Symbolic sequence learning is associated with cognitive-affective profiles in female FMR1 premutation carriers

This study examines implicit sequence learning impairments that may indicate at-risk cerebellar profiles proposed to underlie some aspects of subtle cognitive and affective dysfunctions found among female fragile X mental retardation 1 (FMR1) premutation (PM)-carriers. A total of 34 female PM-carriers and 33 age- and intelligence-matched controls completed an implicit symbolically primed serial reaction time task (SRTT) previously shown to be sensitive to cerebellar involvement. Implicit learning scores indicated a preservation of learning in both groups; however, PM-carriers demonstrated poorer learning through significantly elevated response latencies overall and at each specific block within the symbolic SRTT. Group comparisons also revealed a core deficit in response inhibition, alongside elevated inattentive symptoms in female PM-carriers. Finally, strong and significant associations were observed between poor symbolic SRTT performance and executive, visuospatial and affective deficits in the PM-carrier group. These associations remained strong even after controlling motor speed, and were not observed in age- and intelligence quotient-matched participants. The findings implicate cerebellar non-motor networks subserving the implicit sequencing of responses in cognitive-affective phenotypes previously observed in female PM-carriers. We contend that symbolic SRTT performance may offer clinical utility in future pharmaceutical interventions in female PM-carriers.

To tell or not to tell - what to do about p.C282Y heterozygotes identified by HFE screening

Hereditary hemochromatosis (HH) is a common preventable disorder of iron overload that can result in liver cirrhosis and reduced lifespan. Most HH is due to homozygosity for the HFE p.C282Y substitution. We conducted a study of screening for p.C282Y in high schools where p.C282Y heterozygotes (CY) individuals were informed of their genotype by letter. We studied whether these individuals understood the implications of their genotype, whether this resulted in anxiety or reduced health perception and whether cascade testing was higher in families of CY than wild-type homozygous (CC) individuals. We found 586 of 5757 (1 in 10) screened individuals were CY. One month after receiving their result, 83% correctly answered that they have one copy of p.C282Y. There was no adverse change in anxiety or health perception from prior to screening to 1 month after receiving results. Significantly more family members of CY individuals than CC individuals were informed about HH and had testing for HH. In conclusion, we found that informing CY individuals of their genotype does not increase anxiety and the implications are generally well understood. This leads to cascade testing in a minority of families. CY individuals should be informed of their genetic status when identified by population screening.

First MTP joint arthrodesis for the treatment of hallux rigidus: results of 29 consecutive cases using the foot health status questionnaire validated measurement tool

BACKGROUND

Arthrodesis of the first MTP joint is an accepted and long established joint destructive procedure for the management of hallux rigidus.

OBJECTIVES

This paper presents the results of 29 consecutive first MTP joint arthrodesis procedures for the treatment of hallux rigidus.

METHOD

The outcomes of 29 (18 female and 11 male) consecutive arthrodesis procedures were analysed with the Foot Health Status Questionnaire (FHSQ), minimal important difference scores, and a patient satisfaction questionnaire.

RESULTS

FHSQ foot pain scores improved for 27 (93%) patients; foot function improved for 23 (79%) patients; shoe scores improved for 18 (62%) patients; foot health improved for 20 (68%) patients; general health improved for 12 (41%) patients; physical activity improved for 21 (72%) patients; social capacity improved for 21 (21%) patients; vigour improved for 15 (51%) patients. FHSQ minimal important difference scores were achieved for foot pain in 25 patients (86%); foot function in 17 patients (58%); and general foot health in 19 (65%) patients. Analysis with the matched pairs Wilcoxon rank sum test (p<0.05) revealed statistically significant improvement in all FHSQ domains. Female patients appeared to fare better than male patients in all FHSQ categories other than general health and vigour.

CONCLUSION

Arthrodesis of the first MTP joint can reliably reduce pain relating to hallux rigidus and can improve foot function and allow a return to physical activity.

Educational outcomes of a workplace screening program for genetic susceptibility to hemochromatosis

Education is an essential component of a genetic screening program. Knowledge outcomes were measured after large-scale workplace education and screening for genetic susceptibility to hereditary hemochromatosis. The aim was to assess knowledge of concepts presented, impact of mode of delivery, and knowledge retention. Education in a group setting was delivered via oral or video presentation and knowledge assessed using self-administered questionnaires at baseline, 1 month, and 12 months. Over 60% of 11 679 participants correctly answered all questions at baseline, scoring higher with clinical concepts (disease etiology and treatment) than genetic concepts (penetrance and genetic heterogeneity). Revising the education program significantly increased correct responses for etiology (p < 0.002), whilst modifying the knowledge assessment tool significantly increased correct responses for etiology (p < 0.001) and gene penetrance (p < 0.001). For three of the four concepts assessed, use of video was as effective as oral presentation for knowledge outcomes. A significantly higher proportion of those at increased risk of disease (n = 44) responded correctly at 12 months than did controls (n = 82; p = 0.011 for etiology, p = 0.002 for treatment and p = 0.003 for penetrance). Hence, genetic screening can be successfully offered in a group workplace setting, with participants remembering clinical concepts better than genetic concepts up to 1 year later.

Genetic susceptibility screening in schools: attitudes of the school community towards hereditary haemochromatosis

Carrier screening to provide reproductive options has been offered to students in the school setting for a number of years; however, genetic susceptibility screening for disease predisposition has not been introduced to the school community. Experience has shown that the success of a population-based programme relies on the community's acceptance. Therefore, we sought to establish the Australian secondary school community's attitudes towards genetic susceptibility screening in schools, with hereditary haemochromatosis as the model condition with an available prevention. School students, aged 15-18 (n = 748), completed a questionnaire immediately before and following an oral educational presentation. Their parents (n = 179) and staff (n = 89) received written information and returned a questionnaire by post. Semi-structured interviews were with Government representatives. Attitudes towards genetic screening in schools and knowledge of genetic and clinical features of haemochromatosis, as well as the likelihood of accepting a genetic susceptibility test for haemochromatosis, were all measured. Participants were positive about genetic screening for disease susceptibility in schools. Their knowledge was high following education with no significant differences between participants of each group. Sixty-eight percent of students would be likely to have the test if it were offered, with parents and staff, indicating that they would like the students to be offered a test, on average. Genetic susceptibility screening in schools is a novel concept. The results of our study indicate that it could be a public health success with the support of the community.

Sheep CD4(+) alphabeta T cells express novel members of the T19 multigene family

The sheep T19 multigene family contains at least 50 genes which are thought to be expressed exclusively on gammadelta T cells. The archetypal T19 molecule (represented by a full-length cattle cDNA clone termed WC1) is thought to have a relative molecular mass of about 220 000 and to contain 11 scavenger receptor cysteine rich (SRCR) repeats and a long cytoplasmic tail. In this study, purified CD4(+) and gammadeltaTCR+ sheep lymphocytes were examined by reverse transcriptase-polymerase chain reaction for the expression of T19 molecules. As expected, gammadelta T cells were found to express T19 molecules which closely resembled the archetypal form. However, CD4(+) alphabeta T cells were found to express at least two different types of T19 molecules; one resembled the previously described T19 molecules of gammadelta T cells which possessed the archetypal WC1-like structure, but a novel type of T19 variant which lacked SRCR domains 10 and 11 was also found in CD4(+) T cells but not gammadelta T cells. This novel molecule exhibited an unusual, incomplete SRCR repeat 9 joined directly to a hinge region. The transmembrane and cytoplasmic domains of this unusual T19 variant resembled the cattle T19 clone WC1, except that a complete exon within the cytoplasmic region was missing. These results, in contradistinction to existing serological data, suggest that expression of the T19 gene family is not confined to gammadelta T cells. Selected T19 genes are apparently expressed within CD4(+) T cells and possibly other lymphocytes as well.

A novel multi-gene family of sheep gamma delta T cells

The WC1 protein is a cell surface constituent of bovine gamma delta T cells and is absent from most or all CD4+, CD8+ T cells and from B cells. It is a single polypeptide chain of 1413 amino acids consisting of 11 non-identical repeats of a 110 amino acid consensus sequence, homologous to the macrophage scavenger receptor cysteine rich (SRCR) domain. A 1059 nucleotide segment of the bovine WC1 cDNA sequence was used as a probe to molecularly clone homologous DNA segments from a sheep genomic library in which the presence of numerous positive plaques was documented. The high representation of such recombinants (1-2/1000 clones) within the library suggested the existence of multiple genes for WC1 (called T19 in sheep) and supported Southern blotting data which revealed an unexpectedly high number of WC1/T19 restriction fragments in sheep genomic DNA. Restriction digests of 27 samples of T19 genomic recombinants were examined by electrophoresis and Southern blotting. All but two pairs of recombinants exhibited non-overlapping restriction digest patterns. Four recombinant DNA samples were partially sequenced and in all cases putative exons were identified and exhibited high homology to appropriate segments of the WC1 cDNA at the levels of both nucleotide and amino acid sequence. Furthermore, multiple nucleotide and amino acid differences occurred between all sequences compared, establishing the existence of a repertoire of non-identical T19 genes, each with the potential to encode a different protein.

Lymph node homing cells biologically enriched for gamma delta T cells express multiple genes from the T19 repertoire

Sheep gamma delta T cells have been shown serologically to express T19, a membrane protein of 180-200 kDa which is a member of the scavenger receptor superfamily. Previous work from this laboratory resulted in the detection of a multigene family of T19-like genes in the sheep genome. In this study nucleotide sequences from several T19 genes were determined and are reported along with the corresponding segments of a number of expressed mRNA molecules. A segment of a single sheep T19-like gene was sequenced and these data, along with the corresponding sequences from cloned T19-like cDNA molecules from sheep and cow, were used to design an oligonucleotide primer system suitable for amplification of corresponding segments of many T19 genes and their cDNAs. Between 30 and 40% of cloned T19 genes were amenable to amplification using the selected primers, and sequence analysis of cloned PCR products confirmed that different T19 genes encode unique amino acid sequences. The expression of multiple T19 genes was established using cDNA molecules obtained from a single sample of sheep lymphocyte mRNA. The possible role of the T19 family of genes is discussed.

Testicular descent. II. Ontogeny and response to denervation of calcitonin gene-related peptide receptors in neonatal rat gubernaculum

The gubernaculum guides inguino-scrotal testicular descent by migrating into the scrotum ahead of the testis. Calcitonin gene-related peptide (CGRP) is present in the genitofemoral nerve of the neonatal rat and stimulates gubernacular motility in vitro. In a previous study in vitro autoradiography demonstrated a distinctive distribution of binding sites for CGRP over the developing cremasteric muscle in the gubernaculum. Binding analysis using computerized densitometry revealed a single class of sites. This study aimed to characterize the ontogeny of CGRP receptors in the gubernaculum and their response to denervation. Gubernacular sections from neonatal male rats were incubated with [125I]human CGRP as well as a variety of unlabeled neuropeptides. The expression of CGRP receptors culminates during the first week after birth, when gubernacular migration actually occurs. Significantly higher binding capacities were found in the denervated gubernacula compared with those in controls, which suggests an upregulation of CGRP receptors as a result of the genitofemoral nerve denervation. These results are consistent with the hypothesis that CGRP released from the nerve acts directly on the developing cremaster via its own receptors, which have not been described previously in this tissue.

Demonstration of calcitonin gene-related peptide receptors in the gubernaculum by computerized densitometry

The gubernaculum appears to guide inguinoscrotal testicular descent by migration into the scrotum ahead of the testis. Calcitonin gene-related peptide (CGRP) has been found in the scrotal branches of the genitofemoral nerve of neonatal rats, and is known to stimulate gubernacular motility in vitro. This study aimed to identify CGRP receptors in the gubernaculum, which should be present if CGRP mediates gubernacular migration toward the scrotum. Gubernacular sections from neonatal male rats were incubated with [125I]-human CGRP as well as a variety of unlabeled neuropeptides. By using computerized densitometry, the quantitation of CGRP binding derived from in vitro autoradiography demonstrated a distinctive distribution of binding sites for CGRP over the developing cremasteric muscle in the gubernaculum. The binding analysis showed a single class of sites with a dissociation constant (Kd) of 2.13 nmol/L and a receptor density of 27.4 fmol/mg polymer. These results endorse the hypothesis that CGRP released from the nerve acts directly on the cremaster via its own receptors, which have not been described previously.

Serum levels of müllerian inhibiting substance in boys from birth to 18 years, as determined by enzyme immunoassay

An enzyme immunoassay was set up with the aim of determining the serum levels of Müllerian inhibiting substance (MIS) during childhood. A monoclonal antibody against purified bovine MIS was combined with a polyclonal antibody against recombinant human MIS to make a sandwich assay. This assay detected MIS in human serum within the following criteria. Ninety-eight boys, aged between birth and 18 yr, who had been admitted to the Royal Children's Hospital, were included. MIS levels were measured in samples taken for biochemical screening of unrelated disorders. MIS was detected in the serum up to 16 yr of age, but was low beyond 12 yr and undetectable at 18 yr. High MIS levels were found at 4-12 months, consistent with MIS having an important function at this time. Germ cells undergo an important transformation from gonocytes to spermatogonia at the same time as the MIS levels peak, suggesting a possible function for MIS.

Studies on species cross-reactivity of hemopexin by use of monoclonal and polyclonal antibodies

The extent of immunological cross-reactivity between hemopexins of four species (rat, human, rabbit and chicken) was assessed with four affinity purified polyclonal antibodies and three monoclonal antibodies using RIA, Western blotting and rocket immunoelectrophoresis. Neither the two monoclonal antibodies to rabbit hemopexin (Rb3D11 and Rb3H9), the monoclonal antibody (R4B3) to rat hemopexin nor any of the polyclonal antibodies showed shared antigenic determinants between avian and mammalian hemopexins as judged by RIA or rocket immunoelectrophoresis. Western blotting with polyclonal antibodies revealed some reactivity raising the possibility of a few shared, though distantly related, epitopes. Polyclonal antibodies, raised to the mammalian hemopexins cross-reacted to variable extents with the respective antigens by RIA, results paralleled by data obtained by Western blotting. Anti-rat monoclonal antibodies reacted only with rat hemopexin in Western blots and minimally with rabbit hemopexin in RIA. The anti-rabbit monoclonal antibodies recognized two distinct epitopes one of which is shared with human hemopexin and presumably highly conserved.

Self-care attitude changes of nursing students enrolled in a self-care curriculum--a longitudinal study

The purpose of this 3-year longitudinal study was to determine if nursing students' self-care attitudes change after being socialized through a curriculum based on Orem's Self-Care Deficit Theory. The sample consisted of 40 baccalaureate nursing students and 71 general university students who served as a control group. Pretest-posttest design was used employing the Linn-Lewis Self-Care Attitude Scale. On initial testing, nursing students had more positive attitudes toward self-care than the general university students, but the results were not significant. At the completion of the nursing curriculum, analysis of covariance on posttest mean scores indicated nursing students had significantly higher self-care scores (p less than .001).

Hemopexin is a developmentally regulated, acute-phase plasma protein in the chicken

Identity has been established between chicken hemopexin and alpha 1-globulin "M," a plasma known for the hormone responsiveness of its synthesis in monolayer cultures of embryonic chicken hepatocytes (Grieninger, G., Plant, P. W., Liang, T. J., Kalb, R. G., Amrani, D., Mosesson, M. W., Hertzberg, K. M., and Pindyk, J. (1983) Ann. N. Y. Acad. Sci. 408, 469-489). Identification was based on immunological cross-reactivity, electrophoretic behavior on sodium dodecyl sulfate-polyacrylamide gels, heme-binding capacity, and pattern of cleavage by proteolytic enzymes. Electroimmunoassays were used to investigate plasma protein levels, particularly those of hemopexin, in the acute-phase response and embryonic development. Acute-phase plasma protein production, elicited by injection of chickens with turpentine, bore many similarities to the pattern of hepatocellular plasma protein synthesis produced in response to the addition of specific hormones in culture. The response of the stressed chickens included elevated levels of hemopexin and fibrinogen (5- and 2-fold, respectively) accompanied by a 50% drop in albumin. Hemopexin levels of developing chick embryos were measured for several days before and after hatching. Onset of hemopexin production occurred around the time of hatching, and was followed by a steep increase (more than 1000-fold over 4 days). Similarly, it was not until the 12th h of culture that hepatocytes isolated from both early and late stage chicken embryos began to produce hemopexin, although, from their initiation in culture, they secreted a number of other plasma proteins in quantity. After 12 h, hepatocellular output of hemopexin rapidly accelerated. This precocious induction ex vivo required no hormonal or macromolecular medium supplements. These observations indicate that the embryonic chicken hepatocyte culture system will provide a useful model for studying the regulation of hemopexin biosynthesis in hepatic development and the acute-phase response.

An avian serum alpha 1-glycoprotein, hemopexin, differing significantly in both amino acid and carbohydrate composition from mammalian (beta-glycoprotein) counterparts

We report here on physicochemical characteristics of chicken hemopexin, which can be isolated by heme-agarose affinity chromatography [Tsutsui, K., & Mueller, G. C. (1982) J. Biol. Chem. 257, 3925-3931], in comparison with representative mammalian hemopexins of rat, rabbit, and human. The avian polypeptide chain appears to be slightly longer (52 kDa) than the human, rat, or rabbit forms (49 kDa), and also the glycoprotein differs from the mammalian hemopexins in being an alpha 1-glycoprotein instead of a beta 1-glycoprotein. This distinct electrophoretic mobility probably arises from significant differences in the amino acid composition of the chicken form, which, although lower in serine and particularly in lysine, has a much higher glutamine/glutamate and arginine content, and also a higher proline, glycine, and histidine content, than the mammalian hemopexins. Compositional analyses and 125I concanavalin A and 125I wheat germ agglutinin binding suggest that chicken hemopexin has a mixture of three fucose-free N-linked bi- and triantennary oligosaccharides. In contrast, human hemopexin has five N-linked oligosaccharides and an additional O-linked glycan blocking the N-terminal threonine residue [Takahashi, N., Takahashi, Y., & Putnam, F. W. (1984) Proc. Natl. Acad. Sci. U.S.A. 81, 2021-2025], while the rabbit form has four N-linked oligosaccharides [Morgan, W. T., & Smith, A. (1984) J. Biol. Chem. 259, 12001-12006]. In keeping with the finding of a simpler carbohydrate structure, the avian hemopexin exhibits only a single band on polyacrylamide gel electrophoresis under both nondenaturing and denaturing conditions, whereas the hemopexins of the three mammalian species tested show several bands.(ABSTRACT TRUNCATED AT 250 WORDS)

Possible mechanism for differences in sensitivity to cis-platinum in human prostate tumor cell lines

Two human prostate tumor cell lines which exhibit a 2.4-fold difference in sensitivity to cis-platinum (cis-Pt) were found to possess slightly different sulphydryl contents, and the presence of a metallothionein-like zinc-binding protein was demonstrated in the line exhibiting relative resistance to cis-Pt. Although these factors have been postulated to play a role in the mechanism(s) of resistance to cis-Pt in other cell types, preliminary data in this report suggest that differences found in drug uptake and subsequent binding to DNA are most likely responsible for variations in cis-Pt sensitivity displayed by these prostate tumor cell lines.

In vitro responses of human prostate tumour cell lines to a range of antitumour agents

Four human prostate tumour continuous cell lines were employed for in vitro drug sensitivity testing of nine cytotoxic drugs, X-irradiation and two hormonal preparations. Responses were assessed by measuring cell survival as judged by colony formation in agarose. A marked heterogeneity of responses was noted to many of the agents studied, including X-irradiation. However, in terms of ID70 values for 24-h drug exposures, comparable responses in all the cell lines tested, with values falling within a 1.4- to 2.9-fold range, were noted with actinomycin D, adriamycin, m-AMSA, dibromodulcitol, 5-fluorouracil, hydroxyurea and ICRF-159. In contrast, mixed responses to cis-platinum and methotrexate were particularly marked, with ID70 values differing by factors of 3.8 and 7.5 respectively. In addition, when higher drug concentrations of m-AMSA, cis-platinum, dibromodulcitol and ICRF-159 were employed, significant deviations in the four survival curves became apparent. Continuous exposure to diethylstilboestrol and medroxyprogesterone acetate caused negligible cell kill. Due to these variable responses it was not possible to predict that any agent tested might have specific value in the treatment of prostate cancer. However, preliminary in vitro screening with such a panel of cell lines may complement in vivo studies with models of prostatic cancer and prove useful in investigations of mechanisms of drug resistance.

The metabolism of aflatoxin B1 by hepatocytes isolated from rats following the in vivo administration of some xenobiotics

Isolated rat hepatocytes, an intact cellular system capable of performing phase I and phase II metabolism, have been used to investigate metabolism of aflatoxin B1. These cells were found to metabolise [14C]aflatoxin B1 to aflatoxins M1 and Q1, and to radiolabelled polar material, presumably conjugates, as analysed by h.p.l.c., t.l.c. and radioactive determination. In vivo administration of the mixed function oxidase inducers, phenobarbitone and 3-methylcholanthrene, resulted in enhanced hepatocyte phase I (microsomal) metabolism of aflatoxin B1. In contrast to metabolism of AFB1 by in vitro subcellular systems increased production of polar material (conjugated metabolites) derived from [14C]aflatoxin B1 was also detected in hepatocytes isolated from these pretreated animals. Formation of aflatoxin Q1 by isolated hepatocytes appeared to be mediated by cytochrome P450-linked enzymes whereas cytochrome P448-linked enzymes were apparently involved in aflatoxin M1 production. Chronic feeding of aflatoxin B1 to rats enhanced hepatocyte production of conjugated material only and did not elevate cellular cytochrome P450 levels, thus suggesting that aflatoxin B1 is not an inducer of its own primary metabolism.

Some studies on the relationship between the cytotoxicity of aflatoxin B1 to rat hepatocytes and metabolism of the toxin

Aflatoxin B1 (AFB1) caused marked, rapid (1 h) inhibition of RNA synthesis and subsequent cytotoxic response in isolated and primary cultured hepatocytes, from control rats, which are known to metabolise AFB1. A rat liver-derived cell line, BL8L, was much less susceptible to these effects of AFB1. These cells have no detectable AFB1 metabolising capacity, but a less potent, anti-mitotic action of AFB1 was observed in the BL8L cell line. Thus AFB1 would seem to require metabolism to exert its acute cytotoxic action which is found at very low AFB1 concentrations, although a direct antimitotic effect, independent of metabolism, is seen in dividing cells. Phenobarbitone and 3-methylcholanthrene in vivo pretreatments, known inducers of AFB1 metabolism, resulted in reduced AFB1 inhibition of RNA synthesis and cytotoxicity in hepatocytes, but only at lower concentrations of AFB1 used, whereas cells from AFB1 fed rats were much less susceptible to AFB1 toxicity at all concentrations used. This resistance to cytotoxicity of AFB1 would appear to involve detoxification mechanisms, primarily the formation of polar conjugates of AFB1 metabolites, particularly glutathione conjugates. These cell culture systems are useful for studying association between metabolism and cytotoxicity of AFB1, and other xenobiotics.

Androgen metabolism by human prostatic tumours in organ culture

Metabolism of testosterone and 5 alpha-dihydrotestosterone were investigated in benign and malignant human prostatic tumours maintained for 48 hr in organ culture. When tritiated testosterone was used as substrate there were significant differences between the metabolic pathways of the two types of tumour. Whilst the benign tumour had a predominantly reductive pathway leading to the formation of 5 alpha-reduced metabolites of testosterone, an oxidative pathway producing androstenedione was found to be the major pathway operative in the intermediate and poorly differentiated malignant specimens studied. In contrast to these differences observed in the metabolic pathway of testosterone when tritiated 5 alpha-dihydrotestosterone was used as substrate, no significant differences in the pattern of radiometabolites were observed.

A comparison of the effects of pretreatment with phenobarbitone and 3-methylcholanthrene on the metabolism of aflatoxin B1 by rat liver microsomes and isolated hepatocytes in vitro

In agreement with previous reports (Neal and Colley, Biochem. J., 174 (1978) 839; Gurtoo and Dave, Cancer Res., 35 (1975) 382) the capacity of isolated hepatic microsomes to metabolise aflatoxin B1 (AFB1) is enhanced by pretreatment in vivo with phenobarbitone. Microsomes isolated from rats pretreated with 3-methylcholanthrene also exhibit increased metabolism of AFB1. The levels of metabolism are increased in proportion to the increased levels of cytochromes P-450 and P-448 indicating similar overall efficiencies of the two cytochromes to metabolise AFB1. However, the qualitative aspects of the metabolism induced by the two compounds are very different. In agreement with the previous data (Neal and Colley, Biochem J., 174 (1978) 839) the formation of aflatoxins Q1, M1 and B1-dihydrodiol are enhanced by pretreatment with phenobarbitone whereas pretreatment with 3-methylcholanthrene, while not affecting the production of aflatoxin Q1 and slightly lowering AFB1-dihydrodiol formation, increases the production of aflatoxin M1 greater than 10-fold. Covalent binding of AFB1 to microsomal protein in vitro is increased by pretreatment in vivo with phenobarbitone, but decreased by pretreatment with 3-methylcholanthrene. The changes in the level of protein binding in vitro brought about by these pretreatments are quantitatively similar to the relative changes in AFB1-dihydrodiol tris complex production induced by the two compounds indicating a role for this metabolite in protein binding. Covalent binding of AFB1 to DNA in vitro is also increased by pretreatment in vivo with phenobarbitone, but not by 3-methylcholanthrene and the total level of binding of AFB1 to DNA in the in vitro system is greater than binding to microsomal protein. The possible mechanisms for binding AFB1 to microsomal protein and DNA are discussed. In contrast to the microsomal incubations, only low levels of aflatoxins Q1 and M1 are present after 2 h incubation AFB1 with intact hepatocytes isolated from control, methylcholanthrene or phenobarbitone pretreated rats. Pretreatment with either phenobarbitone or 3-methylcholanthrene induces the formation of polar metabolites, presumably conjugates, emphasising the predominant role of phase 2 metabolism in intact cellular systems.