Opioid preconditioning: myocardial function and energy metabolism

BACKGROUND

Opioid receptor agonists are involved in ischemic preconditioning and natural hibernation. The aim of this study was to determine whether pretreatment with D-Ala2-Leu5-enkephalin or morphine confers cardioprotection in large mammalian hearts. We assessed myocardial functional recovery and global energy metabolism after ischemic cold storage.

METHODS

After pretreatment with D-Ala2-Leu5-enkephalin, morphine sulfate, or saline (n = 6 each), swine hearts were excised and stored for 75 minutes at 4 degrees C, then reperfused in a four-chamber isolated working heart apparatus. Serial myocardial biopsies were performed to assess cellular energy metabolism.

RESULTS

Improved systolic (cardiac output, contractility) and diastolic (tau) left ventricular functions were observed in hearts pretreated with D-Ala2-Leu5-enkephalin or morphine. These benefits were not correlated with changes in high-energy phosphate levels. Cardiac enzyme leakage (creatine kinase, troponin-I) was similar among treated and control groups. Lactate efflux increased significantly in controls, but not in opioid-pretreated hearts (p < 0.01) at 75 minutes of reperfusion.

CONCLUSIONS

D-Ala2-Leu5-enkephalin and morphine pretreatments improve postischemic function after cold storage of swine hearts. Postischemic lactate reduction, but not high-energy phosphate levels, may account for the observed cardioprotective effects.

Isolated four-chamber working swine heart model

BACKGROUND

Isolated heart models separate cardiac characteristics from systemic characteristics with subsequent findings used in cardiac research, including responses to pharmacologic, mechanical, and electrical components. The model objective was to develop the ability to represent in situ physiologic cardiac function ex vivo.

METHODS

Swine hearts were chosen over rat or guinea pig models due to their notably greater anatomical and physiologic similarities to humans. An in vitro apparatus was designed to work all four chambers under simulated in situ physiologic conditions. Using standard cardiac surgical techniques, 12 porcine hearts (mean weight 331 +/- 18 g) were explanted into the apparatus. Preload and afterload resistances simulated in situ input and output physiologic conditions. Hemodynamic characterizations, including cardiac output, max +/- dP/dt, and heart rate, were used to determine in situ function leading to explantation (prethoracic operation, postmedial sternotomy, and postperidectomy) and during in vitro function (t = 0, 60, 120, and 240 minutes).

RESULTS

In vitro performance decayed with time, with statistical differences from base line (t = 0) function at t = 240 minutes (p > 0.05).

CONCLUSIONS

An isolation and in vitro explantation protocol has been improved to aid in the study of isolated cardiac responses, and to determine cardiac hemodynamic function during open chest operation, transplantation, and in vitro reanimation with a crystalloid perfusate. The resulting model offers similar working physiologic function, with real-time imaging capabilities. The resulting model is advantageous in representing human cardiac function with regard to anatomic and physiologic functions, and can account for atrial and ventricular interactions.

The effect of chronic dexamethasone-induced hyperglycemia and its acute treatment with insulin on brain glucose and glycogen concentrations in rats

BACKGROUND

In the rat model of forebrain ischemia, long-term dexamethasone treatment is reported to cause hyperglycemia and worsen postischemic functional and histologic injury. This effect was assumed to result from glucose enhancement of intraischemic lactic acidosis within the brain. Short-term insulin therapy restored normoglycemia but did not return histologic injury completely to baseline values. Using a nonischemic rat model, the current study attempted to identify a metabolic basis for such outcome data.

METHODS

Fifty-eight halothane-anesthetized (1.3% inspired) Sprague-Dawley rats were assigned randomly to be administered either no treatment (N = 18) or 2 mg/kg intraperitoneal dexamethasone (N = 40). The latter were administered dexamethasone 3 h before the study only (N = 8) or for 3 h before the study plus daily for 1 day (N = 8), 2 days (N = 8), or 4 days (N = 16). Of the rats treated with dexamethasone for 4 days, one half (N = 8) were administered an insulin-containing saline infusion subsequently to restore normoglycemia short-term. All other rats (N = 50) were administered an infusion of saline without insulin. Plasma glucose was quantified, and brains were excised after in situ freezing. Brain glucose and glycogen concentrations were measured using enzymatic fluorometric analyses.

RESULTS

After 4 days of dexamethasone treatment, plasma glucose was 159% greater than in rats administered placebo (i.e., 22.01 +/- 4.66 vs. 8.51 +/- 1.65 micromol/ml; mean +/- SD; P < 0.0001). Brain glucose concentrations increased parallel to plasma glucose. An insulin infusion for 27 +/- 5 min restored normoglycemia but resulted in a brain-to-plasma glucose ratio that was 32% greater than baseline values (P < 0.01). Neither dexamethasone nor the combination of dexamethasone plus insulin affected brain glycogen concentrations.

CONCLUSIONS

In a nonischemic rat model, dexamethasone alone had no independent effect on the brain-to-plasma glucose ratio. However, short-term insulin therapy caused a dysequilibrium between plasma and brain glucose, resulting in an underestimation of brain glucose concentrations when normoglycemia was restored. The dysequilibrium likely was caused by the rapid rate of glucose reduction. The magnitude of the effect may account for the failure of insulin to reverse dexamethasone enhancement of neurologic injury completely in a previous report that used the rat model of forebrain ischemia.

Low-frequency magnetic noise in micron-scale magnetic tunnel junctions

We have observed low-frequency noise due to quasiequilibrium thermal magnetization fluctuations in micron-scale magnetic tunnel junctions (MTJs). This strongly field-dependent magnetic noise occurs within the magnetic hysteresis loops, either as 1/f or Lorentzian (random telegraph) noise. We attribute it to the thermally excited hopping of magnetic domain walls between pinning sites. Our results show that magnetic stability is a crucial factor in reducing the low-frequency noise in small MTJs.

Thermally assisted magnetization reversal in submicron-sized magnetic thin films

We have measured the rate of thermally assisted magnetization reversal of submicron-sized magnetic thin films. For fields H just less than the zero-temperature switching field H(C), the probability of reversal, P(exp)(s)(t), increases for short times t, achieves a maximum value, and then decreases exponentially. Micromagnetic simulations exhibit the same behavior and show that the reversal proceeds through the annihilation of two domain walls that move from opposite sides of the sample. The behavior of P(exp)(s)(t) can be understood through a simple "energy-ladder" model of thermal activation.

4-chloro-m-cresol triggers malignant hyperthermia in susceptible swine at doses greatly exceeding those found in drug preparations

BACKGROUND

Chlorocresols are used as preservatives in numerous commercial drugs that have been shown to induce myoplasmic Ca2+ release; the most potent isoform is 4-chloro-m-cresol. The aims of this study were to (1) examine the in vivo effects of 4-chloro-m-cresol on swine susceptible to malignant hyperthermia and (2) contrast in vivo versus in vitro dose-response curves.

METHODS

Susceptible swine (weight: 38.5 kg+/-3.55 kg) were anesthetized and monitored for variations in physiological responses, including end-tidal CO2, heart rate, blood pressure, blood chemistry, and temperatures. In the first animals studied, 4-chloro-m-cresol, at equivalent cumulative doses of 0.14, 0.28, 0.57, 1.14, 2.27, 4.54, and 9.08 mg/kg (n = 3; 12.5, 25, 50, 100, 200, 400, and 800 micromol) were administered, and in a second group, larger doses were used: 1.14, 3.41, 7.95, 17.04 (n = 4), and/or 35.22 (n = 1) mg/kg (100, 300, 700, 1,500, and/or 3,100 micromol). For comparison, in vitro rectus abdominis muscle preparations obtained from normal and susceptible swine were exposed to 4-chloro-m-cresol, at cumulative concentrations of 6.25, 12.5, 25, 50, 100, 200, 400, 800, and 1,600 micromol; standard caffeine and halothane contracture testing was also performed.

RESULTS

Episodes of malignant hyperthermia were not triggered in response to administration of low doses of 4-chloro-m-cresol, but transient cardiovascular reactions (e.g., tachycardia, arrhythmias, and hypotension) were observed. Subsequently, episodes in these animals were triggered when halothane (0.87; 1 MAC) and succinylcholine (2 mg/kg) were given. Animals administered the higher doses of 4-chloro-m-cresol all had fulminant episodes of malignant hyperthermia that were fatal, when equivalent cumulative concentrations were greater than 1,500 micromol. The levels of 4-chloro-m-cresol in the plasma rapidly decreased: e.g., 5 min postadministration of the 1,500-micromol dose, the mean plasma level was only 52+/-18 micromol (n = 4). Hemolysis was detected following 4-chloro-m-cresol administration at concentrations > 200 micromol. In vitro, muscle from susceptible animals elicited contractures > 200 mg at 50-micromol bath concentrations of 4-chloro-m-cresol (n = 29), whereas normal muscle did not elicit such contractures until bath concentrations were > 800 micromol (n = 10).

CONCLUSIONS

4-chloro-m-cresol is a trigger of malignant hyperthermia in susceptible swine, but only when serum concentrations are far above those likely to be encountered in humans. A relatively low concentration of 4-chloro-m-cresol, 50 micromol, is sufficient to activate sarcoplasmic [Ca+2] release in vitro (e.g., contractures); this same bolus dose administered in vivo (0.57 mg/kg) has minimal effects due to the rapid decrease in its plasma levels.

The effect of reduced myocardial cyclic AMP content on the response to milrinone in the isolated guinea pig heart

BACKGROUND

Cardiac beta receptor down-regulation is associated with a reduction of tissue cyclic adenosine monophosphate (AMP) content. Milrinone exerts its effects by inhibiting the metabolism of existing cyclic AMP. The purpose of this study was to evaluate the effect of reduced myocardial cyclic AMP content on the pharmacologic action of milrinone.

METHODS

A reduction of myocardial cyclic AMP content was produced by creating catecholamine depletion in the hearts of adult guinea pigs with intraperitoneal reserpine. Control animals received the reserpine vehicle. Isolated heart perfusion was maintained with modified Krebs buffer, and hearts were paced at 270 beats/min. A latex balloon and transducer-tipped catheter were inserted into the left ventricle. Isovolemic work was maintained at a constant balloon volume. Hearts from control and reserpine treated animals were perfused for 20 minutes with buffer containing either no milrinone, 1.7 x 10(-6), or 1.0 x 10(-4) mol/L milrinone (n = 12 for each dose). Maximal positive and negative dP/dt were assessed. The hearts were then frozen and cyclic AMP was measured.

RESULTS

Cyclic AMP content was significantly lower in the reserpine-treated hearts at each milrinone concentration (0.33 +/- 0.01 vs 0.46 +/- 0.01; 0.33 +/- 0.01 vs 0.53 +/- 0.01; 0.30 +/- 0.01 vs 0.61 +/- 0.02 pmol/mg wet weight, p < 0.05). Milrinone significantly increased positive and negative dP/dtmax (p < 0.05), but no difference was observed between control and reserpine-treated hearts.

CONCLUSIONS

Endogenous catecholamine depletion reduces myocardial cyclic AMP content but does not attenuate the response to milrinone in the isolated heart.

Metabolism of glucose, glycogen, and high-energy phosphates during transient forebrain ischemia in diabetic rats: effect of insulin treatment

BACKGROUND

Hyperglycemia associated with diabetes mellitus will exacerbate neurologic injury after global brain ischemia. Studies in a rat model of forebrain ischemia (bilateral carotid occlusion plus hypotension for 10 min) discovered that acute restoration of normoglycemia in diabetics, using an insulin infusion, resulted in a neurologic outcome that was similar to normoglycemic rats without diabetes. The current study evaluated cerebral glucose, glycogen, lactate, and high-energy phosphate concentrations to identify metabolic correlates that might account for an alteration in postischemic outcome.

METHODS

Fifty-four pentobarbital-anesthetized Sprague-Dawley rats were assigned to three groups: chronically hyperglycemic diabetic rats (D; N = 18); insulin-treated, acutely normoglycemic diabetic rats (ID; N = 18); and nondiabetic rats (ND; N = 18). These groups were further divided into groups of six rats each that received either no ischemia, forebrain ischemia of 10 min duration without reperfusion, or ischemia plus 15 min of reperfusion. Brains were excised after in situ freezing, and metabolites were measured using enzymatic fluorometric techniques.

RESULTS

Before ischemia, D rats had greater concentrations of brain glucose (12.18 +/- 2.67 micromol/g) than did either ID (5.10 +/- 1.33) or ND (3.20 +/- 0.27) rats (P < 0.05). Preischemic brain glycogen was similar in all groups. At the completion of ischemia, brain lactate concentrations in D were 86% greater than in ID and 61% greater than in ND (P < 0.05), reflecting a higher intraischemic consumption of glucose plus glycogen in D (P < 0.05). High-energy phosphate concentrations, as assessed by the energy charge of the adenylate pool, were better preserved in D (energy charge = 0.60 +/- 0.28) than in either ID (0.29 +/- 0.09) or ND (0.36 +/- 0.07; P < 0.05) rats. After 15 min of reperfusion, the energy charge returned to preischemic values (i.e., 0.91-0.92) in all groups.

CONCLUSIONS

These studies demonstrated greater intraischemic carbohydrate consumption and lactate production in D than in ID or ND rats. Under these conditions, intraischemic-but not postischemic-energy status was better in D rats. Acute insulin therapy in ID rats resulted in a metabolic profile that was similar to that of ND rats. These results suggest that, in this model, primary energy failure during ischemia is not the origin of greater injury in hyperglycemic diabetics, nor is energy enhancement the origin of improved outcome after acute insulin treatment.

In vitro contracture testing for determination of susceptibility to malignant hyperthermia: a methodologic update

The in vitro contracture test determines the sensitivity of freshly obtained skeletal muscle specimens to caffeine or halothane applied to a bathing solution. Muscles from persons susceptible to malignant hyperthermia have lower contracture thresholds for these agents than do normal muscle. Thus, known concentrations of these agents must be accurately administered. We describe a system in which the bath concentrations of halothane (0 to 3%) are reproducible within 0.2% halothane from month to month. With use of this system, which includes an on-line gas analyzer, the measured halothane concentration within the bathing solution was independent of the performance of the vaporizer. The system is inexpensive and stable. The methods used to determine the bath concentrations of halothane and caffeine are reviewed. Finally, experimental equipment and a new recording system are described.

Multichannel hybrid system for neuromagnetic measurements

This paper describes progress toward the development of a 28-multichannel system for neuromagnetic measurements. A novel 'hybrid' design consisting of 16 first-order axial gradiometers and 12 first-order planar gradiometers was chosen, which optimises the use of the available cylindrical volume of the dewar tail. This configuration maintains the symmetry of the detected pattern with respect to rotation of a biomagnetic source located under the centre of the array and features a localisation power considerably better than an array of all first-order planar gradiometers. The detecting array permits simultaneous magnetic measurements over a circular scalp region of 16 cm diameter. The magnetic sensors used are Nb/PbAuIn DC SQUIDs fabricated at the IBM. The devices incorporate resonant damping resistors shunting the inductance, resulting in smooth flux-voltage characteristics and, consequently, very low noise figures in a flux-locked loop configuration. A simple and low cost electronic system has been designed and fabricated for the DC SQUID sensors.

Effects of sufentanil on cerebral circulation and metabolism in dogs

The cerebral and peripheral vascular effects of sufentanil (10-200 micrograms/kg) were examined in dogs. The cerebral blood flow (CBF) was measured continuously by an electromagnetic flow probe on the outflow of the posterior sagittal sinus. Sufentanil at all doses significantly increased CBF that lasted for approximately 20 min. The CBF then gradually decreased so that it was significantly below baseline levels by the end of the 60-min study period. The transient increase in CBF was accompanied by an equally transient statistically significant decrease in cerebrovascular resistance. Intracranial pressure did not change. Sufentanil produced an electroencephalographic pattern of deep anesthesia accompanied by a decrease in cerebral oxygen consumption significantly below baseline levels. At the end of the study tissue concentrations of metabolites taken from the cerebral hemispheres were within normal limits, indicative of a normal cerebral energy state. Sufentanil had little effect on systemic hemodynamics. The observation that sufentanil significantly increases CBF in the absence of seizure activity makes it unique among the narcotics. It is hypothesized that in the presence of decreased intracranial compliance, this sudden increase in CBF, although transient, may be detrimental if it is accompanied by an acute increase in intracranial pressure which could produce cerebral ischemia.

Benign smooth muscle tumors of the gastrointestinal tract. A 24-year experience

Between 1963 and 1987, 131 patients with benign gastrointestinal stromal tumors, primarily leiomyomas, were treated at the Massachusetts General Hospital. Eighty per cent of tumors were located in stomach or small intestine. Two thirds of the tumors were discovered in symptomatic patients before operation by a variety of diagnostic studies. A mitotic index (MI) was determined for each tumor, defined as the number of mitoses per 50 high-power microscopic fields. Only gastric and small intestine tumors had MIs more than 2. Tumors were treated by conservative excision in 67% and radical excision in 33%. At a median follow-up of 6 years there were no local recurrences. No patient with a tumor discovered incidentally has recurred. Three symptomatic patients have died of metastatic liver disease. Each patient with recurrence had a tumor with MI of 2 or more, which represents a recurrence rate of 16% in this group. We conclude that symptomatic gastric and small intestine tumors having two or more mitoses per 50 high-power fields carry a significant risk for recurrence, and that routine pathologic assessment of MI may identify a subset of patients who would potentially benefit from close follow-up and consideration for further therapy.

Cerebral effects of fentanyl in dogs

We have studied the cerebral haemodynamic and metabolic effects of fentanyl 50 micrograms kg-1 and 100 micrograms kg-1 in dogs undergoing ventilation with oxygen and nitrogen at normocapnia. Cerebral blood flow was measured continuously by direct measurement of the outflow of the posterior sagittal sinus. Arterial and sagittal sinus blood-gas tensions were measured intermittently for calculation of cerebral metabolism. Systemic pressures were measured continuously with intermittent measurements of cardiac output. These doses of fentanyl had minimal effect on cerebral blood flow, cerebral oxygen consumption and the energy state of the brain reflected by the normal concentration of cerebral metabolites at the end of the study. There was also little effect on systemic haemodynamics. It is concluded that, in the absence of other anaesthetic agents which might influence cerebral haemodynamics and metabolism, large doses of fentanyl have little effect on the cerebral circulation.

Minimal-volume excision of nonpalpable breast lesions

To explore the value of accurate preoperative localization of occult breast lesions, we reviewed 100 consecutive needle-directed breast biopsies performed by the same surgeon over a 1-year period. A spring hookwire device for localization was inserted parallel to the chest wall. Two thirds of biopsies were performed under local anesthesia, and all were performed in an outpatient setting. Sixteen lesions were invasive carcinomas, and eight were ductal carcinomas in situ. In 96 lesions, the localizing wire was placed within 2 mm of the lesion, and in the remaining four it was within 5 mm of the abnormality. The mammographic lesion was excised in the first specimen in 96 cases. One patient required a second biopsy because of failure to excise the lesion in question after three specimens were taken. The only surgical complication was one hematoma, which resolved within 3 months. Median specimen volume for the entire series was 6.0 cm3. Median largest specimen diameter was 2.5 cm. Precise preoperative localization with a spring hookwire to within 2 mm of the mammographic lesion allows the surgeon to excise a median volume of 6 cm3 breast tissue with consistent retrieval of the lesion.

Efficacy of adjuvant interleukin-2 after excision of BALB/c fibrosarcomas

Interleukin-2 (IL-2) has been evaluated as a therapeutic agent in a number of metastatic tumor systems. We hypothesized that administration of IL-2 might be more effective as adjuvant therapy in the presence of a greatly diminished tumor burden after tumor excision. In this BALB/c methylcholanthrene-induced sarcoma model, excision of 0.3 to 0.4 gm tumors results in local recurrence rates of 50% to 70%. Administration of human recombinant IL-2 at a dose of 50,000 units three times daily for 5 days to animals with established tumors resulted in 100% mortality. IL-2 administration started at the time of tumor implantation had no effect on tumor growth. Mice receiving adjuvant IL-2 at 50,000 units per dose after surgery had prolonged survival compared with controls (79% vs. 32%, p = 0.007); addition of concanavalin A-activated lymphocytes to IL-2 therapy did not enhance survival over that with IL-2 alone. Therapy with lower doses of adjuvant IL-2 on the same treatment schedule resulted in improved survival at doses as low as 5000 units (86% vs. 51% for controls, p = 0.003). Although the exact mechanism of this therapeutic effect has not been determined, IL-2 may act by a variety of mechanisms, including a decrease in the immunosuppressive effects of anesthesia and surgery, the generation of endogenous IL-2-activated effector cells, and the augmentation of efflux of circulating effector cells from peripheral blood into the site of surgically induced inflammation.

Treatment of intraductal carcinoma with limited surgery: long-term follow-up

Adequate therapy for ductal carcinoma in situ (DCIS) remains controversial. In spite of limited follow-up, recent studies advocate excision and postoperative radiotherapy as treatment. In an effort to provide long-term follow-up information, we evaluated retrospectively a group of 17 patients treated without mastectomy. Thirteen patients were treated with local excision, while four received excision and postoperative radiotherapy. Median follow-up is 100 months, with minimum follow-up 78 months. Five patients (29%) have recurred locally, at a median of 47 months following initial therapy. Three of the local recurrences were invasive carcinomas; two were DCIS. The patients recurring with invasive carcinoma progressed to disseminated disease and death, at a median of 131 months following their local recurrence. Of the eight patients followed for more than 9 years, four (50%) have recurred. Two patients have developed contralateral breast cancer, both treated by mastectomy. No recurrences have occurred in the group receiving radiotherapy. We conclude that long-term follow-up is required to accurately assess local recurrence rates in this disease, and that many recurrences will be invasive carcinomas. Since this lesion is virtually 100% curable by mastectomy, further analysis of long-term studies is warranted before recommending breast conservation to the majority of patients with DCIS.

Does preoperative needle localization lead to an increase in local breast cancer recurrence?

Between 1978 and 1981, 74 women with nonpalpable breast cancer underwent surgery after localization guides were placed. In 72 patients, guides were introduced parallel to the chest wall; in two the needle was positioned anteroposteriorly under computed tomographic guidance. Fifty-six cases (76%) were infiltrating cancer; 13 (17%), intraductal cancers; two (3%), inflammatory; and three (4%), lobular carcinoma in situ. Surgery was not used to treat the latter five patients. In the remaining 69 women, 42 (61%) were treated by means of modified radical mastectomy; six (9%), total mastectomy; 12 (17%), local excision and radiation therapy; and seven (10%), local excision alone; exact therapy for two women (3%) was unknown. At a minimum follow-up of 5 years, none of the 67 women in whom the parallel approach was used had a local recurrence. The authors conclude that preoperative placement of guides parallel to the chest wall does not appear to increase the risk of local breast cancer recurrence.

Assessment of a new nasopharyngeal airway

A new design of nasopharyngeal airway, which incorporates an introducer, was compared with a standard red rubber airway. The new airway was more frequently of the correct length, but the incidence of bleeding (12.5%) was not significantly different from that with the red rubber airway (27.5%).

Monoclonal antibody-ricin A chain conjugates (immunotoxins): potential therapeutic agents for human colon carcinoma

With the advent of hybridoma technology, monoclonal antibodies (MAbs) can be produced against specific human tumor cell-surface antigens. 44X14, an MAb produced in our laboratory by the immunization of BALB/c mice with colon carcinoma cells, exhibits high affinity for breast, lung, and colon carcinomas. However, this MAb shows little evidence of in vitro cytotoxicity. To enhance the potency of this MAb, it was coupled to the A chain (RTA) of the castor-bean protein ricin. Ricin is composed of two subunits--RTA, which binds to ribosomes and inhibits protein synthesis, and the B chain (RTB), which binds to galactose residues on all human cells and facilitates entry of RTA into the cell. By chemically separating RTA from RTB, RTA can then be coupled to MAb 44X14 so as to redefine its specific toxicity. This immunotoxin 44X14-RTA was assayed for protein-synthesis inhibition in HT-29 colon carcinoma and HT-1080 sarcoma cells by [3H]leucine uptake. Intact ricin (RTA + RTB) inhibited protein synthesis by 50% at concentrations of 0.76 and 4.8 ng/ml in HT-29 and HT-1080 cells, respectively. MAb 44X14 showed the same level of inhibition on HT-29 cells at 6.4 micrograms/ml, whereas the immunotoxin MAb 44X14-RTA showed 50% inhibition at 0.15 micrograms/ml. No effect of either MAb 44X14 or MAb 44X14-RTA at concentrations up to 200 micrograms/ml was seen on HT-1080 cells. Thus, the coupling of RTA to carcinoma-specific MAb 44X14 increased its potency 50-fold without increasing its nonspecific binding to cells that do not contain the appropriate antigen.(ABSTRACT TRUNCATED AT 250 WORDS)

Nonenzymic hydrogen transfer between reduced and oxidized pyridine nucleotides

Mixtures of NADH and NADP+ or NADPH and NAD+ were incubated and periodically assayed for hydrogen transfer by measuring the formation of NADPH and NADH with glutathione reductase (NAD(P)H: oxidized-glutathione oxidoreductase, EC 1.6.4.2) and lactate dehydrogenase (L-lactate: NAD+ oxidoreductase, EC 1.1.1.27), respectively. Each mixture showed a steady nonenzymic transfer of hydrogen from the reduced to the oxidized pyridine nucleotide to yield a product that was completely enzymically active. The results demonstrate the specific nonenzymic transfer of hydrogen from NADH and NADPH to the pyridine C-4 position of NADP+ and NAD+, respectively.