Aryl hydrocarbon receptor ligand production by the gut microbiota is decreased in celiac disease leading to intestinal inflammation

Metabolism of tryptophan by the gut microbiota into derivatives that activate the aryl hydrocarbon receptor (AhR) contributes to intestinal homeostasis. Many chronic inflammatory conditions, including celiac disease involving a loss of tolerance to dietary gluten, are influenced by cues from the gut microbiota. We investigated whether AhR ligand production by the gut microbiota could influence gluten immunopathology in nonobese diabetic (NOD) mice expressing DQ8, a celiac disease susceptibility gene. NOD/DQ8 mice, exposed or not exposed to gluten, were subjected to three interventions directed at enhancing AhR pathway activation. These included a high-tryptophan diet, gavage with Lactobacillus reuteri that produces AhR ligands or treatment with an AhR agonist. We investigated intestinal permeability, gut microbiota composition determined by 16S rRNA gene sequencing, AhR pathway activation in intestinal contents, and small intestinal pathology and inflammatory markers. In NOD/DQ8 mice, a high-tryptophan diet modulated gut microbiota composition and enhanced AhR ligand production. AhR pathway activation by an enriched tryptophan diet, treatment with the AhR ligand producer L. reuteri, or pharmacological stimulation using 6-formylindolo (3,2-b) carbazole (Ficz) decreased immunopathology in NOD/DQ8 mice exposed to gluten. We then determined AhR ligand production by the fecal microbiota and AhR activation in patients with active celiac disease compared to nonceliac control individuals. Patients with active celiac disease demonstrated reduced AhR ligand production and lower intestinal AhR pathway activation. These results highlight gut microbiota-dependent modulation of the AhR pathway in celiac disease and suggest a new therapeutic strategy for treating this disorder.

Microbes and mental health: Can the microbiome help explain clinical heterogeneity in psychiatry?

Trillions of microbes cover the surfaces of our bodies and inhabit our gastrointestinal tract. In the past decade, research efforts examining the role of the microbiome in mental health have moved to the forefront of neuroscience and psychiatry. Based on a foundation of animal studies demonstrating the vital role for microbiota-brain communication in brain development, behavior, and brain function over the life span, clinical studies have started to consider the microbiome in psychiatric disorders. The composition, diversity and function of commensal microbes is influenced by genetic, lifestyle, and environmental factors. This review provides an overview of the factors contributing to individual differences in the microbiome, reviews recent work in psychiatric disorders, and considers what is needed to advance a better understanding of how the microbiome impacts mental health which may help us understand the heterogeneity observed in clinical psychiatric populations.

Tissue response to single-polymer fibers of varying diameters: evaluation of fibrous encapsulation and macrophage density

An in vivo study was conducted to assess the sensitivity of fibrous capsule thickness and macrophage density to polymer fiber diameter. Single polypropylene fibers of diameters ranging from 2.1 to 26.7 microm were implanted in the subcutaneous dorsum of Sprague-Dawley rats. Results at 5 weeks demonstrated reduced fibrous capsule thickness for small fibers. Capsule thickness was 0.6 (+/-1.8) microm, 11.7 (+/-12.0) microm, 20.3 (+/-11.6) microm, and 25.5 (+/-10.0) microm for fibers in the ranges of 2.1 to 5.9, 6.5 to 10.6, 11.1 to 15.8, and 16.7 to 26.7 microm, respectively. Fibers very near to blood vessels had smaller capsules than did those with local vasculature further away. The macrophage density in tissue with fiber diameters 2.1 to 5.9 microm (23.03 +/- 8.67%) was comparable to that of unoperated contralateral control skin (18.72+/-10.06%). For fibers with diameters in the ranges of 6.5 to 10.6, 11.1 to 15.8, and 16.7 to 26.7 microm, macrophage densities were 33.90+/-13.08%, 34.40+/-15.77%, and 41.68+/-13.98%, respectively, all of which were significantly larger (p<0.002) than that for the control. The reduced fibrous capsule thickness and macrophage density for small fibers (<6 microm) compared with large fibers could be due to the reduced cell-material contact surface area or to a curvature threshold effect that triggers cell signaling. A next step will be to extend the analysis to meshes to evaluate fiber-spacing effects on small-fiber biomaterials.

Inductive and inhibitory effects of non-ortho-substituted polychlorinated biphenyls on estrogen metabolism and human cytochromes P450 1A1 and 1B1

The effects of a series of non-ortho-substituted polychlorinated biphenyls (PCBs) on human cytochrome P450 1A1 (CYP1A1), a 17beta-estradiol (E2) 2-hydroxylase, and P450 1B1 (CYP1B1), an E2 4-hydroxylase, were investigated in HepG2 and MCF-7 cells. Elevated rates of 2- and 4-methoxyestradiol (2- and 4-MeOE2) formation in PCB-treated cultures were measured as activities of CYP1A1 and CYP1B1, respectively. Of the congeners investigated, 3,4,4',5-tetrachlorobiphenyl (PCB 81), 3,3',4,4',5-pentachlorobiphenyl (PCB 126), and 3,4',5-trichlorobiphenyl (PCB 39) caused marked stimulation of E2 metabolism in both cell lines. Northern blot analyses confirmed that exposure of MCF-7 cells to PCBs 81, 126, and 39 caused highly elevated levels of the CYP1A1 and CYP1B1 mRNAs. Exposure of MCF-7 cells to 3,3',4,4',5,5'-hexachlorobiphenyl (PCB 169) resulted in elevated levels of the CYP1A1 and CYP1B1 mRNAs, but did not cause elevated rates of E2 metabolism; rather, 4-MeOE2 production was depressed to below control levels in PCB 169-treated cultures. PCB 169 also inhibited the 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced 4-MeOE2 and, to a lesser extent, 2-MeOE2 production in MCF-7 cells, as did PCB 126 and several other congeners. In microsomal assays, inhibition of cDNA-expressed human CYP1B1 by PCBs 169 and 126 was demonstrated. These studies with one subgroup of PCBs, the non-ortho-substituted congeners, underscore the complexity and diversity of effects of PCBs, as individual congeners were found both to induce expression and to inhibit activity of human CYP1B1 and CYP1A1.

Induction and localization of cytochrome P450 1B1 (CYP1B1) protein in the livers of TCDD-treated rats: detection using polyclonal antibodies raised to histidine-tagged fusion proteins produced and purified from bacteria

Knowledge of the response of cytochrome P450 1B1 (CYP1B1) to exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in both humans and rodents is limited. To improve the analysis of CYP1 proteins, specific CYP1B1 and CYP1A1 polypeptides were expressed as hexahistidine-tagged fusion proteins in Escherichia coli, purified to homogeneity and used to produce polyclonal antibodies in rabbits. Immunoblot analyses showed that these antibodies were specific and sensitive, detecting both the human and rat forms of the respective isozymes and exhibiting negligible cross-reactivity between the two known CYP1 subfamilies. We show that CYP1B1, CYP1A1 and CYP1A2 protein levels were induced in the livers of female Sprague-Dawley rats following either acute (single dose of 25 microg TCDD/kg) or chronic (125 ng TCDD/kg/day for 30 weeks) exposure to TCDD. CYP1B1 protein exhibited a dose-response to TCDD that was different from those of CYP1A1 and CYP1A2. CYP1B1 induction appeared to be less sensitive to TCDD exposure, with induction occurring at higher doses of TCDD than that required for induction of CYP1A1 or CYP1A2. Immunohistochemical analysis showed that in animals chronically exposed to TCDD (35 ng/kg/day for 30 weeks), CYP1B1 was induced only in centrilobular hepatocytes, a pattern of expression similar to that of CYP1A1 and CYP1A2. These observations of cellular co-localization of the CYP1 cytochromes in livers of TCDD-treated rats and apparent differences in both protein amounts and dose-response are indicative of both common and unique regulation of CYP1 induction.

Metabolism of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) by human cytochrome P4501B1

Cytochrome P4501B1 (CYP1B1) is the most recently identified member of the dioxin-inducible CYP1 family. CYP1B1 is constitutively expressed in most human tissues, including colon and breast, and can activate numerous chemically diverse carcinogens. We evaluated the metabolism of the dietary heterocyclic amine carcinogen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) by microsomes from yeast expressing the human CYP1B1 protein. PhIP metabolites were analysed by HPLC with fluorescence and absorbance detection. We found that human CYP1B1 metabolizes PhIP to three products: N2-OH-PhIP, a mutagenic activation product; 4'-OH-PhIP, a detoxification product; and 2-OH-PhIP, the mutagenic potential of which is unknown. Metabolite identity was confirmed by co-elution with authentic standards and synchronous fluorescence spectroscopy. The identity of the 2-OH-PhIP standard was additionally confirmed by mass spectrometry. Kinetic studies of the formation of N2-OH-PhIP, 4'-OH-PhIP and 2-OH-PhIP by CYP1B1 indicated apparent Km values of 5.7 +/- 1.3, 2.2 +/- 0.5 and 1.3 +/- 0.2 microM, respectively. Apparent turnover rates were 0.40 +/- 0.03, 0.93 +/- 0.02 and 0.04 +/- 0.00 nmol product/min nmol P450, respectively. At saturating levels of substrate, CYP1B1-mediated formation of the non-mutagenic metabolite 4'-OH-PhIP was favored two-fold over that of the mutagenic metabolite, N2-OH-PhIP and >10-fold over that of 2-OH-PhIP. The formation of N2-OH-PhIP, a potent mutagen implicated in the etiology of human colon and breast cancer, indicates that CYP1B1 may play an important role in PhIP-mediated carcinogenesis.

Induction of cytochrome P450 1B1 and catechol estrogen metabolism in ACHN human renal adenocarcinoma cells

The catechol estrogen metabolites of 17beta-estradiol (E2), 2-hydroxyestradiol (OHE2) and 4-OHE2, differ in hormonal properties and carcinogenic potential. In Syrian hamster kidney, 4-OHE2 induces clear-cell carcinoma whereas 2-OHE2 does not, and an E2 4-hydroxylase appears to be involved in E2-induced carcinogenesis in these animals. Specific E2 4-hydroxylase activity has been observed in extrahepatic tissues from several species. In humans, cytochrome P450 1B1 (CYP1B1) appears to be an extrahepatic E2 4-hydroxylase under the regulatory control of the aromatic hydrocarbon receptor (AhR). As an initial approach to investigating CYP1B1 expression and E2 4-hydroxylase activity in human kidney, we used the ACHN cell line, derived from a human renal adenocarcinoma. In untreated ACHN cells, a very low level of CYP1B1 mRNA expression was observed and CYP1B1 protein could not be detected; however, in ACHN cells exposed to the high-affinity AhR ligand, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), CYP1B1 mRNA levels were elevated 28-fold, and the CYP1B1 protein was detected by immunoblot analysis. Exposure of ACHN cells to TCDD resulted in minimal induction of the CYP1A1 mRNA, and the CYP1A1 protein was not detectable prior to or after exposure to TCDD. E2 hydroxylase activity could not be detected with microsomes from untreated ACHN cells, although activities at C-4 and, to a lesser extent, at C-2 of E2 were observed with microsomes from TCDD-treated ACHN cells. In experiments with intact ACHN cells, elevated rates of formation of 4-methoxyestradiol (MeOE2) and 2-MeOE2 were observed in response to treatment with TCDD. The EC50 for induction of the CYP1B1 mRNA was 1.5 nM TCDD; EC50s for the stimulation of 2- and 4-MeOE2 formation were 0.68 and 1.1 nM TCDD. These results indicate that the ACHN cell line may be a useful in vitro model system to study the regulation of CYP1B1 expression and the cytotoxic effects associated with E2 4-hydroxylation.

17 beta-estradiol hydroxylation catalyzed by human cytochrome P450 1B1

The 4-hydroxy metabolite of 17 beta-estradiol (E2) has been implicated in the carcinogenicity of this hormone. Previous studies showed that aryl hydrocarbon-receptor agonists induced a cytochrome P450 that catalyzed the 4-hydroxylation of E2. This activity was associated with human P450 1B1. To determine the relationship of the human P450 1B1 gene product and E2 4-hydroxylation, the protein was expressed in Saccharomyces cerevisiae. Microsomes from the transformed yeast catalyzed the 4- and 2-hydroxylation of E2 with Km values of 0.71 and 0.78 microM and turnover numbers of 1.39 and 0.27 nmol product min-1.nmol P450-1, respectively. Treatment of MCF-7 human breast cancer cells with the aryl hydrocarbon-receptor ligand indolo[3,2-b]carbazole resulted in a concentration-dependent increase in P450 1B1 and P450 1A1 mRNA levels, and caused increased rates of 2-, 4-, 6 alpha-, and 15 alpha-hydroxylation of E2. At an E2 concentration of 10 nM, the increased rates of 2- and 4-hydroxylation were approximately equal, emphasizing the significance of the low Km P450 1B1-component of E2 metabolism. These studies demonstrate that human P450 1B1 is a catalytically efficient E2 4-hydroxylase that is likely to participate in endocrine regulation and the toxicity of estrogens.

Activation of chemically diverse procarcinogens by human cytochrome P-450 1B1

A human cytochrome P-450 (P450) 1B1 cDNA was expressed in Saccharomyces cerevisiae and the microsomes containing P450 1B1 were used to examine the selectivity of this enzyme in the activation of a variety of environmental carcinogens and mutagens in Salmonella typhimurium TA1535/pSK1002 or NM2009 tester strains, using the SOS response as an end point of DNA damage. We also determined and compared these activities of P450 1B1 with those catalyzed by recombinant human P450s 1A1 and 1A2, which were purified from membranes of Escherichia coli. The carcinogenic chemicals tested included 27 polycyclic aromatic hydrocarbons and their dihydrodiol derivatives, 17 heterocyclic and aryl amines and aminoazo dyes, three mycotoxins, two nitroaromatic hydrocarbons, N-nitrosodimethylamine, vinyl carbamate, and acrylonitrile. Among the three P450 enzymes examined here, P450 lB1 was found to have the highest catalytic activities for the activation of 11,12-dihydroxy-11,12-dihydrodibenzo[a,l]pyrene, 1,2-dihydroxy-1,2-dihydro-5-methylchrysene, (+)-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene, 11,12-dihydroxy-11,12-dihydrobenzo[g]chrysene, 3,4-dihydroxy-3,4-dihydrobenzo[c]phenanthrene, 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole, 2-aminoanthracene, 3-methoxy-4-aminoazobenzene, and 2-nitropyrene. P450 1B1 also catalyzed the activation of 2-amino-3,5-dimethylimidazo[4,5-f]quinoline, 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline, 2-amino-3-methylimidazo[4,5-f]quinoline, 2-aminofluorene, 6-aminochrysene and its 1,2-dihydrodiol, (-)-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene, 1,2-dihydroxy-1,2-dihydrochrysene, 1,2-dihydroxy-1,2-dihydro-5,6-dimethylchrysene, 2,3-dihydroxy-2,3-dihydrofluoranthene, 3,4-dihydroxy-3,4-dihydro-7,12-dimethylbenz[a]anthracene, and 6-nitrochrysene to appreciable extents. However, P450 1B1 did not produce genotoxic products from benzo[a]pyrene, trans- 3,4-dihydroxy-3,4-dihydrobenzo[a]anthracene, trans-8,9-dihydroxy-8,9-dihydrobenzo[a]anthracene, 7,12-dimethylbenz[a]anthracene and its cis-5,6-dihydrodiol, 5-methylchrysene, 11,12-dihydroxy-11,12-dihydro-3-methylcholanthrene, 1,2-dihydroxy-1,2-dihydro-6-methylchrysene, benzo[c]phenanthrene, 2-amino-6-methyldipyridol[1,2-a:3',2'-d]imidazole, 2-acetylaminofluorene, benzidine, 2-naphthylamine, aflatoxin B1, aflatoxin G1, sterigmatocystin, N-nitrosodimethylamine, vinyl carbamate, or acrylonitrile in this assay system. P450 1B1 is expressed constitutively in extrahepatic organs, including fetal tissue samples, and is highly inducible in various organs by 2,3,7,8-tetrachlorodibenzo-p-dioxin and related compounds in experimental animal models. Thus, activation of procarcinogens by P450 lB1 may contribute to human tumors of extrahepatic origin.

The effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin on estrogen metabolism in MCF-7 breast cancer cells: evidence for induction of a novel 17 beta-estradiol 4-hydroxylase

Rates of microsomal 17 beta-estradiol (E2) hydroxylation at the C-2, -4, -6 alpha, and -15 alpha positions are each induced greater than 10-fold by treating MCF-7 breast cancer cells with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The TCDD-induced activities at the C-2, -6 alpha and -15 alpha positions have been attributed to cytochrome P450 1A1 (CYP1A1); however, the low Km 4-hydroxylase induced by TCDD appears to be a distinct enzyme. We report here that antibodies to cytochrome P450-EF (mouse CYP1B1) selectivity inhibited the C-4 hydroxylation of E2 catalyzed by microsomes from TCDD-treated MCF-7 cells. Western blots probed with anti-CYP1B antibodies showed the induction of a 52 kDa microsomal protein in response to treatment with TCDD in MCF-7 cells. Western blots of microsomes from HepG2 cells did not show the TCDD-induced 52 kDa protein, and microsomes from TCDD-treated HepG2 cells did not catalyze a low Km hydroxylation of E2 at C-4. Cellular metabolism experiments also showed induction of both the C-2 and -4 hydroxylation pathways in TCDD-treated MCF-7 cells as evidenced by elevated 2- and 4-methoxyestradiol (MeOE2) formation. In contrast, TCDD-treated HepG2 cells showed 2-MeOE2 formation predominantly over 4-MeOE2. Northern blots of RNA isolated from untreated and TCDD-treated cells, when probed with the human CYP1B1 cDNA, showed induction of a 5.2 kb RNA in MCF-7 cells but not in HepG2 cells in response to treatment with TCDD. These results provide additional evidence for the induction by TCDD of a novel E2 4-hydroxylase in MCF-7 cells but not in HepG2 cells and indicate possible endocrine regulatory roles for the newly discovered group of enzymes of the CYP1B subfamily.

Heparin-protamine mismatch. A controllable factor in bleeding after open heart surgery

OBJECTIVE

To test the effect of a new system designed to reduce heparin-protamine mismatch on bleeding after open heart surgery.

DESIGN

Nonrandomized but consecutive retrospective review of patients undergoing open heart surgery during a 9-month period.

SETTING

Multispecialty referral center.

PATIENTS

A total of 150 patients comparable by age, body surface area, and coagulation status undergoing primary open heart surgery for either coronary bypass or heart valve replacement.

INTERVENTION

In the first 75 patients (group 1), heparin sodium was neutralized with protamine sulfate, using a fixed ratio (1 mg of heparin sodium to 1.3 mg of protamine sulfate). An activated clotting time was used to confirm heparin neutralization. For the subsequent 75 patients (group 2), titration of heparin and protamine from defined lots was accomplished using activated clotting times adjusted and matched to drug lots to minimize biologic variability. Groups 1 and 2 had comparable operations, pump times, and cross-clamp times.

MAIN OUTCOME MEASURES

Doses of heparin and protamine and their effect on blood product transfusion and postoperative bleeding were evaluated in all patients.

RESULTS

The average protamine sulfate dose for group 2 patients (287.56 +/- 8.3 mg) was significantly lower than that for group 1 (346.01 +/- 12.6 mg) (P < .0005). Less protamine was associated with the transfusion of fewer red blood cells (0.92 +/- 0.15 vs 2.57 +/- 0.38 U) (P < .001), platelets (0.72 +/- 0.8 vs 2.96 +/- 0.80 U) (P < .01), and fresh-frozen plasma (0.83 +/- 2.0 vs 2.01 +/- 0.48 U) (P < .03). No patients in group 2 required reexploration for bleeding, compared with eight patients in group 1.

CONCLUSIONS

A reduction in protamine dose was associated with significant decreases in blood product use and postoperative bleeding. Excess protamine warrants consideration as both an important and a controllable factor in coagulopathy after open heart surgery.

Complete cDNA sequence of a human dioxin-inducible mRNA identifies a new gene subfamily of cytochrome P450 that maps to chromosome 2

Previously, levels of a novel human mRNA, detected by a recombinant cDNA designated clone 1, were shown to be increased 50-fold in response to treatment of a keratinocyte cell line with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), in part as a function of increased rates of gene transcription (Sutter, T.R., Guzman, K., Dold, K.M., and Greenlee, W.F. (1991) Science 254, 415-418). Here we report the complete corresponding 5.1-kilobase cDNA sequence. A single open reading frame that predicts a protein of 543 amino acid residues was determined by computer-assisted analysis of the cDNA sequence. This predicted protein identifies a new gene subfamily of cytochrome P450, cytochrome P4501B1 (CYP1B1), that maps to human chromosome 2. Southern blot analysis of genomic DNA indicates that the human CYP1B subfamily is likely to contain only this single gene. Northern blot analysis of RNA isolated from primary cultures of normal human epidermal keratinocytes showed approximately 100-fold increased levels of the CYP1B1 mRNA after treatment with 10 nM TCDD for 24 h. Low levels of constitutive CYP1B1 mRNA were detected in 15 different human tissue samples. These results indicate that CYP1B1 is expressed in many normal human tissues and advance our understanding of the complexity of a gene family of cytochromes P450 whose expression is altered by TCDD.

Effects of Wearing a Helmet on Thermal Balance While Cycling in the Heat

In brief: Many cyclists refuse to wear helmets because they produce discomfort and drag. To determine the effects of wearing a helmet on thermal balance and rating of perceived exertion while cycling in the heat, six male competitive cyclists aged 19 to 32 rode a stationary bicycle attached to a road-racing simulator in an environmentally controlled chamber for two hours at 70% V O2 max. Measurements were taken of rectal and skin temperatures, V O2, heart rate, sweat rate, and rating of perceived exertion. The results showed that (under the experimental conditions used) wearing a helmet while cycling in the heat does not alter thermal balance or cardiovascular strain compared with not wearing a helmet.

High-power-laser adaptive phased arrays

Results of a program to investigate the properties of a phase-conjugation adaptive array driven by independent laser oscillators are described. Data are presented for a five-channel linear array propagating over 1-km range in the adaptive mode with correction of atmospheric effects. Target plane measurements indicate that near diffraction-limited performance has been achieved with a system scalable to high power levels.

Phase locking of a multimode to a single-mode He-Ne laser

Two independent He-Ne lasers operating at 0.6328 microm were phase locked to a very high degree of coherence using feedback control. One of these lasers was single mode and the other multimode. The results suggest that the present technique can be used to generate high-power, coherent light pulses from an array of He-Ne lasers.

Reflection Coefficients for Wires and Cables at 106 mum

Measurements are given of the reflectivity coefficient for a variety of wires and cables at 10.6 mum. The results are presented as a function of wire incidence angle for two polarizations, parallel and perpendicular to the samples. The normal incidence reflectivity is very high, ranging from 610% for aluminum wire down to 16.8% for hemp rope in parallel polarization. The perpendicular polarization results are lower by a factor that varied from 5.9 to 2.04. Depolarization by the wires was also determined. The depolarization ratio was found to vary between 17.7% and 1%, being larger for the more irregular samples. The results indicate that a wire avoidance system could be developed for airplanes or helicopters using a scanning 10.6 microm laser and coherent receiver. The power required for such an application is estimated from the data and is found to be relatively low, only 28 W being required to cover a 20 degrees x 90 degrees field in 1 sec.

Compensation for Atmospheric Phase Effects at 10.6 micro

A holographic technique to compensate for atmospherically induced phase distortion of a 10.6-micro laser beam is presented. After a brief outline of the principle of adaptive phase-distortion compensation, the experimental setup to demonstrate feasibility is described. Results obtained for a reflecting target at distances of 150 m and 4600 m are presented and discussed in detail. It is shown that the power delivered onto a target and thus the return signal can be significantly increased by the principle of adaptive phase-distortion compensation. By compensating for phase distortions in both the transmitted and received beams, the signal-to-noise ratio of the received signal can be improved by a factor of N(2), N being the number of apertures used, if the phase relation was completely random beforehand. The results of these tests demonstrate that large arrays can be utilized in spite of the distorting effects which are normally produced by the atmosphere.