Non-contact whole-chamber charge density mapping of the left ventricle: preclinical evaluation in a sheep model

BACKGROUND

Conventional contact-based electroanatomic mapping is poorly suited for rapid or dynamic ventricular arrhythmias. Whole-chamber charge density (CD) mapping could efficiently characterize complex ventricular tachyarrhythmias and yield insights into their underlying mechanisms.

OBJECTIVE

This study sought to evaluate the feasibility and accuracy of non-contact whole-chamber left ventricular (LV) CD mapping, and to characterize CD activation patterns during sinus rhythm, ventricular pacing, and ventricular fibrillation (VF).

METHODS

Ischemic scar as defined by CD amplitude thresholds was compared to late gadolinium enhancement criteria on magnetic resonance imaging using an iterative closest point algorithm. Electrograms recorded at sites of tissue contact were compared to the nearest non-contact CD-derived electrograms to calculate signal morphology cross-correlations and time differences. Regions of consistently slow conduction were examined relative to areas of scar and to localized irregular activation (LIA) during VF.

RESULTS

Areas under receiver operating characteristic curves (AUCs) of CD-defined dense and total LV scar were 0.92 ± 0.03 and 0.87 ± 0.06, with accuracies of 0.86±0.03 and 0.80±0.05, respectively. Morphology cross-correlation between 8,677 contact and corresponding non-contact electrograms was 0.93±0.10, with a mean time difference of 2.5±5.6 msec. Areas of consistently slow conduction tended to occur at scar borders and exhibited spatial agreement with LIA during VF (AUC 0.90±0.02).

CONCLUSION

Non-contact LV CD mapping can accurately delineate ischemic scar. CD-derived ventricular electrograms correlate strongly with conventional contact-based electrograms. Regions with consistently slow conduction are often at scar borders and tend to harbor LIA during VF.

Combining endocardial mapping and electrocardiographic imaging (ECGI) for improving PVC localization: A feasibility study

INTRODUCTION

Accurate reconstruction of cardiac activation wavefronts is crucial for clinical diagnosis, management, and treatment of cardiac arrhythmias. Furthermore, reconstruction of activation profiles within the intramural myocardium has long been impossible because electrical mapping was only performed on the endocardial surface. Recent advancements in electrocardiographic imaging (ECGI) have made endocardial and epicardial activation mapping possible. We propose a novel approach to use both endocardial and epicardial mapping in a combined approach to reconstruct intramural activation times.

OBJECTIVE

To implement and validate a combined epicardial/endocardial intramural activation time reconstruction technique.

METHODS

We used 11 simulations of ventricular activation paced from sites throughout myocardial wall and extracted endocardial and epicardial activation maps at approximate clinical resolution. From these maps, we interpolated the activation times through the myocardium using thin-plate-spline radial basis functions. We evaluated activation time reconstruction accuracy using root-mean-squared error (RMSE) of activation times and the percent of nodes within 1 ms of the ground truth.

RESULTS

Reconstructed intramural activation times showed an RMSE and percentage of nodes within 1 ms of the ground truth simulations of 3 ms and 70%, respectively. In the worst case, the RMSE and percentage of nodes were 4 ms and 60%, respectively.

CONCLUSION

We showed that a simple, yet effective combination of clinical endocardial and epicardial activation maps can accurately reconstruct intramural wavefronts. Furthermore, we showed that this approach provided robust reconstructions across multiple intramural stimulation sites.

Tracking seasonal changes in diversity of pollen allergen exposure: Targeted metabarcoding of a subtropical aerobiome

The importance of grass pollen to the global burden of allergic respiratory disease is well established but exposure to subtropical and temperate pollens is difficult to discern. Current monitoring of airborne pollen relies on light microscopy, limiting identification of taxa to family level. This informs seasonal fluctuations in pollen aerobiology but restricts analysis of aerobiological composition. We aimed to test the utility of DNA metabarcoding to identify specific taxa contributing to the aerobiome of environmental air samples, using routine pollen and spore monitoring equipment, as well as assess temporal variation of Poaceae pollen across an entire season. Airborne pollen concentrations were determined by light microscopy over two pollen seasons in the subtropical city of Brisbane (27°32'S, 153°00E), Australia. Thirty daily pollen samples were subjected to high throughput sequencing of the plastid rbcL amplicon. Amplicons corresponded to plants observed in the local biogeographical region with up to 3238 different operational taxonomic units (OTU) detected. The aerobiome sequencing data frequently identified pollen to genus levels with significant quantitative differences in aerobiome diversity between the months and seasons detected. Moreover, multiple peaks of Chloridoideae and Panicoideae pollen were evident over the collection period confirming these grasses as the dominant Poaceae pollen source across the season. Targeted high throughput sequencing of routinely collected airborne pollen samples appears to offer utility to track temporal changes in the aerobiome and shifts in pollen exposure. Precise identification of the composition and temporal distributions of airborne pollen is important for tracking biodiversity and for management of allergic respiratory disease.

Regions of High Dominant Frequency in Chronic Atrial Fibrillation Anchored to Areas of Atrial Fibrosis

Regions within the atria with sustained rapid reentrant or focal activity have been defined as a mechanism of persistent atrial fibrillation (AF). However, the mechanism behind the anchoring of these sites and their stability over time is unknown. We tested the hypothesis that fibrosis anchors sites of high frequency activation during AF and that these sites can be non-invasively determined using cardiac T1 Mapping with MRI. A canine rapid atrial paced model of persistent AF was used (n=12, including 6 controls) for the study. Whole heart T1 Mapping was performed prior to an electrical mapping study. Spatial maps of high dominant frequency (DF) probability were constructed to determine stability of the highest DF sites. These sites were then correlated with fibrotic regions determined by T1 Mapping. The chronic AF animals had at least one site of stable, high DF for at least 22.5 (75%) of 30 minutes of AF. Regions of stable high DF bordered regions of fibrosis as determined by T1 Mapping MRI 82% of the time (p<0.05). Heterogeneous atrial remodeling, specifically fibrosis, arising from chronic AF may provide a substrate that anchors sites of high DF. Cardiac T1 Mapping with MRI may determine such sites non-invasively.

Universal School-Based Intervention Does Not Reduce Socioeconomic Inequalities in Weight Status among Adolescents

Background: Differences in weight status by socioeconomic position occur during adolescence and is known as weight social gradient (WSG). The PRALIMAP (Promotion de l'ALIMentation et de l'Activité Physique) trial highlighted that a universal intervention was effective in reducing overweight and obesity prevalence among adolescents. However, its ability to reduce the WSG is unclear. This study aimed to evaluate the impact of the PRALIMAP intervention on the WSG among adolescents. Methods: Data were obtained from 3504 adolescents who participated in the school-based PRALIMAP trial between 2006 and 2009. The PRALIMAP study consisted of three interventional strategies: educational, environmental, screening and care. Weight status was assessed by body mass index (BMI) z-score and overweight and obesity prevalence. The "indice de position sociale des élèves" was used to measure adolescents' socioeconomic status. Linear regression and hierarchical models were used to assess the WSG and its evolution, respectively. Results: Among all adolescents (14-18 years old), significant WSG was identified at baseline: BMI z-score (β = -0.06; p < 0.0001), overweight and obesity prevalence (β = -2.86; p < 0.0001). Overall, the intervention conferred no significant reduction in the WSG: BMI z-score (β = -0.01 [-0.02 to 0.01], p = 0.48), overweight and obesity prevalence (β = -0.01 [-0.07 to 0.05], p = 0.73). Similar results were observed for adolescents whatever the interventional strategy they benefited from in the PRALIMAP trial. Conclusions: This study provided no evidence that the PRALIMAP universal intervention was effective in reducing the socioeconomic inequalities in weight status among adolescents. Different interventions that account for social differences should be considered to tackle these inequalities.

Validation of Dipole Density Mapping During Atrial Fibrillation and Sinus Rhythm in Human Left Atrium

OBJECTIVES

This study sought to validate the accuracy of noncontact electrograms against contact electrograms in the left atrium during sinus rhythm (SR) and atrial fibrillation (AF).

BACKGROUND

Noncontact mapping offers the opportunity to assess global cardiac activation in the chamber of interest. A novel noncontact mapping system, which records intracardiac voltage to derive cellular charge sources (dipole density), allows real-time mapping of AF to guide ablation.

METHODS

Noncontact and contact unipolar electrogram pairs were recorded simultaneously from multiple locations. Morphology correlation and timing difference of reconstructed electrograms obtained from a noncontact catheter were compared with those from contact electrograms obtained from a contact catheter at the same endocardial locations.

RESULTS

A total of 796 electrogram pairs in SR and 969 electrogram pairs in AF were compared from 20 patients with persistent AF. The median morphology correlation and timing difference (ms) in SR was 0.85 (interquartile range [IQR]: 0.71 to 0.94) and 6.4 ms (IQR: 2.6 to 17.1 ms); in AF was 0.79 (IQR: 0.69 to 0.88) and 14.4 ms (IQR: 6.7 to 26.2 ms), respectively. The correlation was stronger and the timing difference was less when the radial distance (r) from the noncontact catheter center to the endocardium was ≤ 40 versus > 40 mm; 0.87 (IQR: 0.72 to 0.94) versus 0.73 (IQR: 0.56 to 0.88) and 5.7 ms (IQR: 2.6 to 15.4 ms) versus 15.1 ms (IQR: 4.1 to 27.7 ms); p < 0.01 when in SR; 0.81 (IQR: 0.69 to 0.89) versus 0.67 (IQR: 0.45 to 0.82) and 12.3 ms (IQR: 5.9 to 21.8 ms) versus 28.3 ms (IQR: 16.2 to 36.0 ms); p < 0.01 when in AF.

CONCLUSIONS

This novel noncontact dipole density mapping system provides comparable reconstructed atrial electrogram measurements in SR or AF in human left atrium when the anatomical site of interest is ≤40 mm from the mapping catheter.

Acute noncontrast T1-weighted magnetic resonance imaging predicts chronic radiofrequency ablation lesions

BACKGROUND

Magnetic resonance imaging (MRI) has been used to visualize radiofrequency (RF) ablation lesions but the relationship between volumes that enhance in acute MRI and the chronic lesion size is unknown.

OBJECTIVES

The main goal was to use noncontrast (native) T1-weighted (T1w) MRI and late gadolinium enhancement (LGE)-MRI to visualize lesions acutely and chronically and correlate the acute area of enhancement with chronic lesion size in histology.

MATERIALS AND METHODS

In a canine (n = 9) model RF ablation lesions were created in both ventricles. Native T1w MRI and LGE-MRI were acquired acutely after the ablation procedure. After 8 weeks, another set of RF ablations was performed, and the MRI study was repeated. Volume and depth of enhancement in native T1w MRI and LGE-MRI acquired after the initial ablation procedure were correlated with chronic lesion volume and depth in histology.

RESULTS

Thirty-three lesions were analyzed. Native T1w MRI visualized the acute lesions but not the chronic lesions. LGE-MRI showed both acute and chronic lesions. Acute native T1w MRI volume (average of 102.1 ± 48.5 mm³ ) and depth (4.9 ± 1.2 mm) correlated well with chronic histological volume (105.9 ± 51.8 mm³ ) and depth (4.8 ± 1.3 mm) with R² of 0.881 (P < 0.001) and 0.874 (P < 0.001), respectively. Acute LGE-MRI had a significantly higher volume of enhancement of 499.7 ± 214.4 mm³ (P < 0.001) and depth of 7.5 ± 1.8 mm ( P < 0.001) when compared with chronic histological lesion volume and depth.

CONCLUSIONS

Native T1w MRI acquired acutely after RF ablation is a good predictor of chronic lesion size. Acute LGE-MRI significantly overestimates the chronic lesion size.

Higher contact force during radiofrequency ablation leads to a much larger increase in edema as compared to chronic lesion size

INTRODUCTION

Reversible edema is a part of any radiofrequency ablation but its relationship with contact force is unknown. The goal of this study was to characterize through histology and MRI, acute and chronic ablation lesions and reversible edema with contact force.

METHODS AND RESULTS

In a canine model (n = 14), chronic ventricular lesions were created with a 3.5-mm tip ThermoCool SmartTouch (Biosense Webster) catheter at 25 W or 40 W for 30 seconds. Repeat ablation was performed after 3 months to create a second set of lesions (acute). Each ablation procedure was followed by in vivo T2-weighted MRI for edema and late-gadolinium enhancement (LGE) MRI for lesion characterization. For chronic lesions, the mean scar volumes at 25 W and 40 W were 77.8 ± 34.5 mm3 (n = 24) and 139.1 ± 69.7 mm3 (n = 12), respectively. The volume of chronic lesions increased (25 W: P < 0.001, 40 W: P < 0.001) with greater contact force. For acute lesions, the mean volumes of the lesion were 286.0 ± 129.8 mm3 (n = 19) and 422.1 ± 113.1 mm3 (n = 16) for 25 W and 40 W, respectively (P < 0.001 compared to chronic scar). On T2-weighted MRI, the acute edema volume was on average 5.6-8.7 times higher than the acute lesion volume and increased with contact force (25 W: P = 0.001, 40 W: P = 0.011).

CONCLUSION

With increasing contact force, there is a marginal increase in lesion size but accompanied with a significantly larger edema. The reversible edema that is much larger than the chronic lesion volume may explain some of the chronic procedure failures.

Characterization of Gadolinium Contrast Enhancement of Radiofrequency Ablation Lesions in Predicting Edema and Chronic Lesion Size

BACKGROUND

Magnetic resonance imaging (MRI) has been used to acutely visualize radiofrequency ablation lesions, but its accuracy in predicting chronic lesion size is unknown. The main goal of this study was to characterize different areas of enhancement in late gadolinium enhancement MRI done immediately after ablation to predict acute edema and chronic lesion size.

METHODS AND RESULTS

In a canine model (n=10), ventricular radiofrequency lesions were created using ThermoCool SmartTouch (Biosense Webster) catheter. All animals underwent MRI (late gadolinium enhancement and T2-weighted edema imaging) immediately after ablation and after 1, 2, 4, and 8 weeks. Edema, microvascular obstruction, and enhanced volumes were identified in MRI and normalized to chronic histological volume. Immediately after contrast administration, the microvascular obstruction region was 3.2±1.1 times larger than the chronic lesion volume in acute MRI. Even 60 minutes after contrast administration, edema was 8.7±3.31 times and the enhanced area 6.14±2.74 times the chronic lesion volume. Exponential fit to the microvascular obstruction volume was found to be the best predictor of chronic lesion volume at 26.14 minutes (95% prediction interval, 24.35-28.11 minutes) after contrast injection. The edema volume in late gadolinium enhancement correlated well with edema volume in T2-weighted MRI with an R² of 0.99.

CONCLUSION

Microvascular obstruction region on acute late gadolinium enhancement images acquired 26.1 minutes after contrast administration can accurately predict the chronic lesion volume. We also show that T1-weighted MRI images acquired immediately after contrast injection accurately shows edema resulting from radiofrequency ablation.

Real-Time MRI-Guided Cardiac Cryo-Ablation: A Feasibility Study

INTRODUCTION

MRI-based ablation provides an attractive capability of seeing ablation-related tissue changes in real time. Here we describe a real-time MRI-based cardiac cryo-ablation system.

METHODS

Studies were performed in canine model (n = 4) using MR-compatible cryo-ablation devices built for animal use: focal cryo-catheter with 8 mm tip and 28 mm diameter cryo-balloon. The main steps of MRI-guided cardiac cryo-ablation procedure (real-time navigation, confirmation of tip-tissue contact, confirmation of vessel occlusion, real-time monitoring of a freeze zone formation, and intra-procedural assessment of lesions) were validated in a 3 Tesla clinical MRI scanner.

RESULTS

The MRI compatible cryo-devices were advanced to the right atrium (RA) and right ventricle (RV) and their position was confirmed by real-time MRI. Specifically, contact between catheter tip and myocardium and occlusion of superior vena cava (SVC) by the balloon was visually validated. Focal cryo-lesions were created in the RV septum. Circumferential ablation of SVC-RA junction with no gaps was achieved using the cryo-balloon. Real-time visualization of freeze zone formation was achieved in all studies when lesions were successfully created. The ablations and presence of collateral damage were confirmed by T1-weighted and late gadolinium enhancement MRI and gross pathological examination.

CONCLUSION

This study confirms the feasibility of a MRI-based cryo-ablation system in performing cardiac ablation procedures. The system allows real-time catheter navigation, confirmation of catheter tip-tissue contact, validation of vessel occlusion by cryo-balloon, real-time monitoring of a freeze zone formation, and intra-procedural assessment of ablations including collateral damage.

Diverse Fibrosis Architecture and Premature Stimulation Facilitate Initiation of Reentrant Activity Following Chronic Atrial Fibrillation

INTRODUCTION

Patients with paroxysmal atrial fibrillation (AF) often transition between sinus rhythm and AF. For AF to initiate there must be both a trigger and a substrate that facilitates reentrant activity. This trigger is often caused by a premature atrial contraction or focal activations within the atrium. We hypothesize that specific architectures of fibrosis alter local conduction to enable AF.

METHODS AND RESULTS

Control goats (n = 13) and goats in chronic AF (for an average of 6 months, n = 6) had a high-density electrode plaque placed on the LA appendage. Conduction patterns following a premature atrial contraction, caused by an electrical stimulation, were quantified to determine regions of conduction slowing. These regions were compared to architecture, either diffuse fibrosis or regions of obstructive fibrosis, and overall fibrosis levels as determined by histology from the mapped region. The chronic AF goats had more obstructive fibrosis than the controls (17.5 ± 8.0 fibers/mm(2) vs. 8.6 ± 3.0 fibers/mm(2)). Conduction velocity of the AF goats was significantly slowed compared to the control goats in the transverse direction (0.40 ± 0.04 m/s vs. 0.53 ± 0.15 m/s) but not in the longitudinal direction (0.70 ± 0.27 m/s vs. 0.76 ± 0.18 m/s).

CONCLUSIONS

AF-induced atrial remodeling leads to increased obstructive fibrosis and conduction velocity slowing transverse to fiber orientation following premature stimuli. The decrease in conduction velocity causes a decrease in the cardiac wavelength, and increases the likelihood of reentry and AF onset.

His bundle activates faster than ventricular myocardium during prolonged ventricular fibrillation

Background

The Purkinje fiber system has recently been implicated as an important driver of the rapid activation rate during long duration ventricular fibrillation (VF>2 minutes). The goal of this study is to determine whether this activity propagates to or occurs in the proximal specialized conduction system during VF as well.

Methods and Results

An 8×8 array with 300 µm spaced electrodes was placed over the His bundles of isolated, perfused rabbit hearts (n = 12). Ventricular myocardial (VM) and His activations were differentiated by calculating Laplacian recordings from unipolar signals. Activation rates of the VM and His bundle were compared and the His bundle conduction velocity was measured during perfused VF followed by 8 minutes of unperfused VF. During perfused VF the average VM activation rate of 11.04 activations/sec was significantly higher than the His bundle activation rate of 6.88 activations/sec (p<0.05). However from 3–8 minutes of unperfused VF the His system activation rate (6.16, 5.53, 5.14, 5.22, 6.00, and 4.62 activations/sec significantly faster than the rate of the VM (4.67, 3.63, 2.94, 2.24, 3.45, and 2.31 activations/sec) (p<0.05). The conduction velocity of the His system immediately decreased to 94% of the sinus rate during perfused VF then gradually decreased to 67% of sinus rhythm conduction at 8 minutes of unperfused VF.

Conclusion

During prolonged VF the activation rate of the His bundle is faster than that of the VM. This suggests that the proximal conduction system, like the distal Purkinje system, may be an important driver during long duration VF and may be a target for interventional therapy.

Chronic atrial fibrillation causes left ventricular dysfunction in dogs but not goats: experience with dogs, goats, and pigs

Structural remodeling in chronic atrial fibrillation (AF) occurs over weeks to months. To study the electrophysiological, structural, and functional changes that occur in chronic AF, the selection of the best animal model is critical. AF was induced by rapid atrial pacing (50-Hz stimulation every other second) in pigs (n = 4), dogs (n = 8), and goats (n = 9). Animals underwent MRIs at baseline and 6 mo to evaluate left ventricular (LV) ejection fraction (EF). Dogs were given metoprolol (50-100 mg po bid) and digoxin (0.0625-0.125 mg po bid) to limit the ventricular response rate to <180 beats/min and to mitigate the effects of heart failure. The pacing leads in pigs became entirely encapsulated and lost the ability to excite the heart, often before the onset of sustained AF. LV EF in dogs dropped from 54 ± 11% at baseline to 33 ± 7% at 6 mo (P < 0.05), whereas LV EF in goats did not drop significantly (69 ± 8% at baseline vs. 60 ± 9% at 6 mo, P = not significant). After 6 mo of AF, fibrosis levels in dog atria and ventricles increased, whereas only atrial fibrosis levels increased in goats compared with control animals. In our experience, the pig model is not appropriate for chronic rapid atrial pacing-induced AF studies. Rate-controlled chronic AF in the dog model developed HF and LV fibrosis, whereas the goat model developed only atrial fibrosis without ventricular dysfunction and fibrosis. Both the dog and goat models are representative of segments of the patient population with chronic AF.

Effects of high altitude exposure on the pharmacokinetics of furosemide in healthy volunteers

INTRODUCTION

A cascade of pathophysiological events occurs with the ascension to high altitude (H). We have performed studies on the effects of exposure to H on the pharmacokinetics of drugs. The hypothesis behind these studies has been that the exposure to H, which produces marked physiological changes in the body, may alter pharmacokinetics, and consequently, pharmacodynamics. Our previous studies suggest that drugs highly bound to plasma proteins are most likely to exhibit altered disposition.

OBJECTIVE

In continuation of our research, we selected furosemide which is about 98% bound to plasma proteins, renally excreted and has low binding to red blood cells.

SUBJECTS, MATERIALS AND METHODS

Furosemide (40 mg) was administered orally to 3 groups of young healthy volunteers. One group who had been residing at sea level (group L), the same group after 15 hours of exposure to high altitude (3,600 m, group HA) and a group of volunteers living at H for at least 6 months (group HC).

RESULTS

Our results are in accordance with the most recent pharmacokinetic studies on furosemide in which a terminal half-life of approximately 20-30 h was reported. Total proteins were 9.3% and 12.7% higher in groups HA and HC, respectively, than in group L. Albumin in group HC was 8.2% higher than group L. Bilirubin increased 17.7% and 41.2% in groups HA and HC, respectively, in comparison with group L. A rapid disposition rate constant in groups HA and HC was the only pharmacokinetic parameter that was significantly different from those in group L. Concentration of furosemide in plasma water increased significantly after H exposure, thus, the binding diminished from 97.2% in group L to 95.1% and 91.1% in groups HA and HC, respectively.

CONCLUSION

Exposure to H produces an increase in the free fraction of furosemide in humans, which could be of therapeutic importance.

The role of dendritic cells in the innate immune system

Dendritic cells (DCs) are bone-marrow-derived leucocytes that are specialised antigen-presenting cells capable of stimulating a primary T-lymphocyte response to specific antigen. In this chapter we discuss the role DCs play in the innate response acting as a critical link with the adaptive response and the influence of the innate response on dendritic cells.

The microphthalmia transcription factor regulates expression of the tartrate-resistant acid phosphatase gene during terminal differentiation of osteoclasts

The defective terminal differentiation of osteoclasts in mice homozygous for the mi allele of the microphthalmia transcription factor (MITF) gene implies that MITF plays a critical role in regulating gene expression during osteoclast ontogeny. To begin addressing the role of this transcription factor in the osteoclast, target genes need to be identified. In the present work, several lines of evidence show that the gene encoding the enzyme tartrate-resistant acid phosphatase (TRAP) is a target of MITF. Analysis of osteoclasts in vivo in the embryonic forelimb showed that MITF and TRAP RNA were coexpressed in a dynamic pattern during the process of endochondral ossification of long bone. Primary osteoclast-like cells (OCLs) produced from mi/mi mutant mice expressed TRAP messenger RNA (mRNA) at 8-fold lower levels than in OCLs derived from normal mice, indicating a direct link between MITF function and TRAP expression. The activity of mouse TRAP promoter-reporter genes was assayed in the primary OCLs by DNA-mediated transfection, and this activity was shown to depend on a conserved sequence (GGTCATGTGAG) located in the proximal promoter. Recombinant MITF protein recognized specifically this conserved sequence element. Expression of a TRAP promoter-green fluorescent protein (GFP) transgene mimicked the expression of the endogenous TRAP gene during differentiation of osteoclast-like cells, and the expression of the transgene was decreased 8-fold when placed into the mutant mi/mi background. These results are consistent with a role for MITF in gene expression during terminal differentiation of the osteoclast and will allow osteoclast-specific mechanisms of gene regulation to be studied in greater detail.

Deficient testicular and adrenal steroidogenesis in mutant cream (e/e) Syrian hamsters

Coat color genes have been shown to be developmental genes with wide pleiotropic actions. The present study was undertaken to analyze the effects of mutations at the e locus of the Syrian hamster on testicular and adrenal steroidogenesis. Although no differences in body weight were detected, cream (e/e) hamsters had larger testes and smaller adrenals than wildtype (+/+) animals. Plasma testosterone levels were lower in e/e than in +/+ hamsters. However; testicular progesterone levels were higher, and 17-OH-progesterone and testosterone levels were lower in e/e when compared to +/+ hamsters. The efficiency of testicular 17-hydroxylase appear to be reduced in e/e hamsters. Adrenal progesterone levels were higher. 17-OH-progesterone, testosterone, dehydroepiandrosterone sulphate and aldosterone levels were similar, and cortisol levels were lower in e/e when compared to +/+ hamsters. The efficiencies of adrenal 17-hydroxylase and 17-hydroxysteroid dehydrogenase appear to be reduced in e/e hamsters. The present data indicate that steroidogenic deficiencies are present in the testes and adrenals of e/e hamsters, and that the gonadal alterations are more severe than the adrenal ones. The e locus, in the hamster, could be a developmental gene, or could be coding for a component in a signaling pathway under the control of such a gene.