Effects of Breath-Hold Deep Diving on the Pulmonary System

This short review focuses on pulmonary injury in breath-hold (BH) divers. When practicing their extreme leisure sport, they are exposed to increased pressure on pulmonary gas volumes, hypoxia, and increased partial gas pressures. Increasing ambient pressures do present a serious problem to BH deep divers, because the semi-rigid thorax prevents the deformation required by the Boyle-Mariotte law. As a result, a negative-pressure barotrauma (lung squeeze) with acute hemoptysis is not uncommon. Respiratory maneuvers such as glossopharyngeal insufflation (GI) and glossopharyngeal exsufflation (GE) are practiced to prevent lung squeeze and to permit equalizing the paranasal sinuses and the middle ear. GI not only impairs venous return, thereby provoking hypotension and even fainting, but also produces intrathoracic pressures likely to induce pulmonary barotrauma that is speculated to induce long-term injury. GE, in turn, further increases the already negative intrapulmonary pressure, thereby favoring alveolar collapse (atelectasis). Finally, hypoxia seemingly not only induces brain injury but initiates the opening of intrapulmonary shunts. These pathways are large enough to permit transpulmonary passage of venous N2 bubbles, making stroke-like phenomena in deep BH divers possible.

Sphenoid sinus barotrauma in diving: case series and review of the literature

About 50% of scuba divers have suffered from barotrauma of the ears and about one-third from barotrauma of paranasal sinuses. The sphenoid sinuses are rarely involved. Vital structures, as internal carotid artery and optic nerve, adjoin the sphenoid sinus. Thus, barotrauma could lead to serious neurologic disorders, including blindness. After searching the literature (Medline) and other sources (Internet), we present some cases of sphenoid sinus barotrauma, because these injuries may be underreported and misdiagnosed due to the lack of awareness and knowledge. Therefore, information is provided, e.g. on anatomical and pathophysiological features. Divers and physicians should have in mind that occasional headache during or after diving sometimes signals serious neurological disorders like vision loss. We show that injuries can develop from both negative and positive pressures in the sinuses. Because visual recovery depends on prompt diagnosis and proper therapy, physicians like otolaryngologists, ophthalmologists and neurologists need to closely collaborate.

Computer-assisted paranasal sinus operation induces diving bradycardia

Unintentional mechanical manipulation anywhere in the distribution of the trigeminal nerve might activate a reflexive bradycardia. Neurosurgeons need to bear in mind detrimental consequences on cardiac function. A female patient (53 years) underwent a computer-assisted (CAS), paranasal sinus operation performed under general anesthesia. During left sided CAS and preparation of the sinus ethmoidalis, heart rate significantly fell from 68 to 32 /min, while systolic arterial blood pressure decreased from 105 to 75 mmHg. Continuation of the preparation again decreased heart rate progressing to transient asystole lasting for 15 s. After removal of the instruments, asystole terminated without medical support. As heart rate decreased after renewed insertion of the CAS probe, sinus ethmoidalis surgery was completed after atropine administration. During neurosurgical procedures, the incidence of the reflex varies between 10 and 18%. To the best of our knowledge, we report for the first time on a direct stimulation of the ethmoidal nerve with instruments (CAS probe) during paranasal surgery. Although normally cardioprotective, exaggeration of the diving reflex can be detrimental and has been implicated in cardiorespiratory disorders, including sudden death and the sudden infant death syndrome.

Diving reflex: can the time course of heart rate reduction be quantified?

In this meta-analysis of diving bradycardia in humans, we sought to quantify any heart rate (HR) reduction using a relatively simple mathematical function. Using the terms "diving reflex,""diving bradycardia,""diving response,""diving plus heart rate," databases were searched. Data from the studies were fitted using HR=c+aexp(-(t-t(0))/τ), where c is the final HR, a is the HR decrease, τ is the time constant of HR decay, and t(0) is the time delay. Of 890 studies, 220 were given closer scrutiny. Only eight of these provided data obtained under comparable conditions. Apneic facial immersion decreased HR with τ=10.4 s and in air alone it was less pronounced and slower (τ=16.2 s). The exponential function fitted the time course of HR decrease closely (r(2)>0.93). The fit was less adequate for apneic-exercising volunteers. During apnea both with and without face immersion, HR decreases along a monoexponential function with a characteristic time constant. HR decrease during exercise with and without face immersion could not readily be described with a simple function: the parasympathetic reaction was partially offset by some sympathetic activity. Thus, we succeeded in quantifying the early time course of diving bradycardia. It is concluded that the diving reflex is useful to diagnose the integrity of efferent cardiovascular autonomic pathways.

Cardiac stunning in the clinic: the full picture

Cardiac stunning refers to different dysfunctional levels occurring after an episode of acute ischemia, despite blood flow is near normal or normal. The phenomenon was initially identified in animal models, where it has been very well characterized. After being established in the experimental setting, it remained unclear, whether a similar syndrome occurs in humans. In addition, it remained controversial, whether stunning was of any clinical relevance as it is spontaneously reversible. Hence, many studies continue to focus on the properties and mechanisms of stunning, although therapies seem more relevant for attenuating and treating myocardial ischemia/reperfusion (I/R) injury, i.e. to bridge until recovery. This article reviews the different facets of cardiac stunning, i.e. myocardial, vascular/microvascular/endothelial, metabolic, neural/neuronal, and electrical stunning. This review also displays where these facets exist and which clinical relevance they might have. Particular attention is directed to the different therapeutic interventions that the various facets of this I/R-induced cardiac injury might require. A final outlook considers possible alternatives to further reduce the detrimental consequences of brief episodes of ischemia and reperfusion.

Correlation between heterogeneous myocardial flow and oxidative metabolism in normoxic and stunned myocardium

Myocardial blood flow exhibits considerable heterogeneity. Consequently, oxygen supply to the myocardium is also heterogeneous, as is myocardial metabolism. Many lines of evidence show a close correlation between local flow and local metabolism in the normoxic myocardium. So far, myocardial metabolism has predominantly been assessed indirectly by using labeled substrates. We used the (18)O isotope, permitting analytical separation of H2(18)O from the (18)O isotope, as well as quantification of regional oxidative metabolism by measuring the tissue residue of oxidation water in the rabbit myocardium. Correlation of local flow with oxidative metabolism was significant in the normoxic myocardium. This correlation was lost in the postischemic/reperfused myocardium. Apart from the established mechanisms underlying myocardial stunning, a mismatch between local flow and oxidative metabolism might thus also contribute to the postischemic dysfunction. In the normoxic myocardium, function should correlate with metabolism and blood flow. For technical reasons, function has not been assessed on a very local scale. Nevertheless, some considerations are presented on the heterogeneity of function as well as on the scale on which heterogeneity should be investigated to convey physiologically meaningful information on regulatory cardiac mechanisms.

Spondyloepiphyseal dysplasia congenita associated with conductive hearing loss

Spondyloepiphyseal dysplasia is a disorder characterized by abnormalities of growth. Previous studies of this disorder have identified a significant incidence of associated hearing loss. Hearing loss has been reported to occur in 25 to 30% of affected patients. To date, all reports of associated hearing loss have indicated the presence of a sensorineural component. In this article, we report the case of a child who was diagnosed with spondyloepiphyseal dysplasia congenita and who was found to have a significant conductive hearing loss with a Carhart's notch, indicating the likely presence of stapes footplate fixation. We also review the diagnosis of this condition and the literature associated with hearing loss as it occurs with this disorder.

Dichromacy characterized by chrominance planes

Dichromacy is described in terms of dichromatic opponent colour spaces. By means of the perceptual criteria 'equally bright', 'neither blue nor yellow' and 'neither red nor green' and embedding in a three-dimensional colour space, it is possible for each type of dichromat to quantify a null-chrominance plane and a null-luminance plane, both of which intersect in the missing colour. These two null planes (or the trace of their intersection with the chromaticity chart) are the chromaticities of the dichromatic opponent primaries. Since a null-luminance plane contains only colour ('chrominance'), it is simply a chrominance plane. Under the assumption that the retinal short-wavelength cones do not contribute to luminance, the chrominance planes of the three types of dichromats intersect in a common straight line, the 'blue' fundamental primary vector. This constellation may serve as a general characterisation of dichromacy.

Childhood pseudohypacusis in patients with high risk for actual hearing loss

OBJECTIVE

While pseudohypacusis or nonorganic hearing loss is a well-recognized phenomenon in adults, it is the aim of this report to heighten the physician's awareness of the occurrence of nonorganic hearing loss in pediatric patients. The medical and otologic histories of 18 cases identified consecutively between 1983 and 1991 at The Children's Hospital, Boston, Massachusetts, were retrospectively reviewed. In these selected cases an analysis of the audiometric configuration, age range, and sex distribution is undertaken. This review highlights the need to rule out pseudohypacusis even in pediatric cases where suspicion is low. A precedent trauma was the presenting complaint in a high percentage of our patient population. This association has not been previously reported in the pediatric literature. While the severity of the traumatic incident was often minor, extensive medical and surgical investigations had been considered before the identification of nonorganic hearing loss.

STUDY DESIGN

A retrospective chart analysis of patients identified with pseudohypacusis over a 7-year period.

METHODS

A tertiary care children's hospital in an urban community. Eighteen consecutively identified patients examined by a staff audiologists at a tertiary care children's hospital. A specific battery of standard audiologic testing with the goal of detecting pseudohypacusis in children.

RESULTS

Successful if additional interventions such as exploratory tympanotomy were avoided.

CONCLUSIONS

Pseudohypacusis was identified in 18 patients with a majority having an antecedent history of trauma. Additional interventions were canceled upon the detection of true threshold values. A high index of suspicion of pseudohypacusis in children and an organized standardized battery of audiologic testing will facilitate early identification of these patients and will avert inappropriate interventions.

Discharge patterns of intramural mechanoreceptive afferents during selective distension of the cat's rectum

The afferent input from the rectum to the central nervous system (CNS) has yet to be thoroughly characterized. The characteristics of mechanoreceptive rectal afferents have been studied in unanaesthetized decerebrate cats. Following lumbo-sacral laminectomy, single-unit activity (occasionally multi-unit activity) was recorded from centrally cut filaments of the sacral dorsal roots (predominantly S2), while a balloon was inflated in the rectum. Starting from their background activities (mean 15.1 imp sec-1, SD 7.6 imp sec-1), afferent discharge rate increased with increasing balloon pressure (mean threshold 6.3 mmHg, SD 3.6 mmHg). The dependence of firing rate on intrarectal pressure began to flatten out at 25 mmHg (mean; SD 10 mmHg). For 22 out of 29 units (76%) complete saturation occurred at 35 mmHg (mean; SD 15 mmHg) with a maximum discharge rate of 31 imp sec-1 (mean; SD 12.6 imp sec-1). In a number of recording sessions, cyclical rectal contractions were observed. In these cases, changes in firing of the units were closely related to changes in intrarectal pressure. Pressure-related afferent activity could be enhanced by parasympathomimetic drugs which augmented rectal contractions. We conclude that sacral dorsal roots contain afferents from low-threshold mechanoreceptors located in the rectal wall, and that these afferents monitor the filling state and contraction level of the rectum.

Magnetic stimulation as a diagnostic tool in cervical nerve root compression and compression-induced neuropathy

Magnetic stimulation of motor cortex and cervical spinal cord was used to assess motor impairment in patients with either cervical nerve root compression or myelopathy. Evoked potentials were recorded from biceps brachii and abductor pollicis brevis. Our interest centered on whether the paresis resulting from root compression is accompanied by an increased latency of magnetically evoked muscle potentials and whether latency is increased in cases of cervical root compression or myelopathy in which no paresis occurs. Latency increase does appear to be a moderately good indicator of disturbed nerve conduction. In particular, prolonged latencies in cases of "subclinical" paresis could be used as an important diagnostic tool for the early detection of motor deficits in cervical compression radiculopathy and myelopathy.

The influence of bacterial collagenase on regeneration of severed rat sciatic nerves

Regeneration of peripheral nerve fibers is impeded by the formation of scar tissue at the site of injury. The possible beneficial effect of collagenase on nerve regeneration was studied using clinical, neurophysiological (evoked potentials) and histological (nerve fiber counts) methods. The sciatic nerves of rats were transected and the severed ends abutted and sewn together. In one series, the area about the lesion was covered with fibrin adhesive and infused with either isotonic saline (controls) or collagenase (treatment group). In the other series, the severed ends of the nerve were inserted into a silicone tube and separated by a collagen plug, which was infused with either saline or collagenase. Compared to the controls, the treated animals showed a significant improvement of clinical and neurophysiological parameters. After 3 months of observation, the collagen content of the transection site was reduced, and in the silicone series, the total number of myelinated axons 5 mm distal to the site of transection was increased, while the fiber diameter distribution was unchanged.

Association of Crohn's disease and multiple sclerosis. Is there a common background?

Crohn's disease (CD) and multiple sclerosis (MS) share familial occurrence and similar epidemiological traits. Apart from one report of both diseases occurring among consanguineous relatives, only three cases of CD and MS in the same patient have thus far been described. We describe here a 29-year-old woman in whom MS developed in 1983 and CD in 1989. The MS may have been the result of a strongly HLA-associated genetic predisposition, while the additional development of CD may have been due either to genetic factors or perhaps simply to chance. Viewing this case in the context of epidemiological data, however, we suggest that the development of CD and MS is based on one or more common genetic factors acting in conjunction with other presumably exogenous factors and triggering HLA antigens to lead to one disease or the other.

[Various genetic models in Crohn disease]

Crohn's disease has a genetic predisposition. In the light of epidemiological data, especially the type of familial clustering, simple modes of inheritance can be excluded. At the first glance, our results implied a polygenic multifactorial basis. Further processing of our data by the "mixed model" of Morton revealed a higher probability for a recessive gene with low penetrance. However, the differences in fit between the various models are relatively slight. Also considering ascertainment problems, a definite decision concerning an appropriate model must be deferred until sure genetic markers have been identified. Nevertheless, only a certain number of manifestations may be ascribed to a genetic predisposition, others have to be catagorized as phenocopies.

Gene and haplotype frequencies of HLA antigens in 269 patients with Crohn's disease

Evidence of strong genetic markers in Crohn's disease (CD) is still absent. Many investigations have focused on HLA antigens, with conflicting results. To obtain more detailed information on the relation of HLA to the disease, we used the HLA data from 269 CD patients to compute the maximum-likelihood estimates of HLA gene and haplotype frequencies. These results provide further evidence that HLA B44 and Cw5 do indeed play a role in the development of CD. Furthermore, it is conceivable from our results that HLA Cw7 may protect against being affected with this disease.

[T-lymphocyte subpopulations in the peripheral blood of patients with Crohn disease]

Immunological disorders seem to be of considerable relevance to the pathogenesis of Crohn's disease (CD). T-cells play a central role in immunoregulation. The T-cell subpopulations of 70 patients with CD were compared to those of age- and sex-matched healthy controls. The suppressor-inducer subpopulations were found to be reduced in CD patients irrespective of wether they were taking steroids or not. In contrast to other subpopulations suppressor-inducer cells remained unchanged during follow-up. The results point to a disturbance in the regulation of suppressor T-cells in patients with Crohn's disease.

Investigation of genetic markers in patients with Crohn's disease and ulcerative colitis

Inflammatory bowel diseases (IBD) as Crohn's disease (CD) and ulcerative colitis (UC) are believed to have a genetic basis. Additional factors are supposed to promote the development of IBD. However, apart from a few reports of HLA associations which await confirmation by other groups strong associations to (a) particular genetic marker(s) are still lacking. We here report on previously unobserved associations of CD to MNSS and UC to the immunoglobulin heavy chain allotype Gm 1,-2,10. We suggest that these factors play a role in a wider spectrum of genetic markers for the development of IBD.

Do dangerousness-oriented commitment laws restrict hospitalization of patients who need treatment? A test

A study at a large urban psychiatric hospital in Pennsylvania evaluated whether the state's dangerousness-oriented commitment criteria restricted hospitalization of patients whom emergency room clinicians considered highly in need of treatment but not dangerous. A total of 390 patients were studied. Eleven patients judged to be highly in need of treatment did not meet any of the commitment criteria, but they were largely compliant with the idea of being treated. An additional 17 patients considered highly in need of treatment met criteria for commitment based on inability to care for self, but most were hospitalized voluntarily. Only one patient who met none of the commitment criteria resisted recommended hospital care, and she was eventually committed involuntarily based on inability to care for self. The data suggest that dangerousness-oriented commitment criteria are flexible enough to provide for treatment of patients in serious need.

Commitment: the consistency of clinicians and the use of legal standards

The reliability and validity of the application of legal criteria for commitment were investigated as part of a larger study. Evaluations of 411 patients by 96 different clinicians showed good interrater reliability for assessment of dangerousness and committability. A strong relationship between ratings of committability and ratings of dangerousness suggests that clinicians were conforming to the logic of the commitment law. Discrepant cases involved patients who desired voluntary admission or whose commitment was completed elsewhere. Results suggest fair application of commitment standards but that two issues of statutory interpretation confused participating clinicians.

On the construction of cross-sectional statistical standards for growth

Cross-sectional growth studies generally produce standardizing groups which are too small to permit the direct construction of standards. This problem can be circumvented by the introduction of appropriate structural assumptions. The two key papers in the literature which focus on this issue, Healy (1962) and Goldstein (1972), give methodologies which involve somewhat different premises. Healy takes the ages of individuals to be uniformly distributed over a well-defined interval (but their precise levels unknown). Goldstein by comparison supposes age levels to be known exactly. Both authors postulate that the characteristic of interest follows a Gaussian density whose mean and variance are each linear functions of time, a + bt and c + dt, say. In this paper we begin to explore the robustness of the two methods. Our results show that Healy's original moment solution to the estimation of (a, b, c and d) may be quite insensitive to departures from a uniform distribution for ages provided that this distribution remains symmetric about the interval mid-point. Moreover, the distribution of the characteristic of interest may deviate from the Gaussian without too much effect, provided that symmetry about the mean a + bt is retained. However, there is much more doubt about asymmetric departures in both cases especially with regard to the estimation of b and d. Opting for simple 'interpolated' estimates of these two parameters (when possible) rather than Healy's original formula-based versions will strongly aid robustness in general.(ABSTRACT TRUNCATED AT 250 WORDS)

HLA antigens in ankylosing spondylitis associated with Crohn's disease. Increased frequency of the HLA phenotype B27,B44

In a consecutive case study 231 patients with Crohn's disease were investigated for ankylosing spondylitis (AS) and HLA-A, B, C, DR antigen association. Eighteen patients (7.8%) had definite AS according to the New York criteria; 13 (72%) were HLA-B27 positive. The phenotype B27,B44 was seen in 8 patients (44%) compared to only 3 (1%) of 300 controls (p less than 10(-7), and 1 (0.5%) of 213 patients with Crohn's disease without AS (p less than 10(-7). We conclude that patients with the phenotype B27,B44 are highly at risk (relative risk = 68.8) for the common manifestation of Crohn's disease and AS.

Association of Crohn's disease with HLA phenotype B44, Cw5

Genetic influence on the development of Crohn's disease (CD) is commonly accepted. However, proof of definite genetic markers is still pending. Most investigations have focused on HLA antigens, and associations with HLA B12 and HLA A2 have been reported, but the design of these retrospective studies is open to criticism. We have undertaken a consecutive study of 96 patients with CD under well-defined conditions in order to test the hypothesis that CD is associated with particular HLA antigens. Our results identify a significant association of CD with the phenotype HLA B44,Cw5. But since a major proportion of the CD patients do not bear this phenotype, other predisposing genetic factors, which have not yet been defined, may exist in addition to environmental factors.

Crohn's disease in a married couple

The aetiopathogenesis of Crohn's disease is still unknown. Multiple occurrence of inflammatory bowel disease among blood relatives of patients with either Crohn's disease or ulcerative colitis is seen much more frequently than would be expected by chance alone, whereas reports on the development of these diseases in spouses are very rare. We describe such a case here, and suggest that chance, rather than an infectious agent, is behind such occurrences.

Monozygotic triplets with Crohn's disease of the colon

Female monozygotic triplets all developed Crohn's disease within a period of 11 mo. The monozygosity was demonstrated by analysis of 24 genetic markers of different chromosomal localization. Crohn's disease was diagnosed using clinical, radiologic, and endoscopic findings. Histologic evaluation of bowel tissue was consistent with Crohn's disease. All 3 patients had colon involvement; the terminal ileum appeared normal. The patient in whom Crohn's disease was first diagnosed had the severest course. Our observations support the role of a genetic influence in the manifestation of Crohn's disease. Nevertheless, environmental factors or microorganisms, or both, have to be taken into account, perhaps as factors promoting the outbreak of Crohn's disease.

Chronic inflammatory polyneuropathy. Reduction of nerve conduction velocities in monkeys by systemic passive transfer of immunoglobulin G

In chronic (relapsing) inflammatory polyneuropathy (CRIP), successful treatment with plasma exchange has led to the concept of pathogenic humoral factors. In 6 patients with CRIP, 5 of whom improved after plasma exchange, the potential pathogenic role of circulating immunoglobulin (Ig) fractions was tested by applying the systemic passive transfer model to marmoset monkeys. After continuous treatment with intramuscular injections for 2-8 weeks, monkeys injected with the crude immunoglobulin fractions or with purified IgG from 5 of the 6 patients showed a significant and partially reversible reduction of the motor nerve conduction velocity (mean 34%, P less than 0.001) when compared with pre-treatment values. In control animals the reduction was 4%. Morphological examination revealed only minor ultrastructural changes of the myelin sheath. Immunocytochemistry revealed that human IgG was able to cross the blood-nerve barrier. It is concluded that the circulating IgG-fraction of patients with CRIP contains a factor that may contribute to the disordered nerve function after crossing the blood-nerve barrier. It may be the removal of this particular factor which is responsible for the rapid recovery of nerve conduction in patients after plasma exchange.

Dynamic properties of Renshaw cells: equivalence of responses to step changes in recruitment and discharge frequency of motor axons

In decerebrate cats, the dynamic responses of Renshaw cells to step changes in input were determined separately both for changes in the number of alpha-axons excited and for changes in the frequency at which they were stimulated. Together, these two input variables to the Renshaw cells describe the level of activity in the motor output from the spinal cord. In either case, the dynamic responses of the interneurons depend only on their static activity before and after an input step occurs, but are otherwise indistinguishable. This favors the interpretation that the two input variables are equivalent under dynamic conditions, i.e., Renshaw cells respond to total motor output.

Static input-output relations in the spinal recurrent inhibitory pathway

The static discharge rate of Renshaw cells (studied in deafferented, intercollicularly decerebrate cats) has a nonlinear dependence on the frequency of trains of stimulus impulses to alpha-motor axons in the ventral root. This dependence is well described by a rectangular hyperbola that approaches saturation with increasing stimulus frequency. The tendency to saturate is independent of the number of motor axons exciting a Renshaw cell. On average, the stimulus frequency at which the discharge rate reaches half its saturation value lies between 10 and 15 Hz. The effect of Renshaw cell activity -- measured as the antidromic inhibition of individual alpha-motoneurons -- reflects the forms of the static frequency characteristics. An electric circuit analog of the Renshaw cell membrane is presented which serves to explain the qualitative features of the static input-output relations; the nonlinearity is the result of synapses with linear properties acting together at the cell membrane.

Lactoperoxidase-catalyzed oxidation of [4-14C]estradiol

The conversion of [4-14C]estradiol to water-soluble products by lactoperoxidase (EC 1.11.1.7) in the presence of added or generated H2O2 was studied using albumin or tyrosine as acceptor. The enzyme was able to catalyze the oxidation and binding of estradiol to albumin even in the absence of 2,4-dichlorophenol at very low concentrations of hydrogen peroxide. Other systems in which H2O2 was replaced by oxygen and Mn2+, light-sensitized riboflavin or glutathione was also shown to be active in the conversion of estradiol to water-soluble products and the effect of inhibitors on these reactions was investigated. Possible mechanisms for the peroxidase-catalyzed formation of these estradio metabolites are discussed.

Effect of oxotremorine on the response of antidromically activated Renshaw cells in decerebrate cats

In intercollicular decerebrate cats, some of which were made spinal in addition, the effect of oxotremorine (intravenous injection, 10-30 mug/kg) was tested on antidromically activated Renshaw cells. Methylatropine premedication prevented the otherwise often fatal drop in blood pressure; ipsilateral dorsal roots L6-S1 and contralateral hindlimb nerves were cut to exclude segmental receptor interference. During supramaximal stimulation of ventral root L7 or the gastrocnemius nerves, an increase of activity ranging from 10-110% was observed. The drug occasionally evoked spontaneous discharges in Renshaw cells, or enhanced activity already present. Alpha motoneuron activity decreased in most cases. The interaction of oxotremorine with atropine and eserine was also investigated on Renshaw cells. Our results suggest that one of the effects of oxotremorine may be a disbalance between motor output and recurrent inhibition.

Metabolism of (4-14C)estradiol by 7,12-dimethylbenz(a) anthracene-induced mammary tumor peroxidase

The peroxidase and estradiol-metabolizing activities of mammary tumors induced by 7,12-dimethylbenz(a)anthracene were determined in fresh and stored tissue. In both cases, a wide variation in peroxidase activity was observed in 47 different tumors tested. The properties of the enzyme found in the tumors were similar to those of lactoperoxidase. It is suggested that the amount of peroxidase present might reflect the ability of tumor cells to differentiate in response to hormonal stimulation and be indicative of the degree of tumor progression.