller was the maximal increase of SCC after aldosterone (Y). This relationship gave the regression equation Y = 128.41 - 1.73X, r = -0.99 (n = 35). Evidence that the inhibition of SCC produced by EEDQ was limited to effects at the mucosal membrane was attested by the following: 1) EEDQ did not alter the stimulation by aldosterone of the osmotic water flow response to antidiuretic hormone; 2) whereas inhibition of protein synthesis by cycloheximide prevented this effect of aldosterone; 3) amphotericin B fully restored SCC previously inhibited by EEDQ to the level produced in tissues not inhibited by EEDQ; 4) comparison of the effects of amiloride vs. EEDQ pretreatment on the SCC response to aldosterone and amphotericin B revealed nearly identical characteristics; 5) in contrast, amphotericin B stimulation of SCC was limited when Na+ transport was limited by antimycin A (an inhibitor of energy production) or by ouabain. The findings fail to provide positive evidence for the hypothesis that aldosterone induces the synthesis of new Na+ channels but are consistent with hormonal activation of previously existing but nonfunctioning Na+ channels.

Functional groups of the Na+ channel: role of carboxyl and histidyl groups

Two titratable groups, with effect on Na+ transport and with apparent acid dissociation constants (pKaS) of 4.2 and 6.7, were found in the apical membrane of toad urinary bladder and are tentatively identified as a carboxyl and an imidazole. N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ), a reagent selective for carboxyl residues, inhibits Na+ transport in the urinary bladder of toads. The underlying chemical reaction whereby EEDQ produces inhibition through potential modification of carboxyl residues was studied. The inhibitory action of EEDQ on Na+ transport was dependent on pH of reaction media and availability of nucleophile, indicating that formation of a covalent acyl-nucleophile bond is probably involved in the irreversible inhibition of Na+ transport. The kinetics of the inhibition showed a stoichiometry of formation of one acyl-nucleophile bond per closure of one Na+ transport site, presumably the Na+ channel. The nucleophile that appears to be involved in the formation of the acyl-nucleophile bond was tentatively identified as having an apparent pKa of 6.7. Amiloride and two analogues of amiloride added to the mucosal Ringer solution (but not serosal amiloride) protected against inhibition of Na+ transport by EEDQ--a finding consistent with the hypothesis that the EEDQ-activated carboxyl group undergoes reaction with a nucleophile at or near the site of specific binding of amiloride onto the apical membrane, most likely at the Na+ channel. Our findings led us to postulate that amiloride must interact with at least two sites on the Na+ channel in order to block the channel. One of the two sites appears to be an ionic interaction between the anionic carboxyl group at the Na+ channel and the cationic guanidinium group of amiloride.

Intramolecular heterogeneity of degradation in plasma membrane glycoproteins: evidence for a general characteristic

Five integral plasma membrane glycoproteins (60, 80, 120, 140, and 160 kilodaltons) were isolated to homogeneity from rat liver by a four-step procedure: (i) extraction of plasma membranes with lithium diiodosalicylate, (ii) solubilization of glycoproteins with Nonidet P-40, (iii) affinity chromatography on concanavalin A-Sepharose, and (iv) semipreparative NaDodSO4/polyacrylamide gel electrophoresis. The glycoproteins contained 48.5--51.5% hydrophobic amino acids. Carbohydrate moieties contained N-acetyl-D-glucosamine, D-mannose, D-galactose, L-fucose, and N-acetylneuraminic acid. N-Acetyl-D-galactosamine was not detectable. Half-lives of degradation of the carbohydrate and protein moieties of the five glycoproteins were measured by pulse-chase experiments in vivo. Protein moieties had half-lives ranging from 52 to 88 hr in the five glycoproteins, with a mean of 73 +/- 15 hr. Terminal sugars, L-fucose, and N-acetylneuraminic acid had significantly shorter half-lives, averaging 18 +/- 2 hr and 29 +/- 3 hr, respectively. The half-life of D-mannose varied between that of the terminal sugars and that of the protein moiety, depending on the type of the glycoprotein. The data show that the carbohydrate moieties are degraded faster than the protein portion of the glycoproteins. As this finding was obtained in each of the five glycoproteins, intramolecular heterogeneity of breakdown may be a general characteristic of plasma membrane glycoproteins in liver.

Effect of dietary fat supplement on lipid metabolism of Holstein Heifers

Twenty Holstein heifers were fed four rations containing 0, 10, 20, and 30% whole sunflower seed as a source of dietary fat. All rations consisted of alfalfa hay, sunflower hulls, and grain mixtures and were isonitrogenous at 12% crude protein and isocaloric at 2.6 Mcal metabolizable energy per kilogram dry matter. Average body weight gains were not different among treatment groups. Heifers fed sunflower seed (fat) diets consumed less total dry matter, significantly improving growth efficiency (gain/feed). Concentration of total lipid and urea nitrogen in blood serum were increased whereas glucose was depressed with higher amounts of dietary fat. High fat diets (20 and 30%) elevated total lipid, triglyceride, and nonesterified fatty acids in the blood. Total and free cholesterol in blood also were increased, but high density lipoprotein-cholesterol remained unchanged with increasing concentration of dietary fat. Dietary fat was correlated positively with lipid components of blood serum and negatively with glucose.

A rapid mixing-photocrosslinking technique to study the dynamics of nucleic acid-protein interactions

A rapid mixing-photocrosslinking technique has been developed to investigate the kinetics of protein-nucleic acid interactions. With this technique, binding of nucleic acid to protein is first synchronized by rapid mixing in a stopped-flow apparatus. The intermediates formed at different stages of the binding process are then "frozen" by photocrosslinking with a 10-microseconds uv light pulse at various times after mixing. By analyzing structural changes of these intermediates as a function of time, one can obtain the information concerning the dynamic aspects of the interaction. This technique may also be applied to other macromolecular interactions in biological systems.

Effects of dietary protein and fiber on growth and selected cholesterol responses of rats

The effect of dietary protein and fiber on growth and metabolic parameters in blood serum, liver and kidney were determined in a 2 X 5 factorial experiment involving 40 Sprague-Dawley rats. Treatment variables were two dietary protein levels (16 and 24%) and five acid detergent fiber levels (6, 10, 16, 24 and 34%). No difference in growth rate of rats was found due to varying levels of either protein or fiber in the diet. Increasing the dietary protein level from 16 to 24% resulted in an 18.5% reduction in blood cholesterol. The dietary treatment containing 16% fiber influenced most metabolic parameters examined, including blood serum cholesterol, liver cholesterol and total lipid content in liver and kidney. Rats receiving the diet containing 16% fiber had the highest serum cholesterol (88.9 mg/dl) and the lowest liver cholesterol (4.4 mg/g) as compared with other fiber groups.

Molecular mechanism of promoter selection in gene transcription. I. Development of a rapid mixing-photocrosslinking technique to study the kinetics of Escherichia coli RNA polymerase binding to T7 DNA

A combined rapid mixing-photocrosslinking technique has been developed to investigate the kinetics of the interaction between Escherichia coli RNA polymerase and T7 DNA. The reactants were rapidly mixed in a modified Durrum stopped-flow apparatus, and the intermediates formed at different stages of the binding process were "frozen" by photocrosslinking with a UV light pulse of 10-mus duration at various times after mixing. The results indicate that the initial binding between RNA polymerase and T7 DNA is a diffusion-controlled reaction. Furthermore, the extents of initial contracts with DNA made with the beta, beta', and sigma subunits of RNA polymerase are roughly proportional to the sizes of these subunits, suggesting that complex formation occurs through random collision between the two reactants. After the initial complex formation, the rate of transfer of polymerase between individual DNA molecules is slow, implying that the polymerase molecules are undergoing predominantly intramolecular transfer during the promoter search. From the kinetic studies of subunit-DNA contacts during RNA polymerase binding to T7 DNA, it can be inferred that the beta, beta', and sigma subunits are directly participating in the promoter search process.

Molecular mechanism of promoter selection in gene transcription. II. Kinetic evidence for promoter search by a one-dimensional diffusion of RNA polymerase molecule along the DNA template

The rapid mixing-photocrosslinking technique, in conjunction with an immunoprecipitation assay developed to measure the change in the distribution of Escherichia coli RNA polymerase molecules bound to T7 DNA, has been applied to investigate the molecular mechanism of promoter search by RNA polymerase. The binding of RNA polymerase to the DNA template can be divided into at least two steps. The initial binding is rapid and occurs at nonspecific sites randomly distributed throughout the DNA molecule. This is followed by a relatively slow promoter search in which RNA polymerase is transferred from nonspecific sites to promoter sites through a series of intramolecular processes. The rate of polymerase loss from a segment of DNA which does not contain promoter sites is a function of the distance from this segment to both the promoter sites and the ends of the DNA molecule. The kinetic data are consistent with a molecular mechanism in which RNA polymerase undergoes a bidirectional linear diffusion along the DNA template to search for the promoter site. This interpretation is supported by the computer simulation which correctly predicts the relative rates of polymerase loss from various DNA segments. The mechanism derived from these studies is in accordance with the notion that the whole DNA molecule serves as an effective sink for trapping and guiding polymerase molecules during promoter search.

Calcium and calcium ionophore A23187 alter protein synthesis and secretion by acini from rat mammary gland

1. Acini (alveoli) from lactating rat mammary gland responded to increasing levels of calcium or calcium ionophore A23187 with increased protein synthesis and secretion. 2. Inclusion of dibutyryl cyclic AMP in incubation medium with calcium or calcium ionophore decreased protein synthesis but increased rate of protein secretion . 3. Calcium ionophore increased both rates of calcium uptake by acini and levels of intracellular calcium. 4. These results suggest a relationship between calcium and cyclic AMP in milk protein synthesis and secretion.

Effects of inhibitors of F0-F1 proton-translocating ATPase on urinary acidification

A proton pump in diverse biological systems consists of two structural units with separate but integrated functions, the F0-F1-ATPase. We tested by chemical perturbation the possibility that such a proton pump might be involved in urinary acidification conducted by urinary epithelia (UF0-UF1-ATPase). Tyrosine-reactive chemicals and N,N'-dicyclohexylcarbodiimide, known to block the proton channel unit (F0), also inhibited urinary acidification, as measured by the reverse short-circuit current (RSCC) in urinary bladders from toads and turtles. Since these chemicals were equally effective under aerobic and anaerobic conditions, the inhibition appears to occur directly on UF0 rather than on mitochondria. In contrast, an inhibitor of F0-F1-ATPase, oligomycin, only inhibited aerobic RSCC and was ineffective on anaerobic RSCC. Thus, oligomycin appears to inhibit mitochondrial F0-F1 rather than any UF0+UF1. Another inhibitor of the F1-ATPase unit, N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline, was without effect on RSCC at a concentration (0.3 mM) that produced over 50% inhibition of short-circuit current. These results support the concept that acidifying urinary epithelia contain a plasma membrane proton channel, UF0, but that UF1, if it exists, is unique in that it is resistant to known inhibitors.

Calcium in the control of renin secretion: Ca2+ influx as an inhibitory signal

The mechanism for the inhibition of renin secretion in vitro from renal cortical slices by angiotensin II, antidiuretic hormone, ouabain, and high K+ concentration was studied. The inhibitory effect of these agents was blocked by a Ca antagonist, verapamil. In addition, epinephrine stimulated renin secretion and its stimulatory action was blocked by ouabain. These results support the hypothesis that Ca2+ influx into juxtaglomerular cells plays a role as an inhibitory signal whereas Ca2+ efflux is a stimulatory signal for renin secretion. Renin secretion was greatly stimulated by lowering incubation temperature, indicating that renin secretion is not energy dependent. The possibility is discussed that Ca2+ of juxtaglomerular cells might activate an enzyme(s) that then modulates some sequential steps of renin secretory processes, thereby controlling the rate of renin secretion.

DNA strand specificity in promoter recognition by RNA polymerase

DNA strand and enzyme subunit specificities involved in the interaction between E. coli RNA polymerase and T7 DNA were studied by photo-crosslinking techniques. In non-specific enzyme-DNA complexes, subunits, sigma, beta, and beta' were crosslinked to both strands of the DNA. Under conditions leading to specific enzyme-promoter complexes, however, only sigma and beta subunits were crosslinked. The sigma subunit was crosslinked preferentially to the non-sense strand at promoter sites. No such strand specificity was observed for the beta subunit. These results provide insight into the molecular mechanism of promoter recognition and indicate that the interaction between RNA polymerase and DNA template is different at promoters and at non-specific sites.

Effect of dietary protein and sunflower meal on blood serum cholesterol of dairy heifers

Effects of dietary protein and protein supplement on cholesterol in blood serum of Holstein heifers were determined in two replications of a 2 X 2 fractorial study involving 16 animals. Treatment variables were two crude proteins, either low (12%) or high (20%), and two protein supplements with soybean meal or sunflower meal. Rations contained 21% acid-detergent fiber supplied by sunflower hulls. Free serum cholesterol (17.9 mg/100ml) from heifers consuming the high protein rations was lower than that of animals on low protein (28.2 mg/100 ml). The same degree and direction of interaction betwen quantities of protein and sources of protein were exhibited by total and esterified cholesterols. Concentrations of total cholesterol were not different among treatment groups, but quadratic responses with weeks of trial were significant. The lowest free cholesterol (16.4 mg/100 ml) was recorded by heifers on sunflower meal on the high protein ration. Composition of serum proteins was not altered by sources or amounts of protein in the ration. Weight gains and growth efficiency (gain/feed) were higher in animals on high protein, irrespective of the protein supplement.

Covalent modification and inhibition of an epithelial sodium channel by tyrosine-reactive reagents

This study sought to elucidate the molecular mechanism involved in the Na+ entry across the apical membrane of the urinary bladder of the toad. Na+ transport, as measured by short-circuit current (SCC), was irreversibly inhibited by three tyrosine-specific reagents: N-acetylimidazole (ID50, 4.6 x 10(-2)M), tetranitromethane (1.8 x 10(-4) M), and 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl; 3.4 x 10(-5) M). The functional specificity of NBD-Cl to block Na+ entry via Na+ channels was attested by the following: 1) NBD-Cl produced comparable inhibition of SCC and Na+ influx under aerobic and anaerobic conditions; 2) amphotericin B produced complete recovery of inhibited SCC; 3) vasopressin increased SCC only in proportion to the uninhibited SCC; 4) Km for Na+ was not changed; and 5) the half time for the inhibition varied as a function of amiloride concentration or pharmacologic activity of its analogues. On the basis of the above findings, these tyrosine-specific reagents are believed to be useful chemical probes for the identification and characterization of Na+ channel protein.

Extracellular amino acid effects on milk protein synthesis and intracellular amino acid pools with bovine mammary cells in culture

Increases in free intracellular amino acids are associated with increased protein synthesis. Responses in synthesis of beta-casein and beta-lactoglobulin and of intracellular amino acid pools to graded concentrations of amino acids in the medium were observed. Mammary tissue from two Holstein cows was dispersed and cultured for 18 h with Eagle's minimal essential medium containing 1, 3, 5, or 7 times the basic concentration of amino acids. Synthesis of beta-casein and beta-lactoglobulin increased with concentration of amino acids in the medium. Intracellular pools of amino acids not provided by the medium (serine, proline, alanine, glycine, glutamic acid, ornithine) generally decreased with increased concentrations of amino acids in the medium, the exception being ornithine which increased with extracellular amino acids. Lysine, histidine, tyrosine, leucine, valine, phenylalanine, isoleucine, arginine, and threonine intracellular pools increased with increased amino acids in medium. Intracellular cystine responded with a small linear increase to increased amino acids in the medium, while intracellular tryptophan and methionine did not respond, indicating potential limitations from these amino acids.