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R C Haynes

Publications and source records attributed to R C Haynes.

At least 19 recordsLinked to original sources
PubMed1997

An experimental study of the failure modes of the Gamma Locking Nail and AO Dynamic Hip Screw under static loading: a cadaveric study.

The sliding compression screw is widely regarded as the optimum treatment for intertrochanteric fractures of the femur, allowing bone fragments to impact until a bony support has been established across the fracture site. This study carried out biomechanical, cadaveric tests to establish the influence of direct static loading situations on the modes of failure of the Gamma Nail compared with the Dynamic Hip Screw (DHS). Clinical studies report DHS failures of lag screws cutting-out, bending of the lag screws and cortical screws pulling out causing plate loosening. Gamma Nail failures include lag screw cut-out or fractures of the femoral shaft around the distal locking screws or nail tip. In this study each failure mode has been isolated, to establish the loads to failure under various fracture configurations. The biomechanical results indicated that the intramedullary Gamma Locking Nail can be recommended over a standard DHS in cases of subtrochanteric fracture or conditions of very poor bone quality.

Aged↗
PubMed1997

Comparative dynamic evaluation of the sliding/characteristics of the Gamma nail: a biomechanical analysis.

This study was directed at establishing the influence of dynamic loading situations on the sliding characteristics of the Gamma locking nail (Howmedica). It was postulated that the changing regions of load contact area that occur within the sliding mechanism during flexion and extension would favourably modify the jamming behaviour observed under static test conditions. The forces required to initiate sliding of the lag screw in the intramedullary device were investigated under a range of conditions representing clinical situations. The optimum sliding performance of the Gamma nail was shown to occur during test conditions of dynamic loading, when the rate of application of the load was rapid and the cyclic angle of flexion was greatest. The size and weight of the patient also influence the sliding characteristics, as a shorter lag screw length protruding from the barrel and a reduced vertical static load (body weight) yielded a lower axial sliding force. The results under dynamic loading conditions suggest that static testing of sliding hip screws does not accurately represent their clinical performance.

Biomechanical Phenomena↗
PubMed1997

The road to justice.

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Environmental Pollution↗
PubMed1992

Physiological concentrations of 2-oxoglutarate regulate the activity of phosphoenolpyruvate carboxykinase in liver.

2-Oxoglutarate was found to inhibit purified rat liver phosphoenolpyruvate carboxykinase when the assay was performed in the direction of either phosphoenolpyruvate or oxaloacetate synthesis. The inhibition was competitive with respect to oxaloacetate or phosphoenolpyruvate, the Ki values being 0.32 +/- 0.04 mM 0.63 +/- 0.19 mM respectively. 2-Oxoglutarate inhibited non-competitively when tested against GTP or Mn2+. The reported cytosolic concentrations of 2-oxoglutarate in rat hepatocytes are such that the enzyme is likely to be significantly inhibited under basal conditions. The cytosolic concentration of 2-oxoglutarate is known to fall precipitously under the influence of glucagon and other hormones that stimulate gluconeogenesis, and it is suggested that the hormone-induced decrease in 2-oxoglutarate content would alleviate the inhibition of phosphoenolpyruvate carboxykinase and stimulate flux from oxaloacetate to phosphoenolpyruvate. The implications of this finding to the rationalization of the role of pyruvate kinase in the stimulation of gluconeogenesis in the fasted state are discussed.

Animals↗
PubMed1990

The role of inhibition of pyruvate kinase in the stimulation of gluconeogenesis by glucagon: a reevaluation.

We have reexamined the concept that glucagon controls gluconeogenesis from lactate-pyruvate in isolated rat hepatocytes almost entirely by inhibition of flux through pyruvate kinase, thereby making gluconeogenesis more efficient. 1. We tested and refined the 14C-tracer technique that has previously yielded the opposite conclusion, that is, that inhibition of pyruvate kinase is a relatively unimportant mechanism. The tracer procedure, as used by us, was found to be insensitive to the size of the pyruvate pool, and experiments using modifications of the technique to obviate a number of other potential errors support the earlier conclusion that control of pyruvate kinase is not the predominant mechanism. 2. Any stimulation of formation of glucose that results from inhibition of pyruvate kinase is the consequence of elevation of the steady-state concentrations of phosphoenolpyruvate and all subsequent intermediates in the gluconeogenic pathway. During ongoing stimulation of glucose synthesis by glucagon in isolated hepatocytes, the concentrations of all measured intermediate compounds between phosphoenolpyruvate and glucose were elevated except triose phosphates and fructose 1,6-bisphosphate. The failure of these compounds to rise above control levels indicates that not all gluconeogenic reactions beyond pyruvate kinase were accelerated thermodynamically as would occur with predominant control at pyruvate kinase. We conclude, therefore, that although glucagon inhibits flux through the pyruvate kinase reaction, this does not account for most of the stimulation of gluconeogenesis. Major control sites are also within the pyruvate-phosphoenolpyruvate segment and the fructose 1,6-bisphosphate cycle.

Adenosine↗
PubMed1986

Control of mitochondrial content of adenine nucleotides by submicromolar calcium concentrations and its relationship to hormonal effects.

Rat liver mitochondria were incubated at 30 degrees C with 4 mM ATP in a medium similar in electrolyte composition to that of hepatic cytosol. Under these conditions, a net increase in mitochondrial adenine nucleotides was observed that was dependent on the concentration of free Ca2+ [( Ca2+]) in the incubation medium. At 0.2 microM [Ca2+] or less, there was no demonstrable uptake of adenine nucleotides; at 0.4 microM [Ca2+], or greater, net uptake occurred. The calcium-dependent accumulation of nucleotides by mitochondria required Mg2+ in the incubation medium and was insensitive to carboxyatractyloside. The uptake of adenine nucleotides was enhanced by the addition of antimycin A or antimycin A together with oligomycin. Accumulation of nucleotides appeared to be associated with a small increase in mean mitochondrial volume, but the membrane potential was not affected. No uptake or loss of NAD-NADH by mitochondria was detected. Ruthenium red failed to inhibit the calcium-dependent uptake of adenine nucleotides by the mitochondria, indicating that stimulation of this process by Ca2+ does not involve transport of the cation into mitochondria by the Ca2+ uniporter. Because glucagon acts to elevate cytosolic [Ca2+] from approximately 0.2 microM to 0.6 microM, the same range affecting nucleotide uptake, it is proposed that the increase in mitochondrial adenine nucleotides that follows treatment with glucagon is mediated by the rise in cytosolic [Ca2+] produced by the hormone. This hypothesis was supported by the observation that epinephrine and A23187, agents that raise cytosolic [Ca2+], increased the content of mitochondrial adenine nucleotides in isolated hepatocytes. Furthermore, cells, incubated under calcium-depleting conditions, had a diminished response to glucagon.

Adenine Nucleotides↗
PubMed1985

Sensitivity of the response of cytosolic calcium in Quin-2-loaded rat hepatocytes to glucagon, adenine nucleosides, and adenine nucleotides.

Hepatocytes from fasted rats were used to study the effect of glucagon on intracellular free cytosolic Ca2+ ([Ca2+]i) indicated by the use of Quin-2-calcium fluorescence. It was found that, in both male and female rats, glucagon increased [Ca2+]i at a half-maximally effective concentration (Kact) of 0.3 nM, a concentration known to be half-maximal for affecting several hepatic functions. Acute chelation of extracellular Ca2+ did not obliterate the hormone effect but shortened its duration. Cyclic AMP, 5'-AMP, ADP, and ATP also increased [Ca2+]i, while adenosine 2':3'-monophosphate and 3'-AMP did not. The rise in [Ca2+]i brought about by glucagon at near physiological concentrations may be responsible for the stimulation of glutamate metabolism produced acutely by glucagon.

Adenine Nucleotides↗
PubMed1985

Acute stimulation by glucocorticoids of gluconeogenesis from lactate/pyruvate in isolated hepatocytes from normal and adrenalectomized rats.

Dexamethasone stimulated gluconeogenesis from lactate/pyruvate in suspensions of hepatocytes isolated from both adrenalectomized and normal fasted rats. This stimulation was observed in incubations with 1 mM pyruvate and at a lactate/pyruvate ratio of 25 but not at a ratio of 10-13. At a lactate/pyruvate ratio of 10-13, the stimulation by dexamethasone was progressively enhanced as the pyruvate concentration was decreased to 0.25 mM. Concurrent administration of a maximally stimulating concentration of dexamethasone with angiotensin II or glucagon yielded an additive stimulation at all concentrations of the peptide hormones tested. No potentiating or permissive actions of acute glucocorticoid administration were observed using hepatocytes from either normal or adrenalectomized animals. The acute stimulation by dexamethasone was antagonized by prior addition of progesterone or cortexolone to the hepatocyte suspensions. Triamcinolone and corticosterone also stimulated gluconeogenesis. Concentrations of the active glucocorticoids needed to elicit half-maximal stimulations (Kact) were approximately 100 nM for dexamethasone and triamcinolone and 400 nM for corticosterone. Deoxycorticosterone, 17 alpha-methyltestosterone, and 5 beta-dihydrocortisol did not stimulate. Stimulation of gluconeogenesis by dexamethasone was seen following a lag averaging 9 min after the time of steroid addition. Preliminary evidence suggests that this effect was not dependent upon a stimulation of protein synthesis, but the observed stimulation and inhibition of control rates of gluconeogenesis by cycloheximide and cordycepin, respectively, demonstrate the difficulties of working with such inhibitors in attempting to answer this question.

Adrenalectomy↗
PubMed1985

The interaction between the cytosolic pyridine nucleotide redox potential and gluconeogenesis from lactate/pyruvate in isolated rat hepatocytes. Implications for investigations of hormone action.

By using very low concentrations of cells to minimize alterations in substrate concentrations, we demonstrated that the lactate/pyruvate ratio of the incubation medium, which determines the cytosolic NADH/NAD+ ratio, affects gluconeogenic flux in suspensions of isolated hepatocytes from fasted rats. At a fixed extracellular pyruvate concentration of 1 mM and with the lactate/pyruvate ratio varied from 0.6 to 10 and to 50, glucose production rates increased from 2.5 to 5.5 and then decreased to 1.8 nmol/mg of cell protein/min. This finding paralleled the observation of Sugano et al. (Sugano, T., Shiota, M., Tanaka, T., Miyamae, Y., Shimada, M., and Oshino, N. (1980) J. Biochem. (Tokyo) 87, 153-166) who noted a similar biphasic response in the perfused liver system when lactate was held constant and pyruvate varied. The biphasic relationship can be explained by the influence of the NADH/NAD+ ratio on the near-equilibrium reactions catalyzed by glyceraldehyde-3-phosphate dehydrogenase and malate dehydrogenase in the hepatocyte cytosol. By shifting the equilibrium of the glyceraldehyde-3-phosphate dehydrogenase reaction, a rise in the NADH/NAD+ ratio decreases the concentration of 3-phosphoglycerate which, because of the linkage of 3-phosphoglycerate to phosphoenolpyruvate through two near-equilibrium reactions, reduces the concentration of phosphoenolpyruvate and therefore causes a decline in flux through pyruvate kinase. This decrease in pyruvate kinase flux results in an enhanced gluconeogenic flux. At higher NADH/NAD+ ratios, however, the oxalacetate concentration drops to such an extent that the consequent decreased flux through phosphoenolpyruvate carboxykinase exceeds the decline in flux through pyruvate kinase, producing a decrease in gluconeogenic flux. The lactate/pyruvate ratio was found to influence the actions of three hormones thought to stimulate gluconeogenesis by different mechanisms. Except for an inhibition by glucagon seen at the lowest lactate/pyruvate ratio tested, the stimulations by this hormone were relatively insensitive to lactate/pyruvate ratios, while angiotensin II produced greater stimulations of gluconeogenesis as the lactate/pyruvate ratio was increased. Dexamethasone, added in vitro, stimulated gluconeogenesis significantly only at very low and very high lactate/pyruvate ratios.

Angiotensin II↗
PubMed1985

Estimation of the relative contributions of enhanced production of oxalacetate and inhibition of pyruvate kinase to acute hormonal stimulation of gluconeogenesis in rat hepatocytes. An analysis of the effects of glucagon, angiotensin II, and dexamethasone on gluconeogenic flux from lactate/pyruvate.

Hepatocytes, isolated from fasted rats, were incubated with graded concentrations of lactate and pyruvate, at a mean constant ratio of 10-13:1, to alter systematically the concentrations of gluconeogenic intermediate metabolites and rates of glucose production. By analyzing glucose production rates as a function of corresponding concentrations of extracellular pyruvate, cytosolic oxalacetate, and cellular 3-phosphoglycerate in the presence and absence of hormones and assuming no primary activation of phosphoenolpyruvate carboxykinase, estimates were made of the relative contributions of stimulation of formation of cytosolic oxalacetate and inhibition of pyruvate kinase to hormonal stimulations of gluconeogenesis. Addition of dexamethasone, glucagon, or angiotensin II did not cause a shift in the relationship between cellular 3-phosphoglycerate concentrations and rates of glucose production, indicating that there was no effect of these agents on the reactions involved in conversion of phosphoenolpyruvate to glucose. All three agents shifted the relationships between rates of glucose production and both cytosolic oxalacetate and extracellular pyruvate. The following conclusions were drawn from computer analyses of these results. At low concentrations of pyruvate, stimulation of oxalacetate production and pyruvate kinase inhibition were approximately equally contributory to the overall stimulations of gluconeogenesis by angiotensin II and dexamethasone. At higher pyruvate concentrations, pyruvate kinase inhibition by angiotensin II played a greater role, accounting for 90% of the overall stimulation. For dexamethasone, as the pyruvate concentration was increased, stimulation of gluconeogenesis resulting from enhanced formation of oxalacetate diminished as did overall stimulation of gluconeogenesis. Glucagon addition resulted in an inhibition of pyruvate kinase flux that accounted for 75% of the hormone's overall effect at low pyruvate concentrations; this increased to 95% at high pyruvate concentrations.

Adenosine Diphosphate↗
PubMed1984

The interaction of glucagon treatment and uncoupler concentration on ATPase activity of rat liver mitochondria.

Mitochondria isolated from livers of rats treated briefly with glucagon show an increased ATPase activity in the presence of appropriate concentrations of protonophoric uncouplers (Yamazaki, R. K., Sax, R.D., and Hauser, M.A. (1977) FEBS Lett. 75, 295-299). With the uncoupler carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP) the effect of glucagon treatment was most evident at concentrations of uncoupler higher than required for maximal stimulation of ATPase in control mitochondria. In this range of FCCP concentrations that produced the greatest contrast in ATPase activity of control and hormone-stimulated mitochondria, there were no significant differences in delta pH, delta psi, or delta p between the two groups. The presence of added succinate in the ATPase assay system mimicked the effect of glucagon treatment, permitting greater activity at high concentrations of uncoupler without significantly affecting delta p. No significant effect of glucagon treatment or uncoupler concentrations on mitochondrial volumes was observed. Following treatment with glucagon, the mitochondria retained a greater content of Mg+ and K+ throughout the range of FCCP concentrations tested. In the upper range of FCCP concentrations there was appreciable loss of K+ from the mitochondria which was greater in control mitochondria than in mitochondria from glucagon-treated rats or in mitochondria assayed in the presence of succinate. The activity of the uncoupler-dependent ATPase was greatly stimulated by increased concentrations of potassium chloride in the assay medium without significantly diminishing the hormone effect. It is proposed that the intrinsic peptide inhibitor of ATPase is dissociated from the enzyme to an increased degree following glucagon treatment and that high levels of uncoupler inhibit by causing an increased association of the enzyme and its inhibitor.

Adenosine Triphosphatases↗
PubMed1983

Hormonal regulation of mitochondrial function. Description of a system capable of mimicking several effects of glucagon.

Isolated rat liver mitochondria were incubated at 0 degrees C in a medium consisting of 225 mM sucrose, 10 mM KCl, 1 mM EDTA, 10 mM KH2PO4, 5 mM MgCl2 and 10 mM Tris-HCl, pH 7.4 (buffer 1) for 10 min, centrifuged and resuspended in 0.3 M sucrose. This treatment resulted in a stimulation of mitochondrial functions, mimicking several of the effects that follow glucagon treatment of the intact rat or isolated hepatocytes. Both phosphate and potassium are required for this effect; the addition of magnesium serves to enhance it. Mitochondrial respiration is essential for the development of the activated state as the stimulation is blocked by increasing concentrations of rotenone in the incubation. The intramitochondrial ATP/ADP ratio is increased, but when this increase was prevented by including low levels of rotenone or oligomycin in buffer 1, the stimulation of mitochondrial function was not diminished, thus demonstrating that an increased ATP/ADP ratio is not essential for activation. The rate of citrulline formation was unaffected by buffer 1 treatment unless glutamate was also included in the medium, indicating that control of this mitochondrial function differs from other functions studied.

Adenosine Diphosphate↗
PubMed1983

Stimulation of mitochondrial functions by glucagon treatment. Evidence that effects are not artifacts of mitochondrial isolation.

(1) Activation of rat liver mitochondrial functions following glucagon treatment was demonstrated in mitochondria that had not been isolated by the conventional technique of differential centrifugation and washing in sucrose solutions. Crude liver homogenates in 0.3 M-sucrose or 0.15 M-KCl prepared from rats treated with glucagon showed stimulation of State-3 and uncoupled respiration, carboxylation of pyruvate, and citrulline synthesis comparable with those previously reported in isolated mitochondria. (2) During the isolation procedure of mitochondria the hormonal stimulations of pyruvate carboxylation and citrulline formation were shown not to be enhanced by sequential washing. (3) Mitochondria isolated from glucagon-treated rats by differential centrifugation and washing in 0.3 M-mannitol/1 mM-EGTA, pH 7.0, exhibited a mean rate of citrulline synthesis that was greater than twice that of the control. Liver homogenates prepared in 0.3 M-sucrose or 0.3 M-mannitol showed identical rates of State-3 respiration and percentage stimulations of respiration by glucagon treatment. (4) Addition of glucagon led to a rapid accumulation of malate and aspartate and decreased the amounts of glutamate and citrate in isolated hepatocytes incubated with L-lactate. When gluconeogenesis was inhibited at the phosphoenolpyruvate carboxykinase (EC 4.1.1.32) reaction these phenomena were accentuated, lending support to the interpretation that they are the direct result of stimulation of carboxylation and oxidation reactions in the mitochondria. These results do not support the proposal [Siess, Fahimi & Wieland (1981) Hoppe-Seyler's Z. Physiol. Chem. 362. 1643-1651] that the mitochondrial effects of glucagon treatment result from a stabilization of mitochondria to detrimental effects of sucrose during their isolation. (5) The mean hormonal stimulation of pyruvate carboxylation in mitochondria isolated in 0.3 M-sucrose was shown to be approx. 2.5-fold when assayed either at 37 degrees C or 25 degrees C. In contrast, on the basis of similar experiments, Siess et al. (1981) concluded that the effects of glucagon on hepatic mitochondria are not characteristic of a true hormonal stimulation. Our data indicate this conclusion to be unjustified.

Animals↗
PubMed1983

Elevated intramitochondrial adenine nucleotides and mitochondrial function.

Several groups of investigators have shown that treatment of rats with glucagon produces an increase in the adenine nucleotide content of hepatic mitochondria. It has been suggested that this enlarged pool of exchangeable nucleotides may be responsible for several of glucagon's stimulatory effects on mitochondrial functions by accelerating the transport of adenine nucleotides across the inner mitochondrial membrane. This hypothesis was tested by loading rat liver mitochondria in vitro with adenine nucleotides to supranormal levels. This procedure did result in stimulation of several metabolic and bioenergetic functions including pyruvate carboxylation, uncoupler-dependent ATPase, and succinic dehydrogenase activity but not formation of citrulline. However, a sham loading that did not increase the nucleotide content of the mitochondria was essentially as effective as the loading procedure in stimulating those functions assayed. Mitochondria, loaded in vitro with supranormal levels of adenine nucleotides, were shown to have an enlarged pool of exchangeable nucleotides. This exchange was atractyloside sensitive, but the rate of exchange was only slightly increased as a consequence of enlargement of the pool. Similarly, mitochondria isolated from glucagon-treated rats showed no increase in the rate of exchange, although the exchangeable pool was increased. There was no correlation between the rate of nucleotide exchange and the rate of the uncoupler-dependent ATPase.

Adenine Nucleotides↗