Biomedical subjects

E M Walker

Publications and source records attributed to E M Walker.

At least 37 records · Page 2Linked to original sources

PubMed1992

Mobilization of lead in mice by administration of monoalkyl esters of meso-2,3-dimercaptosuccinic acid.

The following six monoalkyl esters of meso-2,3-dimercaptosuccinic acid (DMSA) were synthesized and evaluated for relative activities in mobilizing lead from kidneys and brains of lead-bearing mice: n-propyl (Mn-PDMS), i-propyl (Mi-PDMS), n-butyl (Mn-BDMS), i-butyl (Mi-BDMS), n-amyl (Mn-ADMS) and i-amyl meso-2,3-dimercaptosuccinate (Mi-ADMS). DMSA was used as a positive control. When each was administered intraperitoneally (i.p.) as a single dose of 2.0 mmol/kg, DMSA lowered the kidney lead concentration 52%, while the monoesters effected reductions of 54-75%. Mn-ADMS was toxic at this dose. DMSA lowered the brain lead level 20% when given as a single dose, while the monoesters conferred reductions of 64-87%. When given as 5 daily i.p. injections at 0.5 mmol/kg, DMSA reduced the kidney lead concentration 45%, while the monoesters caused reductions of 56-73%. DMSA lowered the brain lead concentration 35% on the 5-day treatment regimen, while the monoesters evoked reductions of 59-75%. Mi-ADMS was equally effective when given orally or i.p. The i.p. LD50 value of this analog in mice is 3.0 mmol/kg, a value which lies between the reported LD50 doses of DMSA (16.0 mmol/kg) and dimercaprol (1.1 mmol/kg). It is suggested that the ability of these monoesters to cross cell membranes may account for their superiority to DMSA in mobilizing brain lead in this animal model.

Animals↗

PubMed1992

N-benzyl-N-lactyl dithiocarbamate treatment of mice after chronic cadmium administration.

Administration of N-benzyl-N-lactyl dithiocarbamate (BLDTC) to mice after chronic cadmium (Cd) administration evoked a prompt, dose-dependent reduction of the whole body burden; 75% of the retained Cd was mobilized and excreted after 20 i.p. injections of BLDTC at 1.0 mmol/kg/injection. This same dose regimen produced 71% and 98% reductions of the renal and hepatic Cd concentrations, respectively. There was no reduction by BLDTC of the endogenous level of any of seven other metals measured: iron, magnesium, selenium, copper, calcium, zinc, and manganese. Renal proximal tubular damage in mice which received Cd followed by BLDTC was much less than that observed in kidneys from mice which received Cd alone. Chronic Cd administration led to substantial epithelial vacuolar damage to renal distal tubules, and this process was not apparently reversed or antagonized by BLDTC treatment to the extent observed in proximal tubules.

Animals↗

PubMed1992

Enhanced mobilization of hepatic cadmium in mice upon coadministration of an N, N-disubstituted dithiocarbamate and an alkyl monoester of dimercaptosuccinate.

Oral (po) administration of mono-iso-amyl (2,3-dimercapto) succinate (Mi-ADMS), 0.5 mmol/kg for three consecutive days, to mice previously injected with cadmium (Cd) chloride reduced the whole body Cd burden 34%. Intraperitoneal (ip) administration of N-iso-amyl-N-glucaminedithiocarbamate (i-AmGDTC) by the same regimen reduced total body Cd 41%. Coadministration of the two compounds reduced the whole body Cd burden 60% (p less than 0.05). The liver Cd concentration was reduced 56% and 50%, respectively, by Mi-ADMS given po and i-AmGDTC given ip, each at 0.5 mmol/kg for three consecutive days. Coadministration of the two chelators reduced the liver Cd concentration 90% (p less than 0.05). The kidney Cd concentration was reduced 10% by Mi-ADMS alone, and 60% by i-AmGDTC alone, but there was only a 47% reduction when the two chelators were coadministered, probably as a result of redistribution of mobilized hepatic Cd to the kidneys. As 50-55% of the administered Cd is sequestered in the liver in this mouse model, it is concluded that coadministration of the two chemical classes of Cd complexing agents may offer a therapeutic advantage over administration of either agent alone.

Administration, Oral↗

PubMed1991

Antifilarial cellular responses detected in a Haitian pediatric population by use of a microblastogenesis assay.

Previous reports have demonstrated age-related shifts in antifilarial humoral immune responses in 6- to 10-year-old Haitian children; the responses consisted of elevated parasite-specific IgG2 and IgG3 in amicrofilaremic children and elevated IgG4 in microfilaremic children. In this study, the cell-mediated immune responses to soluble adult and microfilarial extracts of Brugia pahangi, determined by use of a microblastogenesis assay, were examined. Capillary blood samples were collected by finger prick from 176 Haitian children in an area with endemic Wuchereria bancrofti. Antigen-specific cellular responsiveness varied as a function of infection status but not age or sex; amicrofilaremic children had significantly greater responses to adult antigens than did microfilaremic children. Significant responses were detected in children less than 2 years of age; thus, correlations observed between filarial antigen-specific responses and infection status are established early in life.

Adolescent↗

PubMed1991

Changes in the surface of Leptospira interrogans serovar grippotyphosa during in vitro cultivation.

Surface components of virulent and attenuated Leptospira interrogans serovar grippotyphosa were compared by using Triton X-114 solubilization and phase partitioning, immunoprecipitation of intact organisms, and freeze-fracture electron microscopy. Removal of the leptospiral outer membrane by using 0.1% Triton X-114 was demonstrated by whole-mount electron microscopy and by essentially complete solubilization of a lipopolysaccharidelike substance (LLS) from the outer membrane. Triton X-114 (0.1%) did not solubilize subsurface proteins, such as endoflagellar filaments or penicillin-binding proteins, which are markers for the periplasmic space and inner membrane, respectively. Triton X-114 solubilized material from both the virulent and attenuated strains, which partitioned into the hydrophobic, detergent phase, contained LLS and major proteins of 41 and 44 kDa, which were also immunoprecipitable from intact organisms. The virulent strain contained greater amounts of an LLS component with an apparent molecular mass of 30 kDa (R(f) = 0.57), whereas the attenuated strain contained larger amounts of an LLS component with an apparent molecular mass of 20 kDa (R(f) = 0.74). Differences in protein components between virulent and attenuated organisms were also detected; whereas the 41- and 44-kDa proteins were immunoprecipitated in equal amounts from both the virulent and attenuated strains, a 33-kDa protein was immunoprecipitated in significantly greater amounts from the attenuated strain. Quantitation of outer membrane particle density by freeze-fracture electron microscopy showed that both strains had a low transmembrane outer membrane protein content compared with that of typical gram-negative bacteria. The virulent and attenuated strains had 443 and 990 particles (P less than 0.000001) per micron, respectively, in the concave outer membrane fracture face. These findings suggest that in vitro cultivation of L. interrogans is accompanied by quantitative and qualitative changes in both LLS and outer membrane-associated proteins.

Animals↗

PubMed1991

Treponema pallidum subsp. pallidum has a single, circular chromosome with a size of approximately 900 kilobase pairs.

The genome size and chromosome conformation of Treponema pallidum subsp. pallidum, Nichols strain, were determined by contour-clamped homogeneous electric field electrophoresis, a pulsed-field gel electrophoresis technique. Digestion of T. pallidum subsp. pallidum DNA with the restriction endonucleases NotI and SpeI produced 12 and 26 fragments, respectively. Summation of the physical lengths of the fragments produced by NotI and SpeI cleavage yielded average sizes of 900 and 913 kbp, respectively, for the genome of T. pallidum subsp. pallidum. Contour-clamped homogeneous electric field electrophoresis of T. pallidum subsp. pallidum DNA exposed to 4 krads of gamma irradiation resolved a single band of 800 to 1,000 kbp; treatment of the DNA with 16 krads of gamma irradiation resulted in the production of smaller fragments, whereas untreated DNA did not migrate into the gels. The gamma irradiation results indicate that T. pallidum subsp. pallidum has a single, circular chromosome that was linearized at a dosage of 4 krads of gamma irradiation. The size estimate provided by restriction endonuclease digestion with NotI and SpeI shows that the genome of T. pallidum subsp. pallidum, at approximately 900 kbp, is considerably smaller than the 13,700-kbp genome size calculated from renaturation kinetics.

Chromosomes, Bacterial↗

PubMed1991

Analysis of outer membrane ultrastructure of pathogenic Treponema and Borrelia species by freeze-fracture electron microscopy.

We analyzed the outer membrane (OM) ultrastructure of four pathogenic members of the family Spirochaetaceae by freeze fracture. The OM of Treponema pallidum subsp. pertenue contained a low intramembranous particle concentration, indicating that it contains few OM transmembrane proteins. The concave OM fracture faces of Treponema hyodysenteriae and Borrelia burgdorferi contained dense populations of particles, typical of gram-negative organisms. A relatively low concentration of particles which were evenly divided between a small and a large species was present in the concave OM fracture face of Borrelia hermsii; the convex OM fracture face contained only small particles. As for gram-negative bacteria, the convex OM fracture face particle concentrations of these pathogens were low. These spirochetes cleaved preferentially within the OM, in contrast to typical gram-negative bacteria, which tend to fracture within the inner membrane. The OM ultrastructure of T. pallidum subsp. pertenue provides an explanation for the lack of antigenicity of the treponemal surface and may reflect a mechanism by which this pathogen evades the host immune response.

Borrelia↗

PubMed1991

Purification and characterization of Giardia lamblia antigens in the feces of Mongolian gerbils.

In a recent study, we identified Giardia lamblia 65- and 70-kDa antigens in the feces of infected Mongolian gerbils. The 65-kDa antigen was from a strain isolated from a human with symptoms of giardiasis, and the 70-kDa antigen was from a strain isolated from a human with no symptoms of giardiasis. In this study, we used preparative electrophoresis and electroelution techniques to purify these antigens to a degree which showed a single discrete protein band on silver-stained polyacrylamide gels. By enzyme-linked immunoelectrotransfer blot, common epitopes on the 65- and 70-kDa antigens were indicated by their cross-reactivity with rabbit anti-65-kDa and anti-70-kDa sera. By indirect immunofluorescence assay, the cysts and trophozoites of the two strains cross-reacted with these sera. Of seven lectins tested, only concanavalin A bound to the 70-kDa antigen, suggesting a glycoprotein, and it possessed a low isoelectric point as assessed by preparative isoelectric focusing. Molecular mass estimations of these antigens by sodium dodecyl sulfate-polyacrylamide gradient gel electrophoresis were similar to the 65- and 70-kDa estimations obtained by native polyacrylamide gradient gel electrophoresis. Although the 65- and 70-kDa antigens proved to be resistant to 100 degrees C heat and stable in storage for up to 25 months at -20 degrees C, neither appeared to be the same as a fecal G. lamblia antigen with similar molecular mass found by other investigators. This suggests that variable G. lamblia antigens may be found in the feces of infected humans.

Animals↗

PubMed1991

Experimental Onchocerca volvulus infections in mangabey monkeys (Cercocebus atys) compared to infections in humans and chimpanzees (Pan troglodytes).

Three chimpanzees, three mangabey monkeys (Cercocebus atys), and 14 patas monkeys (Erythrocebus patas) were inoculated with L3 Onchocerca volvulus of Guatemalan origin. One chimpanzee and two mangabey monkeys developed antibody activity to at least three different antigens. Both mangabey monkeys recognized a 20 kDa antigen 3.5-5 months post-inoculation, and the monkeys and the chimpanzee developed antibody activity to 14 and 22 kDa antigens 7.5-13 months post-inoculation. One mangabey monkey and the chimpanzee became microfilaria-positive in skin snips at 16 and 21 months post-inoculation, respectively. Antibody activity to the 20 kDa antigen in the mangabey monkeys is noteworthy because of the prominence of this antigen among putatively immune persons living in onchocerciasis-endemic areas. The two mangabey monkeys responded parasitologically in a manner comparable to immune humans. No microfilariae were detected in one monkey and only scant numbers of microfilariae were observed in the second. The mangabey monkey may be a good animal model for the study of onchocerciasis.

Animals↗

PubMed1991

Infectivity of cryopreserved Giardia cysts for Mongolian gerbils (Meriones unguiculatus).

Although Giardia species trophozoites have been cryopreserved successfully, no report on the successful cryopreservation of cysts could be found. Using infectivity to Mongolian gerbils (Meriones unguiculatus) as a measure of cyst viability, we tested the viability of 4 strains of Giardia cysts that had been cryopreserved for 1-67 wk. Cysts were frozen in either Keister's medium or physiological saline, both containing 5% or 7.5% dimethylsulfoxide as the cryoprotectant. Viability of cryopreserved cysts was dependent upon the number of cysts inoculated, the length of time cysts were held at 4 C before cryopreservation, and the cryopreserving medium. Infection was established in gerbils by inoculating them with cysts that had been cryopreserved for up to 67 wk, cysts that had been held for less than 30 days before cryopreservation, and cysts frozen in Keister's medium. Saline appears to be unsuitable as a freezing medium for the cryopreservation of Giardia cysts.

Animals↗

PubMed1990

Complement activation limits the rate of in vitro treponemicidal activity and correlates with antibody-mediated aggregation of Treponema pallidum rare outer membrane protein.

A modification of the in vitro immobilization assay together with freeze-fracture analysis was used to determine the factors responsible for the prolonged time required in vitro to achieve killing of Treponema pallidum subsp. pallidum. The modified immobilization assay permitted separate determination of the time required for binding of antibody to the surface of T. pallidum and for C activation. Treponemes were preincubated in heat-inactivated immune rabbit serum (IRS) followed by washing the organisms in 2.5% BSA/PBS to remove unbound IRS antibody before the addition of C. The results showed that a comparable degree of C-dependent killing occurred when treponemes were preincubated in heat-inactivated IRS for either 30 min or 16 h, indicating that treponemicidal antibody rapidly binds to the surface of T. pallidum. Preincubation of treponemes for 17 h in heat-inactivated IRS followed by a 1-h incubation in C resulted in the loss of 80% treponemal motility, indicating that C activation results in rapid killing of T. pallidum. Treponemes preincubated in IRS for 1 h, then incubated for 8 h and 16 h in heat-inactivated normal serum also lost a significant level of motility after the addition of C; in contrast, motility was unaffected after 30 min and 4 h of incubation in heat-inactivated normal serum under similar conditions. These results demonstrate that, whereas antibody binding to and C-mediated killing of treponemes can proceed rapidly, the prolonged time to C activation limits the rate at which treponemicidal activity occurs in vitro. In addition, treponemicidal activity using the modified immobilization assay could not be demonstrated with antiserum against T. pallidum endoflagella, antiserum against proteins solubilized from T. pallidum using the detergent Triton X-114, and a mAb to the T. pallidum r190-kDa "4D" protein, suggesting that these molecules are not accessible to surface binding antibody. Freeze-fracture analysis, recently used in our laboratory to demonstrate that the outer membrane of T. pallidum has rare constituent protein, was utilized to demonstrate outer membrane target Ag of IRS antibody. T. pallidum rare outer membrane protein (TROMP) molecules were shown in freeze-fracture electron micrographs to be consistently aggregated following a 16-h incubation of treponemes in IRS. In contrast, no aggregation of TROMP was present in treponemes incubated in normal rabbit serum for 16 h or in treponemes incubated in IRS for 2 h. These findings suggest that the rate of C activation leading to in vitro treponemicidal activity is limited by the time required for aggregation of antibody-bound TROMP molecules.

Animals↗

PubMed1990

Antigenic variation of Giardia lamblia in the feces of Mongolian gerbils.

Enzyme-linked immunoelectrotransfer blot was used to study variations in Giardia lamblia antigens in extracts of feces from infected Mongolian gerbils. A 65-kilodalton antigen was found in feces that contained strain WB (ATCC 30957) cysts and in axenic culture of strains WB and CDC:0284:1 that contained trophozoites. The 65-kilodalton antigen from trophozoites of both strains was membrane associated. A 70-kilodalton antigen was found in feces that contained strain CDC:0284:1 cysts. It was persistent in 16 fecal collections and may be strain specific. Similar variations in antigens may occur in human feces. Coproimmunodiagnostic assays that use monoclonal antibodies will have to include all varieties of G. lamblia antigens present in the feces of giardiasis patients.

Animals↗

PubMed1990

Nephrotoxic and ototoxic agents.

It is well established that many drugs, such as the aminoglycoside antibiotics and the chemotherapeutic drug cisplatin, are capable of inducing both nephrotoxicity and ototoxicity. The factors that selectively predispose the kidney and inner ear to the toxic effects of these agents as well as the mechanism by which damage is produced are not well defined. The two organs differ greatly in their exposure to these toxic agents. The kidney has an abundant vascular supply and tends to selectively concentrate a number of drugs within the renal cortex or medulla, often to toxic levels. The vascular supply of the inner ear is not as extensive. In addition, the stria vascularis of the cochlea may act as a functional regulator of drug entry into inner ear fluids. The absorption of drugs into perilymph and endolymph is poorly understood. Selective accumulation theories of drug accumulation in the inner ear must be questioned because of the results of recent pharmacokinetic studies, which give contrary data. Drug-induced ototoxicity and nephrotoxicity can be explained on a cellular level. Studies using radiolabeled gentamicin suggest that binding mechanisms of the drug to the plasma membrane of the outer hair cells of the cochlea and vestibular apparatus and to the brush border receptors of the renal proximal convoluted tubules are similar. This suggests the same receptor sites for aminoglycosides occur in otic and renal organs. Calcium channels are implicated because of the reversibility of aminoglycoside-induced changes in the cochlear microphonic by calcium and other divalent cations. Calcium channel blockers, such as verapamil, reduce the nephrotoxicity of a number of drugs that are also ototoxic. Studies are needed to assess potential prevention of ototoxicity by use of these same calcium channel blocking agents. Aminoglycosides concentrate within the lysosomes of renal proximal tubular cells. Possibly, they also may concentrate in lysosomes within the cells of cochlear and vestibular structures. Nephrotoxic heavy metals concentrate within proximal tubular cells and, some, such as lead or bismuth, specifically concentrate within intracytoplasmic or intranuclear inclusion bodies. Studies are necessary to determine if the same metals accumulate within the cochlear and vestibular cells, inclusion bodies, or both. These questions and others must be answered before it can be determined why many nephrotoxic drugs and agents are also ototoxic.

Adolescent↗

PubMed1989

Dithiocarbamate-induced biliary platinum excretion and the control of cis-platinum nephrotoxicity.

Treatment with any one of six different dithiocarbamates subsequent to the administration of cis-platinum (CDDP) is shown to promote the biliary excretion of platinum. The administration of the most effective of these compounds, sodium diethyldithiocarbamate (DDTC) at 1.57 mmol/kg, led to a 30-fold increase in the biliary excretion of platinum. For the other dithiocarbamates investigated, a similar dosage led to increases ranging from approximately 5-fold for sodium iminodiacetic acid dithiocarbamate, to 26-fold for sodium sarcosine dithiocarbamate. The presence of alkyl groups on the nitrogen of the dithiocarbamate increased the effectiveness of the compounds. There is no increase in the platinum levels of the brain when DDTC is used in this manner. A histopathological evaluation of the kidneys of rats given 15 mg CDDP/kg in 6.3% saline with and without the use of dithiocarbamates for renal protection shows significant additional protection due to the use of the dithiocarbamates. Dithiocarbamates given at an appropriate dosing schedule can lead to a significant reduction in the renal damage which is revealed by microphotographs. It is suggested that part of the renal protection obtained by the use of dithiocarbamates may be due to this shift of platinum excretion to the bile which obviates additional renal exposure to platinum. It was also found that the simultaneous injection of a dithiocarbamate with the cis-platinum has no obvious effect on the anti-cancer action of cis-platinum against the Walker 256 carcinosarcoma in rats.

Animals↗

PubMed1989

Demonstration of rare protein in the outer membrane of Treponema pallidum subsp. pallidum by freeze-fracture analysis.

The surface of Treponema pallidum subsp. pallidum (T. pallidum), the etiologic agent of syphilis, appears antigenically inert and lacks detectable protein, as judged by immunocytochemical and biochemical techniques commonly used to identify the outer membrane (OM) constituents of gram-negative bacteria. We examined T. pallidum by freeze-fracture electron microscopy to visualize the architecture of its OM. Treponema phagedenis biotype Reiter (T. phagedenis Reiter), a nonpathogenic host-associated treponeme, and Spirochaeta aurantia, a free-living spirochete, were studied similarly. Few intramembranous particles interrupted the smooth convex and concave fracture faces of the OM of T. pallidum, demonstrating that the OM of this organism is an unusual, nearly naked lipid bilayer. In contrast, the concave fracture face of the OM of S. aurantia was densely covered with particles, indicating the presence of abundant integral membrane proteins, a feature shared by typical gram-negative organisms. The concentration of particles in the OM concave fracture face of T. phagedenis Reiter was intermediate between those of T. pallidum and S. aurantia. Similar to typical gram-negative bacteria, the OM convex fracture faces of the three spirochetes contained relatively few particles. The unique molecular architecture of the OM of T. pallidum can explain the puzzling in vitro properties of the surface of the organism and may reflect a specific adaptation by which treponemes evade the host immune response.

Bacterial Outer Membrane Proteins↗

PubMed1989

The increasing problem in Tayside of cervical cancer in younger women.

The incidence of cervical carcinoma in younger women is increasing in Tayside despite a decrease in the overall incidence. However, stage for stage, we did not encounter a poorer survival in younger patients. A number of patients had been sterilised or had a pregnancy when cytological screening was available and not made use of. There were also some false negative smears which were reclassified for retrospective analysis. We would recommend cervical screening every three years and careful inspection of the cervix and a smear taken in cases of abnormal gynaecological symptoms such as post coital bleeding.

Adenocarcinoma↗

PubMed1989

Antipseudomonal effects of selected dithiocarbamates alone and in combination with gentamicin or aztreonam.

The antipseudomonal effects conferred by combinations of substituted dithiocarbamates, gentamicin or aztreonam (Azactam) were measured and compared to those produced by single agents alone in female BALB/C mice bearing overwhelming Pseudomonas aeruginosa infections. Dimethyldithiocarbamate (DMDTC), diethyldithiocarbamate (DEDTC), and sodium N-methyl-D-glucamine dithiocarbamate (NMGDTC) were chosen as representative substituted dithiocarbamates. All three dithiocarbamates rescued some cisplatin-immunosuppressed mice from pseudomonal infections but DMDTC and NMGDTC produced better results than DEDTC. Single daily injections of DMDTC at doses of 5 mg/kg/day or higher for a total of 7 days rescued 14 of 18 mice given 10(6) viable Pseudomonas aeruginosa by tail vein inoculation. Similar dose regimens of 10 mg/kg/day or higher NMGDTC for a total of 7 days rescued 15 of 18 mice. DEDTC at doses of 5 mg/kg/day or higher for 7 days rescued 7 of 18 mice. Combinations of DMDTC or NMGDTC with gentamicin failed to produce better results than each agent alone in mice immunosuppressed with methyl-prednisolone (Solumedrol) at the dose range evaluated in mice inoculated with 10(6) viable organisms via tail veins. Combinations of DMDTC and aztreonam were effective in mice immunosuppressed with methylprednisolone and given overwhelming numbers of viable Pseudomonas aeruginosa (10(7) or more, ip). Combinations of 6 mg/kg/day or higher of each agent with multiple daily injections rescued 11 of 18 mice. The results yielded by either agent alone were not impressive. Similar results were obtained when mice immunosuppressed with cisplatin were given ip injections of 10(8) or more viable bacteria. No mice were rescued by the use of DMDTC, NMGDTC, aztreonam or gentamicin only. Combinations of DMDTC (6 mg/kg) and aztreonam (6 mg/kg) with multiple daily injections for seven days rescued 11 of 20 infected mice while combinations of NMGDTC with aztreonam were less effective (3 of 20 rescued). The concurrent administration of DMDTC and aztreonam offers considerable promise in the treatment of overwhelming pseudomonal infections in mice and may prove to be of value in human patients as well.

Animals↗

PubMed1988

Occult biochemical pregnancy: fact or fiction?

Daily urine samples were obtained from 38 women of proven fertility, who were attempting to conceive, to assess the frequency of clinically unsuspected "biochemical pregnancies' on the basis of late luteal phase rises of hCG. In 25 clinically confirmed conception cycles, the earliest pregnancy-induced hCG rises from baseline occurred 8 days after the endocrinologically defined date of ovulation (mean 11.1 days, SD 1.3). Urine samples obtained throughout 50 non-conception ovulatory cycles provided no evidence of any 'biochemical pregnancies' on the basis of late luteal phase rises of hCG occurring 8 or more days after the endocrinologically defined date of ovulation. If, as in previous studies, the date of ovulation had been estimated on the basis of menstrual cycle length and only the relatively non-specific NIH antiserum had been used in RIAs, 7 of the 50 (14%) cycles would have been classified as resulting in biochemical pregnancies on the basis of hCG greater than 50 m-i.u./ml on one occasion or greater than 20 m-i.u./ml on two or more occasions after day 20 of the cycle. These levels of 'hCG' occurred at or soon after ovulation and could be explained by LH cross-reacting in the RIA. The rises of 'hCG' were not confirmed when the urine samples were retested with an antiserum (Wellcome 895) of very high specificity for hCG. These results raise the possibility that the frequency of clinically unsuspected 'biochemical pregnancy' may have been substantially overestimated.

Adult↗