Low-dose radiography of scoliosis in children. A comparison of methods

STUDY DESIGN

Records of 1,582 conventional and computed radiographic examinations performed to evaluate scoliosis were reviewed and compared to determine differences in total radiation burden.

OBJECTIVE

This study evaluated the impact of computed radiographic imaging (CRI) on radiation exposure in children undergoing serial spinal radiographs for scoliosis assessment and compared exposure from CRI with that of low-dose film-screen combinations.

SUMMARY OF BACKGROUND DATA

CRI permits diagnostic radiographic studies to be performed with a dose reduction of 80%-95% compared to conventional film-screen systems. High speed film-screen systems also permit a significantly lower exposure. Each approach has unique advantages and disadvantages.

METHODS

Over 6 years, we performed 1,582 spinal examinations in children 4-14 years old using reduced dosage techniques with computed radiography. The images were obtained with Fuji FCR 101 and Philips PCR/SP systems. The adequacy of diagnostic image quality in the serial evaluation of scoliosis at different exposure levels was evaluated and compared with regular and film-screen systems with speeds ranging from 250 to 1,200.

RESULTS

Diagnostic-quality images for evaluating scoliosis can be obtained with doses of 5% or less than required with conventional film-screen systems. Computed radiography provides image quality and dose reduction comparable to a 1,200-speed film-screen system.

CONCLUSION

CRI gives satisfactory images at 5% reduction of the standard film-screen dose. Based on comparison with a 1,200 speed film-screen system, CRI provides equal or better image quality at a similar radiation dose. The cost of CRI is higher than for film-screen radiography, but wide latitude and the ability to tailor dose with requirements for image quality are significant advantages for CRI.

CNAD: a potent and specific inhibitor of alcohol dehydrogenase

CNAD (5-beta-D-ribofuranosylnicotinamide adenine dinucleotide) is an isosteric and isomeric analogue of NAD, in which the nicotinamide ring is linked to the sugar via a C-glycosyl (C5-C1') bond. CNAD acts as a general dehydrogenase inhibitor but shows unusual specificity and affinity for liver alcohol dehydrogenase (ADH, EC 1.1.1.1). The pattern of inhibition is congruent to 4 nM, with NAD as the variable substrate. These values are 3-5 orders of magnitude smaller than those obtained for CNAD in other dehydrogenases and are comparable to values observed for the tightest binding ADH inhibitors known. The specificity and affinity of CNAD for ADH are likely due to coordination of the zinc cation at the ADH catalytic site by the CNAD pyridine nitrogen. This is supported by kinetic and computational studies of ADH-CNAD complexes. These results are compared with those for a related analogue, CPAD. In this analogue, displacement of the pyridine nitrogen to the opposite side of the ring removes the specificity for ADH.

Muscle fructose-2,6-bisphosphate and glucose-1,6-bisphosphate during insulin-induced hypoglycemia

Glucose production during insulin-induced hypoglycemia in the fasted state is heavily dependent on the process of hepatic gluconeogenesis. Skeletal muscle glycogen is one possible source of lactate for hepatic gluconeogenesis. Fructose 2,6-bisphosphate (F-2,6-P2) and glucose 1,6-bisphosphate (G-1,6-P2) are two allosteric activators of muscle glycolysis. To investigate their putative role in the control of muscle lactate production during hypoglycemia, fasted rats were infused via jugular catheters with insulin in 0.9% NaCl or with 0.9% NaCl alone for 60 or 120 min. Muscles were removed and clamp frozen in liquid nitrogen. The insulin infusion produced plasma insulin values of 97 +/- 13 microU/ml after 1 h and 100 +/- 9 microU/ml after 2 h. Blood glucose in the saline-infused rats was 4.6 +/- 0.2 mM after 1 h and 5.1 +/- 0.1 mM after 2 h compared with 1.5 +/- 0.01 and 1.0 +/- 0.1 mM after 1 and 2 h, respectively, in the insulin-infused rats. The hypoglycemic rats had significantly elevated plasma epinephrine and blood lactate levels compared with the saline-infused rats. F-2,6-P2 and G-1,6-P2 were increased two- to five-fold in white quadriceps of hypoglycemic rats compared with that of saline-infused rats. The results are consistent with F-2,6-P2 and G-1,6-P2 playing a role in stimulating muscle lactate production as a source of gluconeogenic substrate during insulin-induced hypoglycemia.

Mechanistic studies of uridine diphosphate glucuronosyltransferase

Bisubstrate reaction kinetics and product inhibition studies were used to characterize the kinetic mechanism of a partially purified uridine diphosphate glucuronosyltransferase (UDPGT). These studies indicate that the reaction most likely occurs via a random order sequential mechanism. The effect of electron withdrawing and donating groups on the rate of reaction was also determined. It was found that electron donating groups increased the rate of glucuronide conjugation. This result is consistent with nucleophilic attack of the C-1 carbon of the UDP-glucuronic acid (UDPGA) by an SN2 mechanism. This is the first direct evidence for a SN2 mechanism in UDPGT catalysis.

The pathophysiologic role of fat in dysbaric osteonecrosis

Dysbaric osteonecrosis (DON) can occur in humans and sheep after a single hyperbaric air exposure with inadequate decompression. The authors hypothesize that DON does not result from primary embolic or compressive effects of nitrogen bubbles on the osseous vasculature, but by secondary injury to the marrow adipose tissue by rapidly expanding nitrogen gas that triggers local, and possibly systemic, intravascular coagulation. A 28-year-old scallop diver remained at a depth of 92 feet in sea water for 4.5 hours on surface-supplied compressed air. Decompression sickness occurred after a no-stop ascent to the surface, and he died 70 minutes later. Autopsy showed multiple gas bubbles, not only within the great vessels, but in the fatty marrow of his femoral and humeral heads. Lipid and platelet aggregates were found on the surface of marrow bubbles. Fibrin-platelet thrombi were detected within dilated venous sinusoids adjacent to bubbles, and in veins, capillaries, and arterioles. Since pulmonary, renal, and intraosseous (subchondral) fat embolism and fibrin thromboses were observed, it is suggested that injured marrow adipocytes can release liquid fat, thromboplastin, and other vasoactive substances, which conceivably can also play a systemic procoagulant role in triggering disseminated intravascular coagulation and additional DON.

Slow-binding inhibition of carboxylesterase and other serine hydrolases by chlorodifluoroacetaldehyde

The chlorofluorocarbon substitute 1,2-dichloro-1,1-difluoroethane (HCFC-132b) undergoes oxidative metabolism in rats to give a range of metabolites, including chlorodifluoroacetaldehyde [Harris and Anders (1991) Chem. Res. Toxicol. 4, 180]. The present experiments were undertaken after studies to characterize an unidentified metabolite of HCFC-132b revealed that chlorodifluoroacetaldehyde was toxic in vivo: rats given chlorodifluoroacetaldehyde died showing signs of cholinergic stimulation. Because some fluoroketones are known inhibitors of hydrolases, including acetylcholinesterase, the inhibitory effects of chlorodifluoroacetaldehyde on acetylcholinesterase (electric eel and human erythrocyte), on pseudocholinesterase (horse serum), on carboxylesterase (pig liver), and on alpha-chymotrypsin (bovine pancreas) were studied. In aqueous solution, the ratio chlorodifluoroacetaldehyde:chlorodifluroacetaldehyde hydrate, as determined by 1H nuclear magnetic resonance spectroscopy, was 1:157. Chlorodifluoroacetaldehyde was a slow-binding inhibitor of both acetylcholinesterases, of pseudocholinesterase, and of carboxylesterase; the Ki values, corrected for the aldehyde:hydrate ratio, were 150 nM, 1.7 nM, 3.7 nM, and 23 pM, respectively, as determined by final velocity of the progress curves; the kon values were 9.1 x 10(4), 1.1 x 10(5), 3.2 x 10(4), and 9.2 x 10(5) M-1 min-1, respectively. Chlorodifluoroacetaldehyde did not inhibit alpha-chymotrypsin. Acetaldehyde and trichloroacetaldehyde were classical competitive inhibitors of acetylcholinesterase. These results show that hydrochlorofluorocarbon metabolites may exert significant biological effects.

Fat embolism, intravascular coagulation, and osteonecrosis

A triad of intraosseous fat embolism, intravascular coagulation (both thrombosis and hemorrhage), and osteonecrosis was pathologically demonstrated to coexist for the first time in humans. Specimens were evaluated from the earliest nontraumatic (18 hours) and traumatic (29 hours) femoral head lesions yet reported, and the cause and early pathogenesis were confirmed in a third case. An absolute overload of subchondral fat emboli, with hypercoagulability, stasis, and endothelial damage by free fatty acids, appears to cause end-organ death by triggering intravascular coagulation. This intermediary pathway appears to be capable of producing osteonecrosis by progressive fibrin platelet thromboses, which begin in vulnerable subchondral capillaries and sinusoids, especially when associated with arteriolar vasoconstriction and impaired secondary fibrinolysis (reperfusion of necrotic vessels with peripheral marrow hemorrhages). A relative overload of subperiosteal and subchondral fat emboli, which is below the ischemic/anoxic threshold but insufficient for intravascular coagulation, may cause osteopenia.

Effect of adrenodemedullation on decline in muscle malonyl-CoA during exercise

Malonyl-CoA is an inhibitor of carnitine palmitoyltransferase, a rate-limiting enzyme of fatty acid oxidation. Previous studies have indicated that muscle malonyl-CoA declines in rats during treadmill running. This decrease may be important for allowing an increased rate of fatty acid oxidation during prolonged exercise. This study was designed to determine whether epinephrine is essential for inducing the decline in muscle malonyl-CoA during exercise. Male Sprague-Dawley rats underwent adrenodemedullation (ADM) or sham operation. After allowing 3 wk for recovery, rats were killed (pentobarbital anesthesia) at rest or after running at 21 m/min up a 15% grade for 60 min. Red quadriceps malonyl-CoA decreased from 2.6 +/- 0.3 to 0.8 +/- 0.07 nmol/g in sham-operated rats and from 2.2 +/- 0.3 to 0.8 +/- 0.1 nmol/g in ADM rats. White quadriceps malonyl-CoA decreased to similar levels during exercise in both sham-operated and ADM rats. A second experiment on 24-h fasted rats also showed no impairment in the exercise-induced decline in red quadriceps malonyl-CoA as a result of adrenodemedullation. The hormones of the adrenal medulla are therefore unessential for inducing the decline in malonyl-CoA during exercise.

Predicting the cytochrome P450 mediated metabolism of xenobiotics

The cytochrome P450s play a unique role in the metabolism of xenobiotics. Characteristics which allow a vast number of foreign compounds to be metabolized by a limited number of enzymes include broad substrate specificity and broad regioselectivity. Because of their importance in both the metabolism and toxicity of drugs and environmental contaminants, efforts are being made to use computational methods to predict these biotransformation pathways. This review describes the recent progress towards the prediction of the tertiary structures of the various P450s and the determination of the electronic characteristics of substrates which determine their tendency to be oxidized by the P450s.

The added gradient echo pulse sequence technique: application to imaging of fluid in the temporomandibular joint

PURPOSE

To assess the value of an added gradient echo in the same pulse sequence with a T1-weighted spin echo for determining the presence of an abnormal fluid collection in the temporomandibular joint with no additional imaging time.

MATERIALS AND METHODS

Using a standard T1-weighted sequence used in cine temporomandibular joint imaging, a readout gradient reversal was added and the resulting gradient echo collected. This image was compared with standard T1- and T2-weighted sequences, a short inversion recovery imaging sequence, and a small flip angle fast low-angle shot gradient-echo sequence.

RESULTS

The T1-weighted spin echo preceding the added gradient echo is not affected by the gradient reversal, but the additional gradient echo adds T2* contrast information that displays fluid as bright as and compares favorably with other fluid detection sequences.

CONCLUSION

The added gradient-echo technique adds sensitivity for the detection of an abnormal increase in fluid in the temporomandibular joint without adding to the overall imaging time of a routine T1-weighted sequence.

Laparoscopic intraperitoneal marsupialization: report on a new treatment for lymphoceles

Lymphocele formation, a common complication of pelvic surgery, can produce considerable morbidity. Treatment is problematic, with no single procedure considered optimal. We recently treated a 67-year-old man with a symptomatic lymphocele by laparoscopic internal marsupialization. Total operative time was 45 min, and the patient was discharged home the same day with minimal need for pain medications. Total resolution of the symptoms occurred within 24 h. In comparison to other methods compiled and analyzed from the literature, this highly effective, minimally invasive procedure offers a significant advantage to the patient.

Visualization of myocardial cellular architecture using acoustic microscopy

The resolution of an ultrasound transducer depends on its frequency. The resolution improves when higher frequency transducers are used. A 1000 MHz transducer has a resolution of approximately 1 micron. Acoustic microscopy utilizes very high-frequency ultrasound (600 to 1000 MHz) to visualize structures on a microscopic level. Unstained, deparaffinized, 5 microns sections of myocardial biopsy specimens from 10 patients were placed on a slide and imaged using an Olympus UH3 scanning acoustic microscope. To compare with light microscopy, the section used for acoustic microscopy was subsequently stained with hematoxylin and eosin and a serial section from the paraffin block was stained with PTAH stain. Myocytes, myofibrils, and interstitial tissue were accurately imaged. Pathologic phenomena such as cell fallout, interstitial fibrosis, and lymphocytic infiltration were identified by acoustic microscopy. Intramural vessels, nuclei of endothelial cells, and the media were clearly identified by this technique. There was close correlation between findings by acoustic microscopy and light microscopy. Acoustic microscopy permitted the visualization of cardiac cellular detail with a resolution similar to that of light microscopy. Unlike light microscopy, acoustic microscopy requires no staining of the specimen.

Cine magnetic resonance imaging of the temporomandibular joint

Magnetic resonance imaging (MRI) provides a significant amount of information about both the position of the meniscoligamentous complex and the osseous structures in evaluation of internal derangements of the temporomandibular joint (TMJ). With the advent of computer-driven cine displays, dynamic information is now available, providing cost-effective diagnostic evaluation similar to cine fluoroscopy with arthrography, but without the ionizing radiation exposure or discomfort. Using a bite block, a series of sagittal images are obtained with the patient "posing" at different degrees of jaw opening. The subsequent cine MRIs with "posed" motion are striking and very helpful in evaluating various types of TMJ dysfunction. At the authors' institution, 205 patients were examined with a history of TMJ arthralgia. Correlation of imaging studies and surgical findings reveals a sensitivity (98%) and specificity (96%) for identifying the meniscoligamentous complex.

Laparoscopic cystectomy: initial report on a new treatment for the retained bladder

The retained bladder of a 27-year-old paraplegic woman suffering from recurrent pyocystis was removed laparoscopically. Operative time was 130 minutes. Postoperative hospital stay was 5 days, which was significantly less than that in 5 similar patients undergoing open cystectomy for vesical empyema in whom the mean hospital stay was 20.6 days. We believe that laparoscopic cystectomy represents a plausible, minimally invasive alternative to standard cystectomy for the symptomatic bladder left behind after supravesical urinary diversion.

Laparoscopic diverticulectomy: preliminary report of a new approach for the treatment of bladder diverticulum

Laparoscopic techniques have expanded the possibilities of endo-surgically approaching urological abnormalities that would otherwise be managed via an open operation. We report on another useful application of the laparoscope, bladder diverticulectomy. A large bladder diverticulum, responsible for incomplete bladder emptying and recurrent urinary tract infections in an 87-year-old man, was successfully excised endoscopically. The technique and possible future indications are described.

Pentahaloethane-based chlorofluorocarbon substitutes and halothane: correlation of in vivo hepatic protein trifluoroacetylation and urinary trifluoroacetic acid excretion with calculated enthalpies of activation

The hydrochlorofluorocarbons (HCFCs) 2,2-dichloro-1,1,1-trifluoroethane (HCFC-123) and 2-chloro-1,1,1,2-tetrafluoroethane (HCFC-124) and the hydrofluorocarbon (HFC) pentafluoroethane (HFC-125) are being developed as substitutes for chlorofluorocarbons that deplete stratospheric ozone. The structural similarity of these HCFCs and HFCs to halothane, which is hepatotoxic under certain circumstances, indicates that the metabolism and cellular interactions of HCFCs and HFCs must be explored. In a previous study [Harris et al. (1991) Proc. Natl. Acad. Sci. U.S.A. 88, 1407], similar patterns of trifluoroacetylated proteins (TFA-proteins) were detected by immunoblotting with anti-TFA-protein antibodies in livers of rats exposed to halothane or HCFC-123. The present study extends these results and demonstrates that in vivo TFA-protein formation resulting from a 6-h exposure to a 1% atmosphere of these compounds follows the trend: halothane approximately HCFC-123 much greater than HFC-124, greater than HFC-125. The calculated enthalpies of activation of halothane, HCFC-123, HCFC-124, and HFC-125 paralleled the observed rate of trifluoroacetic acid excretion in HCFC- or HFC-exposed rats. Exposure of rats to a range of HCFC-123 concentrations indicated that TFA-protein formation was saturated at an exposure concentration between 0.01% and 0.1% HCFC-123. Deuteration of HCFC-123 decreased TFA-protein formation in vivo. Urinary trifluoroacetic acid excretion by treated rats correlated with the levels of TFA-proteins found after each of these treatments. No TFA-proteins were detected in hepatic fractions from rats given 1,1,1,2-tetrafluoroethane (HFC-134a), which is not metabolized to a trifluoroacetyl halide.(ABSTRACT TRUNCATED AT 250 WORDS)

Insulin-induced hypoglycemia in fed and fasted exercising rats

To determine running performance and hormonal and metabolic responses during insulin-induced hypoglycemia, fed and fasted male rats (315 +/- 3 g) were infused with insulin (100 mU/ml, 1.5 ml/h) or saline (1.5 ml/h) for 60 min and then killed at rest or after running on the treadmill (21 m/min, 15% grade). Insulin-infused fed rats ran poorly during the second 10 min of a 20-min exercise test. They were capable of running a total of 43 +/- 5 min, compared with 138 +/- 6 min for saline-infused fed rats. Fasted insulin-infused rats were able to run only 12.8 +/- 0.8 min, compared with 122 +/- 15 min for fasted saline-infused rats. In fasted rats, blood glucose was 1.6 +/- 0.1 mM after 60 min of insulin infusion and 1.2 +/- 0.1 mM after running to exhaustion. Artificial increase of plasma free fatty acids had no effect on performance. Intravenous infusion of glucose at the time of fatigue produced an immediate recovery, allowing the formerly fatigued rats to run 20 min without development of fatigue. These results provide evidence that severe hypoglycemia can be a significant cause of fatigue, even if it occurs early in the course of an exercise bout.

Intravascular coagulation and osteonecrosis

Current evidence suggests that intravascular coagulation (IC), an intermediary mechanism, is the most likely final common pathway by which intraosseous fat embolism causes nontraumatic osteonecrosis (ON). Stage 1A lesions (fatty osteocytic necrosis) appear to progress to classic Stage 1B lesions (ischemic degeneration of necrotic osteocytes and adipocytes) when the ischemic threshold is exceeded by absolute subchondral fat overload with insufficient local clearance of procoagulants, especially tissue thromboplastin. The result is vascular stasis, hypercoagulability, endothelial damage (by free fatty acids) and IC, especially if there is coexistent subchondral vasoconstriction and impaired secondary fibrinolysis. Osteonecrosis can be produced in animals by IC, which begins in the vulnerable subchondral microcirculation (Arthus phenomenon). Cartography (embolic scintimetry with superselective angiography) indicates early complete devascularization of the femoral head, suggesting progressive venous and retrograde arterial thrombosis. Increased plasma fibrinopeptide A and direct histologic evidence of intraosseous thromboses and peripheral hemorrhages further indicate that IC is the final pathway. Best evidence are 51 ON lesions complicating disseminated IC in eight children (Shwartzman phenomenon), with collateral histologic evidence of intraosseous thrombosis and ON.

Modification by focused ultrasound pulses of electrically evoked responses from an in vitro hippocampal preparation

The application of short pulses of focused ultrasound was studied as a method of modifying electrically evoked responses in the mammalian brain. The in vitro hippocampal preparation was employed to facilitate delivery and dosimetry of ultrasound, and assessment of mechanisms of ultrasound effects. Cellular and dendritic field potential responses evoked by electrical stimulation of the Schaffer/Commissural afferents were examined before, during and after exposure of a portion of the CA1 region to focused ultrasound pulses for periods ranging from 2 to 15 min. Focused ultrasound with a repetition rate of 150 kHz was delivered in pulses comparable in duration to an electrical pulse that could initiate activity in the nervous system. The pulses had a center frequency of 750 kHz, durations of about 6 microseconds, and spatial-peak-temporal-averaged intensities of about 80 W/cm2. These parameters are markedly different from those employed in conventional diagnostic ultrasound. Temperatures in the bath and tissue were monitored. Extracellular field potentials reflecting the presynaptic fiber volley, dendritic response and cellular discharge were significantly reduced by exposure to ultrasound. Recovery occurred to varying degrees, and in one experiment was complete. Average temperature changes observed were less than 1 degree C. The present study demonstrates that the electrically evoked response in mammalian brain can be altered by ultrasound in a non-thermal, non-cavitational mode, and that such effects are potentially reversible.

Secondary 18O isotope effects for hexokinase-catalyzed phosphoryl transfer from ATP

Secondary 18O isotope effects in the gamma-position of ATP have been measured on phosphoryl transfer catalyzed by yeast hexokinase in an effort to deduce the structure of the transition state. The isotope effects were measured by the remote-label method with the exocyclic amino group of adenine as the remote label. With glucose as substrate, the secondary 18O isotope effect per 18O was 0.9987 at pH 8.2 and 0.9965 at pH 5.3, which is below the pK of 6.15 seen in the V/K profile for MgATP. With the slow substrate 1,5-anhydro-D-glucitol, the value was 0.9976 at pH 8.2. While part of the inverse nature of the isotope effect may result from an isotope effect on binding, the more inverse values when catalysis is made more rate limiting by decreasing the pH or switching to a slower substrate suggest a dissociative transition state for phosphoryl transfer, in agreement with predictions from model chemistry. The 18O equilibrium isotope effect for deprotonation of HATP3- is 1.0156, while Mg2+ coordination to ATP4- does not appear to be accompanied by an 18O isotope effect larger than 1.001.

Scanning acoustic microscopy of neoplastic and inflammatory cutaneous tissue specimens

Acoustic microscopy utilizes high frequency ultrasound to generate microscopic images. The current study was designed to examine representative disorders of the skin by use of a reflective scanning acoustic microscope (R-SAM), and to determine whether the obtainable resolution was sufficient to render a microscopic diagnosis. An Olympus UH3 Scanning Acoustic Microscope was utilized with lenses producing burst wave frequencies at 600 and 800 MHz (600 and 800 million cylces/sec). Cutaneous tissue specimens representing 12 different neoplastic and inflammatory disorders were examined. Acoustic images of unstained sections were compared with conventional light microscopic study of sections stained with hematoxylin-eosin. In most neoplasms examined, it was possible to make a specific diagnosis primarily from low magnification pattern analysis. Although individual cells could be visualized, cytologic atypia was poorly defined. In the inflammatory disorders, a specific diagnosis was possible in all but bullous pemphigoid and lichen planus, because the composition of the inflammatory infiltrate was difficult to determine. The advantages of the R-SAM include the capability of producing an acoustic profile of the tissue and the future possibility of in situ diagnosis.

The double jeopardy of sales promotions

The maturing of most consumer markets in the United States has put great pressure on manufacturers in their search for growth. They have concentrated on building sales and expanding share proportions in the stagnant markets with devices like niche products, product extensions, mergers, and international ventures. They have shifted emphasis to sales promotions at the expense of advertising. But promotions, when you come right down to it, mean price reductions. Trade promotions are almost always rebates, and consumer promotions are usually temporary price reductions or coupons. The cost in reduced profit, demonstrated mathematically through calculations of price elasticity, is severe. Besides, when the promotion is over, the manufacturer has not moved forward an inch in shoring up the brand franchise. Promotions bring volatile demand, whereas the producer seeks stable demand. By sustaining a brand image and building customer loyalty, on the other hand, theme advertising can stabilize demand. Moreover, this type of advertising is less likely than promotion is to invite destructive competitive retaliation. Calculation of the advertising elasticity of a brand indicates that sometimes even modest sales increases can produce healthy profit improvement. In a well-planned marketing campaign, there is often good reason to include trade or consumer promotion--to counter a leading competitor's moves, for example. But there is no point in carrying out wild swings at rivals in a struggle for market share. Mathematical techniques can aid the efficiency of marketing planning and put on a more rational basis the decision on where to put the dollars.

Intrinsic isotope effects suggest that the reaction coordinate symmetry for the cytochrome P-450 catalyzed hydroxylation of octane is isozyme independent

The mechanism of the omega-hydroxylation of octane by three catalytically distinct, purified forms of cytochrome P-450, namely, P-450b, P-450c, and P-450LM2, was investigated by using deuterium isotope effects. The deuterium isotope effects associated with the omega-hydroxylation of octane-1,1,1-2H3, octane-1,8-2H2, and octane-1,1,8,8-2H4 by all three isozymes were determined. From these data the intrinsic isotope effects were calculated and separated into their primary and secondary components. The primary intrinsic isotope effect for the reaction ranged from 7.69 to 9.18 while the secondary intrinsic isotope effect ranged from 1.13 to 1.25. Neither the primary nor secondary isotope effect values were statistically different for any of the isozymes investigated. These data are consistent with a symmetrical transition state for a mechanism involving initial hydrogen atom abstraction followed by hydroxyl radical recombination which is essentially independent of the specific isozyme catalyzing the reaction. It is concluded that (1) in general the porphyrin-[FeO]3+ complex behaves as a source of a triplet-like oxygen atom, (2) the regioselectivity for the site of oxidation is dictated by the apoprotein of the specific isozyme of cytochrome P-450 catalyzing the reaction, and (3) the maximum primary intrinsic isotope effect for any cytochrome P-450 catalyzed oxidation of a carbon center is about 9, assuming no tunneling effects.