The strength of Achilles tendon repair: an in vitro study of the biomechanical behavior in human cadaver tendons

Eighteen fresh frozen human Achilles tendons were used to test the ultimate strength of repaired tendon "ruptures." Three methods, the Kessler, the Bunnell, and the locking loop, were used to test the initial strength of Achilles tendon repair. The Kessler and Bunnell methods are current standard clinical configurations described for Achilles tendon repair. Under uniform and standardized laboratory conditions, the specimens were loaded to failure. The locking loop suture method was substantially stronger than either of the other two standard configurations. The latter two did not differ significantly from each other. The results of this study may be clinically relevant in terms of the choice of the repair method for surgically treated Achilles tendon ruptures.

Research in biomechanics of occupant protection

This paper discusses the biomechanical bases for occupant protection against frontal and side impact. Newton's Laws of Motion are used to illustrate the effect of a crash on restrained and unrestrained occupants, and the concept of ride down is discussed. Occupant protection through the use of energy absorbing materials is described, and the mechanism of injury of some of the more common injuries is explained. The role of the three-point belt and the airbag in frontal protection is discussed along with the potential injuries that can result from the use of these restraint systems. Side impact protection is more difficult to attain but some protection can be derived from the use of padding or a side impact airbag. It is concluded that the front seat occupants are adequately protected against frontal impact if belts are worn in an airbag equipped vehicle. Side impact protection may not be uniform in all vehicles.

Suppression of cytochrome P450 (Cyp1a-1) induction in mouse hepatoma Hepa-1C1C7 cells by methoxsalen

Cultured mouse hepatoma cell line Hepa-1c1c7 cells were treated with methoxsalen to assess the role of methoxsalen in the process of Cyp1a-1 induction. Treatment of Hepa-1c1c7 cultures with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) induced Cyp1a-1, as indicated by analysis of 7-ethoxyresorufin O-deethylation (EROD) activity and P4501A1 protein. When methoxsalen and TCDD were both added to cultures, TCDD-inducible EROD activity was greatly suppressed by methoxsalen in a dose-dependent manner. We find that treatment of Hepa-1c1c7 cells with methoxsalen inhibited CYP1A1 mRNA induction by TCDD as well as the concomitant increase P4501A1 protein. Formation of DNA-protein complexes between the dioxin receptor and its DRE target was inhibited by methoxsalen, as determined by gel mobility shift assays using oligonucleotides corresponding to DRE 3 of the Cyp1a-1 gene. These results suggest that the inhibitory action of methoxsalen on TCDD induction of the Cyp1a-1 gene expression in Hepa-1c1c7 cells might be antagonism of the DNA binding potential of nuclear dioxin receptor.

2-Acetylaminofluorene inhibits the activation of immune responses by blocking cell cycle progression at G1 phase

2-Acetylaminofluorene (AAF) inhibited in a dose dependent manner mouse spleen cell blastogenesis in response to phorbol 12-myristate 13-acetate (PMA)/Ionomycin (Io) activation, the T-cell lectin, concanavalin A (Con A), and following stimulation by alloantigens as measured by the mixed lymphocyte response (MLR). AAF also markedly suppressed the T-cell dependent antibody forming cell (AFC) response to sRBC. AAF was most inhibitory on both the sRBC IgM AFC response and Con A stimulated proliferation when added during the first 24 h following initiation of culture. Direct addition of high concentrations of AAF (100 microM) to spleen cell cultures at 48 h following Con A stimulation produced a very modest inhibition (< 20%) of T-cell proliferation as compared to 90% when added at the time cultures were initiated. Similarly, AAF (75 and 100 microM) produced a greater than 80% inhibition of the in vitro AFC response when spleen cells were sensitized with antigen in presence of AAF. In contrast, no inhibition of the IgM AFC response was produced when AAF (75 microM) was added to spleen cell cultures 48 or 72 h after antigen sensitization. Con A-triggered cell-cycle progression was attenuated at the G1 stage by the addition of AAF (50 and 100 microM) with no inhibition of S to G2/M phase transition. These results suggest that the mechanism of AAF-mediated immune suppression is through a blockade of cell cycle progression from G1 to S phase.

Role of metabolism in cocaine-induced immunosuppression in splenocyte cultures from B6C3F1 female mice

Cocaine has been reported to directly suppress the in vitro immune responses at very high concentrations. In the present study, the possible role of metabolism in cocaine-induced immunosuppression was investigated in splenocyte cultures isolated from B6C3F1 female mice. Since cocaine can be metabolized by both esterase and P-450 monooxygenase, we studied the direct effects of cocaine, benzoylecgonine and norcocaine on the in vitro T-dependent antibody response to SRBC. Direct exposure to cocaine only produced a modest (30%) but nonsignificant suppression of the antibody response, while benzoylecgonine, a primary product of metabolism by the esterase pathway, was devoid of activity. In contrast, direct exposure to norcocaine, the initial product of N-demethylation by the P-450 pathway, produced significant suppression at concentrations greater than or equal to 10 microM. Similar results were observed in studies measuring LPS and Con A mitogenicity. Furthermore, a significant suppression was observed when splenocytes were preincubated for 1 h with 1 mM cocaine in the presence of liver S-9 fractions isolated from phenobarbital-induced mice. Meanwhile, no suppression was obtained when splenocytes were preincubated in the presence of untreated S-9 fractions. To characterize the mechanism of our results, the capacity of both untreated and phenobarbital-induced microsomes to produce formaldehyde from cocaine was compared. The N-demethylation of cocaine was NADPH-dependent and phenobarbital-induced microsomes produced approx. 6-times higher amounts of formaldehyde, indicating a greater portion of cocaine could be metabolized through the P-450 pathway to its toxic metabolites. Finally, because benzoylecgonine shares with cocaine the presence of a methyl group on the tropane nitrogen, we also compared the ability of N-demethylation from cocaine and benzoylecgonine in mouse liver microsomes. Our results indicated that benzoylecgonine could not be demethylated as determined by a failure to generate any formaldehyde. These results offer further support that the N-demethylation pathway is a critical step to cause its immunotoxicity.

Cyclic AMP is an essential factor in immune responses

In the present studies, cAMP, a secondary messenger historically viewed as a negative mediator of immune responses, was demonstrated to possess immunoenhancing activity at low concentrations. In parallel experiments the adenylate cyclase inhibitor, 2',3'-dideoxyadenosine, produced a marked inhibition of humoral and proliferative immune responses suggesting that cAMP at physiologically relevant concentrations acts as a critical second messenger in immune responses. Direct addition of dibutyryl cAMP (10-100 microM), a membrane permeable cAMP analog, to mouse spleen cell cultures produced a marked and dose-related increase (25-100%) in humoral immune responses as measured by the primary IgM antibody forming cell response to the antigen, sheep erythrocytes. Over a similar concentration range, dibutyryl cAMP (5-50 microM) also dose-dependently enhanced (25-50%) phorbol 12-myristate 13-acetate/ionomycin-stimulated lymphoproliferation. Incubation of spleen cells with 2',3'-dideoxyadenosine (40-80 microM), an adenylate cyclase inhibitor, for 30 min depressed significantly the basal level of intracellular cAMP. 2',3'-dideoxyadenosine treatment also significantly decreased both the antibody forming cell response and the proliferative response in a dose-dependent manner. Interestingly, the antibody forming cell response exhibited significantly greater sensitivity to inhibition by 2',3'-dideoxyadenosine than the lymphoproliferative responses. The critical role for cAMP as a positive immunoregulatory signal is further supported by the fact that the immunosuppression by 2',3'-dideoxyadenosine could be reversed completely in the antibody forming cell response to sheep erythrocytes through the addition of dibutyryl cAMP into the culture medium. Partial but not complete reversal of the inhibitory effects of 2',3'-dideoxyadenosine on lymphoproliferation was also demonstrated by dibutyryl cAMP. Taken together, these results suggest that cAMP acts as a positive regulatory signal for immune responses as indicated by the fact that depletion of intracellular cAMP induces a marked inhibition of humoral and proliferative responses.

Suppression of the humoral immune response by cannabinoids is partially mediated through inhibition of adenylate cyclase by a pertussis toxin-sensitive G-protein coupled mechanism

Cannabinoid compounds, including the major psychoactive component of marihuana, delta 9-tetrahydrocannabinol (delta 9-THC), have been widely established as being inhibitory on a broad array of humoral and cell-mediated immune responses. The presence of cannabinoid receptors has been identified recently on mouse spleen cells, which possess structural and functional characteristics similar to those of the G-protein coupled cannabinoid receptor originally identified in rat brain. These findings, together with those demonstrating that delta 9-THC inhibits adenylate cyclase in splenocytes, strongly suggest that certain aspects of immune inhibition by cannabinoids may be mediated through a cannabinoid receptor-associated mechanism. The objective of the present studies was to determine whether inhibition of adenylate cyclase is relevant to mouse spleen cell immune function and, if so, whether this inhibition is mediated through a Gi-protein coupled mechanism as previously described in neuronal tissue. Spleen cell activation by the phorbol ester phorbol-12-myristate-13-acetate (PMA), plus the calcium ionophore ionomycin, produced a rapid but transient increase in cytosolic cAMP, which was inhibited completely by immunosuppressive concentrations of delta 9-THC (22 microM) and the synthetic bicyclic cannabinoid CP-55940 (5.2 microM), which produced no effect on cell viability. Inhibition by cannabinoids of lymphocyte proliferative responses to PMA plus ionomycin and sheep erythrocyte (sRBC) IgM antibody-forming cell (AFC) response, was abrogated completely by low concentrations of dibutyryl-cAMP (10-100 microM). Inhibition of the sRBC AFC response by both delta 9-THC (22 microM) and CP-55940 (5.2 microM) was also abrogated by preincubation of splenocytes for 24 hr with pertussis toxin (0.1-100 ng/mL). Pertussis toxin pretreatment of spleen cells was also found to directly abrogate cannabinoid inhibition of adenylate cyclase, as measured by forskolin-stimulated accumulation of intracellular cAMP. These results indicate that inhibition of the sRBC AFC response by cannabinoids is mediated, at least in part, by inhibition of adenylate cyclase through a pertussis toxin-sensitive Gi-protein coupled cannabinoid receptor. Additionally, these studies further support the premise that cAMP is an important mediator of lymphocyte activation.

Role of hydrocortisone in dimethylnitrosamine-induced suppression of antibody response in the mixed culture of murine hepatocytes and splenocytes

We have previously reported that the hormone-supplemented culture condition for primary hepatocytes is required in dimethylnitrosamine (DMN)-induced suppression of antibody response to sheep erythrocytes in the mixed cultures of murine hepatocytes and splenocytes. In the present investigation, the components of the hormone supplement were screened to identify the component(s) responsible for the increased ability of hepatocytes to activate DMN to its immunosuppressive form. The presence of hydrocortisone in the hepatocyte culture media had the primary role in DMN activation in the co-culture system. Other components of the hormone supplement showed slight or no effects. The effects of hydrocortisone were clearly confirmed through the dose-response study of both DMN and hydrocortisone. To characterize whether the effect of hydrocortisone is glucocorticoid-dependent we tested another potent glucocorticoid, dexamethasone (DEX), and determined if the activity by hydrocortisone could be reversed by RU 486. It was found that hepatocytes cultured in DEX-containing media could also activate DMN to its immunosuppressive form. However, the activity by hydrocortisone to increase DMN-induced immunosuppression was not reversed by RU 486. Furthermore, a possible direct interaction between DMN and hydrocortisone was ruled out. Finally, we transferred DMN-pre-treated culture supernatant from hepatocytes to spleen cell cultures, and found that the metabolite of DMN was very unstable, and that DMN-induced suppression of T-dependent antibody response was hepatocyte-dependent. The present results suggest that glucocorticoids, including hydrocortisone and DEX, in hepatocyte culture media can affect DMN-induced immunosuppression in the hepatocyte/splenocyte co-culture system via a pathway which does not appear to be related to the glucocorticoid receptor.

Structure-antigenicity relationship of peptides from the pre-S2 region of the hepatitis B virus surface antigen

Peptide antigenicity against the pre-S2 region of the hepatitis B virus surface antigen was studied using a pre-S2 specific anti-hepatitis B virus mouse monoclonal antibody (H8 mAb) and synthetic peptides by competitive ELISA. The mAb showed preferences for long peptides with the sequence 120/123-145, though the mAb binding region was located in the sequence 130-145 from the analysis of a conjugation study. The N-terminal residues 120/123-129 play an important role for the maintenance of the highly antigenic structure of the B cell epitope. Among these, the N-terminal hydrophilic residues 124-126 and hydrophobic residue 127 were important, whereas residues 120-122 did not affect antigenicity. Residues 131 and 141 appeared to be critical for the mAb binding. The relationship between peptide structure and antigenicity was also investigated by probing the secondary structure of the peptides by circular dichroism. Highly antigenic peptides elicited more ordered structure in 20% trifluoroethanol than less antigenic peptides. The results suggested that peptide antigenicities against H8 mAb are closely related to the B-cell epitope conformations of peptides.

Parathyroid hormone-related protein: evidence for isoform- and tissue-specific posttranslational processing

Parathyroid hormone-related protein (PTHrP) is expressed by malignant tumors and leads to the syndrome of humoral hypercalcemia of malignancy. It is also expressed by a wide variety of nonmalignant tissues, in which it appears to play distinct paracrine and/or autocrine roles. The human PTHrP gene encodes three cDNA-predicted initial translational products of 139, 141, and 173 amino acids. Most human cell lines contain mRNAs encoding all three PTHrP isoforms. The physiological rationale for the existence of these three highly similar transcripts is unknown. In order to determine whether the protein products derived from these three transcripts differ, we transfected Chinese hamster ovary (CHO) cells and rat insulinoma (RIN) cells individually with cDNAs encoding human PTHrP(1-139), PTHrP(1-141), and PTHrP(1-173). Cell extracts and conditioned medium were then chromatographed using reversed-phase HPLC and analyzed using region-specific PTHrP immunoassays. As we had previously observed in SKRC-1 (renal cell carcinoma) and RIN(1-141) cells, multiple amino-terminal PTHrP species as well as a separate midregion PTHrP species were identified in all six cell lines. In addition, both CHO and RIN cell lines transfected with the PTHrP(1-139) construct contained a previously unrecognized carboxy-terminal fragment that reacted with a PTHrP(109-138) antiserum. This carboxy-terminal fragment was physically distinct from the midregion fragment discovered earlier and was also present in conditioned medium, indicating that it is a secretory form, rather than a biosynthetic intermediate or a degradation product.(ABSTRACT TRUNCATED AT 250 WORDS)

Investigation of how different halos influence pin forces

STUDY DESIGN

This study investigated the effect of the size and material of halo rings on the pin force produced at the halo pin-calvarium complex.

SUMMARY OF BACKGROUND DATA

Loosening of halo pins has been a problem with using the halo-vest apparatus to stabilize cervical spine fractures.

METHODS

One standard halo pin and seven different halo rings were used to test the anterior pin hole of each ring at a constant torque of 8 inch-pounds (0.9 Nm).

RESULTS

Pin force fluctuated from halo to halo, and decreased as the nut was tightened.

CONCLUSIONS

Identical torques applied to different halos will not guarantee the same magnitude of pin force for halo fixation.

Suppression of TCDD-induced cytochrome P450 IA1 activity by staurosporine in mouse primary hepatocyte cultures and hepatoma cells

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) induced cytochrome P450 IA1 activity in mouse primary hepatocyte cultures and mouse hepatoma Hepa-1 cells. Pretreatment with staurosporine, a protein kinase C inhibitor, inhibited TCDD-activated cytochrome P450 IA1 expression dose-dependently in both culture systems. Staurosporine also decreased P450IA1 protein synthesis which was detected using western immunoblot. Increased transcription of CYP1A1 gene by TCDD was also suppressed by staurosporine treatment. However, tyrphostin AG213, a specific tyrosine kinase inhibitor, had no effects on TCDD-induced cytochrome P450 expression. These results suggest that protein kinase C signal transduction may be involved in the cytochrome P450 induction mechanism by TCDD.

Suppressive effects of 2-acetylaminofluorene on concanavalin A-stimulated murine splenocyte proliferation in vitro: inhibition of interleukin-2 receptor expression

Treatment of 2-acetylaminofluorene (AAF) to murine splenocyte culture produced a dose-related suppression on the lymphoproliferative response to concanavalin A (Con A). The amount of interleukin 2 (IL-2) activity in the culture supernatants was increased when AAF was treated for 48 hr. Since IL-2 activity did not increase if AAF was treated for the last 4 hr of a 48-hr culture period, the increase of IL-2 activity in culture supernatants did not appear to be due to the leakage of IL-2 from intracellular pool. Treatment of colchicine, an agent known to increase IL-2 activity in culture supernatants by inducing the cytoskeletal structure modification, increased IL-2 activity in splenocyte culture supernatants in 4 hr treatment. Meanwhile, the IL-2 receptor alpha (IL-2R alpha) positive cell population was decreased by the treatment of AAF. These results suggested that suppressive effects of AAF on the lymphoproliferative response to Con A in murine splenocyte culture may be associated with the inhibition of IL-2 receptor expression.

Parathyroid hormone-related protein as a prohormone: posttranslational processing and receptor interactions

Since the elucidation of the structures of the three human PRHrP isoforms in 1987, information has rapidly accured which indicates that the role of PTHrP in normal physiology will prove to be crucial as well as exceedingly complex. The importance of the role of PTHrP in normal physiology is underscored by its broad tissue expression, by its intense evolutionary conservation, by its extremely early expression after fertilization of the ovum, and by the lethal consequences of PTHrP gene disruption. The complexity of the role of PTHrP in normal physiology increases almost monthly. This complexity is reflected in the broad tissue distribution of the peptide, its complex transcriptional regulation and mRNA instability motifs, and its multiple transcripts and isoforms. It is now clear that additional complexity exists at the level of posttranslational processing. Expression of the PTHrP gene leads to the tissue-specific processing and secretion of an increasingly complex family of derivative peptides, each with its own repertoire of cognate receptors, signal transduction pathways, and physiological consequences. Further elucidation of the posttranslational processing pathways and mechanisms can be anticipated in the coming years, coupled with a corresponding elucidation of multiple PTHrP receptors, their specific signal transduction pathways, and their unique physiological roles. The role of PTHrP in causing HHM is now clearly established. Work in the coming decade will focus on the normal physiological roles played by PTHrP.

Acute focal bacterial nephritis presented as acute renal failure and hepatic dysfunction in a renal transplant recipient

We describe acute focal bacterial nephritis (AFBN) presented as acute renal failure and hepatic dysfunction in a renal transplant recipient. He had received a renal transplantation 5 years previously and maintained good renal function without an episode of acute rejection or any urinary abnormalities. He had been an HBsAg carrier and showed mild elevation of liver enzymes after renal transplantation. For 5 days before admission, the patient suffered from fever, graft kidney swelling, tenderness and oliguria. On admission, renal biopsy was performed and solumedrol pulse therapy was started under the impression of acute rejection. The following laboratory findings revealed acute renal failure and hepatic dysfunction. From the abdomen CT and renal biopsy findings this case was confirmed as AFBN in a grafted kidney. With successive hemodialysis and antibiotic therapy clinical symptoms and renal function improved promptly. In acute hepatic dysfunction we discontinued cyclosporine (CsA) to prevent irreversible fulminant hepatic failure until the normalization of liver function. It should be considered that AFBN must be included in the differential diagnosis of acute rejection, and the early diagnosis and treatment of AFBN is important to save the grafted kidney. In addition, early withdrawal of CsA is essential to prevent irreversible hepatic failure when infection triggers hepatic dysfunction in HBsAg-positive renal transplant recipients.

Recovery of dimethylnitrosamine-induced immunosuppression by pargyline in the mixed cultures of murine hepatocytes and splenocytes

To investigate the role of monoamine oxidase (MAO) in dimethylnitrosamine (DMN)-induced suppression of the antibody response to sheep erythrocytes, the effect of an MAO inhibitor, pargyline, was studied in mixed cultures of murine hepatocytes and splenocytes. When pargyline was added simultaneously with DMN during the coculture, DMN-induced immunosuppression was clearly recovered dose-dependently. Cyclophosphamide was used as a comparative control in these studies. Surprisingly, pargyline also reversed cyclophosphamide-induced suppression of the antibody response in the coculture system. The results with cyclophosphamide were not consistent with a role by MAO, and suggested that pargyline may not be selective for MAO. To confirm our hypothesis, the ability of pargyline to inhibit three cytochrome P-450 (P-450) isozyme-specific monooxygenase activities in vitro was studied using mouse liver microsomes. Pargyline, under the same concentration ranges that we used in the coculture studies, clearly inhibited the P-450IIE1-specific p-nitrophenol hydroxylase activity and P-450IIB1-specific pentoxyresorufin O-dealkylase activity. Taken together, our present results indicate that pargyline inhibits P-450 activity and is not selective for MAO. Although further studies are required to confirm a possible role by MAO in DMN-induced immunosuppression, our results suggest that pargyline may recover DMN-induced immunosuppression by primarily inhibiting the ability of P-450 enzymes in hepatocytes to activate DMN to its immunosuppressive metabolite(s).

Primary aldosteronism detected after renal transplantation

A 44-year old female was admitted to our hospital for evaluation of uncontrolled hypertension. She received renal transplantation 3 months ago and suffered from a tingling sensation and weakness on both hands. Laboratory findings (low serum potassium, low plasma renin activity and elevated plasma aldosterone level) was consistent with primary aldosteronism. Through the postural study for plasma aldosterone and the adrenal CT finding we diagnosed this case as adrenal adenoma, which was confirmed by surgical removal. A retrospective review of medical records showed that characteristic findings in primary aldosteronism (hypokalemia and low plasma renin activity) were masked by renal failure and became evident after successful renal transplantation. It was suggested that impaired urinary potassium excretion and excess release of renin from the ischemic kidney masked the characteristic findings of primary aldosteronism. To our knowledge, this is the first report documenting the change of renin-angiotensin-aldosterone system after renal transplantation in a case of coexistence of primary aldosteronism and chronic renal failure.

The C-reactive protein (CRP) in patients with long bone fractures and after arthroplasty

Between March 1991 and February 1992 serial serum C-reactive protein (CRP) levels were measured prospectively for three weeks in 57 consecutive patients with fractures of long bones, and also in 11 patients who had undergone primary total hip or knee arthroplasty. A semi-quantitative capillary floculation method was used for measuring the CRP level. The highest values were usually recorded 2-3 days after trauma or operation, and the CRP was nearly normal by three weeks. In the patients with long bone fractures the amplitude of CRP response was affected by the type of treatment. Lower values were observed in those patients treated conservatively than in those who underwent operation, but the profile of CRP response was similar, regardless of the type of treatment. The CRP response was also affected by the severity of the trauma in conservatively treated patients, but in those who underwent operation the CRP response was similar, regardless of the severity of the injury. In patients with primary total hip or knee arthroplasty the pattern of CRP response after operation was similar to that in the patients with long bone fractures who underwent surgical treatment. Awareness of the natural course of the CRP response after fracture and arthroplasty may help in the diagnosis of early post-traumatic and postoperative complications, especially infections.

Mouse interferon gamma pretreated hepatocytes conditioned media suppress cytochrome P-450 induction by TCDD in mouse hepatoma cells

Mouse interferon gamma (IFN-G) markedly suppressed 7-ethoxyresorufin o-deethylase (EROD) activity when added at the same time as TCDD in mouse primary hepatocyte cultures. IFN-G, however, had no effect on EROD induction by TCDD in Hepa-1 cells, a mouse hepatoma cell line, or Hepa-1 cells cocultured with Kupffer cells when added directly to the culture. EROD induction by TCDD in Hepa-1 cells was suppressed when cells were cultured with IFN-G pretreated mouse hepatocytes conditioned media. The magnitude of suppression was related to the dose of IFN-G and the density of hepatocytes used for the preparation of the conditioned media. Treatment of the monoclonal antibody against IFN-G to the conditioned media did not block the suppression of EROD induction. The suppressive effect of IFN-G pretreated hepatocytes conditioned media on EROD induction, however, was blocked when the conditioned media was heated or treated with trypsin. These results suggested that IFN-G pretreated mouse hepatocytes may release a soluble protein factor(s) which suppressed the EROD induction by TCDD in Hepa-1 cells.

Suppression of the in vitro immune response by 7,12-dimethylbenz[a]anthracene in mouse splenocytes co-cultured with rat hepatocytes

7,12-Dimethylbenz[a]anthracene (DMBA) produced a dose-related suppression of in vitro polyclonal antibody response to lipopolysaccharide in mouse splenocytes co-cultured with rat hepatocytes. Addition of alpha-naphthoflavone (ANF), the cytochrome P-450 inhibitor, to the coculture reversed the DMBA-induced immunosuppression. The amount of [3H]DMBA bound to splenocyte DNA increased in a time-dependent manner up to 4 hr of co-culture and treatment of ANF reduced the binding. The addition of extracellular DNA to the co-culture prevented the suppression of the antibody response by DMBA. These results suggested that reactive metabolite(s) of DMBA were released from hepatocytes and that the suppression of the antibody response by DMBA is mediated via these reactive intermediate(s). DNA represents the primary macromolecular target for the reactive intermediate(s) of DMBA.

Hepatocyte growth factor enhances B-cell activity

Hepatocyte growth factor (HGF), is one of the growth factors induced and secreted into the serum of partially hepatectomized or hepatotoxin-treated mice that mediates regeneration of hepatic tissue. Results are presented here demonstrating that in addition to hepatotrophic effects, HGF also possesses immunologic activity. In particular, addition of HGF to B6C3F1 mouse spleen cell cultures enhanced humoral immune responses by augmenting the ability of B-cells to secrete immunoglobulin.

Computer simulation of occupant neck response to airbag deployment in frontal impacts

A mathematical simulation was performed to study the potential of head and neck injury to an unbelted driver restrained by an airbag. The baseline study represented a 50th percentile male dummy driving in a compact car with the steering wheel perpendicular to the floor. The vehicle was moving at 48 km/hour at the time of impact. Model predictions were compared with sled test results. The data agreed reasonably well. A parametric study was performed to study the effect of changing the steering wheel angle and the size of the airbag. It was found that when the standard 20 degrees angle steering wheel was used, neck joint torques were decreased by 22 percent while the resultant head acceleration increased 41 percent from the base line study. When the vertical dimension of the airbag was reduced by 10 percent, neck joint torques were increased by 14 percent, while head acceleration showed a slight decrease of 9 percent.

Induction of cytochrome P-450 by dimethyl sulfoxide in primary cultures of adult rat hepatocytes

Treatment of hepatocyte cultures with dimethyl sulfoxide (DMSO) induced P-450IIE1-specific aniline 4-hydroxylase activity and P-450IA1-specific ethoxyresorufin O-deethylase activity at a concentration of 0.1% (v/v). The P-450IIB-specific pentoxyresorufin O-deethylase activity was induced only at the 2% (v/v) level. Dot blot analysis of the total cellular RNA and cycloheximide treatment of the culture suggested that induction of ethoxyresorufin O-deethylase activity by DMSO may be due to the increase of de novo synthesis of the P-450IA1 protein, not to accumulation of mRNA in the hepatocyte culture.

Effect of porcine bone morphogenetic protein on healing of bone defect in the rabbit radius

Segmental long bone defects due to infection or trauma is a difficult problem to manage in patients. We studied the effect of porcine bone morphogenetic protein (pBMP) on healing of defects in the rabbit radius. Porcine BMP was separated and purified from the tibia and femur of pigs by repeated solubilization and precipitation of the protein with different concentrations of urea and GuHCl. The osteoinductive activity of pBMP was confirmed by bioassay using No. 615 mice. In rabbits, about a 15 mm length of radii were removed and 20 mg of pBMP was implanted in the defected area with fibrin sealant (FS), while only FS was implanted in controls. Union of the affected area was observed in 6 weeks in the experimental side. There was no definite evidence of bone bridging across the affected area in the controls. This suggests that pBMP has a bone forming activity in other species and the clinical use of pBMP in treating patients with segmental bone defects is promising.

Cloning of a Clostridium botulinum type B toxin gene fragment encoding the N-terminus of the heavy chain

Two lambda gt11 clones of the toxin gene of Clostridium botulinum type B were identified by the monoclonal antibody specific to the heavy chain of type B toxin. Neither of the expressed fusion proteins from the lysates of lysogenic E. coli Y1089 showed any botulinal toxic activity. One of the clones hybridized to the oligonucleotide probe which was synthesized according to the amino acid sequence of N-terminus of heavy chain. The sequence analysis revealed that highly homologous regions in N-terminus of heavy chain exist among botulinum neurotoxins (type A, B) and tetanus toxin on the amino acid sequence level.

Importance of hepatocyte culture conditions in dimethylnitrosamine-induced suppression of antibody response in the mixed cultures of murine hepatocytes and splenocytes

The role of the hepatocyte culture media in dimethylnitrosamine (DMN)-induced suppression of antibody responses by splenocytes against sheep erythrocytes (SRBCs) was investigated using the mixed culture system of murine hepatocytes and murine splenocytes. It was observed that hormone-supplemented complete media was required for hepatocyte cultures to optimally activate DMN to its immunosuppressive form(s). In the absence of the hormone supplement, the concentration of DMN required to produce a 50% suppression (IC50) was increased by over 10-fold (i.e., compare the IC50 in complete media of less than 0.5 mM to the IC50 in basal media of almost 10.0 mM). In contrast, the activation of cyclophosphamide (cytoxan, CTX), which was used in these studies as a comparative control, was not affected by the absence of the hormone supplement. These results indicate that the observed effect on the activation of DMN was not due to a generalized loss of metabolic capability of hepatocytes cultured without hormones. To examine the role of drug metabolizing capabilities of hepatocytes in the differential activation of DMN, we compared phase I and phase II enzyme activities of hepatocytes cultured for 24 h in either basal media or hormone-supplemented complete media. Our results indicated that there was a significant decrease of phase I monooxygenase activities of cultured hepatocytes when compared to freshly isolated hepatocytes. However, our results failed to show any difference in the activities of hepatocytes cultured in the two media. Most notably, there was no difference in the activity of either high- or low-affinity DMN demethylase, as measured by the generation of formaldehyde. We observed a similar profile with phase II conjugative capabilities, specifically sulfotransferase and glucuronyltransferase. These results indicate that the activation of DMN to its immunosuppressive form(s) can be modulated in the co-culture system by culturing hepatocytes under different conditions. Because we failed to show any differences in the metabolic capabilities of hepatocytes cultured under the two media conditions, the results suggest that the modulation of immunosuppressive activity may not be related to a change in the generation of the immunosuppressive metabolite(s).

Effects of sinefungin and 5'-deoxy-5'-S-isobutyl-adenosine on lipopolysaccharide-induced proliferation and protein N-methylation of arginyl residues in murine splenic lymphocytes

The effects of sinefungin (SF) and 5'-deoxy-5'-S-isobutyl-adenosine (SIBA) on lymphoproliferation and protein N-methylation of arginyl residues were investigated in splenic lymphocyte culture in vitro. Both SF and SIBA produced a dose-related inhibition of the lymphoproliferative response to lipopolysaccharide (LPS). The time-course of the inhibition indicated that SIBA had a more inhibitory effect than that of SF at short incubation periods, but SF showed more inhibition when the incubation was prolonged. The effects of SF and SIBA on the lymphoproliferative response corresponded with their effects on the protein N-methylation of arginyl residues by protein methylase I.

Differentiation of human motion data using combined spline and least squares concepts

A differentiation method, which combines the concepts of least squares and splines, has been developed to analyze human motion data. This data smoothing technique is not dependent on a choice of a cut-off frequency and yet it closely reflects the nature of the phenomenon. Two sets of published benchmark data were used to evaluate the new algorithm.

Early predictor of the efficacy of immunoprophylaxis against perinatal hepatitis B transmission: analysis of prophylaxis failure

To research early predictors of the efficacy of the ongoing mass immunoprophylaxis against perinatal hepatitis B virus (HBV) transmission in Taiwan and to analyse the possible causes of immunoprophylaxis failure, 52 hepatitis Be antigen (HBeAg)-positive carrier mothers were recruited for the study. Maternal blood samples were taken at the first and third trimesters and delivery. Umbilical blood was collected and venous blood samples were taken at 4, 7, 11 and 14 months of age. Serum hepatitis B surface antigen (HBsAg) and antibody titres, HBeAg titre and HBV-DNA concentration were analysed. All the umbilical cord blood samples were negative for HBsAg. Among the 52 vaccinated infants, four were poor responders (anti-HBs less than 10 mIU ml-1 before vaccine booster). Another five infants became HBsAg-positive by 4 months of age and remained carriers. All these five carrier mothers were HBV-DNA-positive and three of them had risk factors related to maternal-fetal haemorrhage during pregnancy or delivery. The remaining 43 infants showed protective anti-HBs level (greater than 10 mIU ml-1) by 4 months of age. Three mothers out of these 43 cases also had the same haemorrhage risk factors during pregnancy or delivery, but were HBV-DNA-negative. Therefore, the anti-HBs level at 4 months is a predictor of the success of immunoprophylaxis. It may be helpful to distinguish HBV-DNA-positive carrier mothers among HBeAg-positive ones, to avoid inducing more maternal-fetal haemorrhage in such cases during pregnancy or delivery. Otherwise, additional hepatitis B immune globulin may be indicated in such cases to raise the successful prevention rate.

Malignant glomus tumor originating in the superior mediastinum--an immunohistochemical and ultrastructural study

An extremely rare case of malignant glomus tumor originating in the superior mediastinum was evaluated immunohistochemically and ultrastructurally. A 78-year-old woman who had been suffering from dysphagia and dyspnea had poorly-defined soft tissue mass, 4.5 x 2.5cm, in the superior mediastinum with direct invasion into the esophagus, trachea, and bilateral thyroid glands. This case is believed to be unique in several respects. There were neither recognizable findings of benign glomus tumor nor sarcomatous areas, in contrast to the previously reported cases. A definite direct invasion into the surrounding organs was identified. We therefore interpreted this case as primary malignant glomus tumor, not as glomangiosarcoma arising in a benign glomus tumor.

Solitary myeloma with massive extracellular crystalline structures--a case report

We describe a case of solitary myeloma showing cystic change filled with massive crystalline structures in a 54-year-old woman. A bone X-ray showed a solitary cystic osteolytic lesion in the right iliac bone. Serum and urine protein electrophoresis showed no demonstrable M-protein, and bone-marrow aspirates did not show any myeloma cells. Histologic examination of the tumor revealed aggregation of plasma cells with massive extracellular infiltration of the rhomboid-shaped crystalline structures. In immunoperoxidase staining, both these crystalline structures and the cytoplasms of the myeloma cells demonstrated a positive reaction for lambda light chain. By electron microscope, the large extracellular crystalline structures were observed, and we found unique rhomboid or rectangular-shaped crystalline structures in the cytoplasms of the myeloma cells.

Relationship between lower limb dynamics and knee joint pain

To test the hypothesis that appropriate and timely neuromuscular control of limb motions plays an important role in the preservation of joint health, we kinematically and kinetically examined the behavior of the legs of young adult subjects at heel strike during natural walking. We compared a group of 18 volunteers, who, we presumed, were preosteoarthrotic because of mild, intermittent, activity-related knee joint pain, with 14 age-matched asymptomatic normal subjects. The two groups of subjects exhibited similar gait patterns with equivalent cadences, walking speeds, terminal stance phase knee flexion, maximum (peak) swing angular velocity, and overall shape of the vertical ground reaction. However, our instrumentation detected statistically significant differences between the two groups within a few milliseconds of heel strike. In the knee pain group, the heel hit the floor with a stronger impact in this brief interval. Just before heel strike, there was a faster downward velocity of the ankle with a larger angular velocity of the shank. The follow-through of the leg immediately after heel strike was more violent with larger peak axial and angular accelerations of the leg echoed by a more rapid rise of the ground reaction force. This sequence of events represents repetitive impulsive loading, which consistently provoked osteoarthrosis in animal experiments. We refer to this micro-incoordination of neuromuscular control not visible to the naked eye as "microklutziness."

Mechanism of disc rupture. A preliminary report

Lumbar intervertebral disc herniation is thought to be related to senescent changes in the nucleus pulposus except in rare instances of trauma. This investigation provides the first in vitro model of disc prolapse that reliably ruptures discs under physiologically reasonable stress. Fourteen vertebral motion segments with intact posterior elements were loaded repetitively at 1.5 Hz in a combination of flexion (7 degrees), rotation (less than 3 degrees), and compression (1,334 N) for an average of 6.9 hours (range, 3.0-13.0 hours) in a materials testing machine. Loading was terminated when reaction force leveled off for more than 1 hour. Ten discs failed through annular protrusions, and four failed by nuclear extrusion through annular tears, supporting the hypothesis that intervertebral disc prolapse is peripheral in origin. The annulus fibrosus is the site of primary pathologic change.

An experimental study on prevention of postlaminectomy scar formation

In repeat lumbar surgery for failed back syndrome, well organized fibrous scar tissue is often noted, binding together the dura, nerve roots, and paraspinal muscles. An animal experimental study was done to investigate the prevention of scar formation after lumbar laminectomy by using dacron and sodium hyaluronate. The experimental animals consisted of three groups: 1) control group, 2) D group (covering the laminectomy defect with dacron sheet), and 3) H group (covering the laminectomy defect with sodium hyaluronate gel). Animals were sacrificed at varying intervals (3-12 weeks) and the lumbar spines were evaluated with histologic preparations. Scar adhesion to the dura was most significantly suppressed in the D group, followed by the H group and the control group.

Binding of Clostridium botulinum type B toxin to rat brain synaptosome

Purified toxin and its subunits from Clostridium botulinum type B were labeled with 125iodine and binding of them to rat brain synaptosomes was studied. Labeled toxin and heavy chain were shown to bind to synaptosomes and there was no significant difference in the molar quantity of bound toxin and heavy chain at several concentrations of synaptosomes, whereas labeled light chain did not bind to synaptosomes. The binding of labeled heavy chain to synaptosomes was inhibited by unlabeled toxin and heavy chain to a similar degree as that of labeled toxin. The binding of labeled toxin and heavy chain to synaptosomes were inhibited by a monoclonal antibody which is specific for the heavy chain.

Chronological changes in genetic variance and heritability of anthropometric characteristics among Chinese twin infants

In order to examine the chronologic changes in genetic variance and heritability of anthropometric characteristics of Chinese infants in Taiwan, a total of 521 pairs of same-sexed twin neonates given birth in four major general teaching hospitals in Taipei City were studied. Based on the placental pattern and 12 red blood cell antigens, 428 MZ and 93 DZ twin pairs were identified and followed up to the age of one year. There was no significant genetic variance for all anthropometric characteristics adjusted for sex and gestational week before the age of six months. After adjusting for sex and gestational week, a significant genetic variance was observed at the age of six months, with heritability values of 0.51 (weight), 0.63 (head circumference), 0.77 (chest circumference), and 0.53 (arm circumference), as well as at one year, although with considerably lower heritability values. This implies that growth is dynamically determined by both genetic and environmental factors during infancy.

Genetic variance and heritability of temperament among Chinese twin infants

In order to examine the genetic variance and heritability of temperament among Chinese infants in Taiwan, a total of 62 pairs of same-sexed twin infants given birth in four major general teaching hospitals in Taipei City were studied. Based on placentation and 12 red blood cell antigens, 44 MZ and 18 DZ pairs were identified. Temperament was assessed at the age of six months by the Chinese edition of Carey's Temperament scale. Significant genetic variance was observed for activity level, approach or withdrawal, intensity of reaction, quality of mood, and threshold of responsiveness, with a heritability of 0.64, 0.56, 0.74, 0.39, and 0.45, respectively. There was no significant intrapair difference in temperamental characteristics between monochorionic and dichorionic MZ twins.

45,XO/46,XY in a newborn with the stigmata of Turner syndrome: report of one case

A newborn with ambiguous external genitalia and the stigmata of Turner syndrome presented with the following features: short stature, hypertelorism, bilateral epicanthal folds, ptosis, low-set ears with prominent auricles, high-arched palate, low posterior hairline, webbed neck, broad and short chest, widely-spaced and hypoplastic nipples and clitoris-like phallus with hypospasdias. He also had patent ductus arteriosus, the secundum type of atrial septal defect and mitral stenosis. Chromosomes of peripheral blood showed mosaicism of cells with 45,XO/46,XY. An exploratory laparotomy was performed at five months of age. The right side ovotestis-like gonad was removed. The left side gonad in the scrotum was normal. No pathological gonadoblastoma was found.

A dynamic finite element analysis of impulsive loading of the extension-splinted rabbit knee

A dynamic nonlinear finite element model was developed to study juxtarticular stresses in the splinted rabbit knee, an established laboratory model for creating osteoarthrosis due to impulsive loading. Plane strain finite element results were validated by comparison with corresponding experimental data. Parametric effects studied included the input tibial displacement speed, the local bone density distribution, and the modulus of cartilage and subchondral bone. While the computed resultant contact force magnitude was sensitive to a number of model parameters, the stress patterns, when normalized to a given resultant force magnitude, were not. Despite comparable force peaks, the finite element results showed approximately six-fold higher effective strain rate levels for a severely impulsive loading protocol known to induce rapid osteoarthrosis, versus those for a mildly impulsive loading protocol not usually associated with cartilage damage. A propensity for elevated shear in the deep cartilage layer near the contact periphery, observed in nearly all computed stress distributions, is consistent with previous experimental findings of fissuring at that level in the impulsively loaded rabbit knee.

High-level expression of human insulin-like growth factor II in Escherichia coli

A gene encoding mature human insulin-like growth factor II (IGF-II) was constructed from the modified IGF-II cDNA sequence and two double-stranded synthetic oligodeoxynucleotide linkers. It was fused to a truncated lacZ gene such that IGF-II was expressed as part of C-terminus of beta-galactosidase. This fused lacZ'-IGF-II gene was under the control of tac promoter and we overproduced the beta-galactosidase-IGF-II fusion protein in the Escherichia coli. The fusion protein formed inclusion bodies inside the cells. The fusion protein was purified from the isolated inclusion bodies and IGF-II protein was obtained from their fusion protein by CNBr cleavage. The released IGF-II was confirmed by its molecular weight as determined by SDS-PAGE and by its ability to bind anti-IGF antibody.

Chronological changes in genetic variance and heritability of systolic and diastolic blood pressure among Chinese twin neonates

In order to examine the chronological changes in genetic variance and heritability of arterial systolic and diastolic blood pressure (SBP and DBP of Chinese infants in Taiwan, a total of 339 same-sexed twin neonates born in four major general teaching hospitals in Taipei City were studied. Based on placentation and 12 red blood cell antigens, 274 monozygotic (MZ) and 65 dizygotic (DZ) twin pairs were identified and followed up to the age of one year. Both SBP and DBP were measured by Doppler blood pressure monitor. Within-pair mean squares of SBP and DBP were consistently smaller in MZ than DZ twins at ages one month and over. The findings remained unchanged after the adjustment for the effects of age, sex, gestational age, placentation and physical state during blood pressure measurement. Falconer's heritability indices for adjusted SBP and DBP at ages two months and over ranged from 0.29 to 0.55 and from 0.27 to 0.45, respectively. The study indicates an important genetic influence on blood pressure during infancy.

Genetic variance and heritability of serum cholesterol and triglycerides among Chinese twin neonates

In order to examine the genetic variance and heritability of serum total cholesterol, high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C) and triglycerides, a total of 349 pairs of same-sexed twin neonates born in four major general teaching hospitals in Taipei City were studied. Based on the placental pattern and 12 red blood cell antigens, 271 monozygotic (MZ) and 78 dizygotic (DZ) twin pairs were identified. There was a significant genetic variance for total cholesterol, HDL-C, LDL-C, and triglycerides both unadjusted and adjusted for sex, gestational age and placentation. The unadjusted heritability of total cholesterol, HDL-C, LDL-C, and triglycerides was 0.59, 0.30, 0.25 and 0.75, respectively; while the corresponding adjusted heritability was 0.74, 0.38, 0.31, and 0.49, respectively. Intrapair variance of serum lipids was not significantly different between monochorionic and dichorionic MZ twins.

Regulation of the hydrolytic and transfer activities of gamma-glutamyl transpeptidase

The activity of gamma-glutamyl transpeptidase was inhibited and stimulated by hippurate with and without acceptor molecules, respectively. Substrate activation was observed when acceptor molecules was not present but the activation was disappeared by the addition of hippurate. When glutamine was absent the inhibition degree of hippurate at pH 8.0 was greater than at pH 7.0, whereas in the presence of both hippurate and glutamine the results were opposed. These show a possibility that glutaminase is activated by hippurate under the condition of physiological pH. The activation of glutaminase by hippurate was also confirmed directly. The inhibition degree of transfer activity by glutamine was increased along the increase of acceptor concentration only in the presence of hippurate. Gamma-Glu-Phe-Gly satisfying prerequisites for donors doesn't act as a substrate, which shows that L-gamma-glutamyl-p-nitroanilide itself hardly acts as an acceptor. This contradicts to an idea that substrate activation caused by autotranspeptidation. The change of apparent Km and Vmax according to the change of pH in the presence of hippurate was different from that in the presence of acceptors. This shows a possibility that the active site on small subunit is inhibited and the latent active site in large subunit is exposed by the interaction of hippurate to the enzyme.

Renal abnormalities in schoolchildren

To establish prevalence of some renal abnormalities in schoolchildren, an epidemiologic study of 132,686 schoolchildren, including 69,903 boys and 62,783 girls, was conducted from March 1987 to May 1988 in the city of Taipei. At the health station of each school, the students were screened quickly by a physician with portable real-time ultrasound equipment. When a renal abnormality was detected or suspected, the examinee was referred to Taipei Municipal Women and Children's Hospital for further investigation. Radiologic and urologic procedures were then selectively performed to establish the correct diagnosis. Renal abnormalities were detected in 645 students (approximately 0.5% of total population screened). There were 256 cases of hydronephrosis, 103 cases of unilateral renal agenesis, 128 cases of unilateral small kidney, 90 cases of renal cystic disorders, 30 cases of ectopic kidney, and 38 cases of other abnormalities. Surgically correctable lesions were demonstrated in 50 of these students. Rapid renal ultrasonography was found to effectively detect some renal abnormalities initially, and prevalence could then be established after further investigations.

Postpartum subsidence of hepatitis B viral replication in HBeAg-positive carrier mothers

To elucidate the effects of pregnancy and delivery on hepatitis B e antigen (HBeAg)-positive carrier mothers, 31 HBeAg-positive carrier mothers were followed-up postpartum 1 year, with 30 HBeAg-positive nonpregnant female carriers as controls. Serum hepatitis B surface antigen (HBsAg), HBeAg titer, and hepatitis B virus (HBV)-DNA concentration were studied at defined intervals. The results revealed that in the control group HBeAg titers and HBV-DNA concentrations fluctuated, whereas the HBsAg titers showed little change, but HBeAg clearance or seroconversion to anti-HBe were not noted on follow-up. In contrast, one carrier mother seroconverted to anti-HBe during pregnancy and the antibody persisted thereafter. Five of the remaining 30 carrier mothers cleared HBeAg postpartum, and among these five cases, one also seroconverted to anti-HBe. In addition, in another five of the 30 cases, the HBV-DNA fell to undetectable level (less than 0.04 ng/ml). All these ten cases had a common tendency of showing a decrease in HBeAg titers and/or HBV-DNA concentrations 1-2 months after delivery. The HBeAg titers and HBV-DNA concentrations in the other 11 cases remained unchanged, whereas the remaining nine cases had increased levels. It is concluded that subsidence of HBV replication is precipitated by delivery in one-third of HBeAg-positive carrier mothers in Taiwan, and this occurs most frequently 1-2 months postpartum.

Immunosuppressive effects of 2-acetylaminofluorene and 2-aminofluorene on murine splenocytes culture

The immunosuppressive effects of 2-acetylaminofluorene (AAF) and 2-aminofluorene (AF) were studied in BALB/c mouse splenocyte culture. Direct addition of AAF and AF to the splenocyte culture produced a dose-related suppression of the in vitro antibody response to sheep erythrocytes(SRBC), DNP-Ficoll, and lipopolysaccharide(LPS). AAF and AF also produced suppression on lymphoproliferative responses to LPS and concanavalin A(Con A). The immunosuppressive effects of AAF and AF, however, were diminished when AAF and AF were incubated in the splenocyte-hepatocyte coculture system for 4 hr. When hepatocyte cultures were pretreated with SKF 525A, a cytochrome P-450 inhibitor, before coculture with spleen cell along with AAF and AF, the suppression of in vitro antibody response reappeared. Meanwhile, both AAF and AF produced a dose-related DNA single-strand breaks in spleen cells only if AAF and AF were treated to spleen cells cocultured with hepatocytes. These results indicate that the immunosuppression by AAF and AF is not mediated by the reactive metabolites implicated to DNA damage.

Production of DNA single-strand breaks in unstimulated splenocytes by dimethylnitrosamine

In an attempt to elucidate the mechanism whereby primary hepatocytes, but not liver S9 homogenates, generate immunosupprssive metabolites of dimethylnitrosamine (DMN), the production of DNA single-strand breaks (SSB) in unstimulated splenocytes was investigated with alkaline-elution analysis. Both hepatocytes and S9 homogenates induced SSB in cultured splenocytes by DMN - minimum detectable doses with the two metabolic activation systems (MAS) were 1 microM and 5 mM, respectively. DNA elution profiles were linear in splenocytes co-cultured with DMN and hepatocytes and convex in splenocytes incubated with DMN and S9 homogenates. Aminoacetonitrile (AAN; 10 mM), a DMN demethylase inhibitor, reversed SSB in splenocytes when incubated with either MAS. Addition of exogenous calf-thymus DNA to the hepatocyte co-culture medium did not affect the production of SSB. Rocking the hepatocyte-splenocyte cultures changed the elution profile from linear to convex. All of these treatments have been previously shown to block the immunosuppression by DMN in the hepatocyte co-culture system. These results indicate that the immunosuppression by DMN is not related to DNA damage, as measured by the production of SSB, and suggest that the metabolism of DMN to intermediates capable of producing genotoxicity and immunotoxicity may be qualitatively and/or quantitatively different.

The effects of altered strain environments on bone tissue kinetics

This study defines the alteration in bone tissue kinetics responsible for the "adaptive remodeling" response to altered strain environments. Adult beagle dogs were separated into three experimental groups: ulnar osteotomy, ulnar osteotomy with fracture fixation plate spanning the gap and sham surgery. Four sets of double fluorochrome labels were administered. Prior to sacrifice at 1, 3, and 6 months, strains were measured through rosette strain gages on the cranial and caudal surfaces of the intact radius. Histomorphometric analysis indicated that the increased bone mass in response to elevated strain results from increased activation frequency of modeling with more sites undergoing formation processes than resorption processes on periosteal and endocortical surfaces. Increased remodeling activation did not lead to increased bone mass. There was no evidence that elevated strain changes the individual vigor of osteoclasts or osteoblasts, or that the sigma period was altered by elevated strain.