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PubMed1981

Effects of casein versus soy protein diets on serum cholesterol and lipoproteins in young healthy volunteers.

The effects of casein and soy protein on serum cholesterol levels and lipoprotein composition were studied in 69 healthy volunteers (18 to 28 yr of age) under strict dietary control. Subjects were fed for 6 wk on diets containing 13% of energy as protein, 38% as fat (P/S ratio = 0.6) and about 380 mg cholesterol per day. Of the protein in the diets 65% consisted of casein or soy protein or a 2:1 mixture of casein and soy protein. After a control period of 10 days during which all the subjects received the casein-soy diet, 20 subjects continued on this diet for the next 4 wk as a base-line control, 25 subjects switched to the casein diet, and the remaining 24 subjects switched to the soy diet. Both food records and chemical analysis of double portions revealed that the diets were completely identical except for the type of protein. Average serum cholesterol levels at the end of the control period were 152 +/- 27 mg/dl (3.93 +/- 0.69 mmol/l) and 153 +/- 23 mg/dl (3.95 +/- 0.60 mmol/l) (mean +/- SD) for the casein and soy group, respectively. At the end of the test period the levels were 149 +/- 24 and 150 +/- 23 mg/dl, respectively; thus there was no significant change on either diet. On the casein diet there was no change in the low-density lipoprotein cholesterol concentration, and only a slight, nonsignificant increase in the high-density lipoprotein cholesterol concentration. On the soy diet, however, there was a significant decline in low-density lipoprotein-cholesterol (-6.6 mg/dl; -0.17 mmol/l) and a significant increase in high-density lipoprotein-cholesterol (+5.8 mg/dl; +0.15 mmol/l). The decline in low-density lipoprotein cholesterol in the soy group was significantly different from the small change in the casein group, but the difference in increase in high-density lipoprotein cholesterol in the soy and the casein group was only weakly significant. This suggest that soy protein could have a slight beneficial effect on the distribution of cholesterol over the various lipoprotein fractions, even at constant total cholesterol concentration.

Adolescent↗
PubMed1982

Binding of zinc to casein.

An investigation of the binding of zinc to cow's milk proteins has shown that zinc binds avidly in a pH-dependent manner to casein, but has little affinity for the total whey protein fraction. At slightly alkaline pH 1 mg casein binds 8.4 micrograms zinc. No zinc binds to casein at pH 2 and to dephosphorylated casein at pH 7.4. Bound zinc is released only by casein precipitation at pH 4.6 but not by casein precipitation using Ca2+-ions or rennin. It could also be shown that zinc binds to phosphopeptides derived from tryptic or chymotryptic casein digestion and that metal complexing agents, such as citrate or picolinic acid compete for zinc binding with these phosphopeptides and casein. Binding of zinc to casein and its tryptic or chymotryptic phosphopeptides may explain in part the comparatively low zinc availability from cow's milk and some milk-based infant formulas.

Animals↗
PubMed1997

Inhibition of beta-glucuronidase by casein hydrolysate formula.

BACKGROUND: A casein hydrolysate infant formula has been shown to be associated with lower levels of neonatal jaundice than are standard infant formulas. Because beta-glucuronidase is related to neonatal jaundice, this study examined the effect of a casein hydrolysate formula on beta-glucuronidase. METHODS: Beta-glucuronidase activity was measured with or without added dietary components. The beta-glucuronidase sources used were meconium, breast milk, and the purified bovine liver enzyme. The dietary components assayed for their effect on beta-glucuronidase activity included casein hydrolysate formula (Nutramigen), whey-predominant formula (Enfamil), breast milk; enzymatically hydrolyzed casein, and other constituents of the casein hydrolysate formula. Stool samples of 6-day-old infants, who were exclusively fed one of the two formulas or breast milk, were also assayed for inhibition of beta-glucuronidase. RESULTS: Only Nutramigen, enzymatically hydrolyzed casein, and stool from Nutramigen-fed infants consistently demonstrated significant inhibition of beta-glucuronidase activity, ranging from 45% to 85% of that in controls. The inhibition of beta-glucuronidase in purified bovine liver demonstrates a dose response in a pH range from 4 to 7.3. CONCLUSIONS: Hydrolyzed casein contains a beta-glucuronidase inhibitor that, in casein hydrolysate-fed infants, persists after passage through the digestive tract. These data are consistent with the possibility that inhibition of beta-glucuronidase is a mechanism by which infants fed casein hydrolysate have lower jaundice levels than infants fed routine formulas or breast milk. Further study of this mechanism is needed.

Animals↗
PubMed1979

The identification of 'casein' in human breast cancer.

A retrospective study of ninety-six cases of breast cancer was carried out to determine the prognostic values of a casein immunolocalization technique. This was performed using an indirect immunofluorescence method with antisera raised in rabbits to pooled human casein. Fluorescence positivity was graded according to its intensity and distribution. The pathology of each tumour was studied and the tumour type, histological grade and tissue response assessed. The relationship between these observations and the casein content of the tumour was studied. In addition the correlation between casein content and age, menopausal state, clinical staging and survival was investigated. The incidence of casein positivity in our series was 50% with approximately half of the positive cases showing strong fluorescence. There was a relationship between casein content and the age of the patients, with casein being more frequently found in tumours from younger patients. Tumours with a high casein content, in general, show a poorer survival than the group as a whole. This difference in survival was most marked in the first eight years after operation and restricted to those tumours in clinical stage I and histological grade I. The presence of casein in the tumours did not appear to be related to the other factors examined.

Adult↗
PubMed1985

Protective effect of casein toward Salmonella typhimurium in acid-milk.

Lactic acid is the inhibitory agent in yoghurt responsible for the inhibition of Salmonella typhimurium. Casein, however, may exert a protective effect toward the survival of the salmonella in acid-milk products. Salmonella typhimurium was found to die-off 21.2% more rapidly in 18-h yoghurt-whey than in 18-h yoghurt at 37 degrees C with a pH of 3.85 and 1.42% lactic acid. When casein was added to yoghurt-whey, the die-off rate of the salmonellas was reduced to that found in yoghurt. The rate remained unchanged when 4.8% sodium caseinate was added to the whey. When 0 to 14% casein was added to the acid-whey the die-off rate changed from 9.7 to 24.0 min/log reduction of cells, respectively. There was a direct correlation between the increase in casein concentration and length of survival of the salmonellas. At a pH of 3.85, 4.2 or 4.5, the die-off rate was 6.5, 13.0 or 40 min/log reduction of cells in milk containing 1.42% lactic acid, and was 4.0, 10.0 or 33.3 min/log reduction, respectively, in whey with 1.42% lactic acid. Thus, the protective effect of casein toward Salm. typhimurium increased as the pH increased. This indicated that casein exerts a protective effect on Salm. typhimurium in acid dairy products and the degree of protection depends on the casein concentration, the form of the casein molecule and the pH.

Animals↗
PubMed1980

Role of prolactin in the transcription of beta-casein and 28-S ribosomal genes in the rabbit mammary gland.

Isolated mammary nuclei were incubated in the presence of HgCTP and the neosynthesized RNA was isolated with a SH-Sepharose column. The concentration of beta-casein mRNA and 28-S ribosomal RNA in the neosynthesized RNA fractions was evaluated using [3H]DNA probes complementary to beta-casein mRNA and 28-S rRNA respectively. In the unstimulated pseudopregnant rabbit, the transcription of both genes was easily detectable. Injections of prolactin progressively enhanced the transcription rate of both genes and preferentially the beta-casein gene. A comparison between the transcription rates and the accumulation of the corresponding gene products in the cell revealed that there is a good correlation between these two parameters for the 28-S rRNA gene. By contrast, the acceleration of beta-casein gene transcription by prolactin is unable to account for the simultaneous accumulation of beta-casein mRNA, indicating that prolactin is a potent stabilizer of casein mRNA. Injections of CB154 into lactating rabbits (a drug which suppresses the secretion of prolactin by hypophysis), induced a rapid drop of beta-casein mRNA concentration and a slow decline of beta-casein gene transcription. Simultaneously the drug was responsible for a marked and rapid decrease of 28-S rRNA gene transcription, while the concentration of the rRNA remained elevated. During weaning the transcription of the beta-casein gene and, to a lower degree, the transcripton of the 28-S rRNA gene proceeded more slowly and this phenomenon was accompanied by a progressive decline of the RNA concentrations.

Animals↗
PubMed1981

Role of progesterone and glucocorticoids in the transcription of the beta-casein and 28-S ribosomal genes in the rabbit mammary gland.

Isolated mammary nuclei were incubated in the presence of HgCTP and the neosynthesized RNA was isolated with a SH-Sepharose column. The concentration of beta-casein mRNA and 28-S ribosomal RNA in the neosynthesized RNA fractions was measured using [3H]cDNA probes complementary to beta-casein mRNA and 28-S rRNA respectively. Prolactin injected into pseudopregnant animals accelerates the transcription of both genes and increases the stability of the beta-casein mRNA but not of the 28-S rRNA. Progesterone injected simultaneously with prolactin reduced considerably all these effects of prolactin, with a lower efficiency when the highest doses of prolactin were injected. These observations suggest that progesterone attenuates the transfer of prolactin information related to the lactogenesis into the mammary cell. Glucocorticoids injected with prolactin amplify the prolactin action on the expression of the beta-casein gene but not of the 28-S rRNA genes. In the absence of prolactin (a situation obtained by injecting simultaneously CB 154, a drug which inhibits pituitary prolactin secretion) glucocorticoids exhibit no effect. In the lactating rabbit glucocorticoids do not delay significantly the drop of beta-casein gene transcription rate provoked by weaning or by prolactin withdrawal obtained by injecting CB 154. A comparison of the beta-casein mRNA accumulation and the transcription rate of the beta-casein gene indicates that glucocorticoids act essentially by amplifying the activation of beta-casein transcription supported by prolactin, but not by enhancing the stability of the beta-casein mRNA.

Animals↗
PubMed1981

Characterisation of a membrane-bound serine-specific casein kinase isolated from lactating guinea-pig mammary gland.

Serine-specific and threonine-specific casein kinase activities have been identified in a Golgi-enriched membrane fraction isolated from the lactating guinea-pig mammary gland. The serine-specific casein kinase has been purified 2000-fold by affinity chromatography on ATP-agarose. The enzyme has an estimated Mr of 100000 as determined by sucrose gradient centrifugation and phosphorylates the serine residues of dephosphorylated guinea-pig caseins A and B in a qualitatively and quantitatively identical manner to caseins A and B secreted by lactating mammary gland explants in organ culture. The enzyme also phosphorylates casein C at serine, but not threonine residues. Studies on the relative location of the enzyme within a Golgi-enriched membrane fraction show that it is an integral component of the membrane, either in the form of a transmembrane protein or exposed on the luminal side of the membrane. Although casein kinase activity is not associated with the endoplasmic reticulum, it remains to be proven whether it is truly a Golgi enzyme, since analysis of subcellular membrane components fractionated by sucrose gradient centrifugation shows that the particulate protein kinase activity of the lactating mammary gland does not cosediment with galactosyl transferase, possibly a reflection of the heterogeneous nature of mammary gland Golgi apparatus. It seems likely that the serine-specific casein kinase activity described is responsible for the phosphorylation of caseins in the lactating guinea-pig mammary gland, and that this occurs after the sequestration of processed but unphosphorylated caseins within the lumen of the endoplasmic reticulum.

Animals↗
PubMed1991

Multiple mRNA species code for two non-allelic forms of ovine alpha s2-casein.

The two non-allelic forms of alpha s2-casein, occurring in ovine milk, differ by an internal deletion of nine amino acid residues, including both cysteine residues at positions 34 and 42 in the mature chain. Sequencing of several alpha s2-casein cDNA, isolated from the mammary cDNA library of a single lactating ewe, showed three new types which differed from that previously studied. In addition to the expected deletion of codons +34 to +42 affecting 30-40% of mRNA, another structural difference involving an internal stretch of 44 nucleotides in the 5' untranslated region, was found. S1-nuclease protection assays confirmed the existence of several types of the relevant mRNA and sequencing of in-vitro-amplified genomic DNA demonstrated the presence of the 44-nucleotide stretch in the alpha s2-casein transcriptional unit, thus ruling out the possibility of a cloning artefact. The different alpha s2-casein mRNA, four in terms of deletion and two in terms of nucleotide substitutions for a given ewe, can be readily explained by partial exon skipping and allelic differences, respectively. This assumption is well supported by the following observations: 5' and 3' ends of both deleted DNA fragments are similar to those of exons; sequences neighbouring the 44-nucleotide stretch of the genomic DNA perfectly match consensus sequences described for 3' and 5' ends of introns; the rather simple patterns observed on Southern blots of different enzymatic digests of genomic DNA strongly suggest the occurrence of only 1 copy alpha s2-casein gene/haploid genome. During the course of evolution, the alpha s2-casein-encoding gene has undergone many mutations and some of them might have occurred in regions corresponding to consensus splicing regions of the pre-mRNA. Thus, complete skipping of some exons might be responsible for the shorter sizes of rat and mouse alpha s2-casein mRNA. If so, the overall organization of the alpha s2-casein gene in the different species might be more similar than expected from structural comparisons of the cognate mRNA or caseins.

Amino Acid Sequence↗
PubMed1997

Differential splicing of pre-messenger RNA produces multiple forms of mature caprine alpha(s1)-casein.

The identity of multiple forms of caprine alpha(s1)-casein in variants A, B, and C has been determined by structural characterisation using mass spectrometry, automated Edman degradation and peptide mapping. Mature goat alpha(s1)-casein exists as a mixture of at least four molecular species which differ in peptide chain length. The main component corresponds to the 199-residues form already described. The other three, in lesser amounts, were shorter forms of alpha(s1)-casein and differed for the deleted peptides 141-148, as shown previously for ovine alpha(s1)-casein, peptide 110-117, or Gln78. Analysis of alpha(s1)-casein mRNA from milk somatic cells demonstrated that these forms originated from skipping events at the level of exon 13 (codifying for peptide 110-117) and 16 (codifying for peptide 141-148) and from the presence of a cryptic splice site within exon 11 (whose first CAG triplet encodes Gln78) during primary transcript processing. The finding of these splicing abnormalities in the three common variants A, B, and C suggests that this is a general feature of alpha(s1)-casein in goat. A further source of heterogeneity of caprine alpha(s1)-casein was identified in the discrete phosphorylation of seryl residues. Eight serine residues (at positions 44, 46, 64 to 68 and 75) are fully phosphorylated (except in variant A because of the replacement Glu77-->Gln which prevents phosphorylation of Ser75). Conversely, Ser115 and Ser41 are phosphorylated only to about 50% and 20%, respectively. Ser12, although located in a consensus triplet, is never phosphorylated, similarly to the ovine alpha(s1)-casein variants. These results confirm that there are stabilised mechanisms of simultaneous synthesis of alpha(s1)-casein at different length and of post-translational modification in both caprine and ovine species.

Alternative Splicing↗
PubMed1989

The concentration of dietary casein required for normal mandibular growth in the rat.

To determine a suitable casein concentration for normal, undeformed mandibular growth, we placed weanling male rats on diets containing graded levels of casein between 0% and 30% for 19 days. Some weanlings were killed so that initial values could be established. Ten linear dimensions corresponding to the six skeletal units of the mandible were evaluated so that their growth rates at the end of the experimental period could be established. Other dimensions were also evaluated for study of the growth rate of the bone as a whole. The macroscopic growth of the mandible showed a sigmoidal relationship with dietary casein concentration, most of the measurements reaching a plateau at 20% casein. Within the skeletal units, four dimensions corresponding to the alveolar and symphyseal regions did not change with age and were not affected by the casein content of the diet. The remaining six dimensions-corresponding to condylar, coronoid, angular, and basal regions of the mandible-increased with age and were related positively to dietary casein concentration. Their growth patterns were not uniform, although all of them reached maximal values when the diet contained 20% casein. Therefore, deformation of the mandible appears to occur in rats fed diets with a casein concentration lower than 20%. It appears that a dietary casein concentration of 20% is required for normal, undeformed mandibular growth.

Animals↗
PubMed1990

Hormonal induction of beta-casein gene expression: requirement of ongoing protein synthesis for transcription.

Hormonal induction of beta-casein gene expression was studied using a two-step culture of mouse mammary explants and RNA blotting analysis. The explants prepared from pregnant mice were cultured first for 4 days under nonlactogenic conditions to reduce the initial level of beta-casein transcripts and then induced to express beta-casein gene in the presence of insulin, hydrocortisone, and PRL for up to 3 days. Among the six different combination of hormones tested in the first incubation period, the combinations of insulin and epidermal growth factor was found to reduce the residual level of beta-casein transcripts in cultured explants to a nearly undetectable level and allow the highest induction in the second incubation period. The increase in beta-casein transcripts was detected as early as 30 min of induction with insulin, hydrocortisone, and PRL, and its level increased more than 100-fold over the initial level at 24 h. The increase in beta-casein transcripts was blocked by concomitant addition of the protein synthesis inhibitors cycloheximide or puromycin with the three hormones. Cycloheximide inhibited the increase in beta-casein gene transcription that was elicited by insulin, hydrocortisone, and PRL, but did not alter the stability of beta-casein transcripts. These results suggested that protein synthesis was required for hormonal activation of beta-casein gene transcription.

Animals↗
PubMed1989

Relative contribution of promoter and intragenic sequences in the hormonal regulation of rat beta-casein transgenes.

In order to identify DNA sequences responsible for the regulation beta-casein gene expression, lines of transgenic mice bearing the entire rat beta-casein gene and two rat beta-casein promoter chloramphenicol acetyltransferase (CAT) fusion genes have been established. All three transgenes have been shown previously to be regulated in a tissue- and stage specific manner. To investigate the relative contribution of promoter and intragenic sequences in the hormonal regulation of the beta-casein gene, mammary explant cultures derived from these lines of mice have now been performed, and the effects of PRL and glucocorticoids on transgene as compared with endogenous beta-casein gene expression have been quantified. After the addition of PRL to cultures performed in the presence of insulin and glucocorticoids, a 25- to 40-fold induction of endogenous mouse beta-casein mRNA was observed after 48 hr. A comparable greater than 25-fold induction of transgene expression after PRL addition was observed in explant cultures derived from a line of mice expressing the entire rat beta-casein gene. In contrast, PRL addition elicited only a 1- to 4.5-fold increase in CAT activity in cultures derived from two lines of mice bearing casein-CAT fusion genes with either 524 or 2300 base pairs of 5'-flanking DNA. In the presence of insulin, glucocorticoid or PRL addition alone increased endogenous beta-casein gene expression 2- to 2.5-fold and 5- to 10-fold, respectively, but only a 1.2- to 2.5-fold induction of CAT activity was observed for each hormone.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2002

Purification of porcine beta-casein, N-terminal sequence, quantification in mastitic milk.

The objectives of the study were to purify porcine beta-casein from sow's milk, to determine N-terminal amino acid sequence, to develop specific antisera against porcine beta-casein, and to use that antisera to evaluate milk samples from a mastitis study. Milk was collected by hand milking a Yorkshire by Duroc crossbred sow following oxytocin administration on d 27 of lactation. A casein-enriched fraction was then prepared by iso-electric precipitation. Porcine beta-casein was then purified by liquid chromatography on a Mono Q anion-exchange column, and checked for purity with SDS-PAGE. An apparent molecular weight of 29,000 Da was estimated from SDS-PAGE. N-Terminal amino acid sequence was determined by Edman degradation to be RAKEELNASGETVE. Rabbits (n = 2) were immunized with beta-casein mixed with Freund's complete (primary) or incomplete (boosters) adjuvant at 4-wk intervals. Antiserum collected from one rabbit 112 d after primary immunization detected 30 to 100 ng beta-casein by Western blot procedure when used at a dilution of 1:2 x 10(6). The antiserum was specific for porcine beta-casein, but showed some cross-reactivity with equine casein. It was determined by Western blot procedure that mammary inflammation induced by lipopolysaccharide infusion resulted in a 41% decrease in the beta-casein concentration of sow milk.

Amino Acid Sequence↗
PubMed2004

Nitrogen balance in lambs fed a high-concentrate diet and infused with differing proportions of casein in the rumen and abomasum.

Twenty-five wether lambs (34 +/- 0.9 kg) fitted with ruminal and abomasal infusion catheters were used in a completely randomized design to determine the effects of differing proportions of ruminal and abomasal casein infusion on N balance in lambs fed a high-concentrate diet (85% corn grain, 1.6% N; DM basis) for ad libitum intake. Wethers were infused with 0 (control) or 10.4 g/d of N from casein with ruminal:abomasal infusion ratios of 100:0, 67:33, 33:67, or 0:100% over a 14-d period. Feed, orts, feces, and urine were collected over the last 5 d. Total N intake and excretion were greater (P < 0.01) in lambs infused with casein than in controls; however, N retention did not differ in lambs infused with casein compared with controls, suggesting that N requirements were met without casein supplementation. Total N intake and total N excretion did not differ among casein infusion treatments. Urinary N excretion decreased linearly (P = 0.07) with decreasing ruminal infusion of casein. Site of casein infusion quadratically (P = 0.06) influenced N retained (g/d), with the greatest retention observed in the 33:67 ruminal:abomasal infusion treatment. Dry matter intake from feed decreased from 1,183 to 945 g/d (P = 0.02) in lambs infused with casein compared with controls, but apparently digested DM did not differ among treatments. These data indicate that decreasing the ruminal degradability of supplemental protein above that required to maximize N retention results in decreased urinary excretion of N without greatly affecting apparent diet digestion.

Abomasum↗
PubMed1986

The effect of casein derivatives on glycine enhancement of beta-lactamase production in Enterobacter cloacae ATCC.13047.

Our earlier work showed that glycine enhancement of class I beta-lactamase production in Enterobacter cloacae ATCC.13047 was greater on Isosensitest Agar than on other laboratory media. In the present study it was demonstrated that Casein Hydrolysate was the constituent of Isosensitest Agar which was necessary for glycine enhancement of beta-lactamase production. Also, a comparison of the effect of casein and casein derivatives on glycine enhancement of beta-lactamase production showed that acid hydrolysis of casein was a prerequisite for glycine enhancement of beta-lactamase production. Enterobacter cloacae ATCC.13047 failed to grow on a medium containing casein, and glycine enhancement of beta-lactamase production did not occur on a medium containing tryptic hydrolysate of casein. The effect on beta-lactamase production of variations in the concentrations of both Casein Hydrolysate and glycine was examined by titration of both components in a chequerboard fashion. Beta-lactamase production was influenced by the concentrations of both Casein Hydrolysate and glycine. This inter-relationship indicated that there was a balance between the concentrations of Casein Hydrolysate and glycine and that alterations in this balance modified beta-lactamase production. The significance of the observations is discussed in relation to the factors which influence glycine enhancement of beta-lactamase production in Enterobacter cloacae ATCC.13047.

Caseins↗
PubMed1998

Pretreatment with glucocorticoid is essential for lactogenic induction of the bovine beta-casein/CAT expression in HC11 cells.

Hormonal regulation of the bovine beta-casein gene expression was studied in a murine mammary epithelial HC11 cells and compared with that of the rat beta-casein gene expression. CAT expression vectors driven by their promoter sequences were transfected into HC11 cells. Stable transfectents were treated with lactogenic hormones, dexamethasone and prolactin for 2 days in confluent cultures. While the lactogenic hormones synergistically induced a strong activation of the rat beta-casein/CAT expression, neither a single or combined treatment of dexamethasone and prolactin induced the bovine beta-casein/CAT expression. To test a sequential treatment effect of lactogenic hormones on the bovine beta-casein/CAT expression, cells were first treated with either dexamethasone or prolactin for various days and then subjected to the second treatment with both hormones for 2 days. Only dexamethasone-, but not prolactin-pretreated cells showed a strong lactogenic induction. Moreover, the fold induction of dexamethasone-pretreated cells increased gradually as a function of duration of dexamethasone pretreatment. A series of the bovine beta-casein/CAT constructs with different length of the bovine beta-casein 5' flanking region ranged from 0.3 kb to about 15 kb was analyzed in 12-days dexamethasone-pretreated cultures. CAT expression was increased even in 0.3 kb-containing construct, but prominent induction was seen in more than 1.8 kb-containing constructs. Therefore, it could be concluded that a long-term dexamethasone pretreatment is essential for lactogenic induction of the bovine beta-casein expression and the 0.3 kb proximal promoter region is important, but more distal promoter element(s) is necessary for mediating the coordinated action of lactogenic hormones to the bovine beta-casein expression.

Animals↗
PubMed1994

Involvement of opioid peptides from casein on reticular motility and digesta passage in steers.

Experiment 1 determined the effects of incremental abomasal casein infusion on reticular motility and digesta passage of mature steers in a 4 x 4 Latin square study. Casein solutions were infused at 0, 1.25, 2.5, and 5.0% (wt/vol) for 3 h at 16.7 ml/min. Steers were fed for maintenance every 2 h. Casein resulted in a linear decrease in frequency, duration, and amplitude of reticular contractions measured manometrically. Total area of reticular contractions from physiographic tracings decreased 10.4 to 18.5%. Ruminal DM contents decreased 4.5 to 7.5%. Experiment 2 characterized the effects of casein on reticular contractions to be mediated by opioid peptides. Steers were infused abomasally (4 h) with either a 5% (wt/vol) solution of casein or its hydrolysate with or without a predose of naltrexone as an opiate antagonist (.5 mg/kg of BW) in a 2 x 2 factorial. Both casein and hydrolysate reduced frequency and duration of reticular contractions. Hydrolysate decreased contraction frequency within 30 min of infusion and 60 min prior to effects of casein. Naltrexone reversed the effects of casein and accentuated the effects of hydrolysate. Ruminal liquid outflow was decreased 19.7% with hydrolysate. Postruminal infusion of casein or its hydrolysate resulted in casomorphin-like activity on reticular motility and digesta passage.

Abomasum↗