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Biomedical subjects

S R Davis

Publications and source records attributed to S R Davis.

At least 91 records · Page 5Linked to original sources
PubMed1994

Effect of milking frequency and somatotropin on the activity of plasminogen activator, plasminogen, and plasmin in bovine milk.

Six pairs of identical twin cows during late lactation (213 d) were used to study the effect of milking frequency (twice vs. once daily) and bST during once daily milking on the activity of plasminogen activator, plasminogen, and plasmin in milk. Less frequent milking increased the activity of plasminogen, plasmin, and plasminogen activator in milk. The ratio of plasminogen to plasmin, a measure that is independent of milk volume, decreased during less frequent milking, suggesting that at least part of the increase in activity of plasmin was due to the accelerated conversion of plasminogen to plasmin. Changes in the activity of plasminogen and plasmin in milk were positively correlated with increases in the concentrations of milk BSA and plasma lactose, both of which are indicators of disruption of tight junctions between mammary epithelial cells, indicating that paracellular leakage may have contributed to increased protease activity in milk during less frequent milking. No correlation existed between changes in plasminogen activator and indicators of tight junction disruption, suggesting that increased activity of plasminogen activator in milk was not due to leakage across the mammary epithelium, but rather to increased local production in the mammary gland. Administration of bST during once daily milking did not significantly affect milk protease activity.

Animals↗
PubMed1993

Isolation and sequencing of deer and sheep insulin-like growth factors-I and -II.

We have developed a simple method for the isolation of highly purified cervine (c) and ovine (o) insulin-like growth factors-I (IGF-I) and -II. The IGFs were isolated from acidified serum by cation exchange chromatography and then purified by gel filtration, chromatofocusing, and reverse-phase chromatography. The IGF preparations are > 95% pure. The cIGF-I preparation contains < 0.056% cIGF-II and the oIGF-I preparation contains < 0.01% oIGF-II. Both the IGF-II preparations contain < 0.01% IGF-I. The amino acid sequence of cIGF-I has two differences when compared with human (h) IGF-I. The cIGF-II sequence, which is identical to bovine IGF-II, has three differences when compared with hIGF-II.

Amino Acid Sequence↗
PubMed1993

Effects of oxytocin, machine stripping and milking rate on production loss of cows milked once a day.

The effect of treatments designed to improve the efficiency of milk removal and minimize loss of production in cows milked once a day (OAD) was assessed in short-term trials involving Friesian and Jersey cows. Trial 1 involved 80 cows and compared twice a day (TAD) milking with OAD milking with the administration of 20 i.u. of oxytocin (OX), OAD milking with udder massage before and during milking (OS) and no treatment during OAD milking (OC). The OX and OS groups had increased yields of milk and milk solids when treatments were applied, though yields were not restored to previous TAD levels. The percentage increase shown by OX cows was greater than that of OS cows for fat yield. The level of residual milk in the udder after milking was lower for the OX group than for the OAD and TAD controls. In Trial 2, 12 cows were subjected to fast or slow rates of milking OAD in each of two periods. Losses in milk, fat and protein yields averaged 9.1, 9.9 and 1.0% respectively. Increased rate of milking reduced milking time and time to let-down but did not affect response to OAD milking. The results showed that treatments that increased the evacuation of the udder during milking and decreased the level of residual milk reduced losses in production that occur on OAD milking. Increasing the rate of milking was ineffective in reducing losses on OAD milking.

Animals↗
PubMed1993

Oxidative stress and Trichomonas vaginalis: the effect of hydrogen peroxide in vitro.

The oxidative stress response induced in Trichomonas vaginalis by exposure to various concentrations of hydrogen peroxide (H2O2) was traced by metabolic labeling and monitored by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and fluorography of trichloroacetic acid-precipitated proteins. Concentrations of H2O2 > 450 microM decreased incorporation of radiolabel into protein and altered protein synthesis resulted in a banding pattern similar to the heat shock protein profile. The proteins produced by oxidative stress included molecules with average molecular masses of 145-165, 92-84, 66, 43-46, and 35-36 kD. Oxidative stress induced changes in T. vaginalis protein synthesis slowly. Full conversion to oxidative stress response occurred within 150-180 min after stress initiation. The oxidative stress responses of three strains freshly initiated from stabilates were compared with the responses of the same strains cultured in vitro for extended periods (culture adapted). Both freshly initiated and culture adapted T. vaginalis of the three strains synthesized the 92-84- and 66-kD heat shock proteins but differed in the synthesis of the 74-75-, 43-, and 35-36-kD molecules. Culture adaptation did not modify the oxidative stress response of the three strains tested.

Animals↗
PubMed1992

Cytoplasmic delivery of ribozymes leads to efficient reduction in alpha-lactalbumin mRNA levels in C127I mouse cells.

Ribozymes targeted to five sites along the alpha-lactalbumin (alpha-lac) mRNA were delivered to the cytoplasm of mouse C127I mammary cells using the T7-vaccinia virus delivery system and the amount of alpha-lac mRNA was monitored 24-48 h post-transfection. Three target sites were selected in the alpha-lac coding region (nucleotides 15, 145 and 361) and two were located in the 3' non-coding region (nucleotides 442 and 694). Acting in trans and at a target:ribozyme ratio of 1:1000, ribozymes targeting sites 361 and 694 reduced alpha-lac mRNA by > 80%; another two ribozymes (targeting nucleotides 442 and 145) reduced mRNA levels by 80 and 60% respectively; the fifth ribozyme (targeting nucleotide 15, near the AUG) was largely ineffective. The kinetic activity (kcat) of each ribozyme in vitro was somewhat predictive of the activity of the two ribozymes that targeted nucleotides 361 and 694, but was not predictive of the in vivo activity of the other three ribozymes. Down-regulation of the intracellular levels of alpha-lac paralleled the ribozyme-dependent reduction achieved for mRNA. For site 442, the reduction in both mRNA and protein was attributed to the catalytic activity of the ribozyme rather than to the antisense effects of the flanking arms, because delivery of an engineered (catalytically-inactive) variant had no effect on mRNA levels and a minimal effect on the level of alpha-lac present in the cell.

Animals↗
PubMed1992

Effect of colostrum intake on alpha-lactalbumin concentrations in serum of calves.

Seven Friesian calves were fed colostrum for four days beginning within 24 hours of birth, and milk thereafter. The concentration of alpha-lactalbumin in serum was measured by specific radioimmunoassay and compared to IgG assayed by electroimmunodiffusion. Serum concentrations of alpha-lactalbumin peaked at 387 +/- 85 ng ml-1 within eight hours of initial intake of colostrum, declining to 12 +/- 3 ng ml-1 by day 6. IgG rose steadily to 17 mg ml-1 by 48 hours of birth and remained relatively constant thereafter. The temporal pattern of alpha-lactalbumin in serum following colostrum intake confirms previous studies suggesting reduced absorption of colostral proteins between 24 and 36 hours. The presence of variable amounts of alpha-lactalbumin in serum even after 17 days, however, indicates limited transfer of milk-derived proteins across the gut at this time. The data further show that cessation of maximal gut transfer does not relate to molecular weight of transferred protein.

Animals↗
PubMed1992

Expression of alpha-lactalbumin, alpha-S1-casein, and lactoferrin genes is heterogeneous in sheep and cattle mammary tissue.

We used 35S-labeled cRNA probes to localize the sites of alpha-lactalbumin, alpha-S1-casein, and lactoferrin mRNA synthesis in sheep and forcibly weaned cattle mammary tissue. Expression of alpha-lactalbumin was absent in three of four "virgin" glands studied, present in some alveoli of "pregnant" glands but not in others, despite a similar histological appearance. In the early lactating gland, expression was high in those alveoli with few fat globules in their cells and lumen and was absent in alveoli with abundant fat globules. These observations suggest either that alpha-lactalbumin gene expression is linked to the long-term secretory activity of cells and falls once cells are resting or regressing, or that there are cyclical variations in expression, or that in the lactating gland some groups of epithelial cells are synthesizing alpha-lactalbumin and some are synthesizing fat. Expression patterns of alpha-S1-casein were similar to those of alpha-lactalbumin. Lactoferrin, in contrast, was expressed almost exclusively in the "fatty alveoli" of both species. Our results show that dramatic variations in milk gene expression can occur throughout the mammary gland of sheep and cattle and that at no stage of pregnancy, lactation, or involution can the gland be considered metabolically homogeneous.

Animals↗
PubMed1992

Effect of growth hormone treatment on the distribution of insulin-like growth factor-I between plasma and lymph of lactating sheep.

Plasma and mammary efferent lymph concentrations of insulin-like growth factor I (IGF-I) were determined in lactating ewes before and after treatment with GH (10 mg/day) for 3 days. The lymph:plasma ratio of IGF-I increased from 0.34 to 0.47 after GH treatment when the IGF-I content of plasma increased by 19.4 nmol/l (from 32.1 nmol/l) and lymph by 13.7 nmol/l (from 10.7 nmol/l). This increase in the relative content of IGF-I in lymph was associated with increased lymph content of IGF-I in a lower molecular mass pool (nominally 50 kDa) derived by size exclusion chromatography. GH treatment increased the total binding capacity for IGF-I in both high (150 kDa) and low (50 kDa) molecular mass pools of plasma and the 150 kDa pool in lymph but there was a proportionally greater increase in 50 kDa total binding in lymph relative to plasma. Further, GH treatment increased the 'saturation' of the 50 kDa binding proteins but decreased the 'saturation' of the 150 kDa fraction, in both plasma and lymph. Ligand blot analysis of IGF-binding proteins (IGFBPs) in plasma and lymph showed that GH treatment of lactating sheep increased IGFBP-3 and decreased IGFBP-2 in plasma and lymph. Radioimmunoassay of IGFBP-2 showed that while GH treatment reduced the plasma content of IGFBP-2 by about half, the lymph:plasma ratio was increased from 0.68 to 0.87. GH treatment of lactating ewes not only increased the IGF-I content of plasma but increased the apparent efficiency of transfer of IGF-I across capillary endothelium to mammary efferent lymph.

Animals↗
PubMed1992

Milking frequency alters the milk yield and mammary blood flow response to intra-mammary infusion of insulin-like growth factor-I in the goat.

The milk yield and mammary blood flow responses to close-arterial, intra-mammary infusion of IGF-I were investigated in five Saanen goats milked frequently or normally the day before. Animals were infused for 6 h with recombinant human IGF-I (1.3 nmol/min) and milked hourly following i.v. injection of oxytocin beginning 2 h before infusion and then every 2 h. On one occasion animals were milked five times (after i.v. injection of oxytocin) on the day before infusion and on the other they were milked twice, without oxytocin. The ratio of milk yield from the infused to that from non-infused gland increased by 17 +/- 4% (mean +/- S.E.M.) in goats milked twice the day before infusion and by 6 +/- 2% when the infusion was preceded by frequent milking. Maximal responses were obtained 4 h after the start of the infusion and differed significantly (P < 0.05), according to pretreatment milking. Blood flow through the infused gland rose in parallel to the milk yield response. At 5 h, when maximal levels were achieved, blood flow was 182 +/- 23% of the pre-infusion flow rate following twice-daily milking and 139 +/- 3% of the pre-infusion flow rate following more frequent milk removal. Thus, more frequent milk removal on the day before close-arterial infusion of IGF-I attenuated both the milk yield and mammary blood-flow response to the infusion of IGF-I.

Animals↗
PubMed1992

Characterization of the heat-shock response of Trichomonas vaginalis.

The heat-shock response induced in Trichomonas vaginalis by exposure to various incubation temperatures was traced by metabolic labeling and monitored by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and fluorography. Increasing the incubation temperature from 37 degrees C to 43 degrees C depressed normal protein production and enhanced synthesis of heat-shock proteins (hsp). Smaller increases in incubation temperature resulted in little change in protein synthesis, whereas larger temperature increases inhibited protein synthesis. The hsp produced by T. vaginalis included molecules with approximate molecular masses of 85, 78, 66, 61, 35-31, 20-15, and 12 kD. Trichomonas vaginalis switched to hsp synthesis gradually. Full conversion to hsp production occurred within 60-90 min after the initiation of the 43 degrees C stress. The period of synthesis was different for individual hsp, suggesting independent regulation of hsp production. Four strains of freshly reinitiated and culture-adapted (extended in vitro culture) T. vaginalis synthesized the 85-, 78-, and 66-kD hsp, but varied in the synthesis of the 61-, 35-, 34-, 32-, and 31-kD molecules. Culture adaptation affected the heat-shock response of two of the four strains tested.

Animals↗
PubMed1991

Superior vena cava syndrome caused by an intrathoracic plasmacytoma.

A case of an extramedullary intrathoracic plasmacytoma causing superior vena cava syndrome is described. Review of the literature on intrathoracic plasmacytomas and superior vena cava syndrome revealed that no similar cases have been described to date. The initial presentation, management, and response to treatment are described.

Humans↗
PubMed1991

Fetal habituation to vibroacoustic stimulation in uncomplicated term pregnancies.

The use of transabdominal vibroacoustic stimulation has been shown to improve the efficiency of antepartum fetal surveillance. The ability of the fetus to habituate to such a stimulus has also been suggested as a means of assessing the function of the central nervous system. The purpose of this blinded prospective investigation was to evaluate fetal habituation in a group of low-risk pregnancies anticipated to deliver within 1 week. One hundred sixteen uncomplicated pregnancies underwent repetitive vibroacoustic stimulation using a Corometrics Model 146 fetal acoustic stimulator. Fetal habituation was defined as a sustained elevation of the heart rate baseline for more than 15 minutes or a failure to produce an adequate acceleration of the fetal heart rate after an initial response. Habituation was present in 106 (91.4%) cases, whereas 10 (8.6%) failed to habituate to the stimulus. All infants failing to habituate in utero ultimately did well after delivery. Their birthweights, Apgar scores, umbilical artery blood gas determinations, and courses in the newborn nursery were similar to those of infants who responded to in utero sound stimulation. However, cesarean delivery for fetal distress and gross placental abnormalities (such as infarction and abruption) occurred more commonly in those fetuses failing to habituate. Additional investigations of fetal habituation to a vibroacoustic stimulus may be helpful in the intrapartum risk assessment of uncomplicated term pregnancies.

Acoustic Stimulation↗
PubMed1991

Distribution of circulating insulin-like growth factor-I (IGF-I) into tissues.

Intravenous infusions of amino terminal methionyl insulin-like growth factor-I (N-Met IGF-I; 8 micrograms/kg body wt x h; 24 h) were performed in lactating sheep and samples of mammary lymph, cerebrospinal fluid, and postinfusion tissues collected to examine distribution of the recombinant analog outside the vascular space. Samples were analyzed using an antibody specific for N-Met IGF-I and a second IGF-I antibody which recognized endogenous IGF-I and the N-Met variant equally. N-Met IGF-I infusion increased total plasma IGF-I immunoreactivity (ir) from 150 to 290 ng/ml. N-Met IGF-I was distributed into mammary lymph, increasing total lymph IGF-I from 60 to 130 ng/ml. By contrast iv N-Met IGF-I had no significant effect on IGF-I ir in cerebrospinal fluid. N-Met IGF-I was distributed on plasma and lymph IGF binding protein as endogenous IGF-I with binding to the 150,000 mol wt species predominant in plasma and the 40,000-50,000 mol wt pool of proteins predominant in lymph. N-Met IGF-I was also distributed into extra-vascular tissue accounting for 36% (kidney) to 62% (spleen) of total tissue IGF-I ir at the end of the infusion. The IGF-I antibodies were also used for the autoradiographical localization of IGF-I in postinfusion muscle and mammary tissue. No significant difference in antibody binding was observed to muscle fiber and mammary epithelium, but in marked contrast binding of the N-Met specific antibody to connective tissue of muscle and mammary was significantly less than the total IGF-I antibody (P less than 0.001; N-Met/total, 0.12). The data suggest that the contribution of blood-derived N-Met to total IGF-I varies markedly between tissues and provides evidence that blood-borne IGF-I may fill specific endocrine functions in selected tissues.

Animals↗
PubMed1991

Physiological responses to somatotropin in the ruminant.

The physiological responses to somatotropin supplementation of ruminants are reviewed with particular reference to the dairy industry. Exogenous somatotropin improves lactational performance by altering the partitioning of absorbed nutrients. Lipid accretion is reduced, lipid mobilization is increased, and glucose uptake by peripheral tissues and whole body oxidation of glucose and amino acids are reduced. The net effect of these changes is that the limited supply of glucose and amino acids is spared for synthesis of milk components, and lipid reserves are preferentially used as an energy source. The increase of cardiac output and mammary blood flow are prominent physiological responses to somatotropin by the dairy cow. These responses permit a greater share of nutrient input to the mammary gland. The lack of evidence for functional membrane receptors for somatotropin in mammary tissue demands the involvement of endocrine mediators to explain the increase of mammary gland metabolism with somatotropin treatment. An increase of high affinity somatotropic receptors in the liver and increased plasma insulin-like growth factor-I and -II appear to be one of the most prominent endocrine responses to somatotropin treatment. However, the relative role of the insulin-like growth factors and the multiple forms of their plasma-binding proteins and receptors remain to be resolved.

Amino Acids↗
PubMed1990

Effects of growth hormone injections on ovulation rate in ewes.

Coopworth ewes were either treated with 5 mg recombinant-derived bovine growth hormone per day for each day of the oestrous cycle or were untreated. Ovulation rates at the pre-treatment, post-treatment and a subsequent oestrus were determined by endoscopy. These were 1.34, 1.51, 1.38 for the treated ewes and 1.32, 1.43, 1.39 for the control ewes. The ovulation rate post-treatment was significantly higher than for the other two cycles in the treated ewes but it was not significantly different from the post-treatment value of the control ewes. Plasma concentrations of insulin-like growth factor-I (IGF-I) were elevated during treatment (90-130 nmol L-1) compared with concentrations of 25-50 nmol L-1 in the control ewes. No relationship was found between plasma IGF-I concentration and ovulation rate. Injection of ewes grazing ryegrass/white clover pasture with bovine growth hormone did not result in increased ovulation rate.

Animals↗
PubMed1990

Plasma clearance of radiolabelled IGF-1 in the late gestation ovine fetus.

We investigated the distribution of radiolabelled IGF-1 in the late gestation ovine fetus by exclusion gel chromatography following intravenous injection of 125I rh (recombinant human) met-IGF-1 into the chronically instrumented fetal lamb (120-130 days, n = 7). One minute after injection of 125I rh met-IGF-1 into the fetal femoral vein, 20.9 +/- 3.1% of the counts circulated in the 150K binding protein region, 55.0 +/- 3.7% in the 50K binding protein region and 18.7 +/- 0.6% in the free or 7K region. The chromatographic profiles obtained in the fetus were in general similar to those previously seen in the adult sheep. After an initial equilibration phase the half life of IGF-1 associated with the 150K binding fractions were 412.1 +/- 103.6 min. Two phases of clearance were observed for IGF-1 in association with the 50K binding fractions, an initial phase with a half life of 30.6 +/- 4.5 min followed by a second phase with a half life of 202.3 +/- 10.3 min. The 7K or 'free' form of IGF-1 had an initial half life of 12.6 +/- 5.1 min. Chromatography of samples of fetal tracheal fluid, fetal urine, amniotic fluid, maternal uterine venous plasma and maternal systemic plasma showed no movement of intact IGF-1 out of the fetal circulation into the fetal fluids or into the maternal circulation. However, when simultaneous samples were obtained from the fetal femoral artery and umbilical vein, higher radioactivity was consistently observed in the fetal femoral artery raising the possibility of placental uptake of IGF-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Binding protein, radioreceptor and biological activities of recombinant methionyl insulin-like growth factor-I variants.

Reversed-phase chromatography (RPC) was used to resolve two variants of recombinant amino terminal methionyl residue (N-Met) insulin-like growth factor-I (IGF-I) with the same amino acid constitution but different disulphide linkages. Following radioiodination, equilibration with plasma and size exclusion chromatography at neutral pH the major form on RPC (approximate abundance 60%) demonstrated greater than 80% binding to 150 kDa and 40-50 kDa IGF binding proteins. This peptide has the RPC elution characteristics and disulphide assignment (Cys6-Cys48, Cys18-Cys61, Cys47-Cys52) of authentic with mismatched disulphides (Cys6-Cys47, Cys18-Cys61, Cys48-Cys52; N-Met IGF-I peak 1 peptide) demonstrated less than 15% binding under similar conditions. Potency of the peptides was investigated in competitive IGF-I plasma binding protein and L6 myoblast radioreceptor assays. The peak 2 peptide proved equipotent to purified ovine plasma IGF-I in each system but by contrast the peak 1 peptide was 40-fold and 200-fold less potent in the binding protein and radioreceptor assays respectively. Biological potency was examined in a non-competitive assay based on incorporation of [3H]leucine into confluent cultures of L6 myoblasts. In this system the N-Met IGF-I peak 1 peptide proved 15-fold less potent than the peak 2 peptide with correct disulphide linkages. Refolding variants may prove useful in establishing structure/function relationships for IGF-I.

Amino Acid Sequence↗