Protein requirements of sheep in late pregnancy: partitioning of nitrogen between gravid uterus and maternal tissues

The objective of this study was to quantify effects of maternal protein nutrition on N accretion or loss in conceptus and maternal tissues of ewes during late pregnancy. Ewes, pregnant with twins, were fed low (LP, 79 g CP/kg DM), medium (MP, 116 g CP/kg DM), or high (HP, 157 g CP/kg DM) protein diets, each with an estimated ME concentration of 2.7 Mcal/kg DM, between d 111 and 140 of pregnancy; all ewes had been fed the same diet (2.7 Mcal ME, 120 g CP/kg DM) for the previous 30 d (d 80 to 110). Dry matter intakes were varied (LP = 1.0, MP = 1.2, and HP = 1.4 kg/d) according to predicted energy costs of protein deposition for each diet. Nitrogen accretion was estimated by comparative slaughter (d 140 minus d 110) and by collection of excreta between d 120 and 130. Fresh weights of maternal and gravid uterine tissues were measured at slaughter, before proximate analysis of these components. Whole-body N retention was directly and linearly related to N intake, but efficiency of deposition of apparently absorbed N decreased linearly with increasing N intake (LP, .79; MP, .70; HP, .62). Nitrogen accretion in the gravid uterus, maternal viscera, and mammary gland was significantly less in LP than in MP or HP ewes. Nitrogen balance in maternal carcass tissues was linearly related to N intake, ranging from a negative value in LP ewes to a positive value in HP ewes (LP, -63 g; MP -39 g; HP, 55 g). These data provide the basis for estimating N requirements for protein accretion in the conceptus and in maternal tissues during late pregnancy. They also highlight the capacity of maternal carcass tissues to mobilize or deposit amino acids in response to variations in dietary protein supply.

Effect of chronic infusion of placental lactogen on ovine fetal growth in late gestation

To test the hypothesis that placental lactogen (PL) is a humoral regulator of fetal growth, six singleton sheep fetuses received a continuous intravenous fusion of 1.2 mg/d of purified ovine PL (oPL) for 14 d, beginning on Day 122 of gestation. The plasma concentration of oPL was approximately four-fold higher in infused fetuses than in six control fetuses that received a continuous infusion of saline. The circulating insulin-like growth factor 1 (IGF-I) concentration was also significantly elevated in PL-infused fetuses (43.1 +/- 1.7 vs. 31.9 +/- 4.1 ng/ml; P < 0.05). Animals were slaughtered on Day 136, and the placenta and all major fetal tissues were dissected, weighed, and subsampled for chemical analysis. Fetal weight and crown-rump length were not significantly affected by treatment; however, the aggregate weight of the brain, liver, lungs, and heart tended to be larger (85.3 +/- 2.1 vs. 79.9 +/- 1.5 g/kg fetus; mean +/- SE, P = 0.07) and the thyroid gland was smaller (0.18 +/- 0.1 vs. 0.26 +/- 0.02 g/kg fetus; P < 0.05) in the PL-infused fetuses. The livers of the PL-infused fetuses had also accumulated additional glycogen (13.1 +/- 1.7 vs. 8.4 +/- 0.7 g; P < 0.05). In late gestation, PL within the fetal compartment increases fetal plasma IGF-I concentration and hepatic glycogen deposition and may affect the growth of several vital organs.

Both murine SAA1 and SAA2 yield AA amyloid in alveolar hydatid cyst-infected mice

Amyloid susceptible C57BL/6 and partially amyloid resistant A/J mice, infected intraperitoneally with 250 alveolar hydatid cyst (AHC), the larval stage of a cestode parasite Echinococcus multilocularis, develop multiple organ amyloid deposits at approximately 1 and 4 weeks post infection (p.i.), respectively. Pooled spleens and livers from each mouse strain, at 8 and 10 weeks p.i., were used for the purification of protein AA utilizing a HiLoad Superdex 200 column equilibrated with 5 M guanidine-HCl. Protein AA from each mouse strain was separated on 16% Tris-tricine SDS-PAGE gels and immunoblotted with monospecific rabbit anti-mouse AA IgG; five and six immunoreactive AA subspecies were detected in the C57BL/6 and A/J materials, respectively. N-Terminal amino acid sequence analysis was performed on the bulk column-purified protein AA as well as on the electroblotted AA subspecies from each mouse strain. The results show a mixture of serum amyloid A1 (SAA1) and (SAA2)-derived AA protein from each mouse strain; SAA1-derived AA, although alluded to, has never been demonstrated as tissue deposits in mice. These findings suggest that the intense and persistent inflammatory processes in AHC-infected mice may have induced conversion of weakly amyloidogenic SAA1 to AA. This conversion could be detected by amino acid sequencing of electrophoretically separated AA subspecies.

Growth and metabolism of the ovine placenta during mid-gestation

The timing and metabolic basis for the rapid increase then cessation of placental growth in sheep and the accompanying changes in tissue cellularity were defined in the present study. Placental growth proceeded rapidly from day 40 of gestation to an apex at day 75-80 with no change is tissue dry matter content observed thereafter to day 100. These macroscopic growth patterns are similar to those observed previously, but present results define an earlier apex in placental mass. Absolute growth rate of the placenta reached a maximum near day 55, as derived from the Gompertz equation, concomitant with a period of maximum hyperplastic growth between days 50 and 60. A rapid increase in DNA synthesis and tissue mass per nuclei number from day 40-50 was followed by proliferative growth to day 70. Net cellular proliferation apparently ceased by day 80 as indicated by the apex in DNA content and the beginning of a static, low rate of DNA synthesis that continued to day 100. Patterns of change in the fractional rates of protein synthesis (Ks) and accretion (Kg) were similar suggesting that changes in Ks explain much of the change in Kg. This study, through its identification of key phases in the cellular growth of the ovine placenta, has laid the foundation for future research on mechanisms of placental growth regulation.

Growth and accretion of energy and protein in the gravid uterus during late pregnancy in Holstein cows

Multiparous Holstein cows (n = 18) were bred artificially to the same bull and then slaughtered at times ranging from 190 to 270 d postconception to assess accretion of energy, protein, fat, and ash by the conceptus. Wet weights, dry weights, and concentrations of energy, CP, crude fat, and ash were obtained for the following: fetus, combined amniotic and allantoic fluids, fetal membranes, cotyledons, caruncles, and uterine tissues. Rates of accumulation of these components in the gravid uterus (sum of all uterine contents) and fetus were described by linear or quadratic equations. Estimated rates of accretion of energy in the gravid uterus (i.e., conceptus) increased from 567 kcal/d at 190 d of gestation to 821 kcal/d at 270 d of gestation; corresponding rates of accretion of CP were 62 and 117 g/d. These daily rates represent net energy and protein requirements for conceptus growth during late pregnancy in mature Holstein cows. Conversion of predicted net energy to metabolizable energy requirements for conceptus growth, using the accepted efficiency factor of .14, yielded estimates that were consistent with current NRC recommendations. Factorial estimation of absorbed protein requirements is hampered by lack of precise information on the efficiency with which absorbed AA are deposited in conceptus tissues.

Regulation of organic nutrient metabolism during transition from late pregnancy to early lactation

Conceptus energy and nitrogen demands in late pregnancy are mostly met by placental uptake of maternal glucose and amino acids. The resulting 30 to 50% increase in maternal requirements for these nutrients is met partly by increased voluntary intake and partly by an array of maternal metabolic adaptations. The latter include increased hepatic gluconeogenesis from endogenous substrates, decreased peripheral tissue glucose utilization, increased fatty acid mobilization from adipose tissue, and, possibly, increased amino acid mobilization from muscle. Within 4 d of parturition, mammary demands for glucose, amino acids, and fatty acids are several-fold those of the pregnant uterus before term. Even unusual postparturient increases in voluntary intake cannot satisfy this increased nutrient demand. Therefore, rates of hepatic gluconeogenesis and adipose fat mobilization are greatly accelerated. Concomitant changes in amino acid metabolism include increased hepatic protein synthesis and, possibly, decreased amino acid catabolism, and increased peripheral mobilization of amino acids. Insulin resistance in adipose tissue and muscle, developed during late pregnancy, continues postpartum; adipose lipolytic responsiveness and sensitivity to adrenergic agents are increased postpartum beyond their levels during late pregnancy. Before parturition, these homeorhetic adjustments may be coordinated with lactogenesis by increased secretion of estradiol and prolactin. Their amplification and reinforcement at and soon after parturition may be regulated mostly by somatotropin.

Effects of bovine somatotropin and insulin on whole-body and hindlimb glucose metabolism in growing steers

Six Holstein steers (245 kg initial BW) were surgically prepared with chronic catheters to allow measurement of blood flow and nutrient flux across the hindlimb. Steers were used in a single-reversal design with 16-d treatment periods of daily i.m. injection of either excipient (control) or recombinantly derived bovine somatotropin (120 micrograms/kg BW). On d 15 of each period, whole-body and hindlimb glucose metabolism were studied during a primed continuous infusion of [6(-3)H]glucose, under both basal conditions and during a hyperinsulinemic/euglycemic clamp. Somatotropin increased (P < .01) basal blood glucose and serum insulin by 7 and 150% respectively, with no change in glucose irreversible loss rate (ILR). There was no effect of somatotropin on hindlimb blood flow or oxygen consumption. In contrast, hindlimb lactate uptake (P < .02) and the ratio of glucose to oxygen uptake (P < .08) were reduced by somatotropin. Insulin infusion stimulated (P < .01) glucose ILR and inhibited (P < .02) endogenous glucose production to a lesser extent during somatotropin treatment. Basal plasma nonesterified fatty acid concentrations were increased (P < .01) during somatotropin treatment and decreased (P < .02) during insulin infusion. Insulin infusion increased hindlimb blood flow and glucose uptake to similar extents during both treatment periods. These data demonstrate that somatotropin treatment of growing steers decreases response of tissues to insulin (sensitivity in muscle, sensitivity, and responsiveness in liver and adipose tissue), thereby increasing glucose availability to other tissues.

Identification of a chemotaxis operon with two cheY genes in Rhodobacter sphaeroides

A large chemotaxis operon was identified in Rhodobacter sphaeroides WS8-N using a probe based on the 3' terminal portion of the Rhizobium meliloti cheA gene. Two genes homologous to the enteric cheY were identified in an operon also containing cheA, cheW, and cheR homologues. The deduced protein sequences of che gene products were aligned with those from Escherichia coli and shown to be highly conserved. A mutant with an interrupted copy of cheA showed normal patterns of swimming, unlike the equivalent mutants in E. coli which are smooth swimming. Tethered cheA mutant cells showed normal responses to changes in organic acids, but increased, inverted responses to sugars. The unusual behaviour of the cheA mutant and the identification of two homologues of cheY suggests that R. sphaeroides has at least two pathways controlling motor activity. To identify functional similarity between the newly identified R. sphaeroides Che pathway and the methyl-accepting chemotaxis protein (MCP)-dependent pathway in enteric bacteria, the R. sphaeroides cheW gene was expressed in a cheW mutant strain of E. coli and found to complement, causing a partial return to a swarming phenotype. In addition, expression of the R. sphaeroides gene in wild-type E. coli resulted in the same increased tumbling and reduced swarming as seen when the native gene is overexpressed in E. coli. The identification of che homologues in R. sphaeroides and complementation by cheW suggests the presence of MCPs in an organism previously considered to use only MCP-independent sensing. The MCP-dependent pathway, appears conserved.(ABSTRACT TRUNCATED AT 250 WORDS)

Proteolysis of glucagon within hepatic endosomes by membrane-associated cathepsins B and D

The acidic glucagon-degrading activity of hepatic endosomes has been attributed to membrane-bound forms of cathepsins B and D. Endosomal lysates processed full-length nonradiolabeled glucagon to 32 different peptides that were identified by amino acid analysis and full-length sequencing. These indicated C-terminal carboxypeptidase, endopeptidase as well as N-terminal tripeptidyl-aminopeptidase activities in endosomes. Glucagon proteolysis was inhibited 95% by E-64 and pepstatin A, inhibitors of cathepsins B and D, respectively. This was confirmed by the pH 6-dependent chemical cross-linking of [125I]iodoglucagon to a polypeptide of 30 kDa, which was immunodepleted by polyclonal anti-cathepsin B antibody, and the removal of greater than 80% of glucagon-degrading activity by polyclonal antibodies to cathepsins B and D. By similar criteria, insulin-degrading enzyme was ruled out as a candidate enzyme for endosomal proteolysis of glucagon. Lysosomal contamination was unlikely since all forms of cathepsin B in endosomes, i.e. the major 45-kDa inactive precursor as well as the lesser amounts of the 32- and 28-kDa active forms, were tightly bound to endosomal membranes. Furthermore the mature 29-kDa single-chain and 22-kDa heavy-chain forms of cathepsin L were undetectable in endosomes, although high levels of the 37-kDa proform were observed. Membrane association of the cathepsins B and D was not to the mannose 6-phosphate receptor since association was unaffected by mannose 6-phosphate and/or EDTA, thereby indicating a distinct endosomal receptor. Hence, a pool of active cathepsins B and D as well as a poorly defined tripeptidyl aminopeptidase is maintained in endosomes by selective membrane retention. These hydrolases degrade glucagon internalized into liver parenchyma early in endocytosis.

Effects of exogenous somatotropin on whole-body glycemic response to insulin in young preruminant and ruminant lambs

The purpose of this study was to determine the effects of exogenous recombinant bovine somatotropin (bST) treatment on whole-body glycemic responsiveness and sensitivity to exogenous insulin in preruminant and ruminant lambs. Twelve milk-fed (MF) and 12 ruminating (RUM) wether lambs weighing 20 +/- 0.6 kg were assigned to one of four treatment groups: MF control, MF plus bST, RUM control, and RUM plus bST. Lambs received a daily subcutaneous injection of 160 micrograms of sometribove (recombinant methionyl bST) bST/kg live weight or the equivalent volume of sterile water (control) for 10 d. The MF lambs had higher plasma insulin and nonessential fatty acids and lower acetate concentrations than RUM lambs (all P < 0.05). Plasma insulin-like growth factor concentrations were similar in both. The administration of bST raised plasma insulin-like growth factor-1 (P < 0.001) and insulin (P < 0.05) in MF and RUM lambs, but with greater effect in MF lambs (P < 0.01 and P < 0.1, respectively). Six successive dose-incremented insulin challenges (50, 100, 200, 300, 500, and 700 mU/kg body weight) were performed two per day on Days 8, 9, and 10 of treatment. Dose-response curves for absolute decline in glucose concentration from preinjection baseline to nadir were used to characterize whole-body responsiveness and sensitivity (ED50) to insulin. Somatotropin treatment increased insulin ED50 values 64 and 70% (P < 0.07) in RUM and MF lambs, respectively, suggesting that sensitivity to insulin was reduced. Insulin ED50 values were 40% higher in MF than in RUM lambs (P < 0.05). Insulin clearance rates increased with each dose increment to 300 mU/kg body weight (P = 0.001) and were 50% lower in bST-treated MF lambs than in all other treatment groups (P < 0.05). Results suggest that somatotropin modulates the insulin control of glucose homeostasis similarly in preruminant and ruminant lambs by decreasing sensitivity but not maximum responsiveness.

Nutrient uptake by the hindlimb of growing pigs treated with porcine somatotropin and insulin

The shift in nutrient partitioning induced by porcine somatotropin (pST) is accompanied by a decrease in insulin sensitivity for whole-body glucose uptake. The relative contribution of metabolic changes in the hindlimb was investigated in eight pigs (55 kg) that had received recombinant pST (120 micrograms/kg) or excipient (control) for 7 d. Uptake of metabolites by the hindlimb was measured under basal conditions and during hyperinsulinemic-euglycemic clamps at low [14 ng/(kg.min)] and high [360 ng/(kg.min)] insulin infusion rates. Dextrose infusion rate required to maintain euglycemia was used as an index of whole-body glucose uptake in response to exogenous insulin. Effects of pST on hindlimb and whole-body glucose uptake were evident only at physiological levels of insulin (basal and low insulin infusion rate). During the low rate of insulin infusion, dextrose infusion rate was 79% lower for pST-treated pigs and glucose uptake by the hindlimb was 59% lower compared with control pigs. The decrease in glucose uptake by the hindlimb was entirely accounted for by the estimated reduction in glucose utilization by adipose tissue of the hindlimb. Glucose:oxygen quotients were reduced during basal (57%) and low insulin infusion (63%) with pST treatment, indicating a change in the pattern of substrate utilization. This is consistent with the concept that pST directs nutrients away from adipose and towards muscle growth by altering the response of tissues to homeostatic signals such as insulin.

Identification of a cell-type-specific transcriptional repressor in the promoter region of the mouse hepatocyte growth factor gene

Hepatocyte growth factor (HGF), a cytokine with multiple functions, exhibits cell-type-specific as well as cytokine- and steroid hormone-regulated expression. The HGF gene is known to be expressed predominately in mesenchymal but not in epithelial cells. In this study, we report the identification of a cell-type-specific transcriptional repressor in the promoter region of the mouse HGF gene, which is evidently responsible for the suppression of HGF expression in epithelial cells. Gel mobility shift assays and DNase I footprinting studies revealed that a 27-bp element (-16 to +11) around the transcription initiation site is responsible for the binding of a nuclear protein which is present in epithelial but not in mesenchymally derived cells. Further analysis of the binding activity of the DNA region with nuclear protein revealed that an approximately 19-bp sequence containing a unique palindromic structure (5'-AACCGACCGGTT-3') overlapped by a CAP box is essential for binding. Substitution of a single base (the contact site) within this region by site-directed mutagenesis resulted in total abrogation of the binding of the nuclear protein and a concomitant increase in the transcriptional activity of various lengths of HGF-chloramphenicol acetyltransferase fused genes when transfected into the epithelial cell line RL95-2 but not the mesenchymal cell line NIH 3T3. Southwestern (DNA-protein) analyses revealed that the nuclear protein which binds to this repressor element is a single polypeptide of approximately 70 kDa. Analysis of the nuclear extract prepared from regenerating mouse liver at various times after two-thirds partial hepatectomy by gel mobility shift assay revealed a substantial reduction (more than 75% within 3 h) in the binding of the repressor to its cognate binding site. Our results suggest that a cis-acting transcriptional repressor in the promoter region of the mouse HGF gene is involved in cell-type-specific regulation through binding to its cognate trans-acting protein which exists in epithelial cells but is absent in fibroblast cells.

The mouse hepatocyte growth factor-encoding gene: structural organization and evolutionary conservation

A mouse genomic phage library was screened by using a cDNA probe coding for mouse hepatocyte growth factor (HGF). Five overlapping genomic clones which contained the entire mouse HGF gene were isolated and characterized by restriction mapping, Southern hybridization and DNA sequencing. HGF spans about 65 kb and consists of 18 exons separated by 17 introns, similar to its human counterpart. The nucleotide (nt) sequences of the introns at the exon-intron junctions are GT-AG, analogous to those found in other eukaryotic genes. The exon-intron gene organization of HGF is highly homologous to that of several other genes encoding kringle-containing proteins, especially HGF-like protein and plasminogen. This result suggests that HGF probably evolved through gene duplication and/or exon shuffling events from an ancestral gene. Southern hybridization of genomic DNA from different species revealed that a high degree of homology exists among a variety of vertebrates, including chicken, when a mouse HGF cDNA was used as a probe. This evolutionary conservation of HGF strongly suggests that the protein may play an important role in normal cell physiology. Our current results on mouse HGF structure provide basic and detailed information to carry out further manipulation, such as gene targeting.

Sulfur and selenium accretion in the gravid uterus during late gestation in Holstein cows

Multiparous Holstein cows (n = 18) were bred artificially to the same Holstein bull and then slaughtered at times from 190 to 270 d postmating to assess S and Se accretion in the fetus and nonfetal components of the conceptus. Concentrations of S and Se were obtained for the fetus, fetal fluids, fetal membranes, cotyledons, caruncles, and uterine tissues. Also, Se concentrations were determined in liver samples from 15 of the fetus-dam pairs. The Se concentration in fetal liver was greater than the corresponding Se concentration in maternal liver for all fetus-dam pairs. Accumulation rates of S and Se in components of the conceptus were determined from linear or exponential functions relating S and Se contents to day postmating. When estimated from linear regression coefficients, accretion rates of S for the fetus and entire conceptus were 1.26 and 1.51 g/d, respectively; corresponding accretion rates for Se in the fetus and entire conceptus were 41 and 55 micrograms/d, respectively. These rates provided estimates of net amounts of S and Se utilized for conceptus growth during late pregnancy. Estimates of total needs for S and Se during late pregnancy in dairy cows may be obtained by adding requirements for conceptus development to allowances for maternal maintenance. Current dietary allowances for S and Se appear to be sufficient to meet the requirements for S and Se for growth of the conceptus during the dry period.

Nutrient utilization and protein turnover in the hindlimb of cattle treated with bovine somatotropin

Our objectives were to assess the effects of chronic administration of recombinant bovine somatotropin (bST) on nutrient utilization and protein turnover in the hindlimb of growing Holstein steers. External iliac vessels were catheterized to allow for hindlimb measurements of arteriovenous differences and blood flow. Animals were used in a single-reversal design with 16-d treatment periods of daily intramuscular injection of either excipient or 120 micrograms/kg body wt of bST. On d 11 and 13 of each period, a primed-continuous infusion of L-[sidechain-2,3-3H]tyrosine was initiated, followed by a 4-h sampling period to assess hindlimb nutrient utilization and protein kinetics. Somatotropin did not alter blood flow or the consumption of acetate and oxygen across the hindlimb. In contrast, glucose uptake was reduced by 22% despite increases in arterial concentrations of glucose and insulin of 10 and 114%, respectively. Treatment with bST increased hindlimb protein accretion (estimated from net uptake of tyrosine) and whole-body N balance, each by approximately 40%. A modest increase (10%) in the absolute rate of protein synthesis seemed to account for the improved N retention in the hindlimb with no change in the rate of protein degradation. Thus, bST reduced the responses of the hindlimb to insulin, and a small alteration in protein synthesis was sufficient to explain substantial improvement in protein deposition.

Mineral accretion in the fetus and adnexa during late gestation in Holstein cows

Multiparous Holstein cows (n = 18) were bred artificially to the same Holstein bull and then slaughtered at times ranging from 190 to 270 postmating to assess mineral accretion by the conceptus. Fresh weight, DM, and concentrations of Ca, P, Mg, K, Na, Fe, Zn, Cu, and Mn were obtained for the fetus, fetal fluids, fetal membranes, cotyledons, caruncles, and uterine tissues. Rates of accumulation of individual minerals in different components of the conceptus during late gestation were described by either linear or exponential relationships. Estimated Ca accretion rate in the conceptus increased from 2.3 g/d at 190 d of gestation to 10.3 g/d at 280 d of pregnancy; corresponding P accretions were 1.9 and 5.4 g/d. Rates of accretion of Mg, K, and Na in the conceptus in late pregnancy were about .2, 1.0, and 1.4 g/d, respectively, and Fe, Zn, Cu, and Mn accumulated in the conceptus at rates of 18.0, 11.7, 1.6, and .3 mg/d, respectively. These daily rates represent net mineral requirements for conceptus growth during late pregnancy in mature Holstein cows. In general, our values are consistent with current dietary recommendations for minerals during the dry period.

Pregnancy and undernutrition alter glucose metabolic responses to insulin in sheep

Nonpregnant and late-pregnant ditocous ewes were fed either to maintain zero energy balance in maternal tissues (fed) or at 50% of this level (underfed) for several weeks. Whole-body kinetics of glucose metabolism were measured under basal conditions, and the hyperinsulinemic, euglycemic clamp technique was used to define insulin-dose response profiles for several indices of whole-body glucose utilization, and for endogenous glucose production. Pregnancy increased and undernutrition decreased basal glucose entry rate (GER), glucose metabolic clearance rate (GMCR) and insulin-independent glucose utilization (IIGU). The consistent increment in IIGU of pregnant over nonpregnant ewes was comparable to previous estimates of uterine glucose uptake. Pregnancy resulted in higher plasma concentration for 50% maximal responses (ED50) to insulin of GER, GMCR, steady-state glucose infusion rate (SSGIR) to maintain euglycemia and insulin-dependent glucose utilization (IDGU). These changes were especially large in underfed pregnant ewes. Effects on the maximal response to insulin of these variables (Rmax) were relatively small (GMCR, IDGU) or nonsignificant (GER, SSGIR). Maximum insulin-induced suppression of endogenous glucose production was significantly lower due to undernutrition; neither Rmax nor ED50 for this response was affected by pregnancy. Insulin resistance in late-pregnant ewes is primarily due to decreased insulin sensitivity in (presumably) peripheral tissues, implying an alteration of receptor function or of early postreceptor signal transduction.

Evaluation of the arteriovenous difference technique to simultaneously estimate protein synthesis and degradation in the hindlimb of fed and chronically underfed steers

Our objectives were to validate a technique to measure protein turnover based on net fluxes of tyrosine radioactivity and mass across the hindlimb, and to describe the impact of nutrition on hindlimb protein kinetics and nutrient utilization in growing Holstein steers. External iliac vessels were catheterized to allow for measurements of hindlimb arteriovenous (AV) differences and blood flow. Animals were used in a single reversal design with 16-d periods. Treatments were either 60% (0.6M) or 220% (2.2M) of the energy required for maintenance. On d 12 and 14 of each period, a primed-continuous infusion of L-[side chain-2,3-3H]tyrosine was initiated, followed by a 4-h sampling period to assess hindlimb nutrient utilization and protein kinetics. Well-fed steers exhibited rates of hindlimb utilization for non-nitrogenous energy substrates and amino acids that were consistent with values previously reported for well-fed ruminants. Underfeeding decreased hindlimb blood flow (62%), oxygen consumption (51%) and utilization of respiratory fuels (64-73%). Protein synthesis was also reduced (49%), leading to net nitrogen loss from the hindlimb. The estimated energy cost of protein synthesis accounted for 13% of hindlimb oxygen consumption across intake levels. Hindlimb protein balance was consistent with whole-body balance, adding credence to derived rates of degradation. Overall, data support the validity of the AV difference technique to estimate components of hindlimb protein turnover.

Chronic catheterization of external iliac vessels in growing cattle

Bovine preparations that allow for in vivo measurement of metabolic fluxes across the hindlimb often suffer from limited durability, usually because of failure of the venous catheter. A catheterization procedure that virtually eliminates this occurrence is presented. A silicone rubber catheter is implanted permanently in the femoral vein. It accommodates the repeated insertion and removal at each sampling session of a temporary sampling catheter. A simple and reliable method ensures the positioning of this catheter in the external iliac vein of a conscious, normally standing animal. The application of this approach allowed the study of hindlimb metabolism of cattle for up to 4 mo without a single planned sampling session postponed or missed. This preparation is particularly well suited for studies that require repeated measurements of hindlimb metabolism on the same animals over a period of many months.

Analysis and pharmacokinetics of cimaterol in growing Holstein steers1

Pharmacokinetic parameters for the beta 2-adrenergic agonist, cimaterol (CIM), were determined in growing Holstein steers. Compartmental analysis was used after measurement of CIM in body fluids by affinity chromatography and HPLC using UV detection. Recoveries from spiked plasma and urine standards were 70 +/- 1.2% and 68 +/- 1.1%, respectively. The minimum detection level in plasma was 1 ng/mL and the average CV was 5.1% for concentrations that ranged from 1 to 30 ng/mL. Four steers (276 +/- 24 kg) received 15 mg of CIM by bolus intravenous injection. Plasma CIM levels declined in a biphasic manner with half-lives of 2.5 min for the distribution phase and 54 min for the elimination phase. A two-compartment open model was used to describe the disappearance of CIM and the following pharmacokinetic parameters were obtained: central compartment volume (Vc) = .76 L/kg, apparent volume of distribution (Vd) = 4.1 L/kg, and transfer rate constants from the central to peripheral compartment (k12) = .177/min, from the peripheral to central compartment (k21) = .054/min and elimination from the central compartment (kel) = .074/min. After 8 h, total urinary CIM accounted for only 18.3% of the administered dose. Results suggest that circulating concentrations of CIM in growing steers are influenced by its accumulation in an unidentified peripheral pool and its conversion into unknown metabolite(s) before elimination.

Casein kinase II phosphorylation of signal sequence receptor alpha and the associated membrane chaperone calnexin

Signal sequence receptor alpha (SSR alpha) and calnexin are major calcium-binding proteins of the endoplasmic reticulum (ER) which are implicated in chaperone functions. They were identified as major membrane substrates after in vitro phosphorylation of ER membranes with [gamma-32P]GTP (Wada, I., Rindress, D., Cameron, P. H., Ou, W. J., Doherty, J.-J., II, Louvard, D., Bell, A. W., Dignard, D., Thomas, D. Y., and Bergeron, J. J. M. (1991) J. Biol. Chem. 266, 19599-19610). Using purified SSR alpha and associated calnexin as substrates, we have attempted to identify the kinase(s) responsible for their phosphorylation. A salt extract from canine pancreatic ER membranes and cytosol possessed SSR alpha kinase activity which showed identical chromatographic behavior through phosphocellulose, DEAE-Sepharose, and hydroxylapatite purification protocols. Final purification was effected from the cytosol with three polypeptides of 38, 36, and 28 kDa detected by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. On the basis of primary sequence analysis of the three subunits of the purified kinase and the reconstitution of phosphorylation of SSR alpha and associated calnexin in heat-inactivated ER membranes by the addition of the purified kinase we conclude that the ER-associated kinase responsible for the GTP phosphorylation of SSR alpha and associated calnexin is casein kinase II.

Ontogeny of fetal hepatic and placental growth and metabolism in sheep

Ontogeny of fetal hepatic and placental growth and in vitro oxygen consumption (VO2) was investigated in fetal lambs at 75, 100, and 136 days postconception. Fetal hepatic relative weight and placental absolute and relative weights declined during this period. Oxygen consumption per gram dry weight of fetal liver and maternal placenta declined between mid and late gestation while fetal placental VO2 was unchanged. Estimated VO2 of the whole placenta did not change while the estimated total hepatic VO2 increased more than threefold between 75 and 136 days. Total hepatic VO2 was highly correlated with total placental VO2 at 136 days (r = 0.84). The results suggest that the placenta reaches its maximum growth and metabolic capacity before 100 days and possibly at or before midgestation. Changes in hepatic weight-specific total VO2, in addition to the declining relative size of the fetal liver, must contribute to the progressive decline in metabolic rate of the whole fetus during the second half of pregnancy. Correlations between placental and fetal liver weights and metabolic rates suggest the possibility of placental regulation of fetal hepatic growth and metabolism.

Kinetics of placental lactogen in mid- and late-gestation ovine fetuses

Placental lactogen (PL) is found in fetal plasma throughout gestation, and PL receptors occur on many types of fetal cells. In this study, the entry rate of PL into the fetal circulation was estimated by injection of 125I-labelled ovine PL into two mid- and four late-gestation fetuses. At both ages, PL appears to be distributed into two body pools. One pool has a rapid half-life (approximately 9 min) and a volume of distribution approximately 8% of body weight, while the second pool has a longer half-life (approximately 45 min) and a distribution volume only 4% of body weight. The first pool is presumably blood plasma, but the physiological identity of the second pool is unknown. The effective half-life of PL is approximately 15 min, and the liver is suggested as a probable major site of degradation. These estimates were confirmed in late gestation by measuring fetal plasma concentrations of PL in response to a continuous infusion of unlabelled PL. The kinetic parameters estimated in this study can be used to determine the quantity of exogenous hormone required to alter PL concentration in fetal plasma in a predictable manner.

Temporal response of circulating metabolites and hormones during somatotropin treatment of growing pigs

Temporal responses in the circulating concentrations of a number of intermediary metabolites and metabolic hormones were studied in chronically catheterized barrows (n = 4 per treatment) after either daily i.m. injection of porcine somatotropin (pST, 120 micrograms/kg of BW) or excipient. Blood sampling (every 1 or 2 h) began 24 h before the first injection (d 0) and continued until the end of d 2. Sampling was repeated on d 7 of treatment. Feed intake declined by d 3 in the pST-treated pigs and was 31% lower by d 7 of treatment (P less than .05). Blood glucose and plasma insulin concentrations began to increase about 3 h after the first pST injection, almost returning to preinjection levels before the next injection. By the end of d 2, circulating levels of glucose and insulin were higher in pST-treated pigs than in the controls. A temporal pattern of hyperglycemia and hyperinsulinemia was observed postinjection on each day of treatment. Although pST treatment did not chronically increase basal plasma concentrations of nonesterified fatty acids and glycerol, both metabolites exhibited transient postinjection elevations, the magnitudes of which were augmented by duration of treatment. Plasma urea nitrogen concentrations began to decrease within a few hours after the first pST injection and by d 7 were 70% (P less than .01) lower in the pST-treated pigs. A model is presented implicating pST-induced decreases in peripheral tissue insulin sensitivity and(or) responsiveness in the observed temporal responses in lipid and carbohydrate metabolism.