Characterization of trihalomethane (THM)-induced renal dysfunction in the rat. II: Relative potency of THMs in promoting renal dysfunction

Single non-lethal doses (3 mmol/kg) of chloroform (CHCl3), dichlorobromomethane (CHCl2Br), dibromochloromethane (CHClBr2), and bromoform (CHBr3) were administered by intraperitoneal injection to male Sprague-Dawley rats and proximal tubular secretion and reabsorption was assessed at varied times following treatment. Each of the trihalomethanes (THMs) at this dose inhibited proximal tubular secretion, as indicated by decreased in vitro renal cortical slice accumulation of organic anion p-aminohippuric acid (14C PAH). The time of maximal THM interference with 14C PAH uptake occurred at 8 h, with recovery being demonstrated by 48 h. Each of the THMs also demonstrated interference with tubular reabsorption, as assessed by urinary glucose excretion, with maximal interference occurring during the first day post-treatment and recovery being observed during the second day post-treatment. In each case, CHCl2Br was the most potent inhibitor of proximal tubular function. Combining these data with those of the preceding paper, the relative potency in disrupting renal function was, in general, CHCl2Br > CHCl3 > CHClBr2 > CHBR3. Since the time course of this investigation indicates that proximal tubular dysfunction precedes other THM-induced renal function interferences, it also appears that proximal tubular damage is the primary event leading to further manifestations of renal dysfunction.

The tumor necrosis factor beta * 1 allele is linked significantly to HLA-DR8 in Koreans with atrophic autoimmune thyroiditis who are positive for thyrotropin receptor blocking antibody

The localization and functional characteristics of tumor necrosis factor(TNF) beta gene raise the possibility that it may be involved in the susceptibility to autoimmune thyroid diseases. To investigate whether a TNF beta gene polymorphism is associated with autoimmune thyroiditis, we analyzed the TNF beta gene polymorphism with the restriction enzyme NcoI in 48 Korean patients with atrophic autoimmune thyroiditis [23 were found to be thyrotropin binding inhibitor immunoglobulin(TBII) positive, 25 TBII negative], 52 goitrous autoimmune thyroiditis, and 129 healthy controls. Two TNF beta alleles were identified from the restriction fragment length polymorphism studies of amplified genomic DNA. In atrophic autoimmune thyroiditis patients positive for TBII, 7 of 23 patients were homozygous for the TNF beta * 1 allele, 3 were homozygous for the TNF beta * 2 allele, and 13 were TNF beta * 1/2 heterozygous compared to controls(P = 0.20). Also, there were no associations between the TNF beta gene polymorphism and either TBII-negative atrophic autoimmune thyroiditis or goitrous autoimmune thyroiditis. Of the HLA-class II antigens, the frequency of HLA-DR8 was significantly greater among the 23 Korean patients with TBII-positive atrophic autoimmune thyroiditis compared to control subjects (Pc = 0.003). When the HLA-DR8 positive patients with TBII-positive atrophic autoimmune thyroiditis and controls were analyzed separately, the DR8 positive patients with TBII-positive atrophic autoimmune thyroiditis had more homozygotes for the TNF beta * 1 allele(6/12, 50.0%) and no homozygotes for the TNF beta * 2 allele, as compared to the DR8 negative patients with TBII-positive atrophic autoimmune thyroiditis and DR8 positive controls(P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Prenatal diagnosis of unusual hemoglobinopathies

While analyzing 280 hemoglobinopathy kindreds with prescribed molecular tests, 3 unusual mutations were observed that required additional characterization. In the first case, the hypervariable region flanking the alpha-globin genes generated an intermediate length 8.2 kb psi zeta-globin gene fragment on a Southeast Asian chromosome with two deleted alpha-globin genes. Rehybridization of the Southern blot with alpha-globin probe distinguished the mutation unambiguously. In the second case, restriction enzyme analysis of a PCR amplified black beta-globin gene detected a novel beta-83 point mutation adjacent to a promoter element. In the third case, which was uninformative with available allele specific oligonucleotides (ASOs), total genomic PCR amplification and sequencing identified a single basepair insertion in codon 36/37 of an Iranian beta-globin gene that shifted the reading frame and obliterated gene activity. Developing additional region-specific ASOs will further diminish the number of cases that must be characterized by genomic PCR sequencing.

Nucleotide sequence and expression of a gentamicin resistance gene isolated from the R plasmid in Serratia marcescens

The 1.0 kb fragment carrying a gentamicin resistance determinant was subcloned from the R plasmid in clinical isolates of Serratia marcescens and its nucleotide sequence was determined. It contains an open reading frame composed of 858 nucleotides, which shows 97% homology to the aacC2 gene in nucleotide sequence. Minicells carrying the 1.0 kb insert DNA on the plasmids produced a 30 kd protein that was consistent with the expected size of the deduced amino acid sequence from the open reading frame. A search for the promoter revealed a putative promoter of which the -35 region was provided by the right end of Tn3, suggesting that the expression of the gentamicin resistance gene is dependent on the Tn3 sequence.

A comparative study of the cytotoxicity of skin irritants on cultured human oral and skin keratinocytes

The cytotoxicity of irritants on human oral and skin keratinocyte culture models was compared. Keratinocytes were exposed to sodium lauryl sulphate and benzalkonium chloride at concentrations of 10(-4)-10(-7) M for 24 h. Cytotoxicity was evaluated by changes in mitochondrial metabolic activity (MTT assay) and plasma membrane integrity (LDH leakage). Our results showed that oral and skin keratinocytes are equally sensitive to the irritants tested. There were marked similarities in susceptibility between each cell type cultured from six individuals. The immunohistochemical staining pattern of both cell types resembled that of the basal cell. These observations suggest that the skin keratinocyte culture model may be useful in evaluating the cytotoxicity of agents which are irritants on either the skin or oral mucosa.

Role of quinone reductase in in vivo ethanol metabolism and toxicity

Quinone reductase (QR), in the presence of suitable substrate, results in the regeneration of NAD+ from NADH. To test the hypothesis that QR can play a role in ethanol metabolism and toxicity, we studied the effect of a quinone as well as of induced levels of QR on ethanol administered in vivo to male rats and mice. Butylated hydroxyanisole (BHA) is known both to induce QR and to be metabolized to tert-butyl quinone (TBQ). Dietary BHA (0.75% for 10 days), followed by oral ethanol (4 g/kg, by gavage), increased the rate of ethanol disappearance and decreased the area under the curve (AUC) for blood ethanol in both rats and mice. In addition, BHA pretreatment of rats was shown to prevent ethanol-induced 24-hr hepatic triglyceride accumulation. Also, in rats, TBQ (5 mg/kg, ip) led to decreased AUC and hepatic triglyceride accumulation, although the ethanol disappearance rate was not significantly affected. TBQ in BHA-fed rats resulted in even greater effects on the ethanol disappearance rate and AUC than TBQ or BHA treatment alone. None of these treatment regimens resulted in a significant change in volume of distribution of ethanol. Thus, these results support the hypothesis that induction of QR and/or administration of quinones lead to enhanced in vivo metabolism of ethanol and decreased hepatotoxicity.

Degradation products of streptozotocin do not induce hyperglycemia in rats

The present study was conducted to determine whether degradation products of streptozotocin formed under various conditions induce hyperglycemia in rats. Streptozotocin is completely degraded in pH 7.4 buffer in 4 hr and even more rapidly in plasma. Streptozotocin degradation products resulting from incubation in pH 7.4 phosphate buffer or in plasma were not diabetogenic in rats.

Negative correlation between the conversion of thyrotropin receptor-bound blocking type thyrotropin receptor antibody to the stimulating type by anti-human IgG antibodies and the biological activity of blocking type thyrotropin receptor antibody

It has been reported that receptor-bound blocking type TSH receptor antibody (TRAb) can be converted to the stimulating type by anti-human IgG antibodies. To evaluate the relationship between the conversion of receptor-bound blocking type TRAb to the stimulating type and the biological activity of blocking type TRAb, we compared converting activities of blocking type TRAb from 10 patients with primary nongoitrous hypothyroidism with both the doses of blocking type TRAb which show 50% inhibition of 125I-bTSH binding to the TSH receptor and those which show 50% inhibition of TSH-stimulated cAMP production in cultured rat thyroid cells (FRTL-5). The additions of anti-human IgG antibody to FRTL-5 cell-bound blocking IgGs resulted in the increase in cAMP production in a dose-dependent manner and the converting activities (percent increase of cAMP production) also depended on the doses of blocking IgGs. The converting activities were significantly correlated with the doses of blocking IgGs which showed 50% inhibition of 125I-bTSH binding to the TSH receptor (r = 0.71, p = 0.011). And these converting activities were also significantly correlated with the doses of blocking IgGs which showed 50% inhibition of TSH-stimulated cAMP increase (r = 0.81, p = 0.002), and were negatively correlated with thyroid stimulation blocking antibody activities (r = 0.58, p = 0.02). We have demonstrated that all cell-bound blocking type TRAb were converted to the stimulating type by anti-human IgG antibody and the degree of conversion was negatively correlated with the biological activity of blocking type TRAb.(ABSTRACT TRUNCATED AT 250 WORDS)

A strong association between thyrotropin receptor-blocking antibody-positive atrophic autoimmune thyroiditis and HLA-DR8 and HLA-DQB1*0302 in Koreans

We investigated whether the associations between HLA alleles of patients with autoimmune hypothyroidism varied according to the presence or absence of TSH receptor-blocking antibody (TRBab). We analyzed the HLA-A, -B, -C, and -DR antigens by serotyping and the DQA1 and DQB1 genes using both enzymatic DNA amplification and sequence-specific oligonucleotide hybridizations. The patient population consisted of 47 Korean patients with atrophic autoimmune thyroiditis and 62 patients with goitrous autoimmune thyroiditis. The antigen frequency of HLA-DR8 was significantly increased in 23 atrophic autoimmune thyroiditis patients that were positive for TSH binding inhibitor immunoglobulin (TBII) compared to 136 controls [52% vs. 16%; chi 2 = 13.1; Pc (corrected P value) = 0.003]. This relative risk was 5.7; the etiological fraction was 0.43. HLA-DQB1*0302 was also increased in patients with TBII-positive atrophic autoimmune thyroiditis (24% vs. 7%; chi 2 = 11.2; Pc = 0.012; relative risk = 4.4; etiological fraction = 0.19). No specific DR antigens or DQB1 alleles were increased in either TBII-negative atrophic autoimmune thyroiditis or goitrous autoimmune thyroiditis. A significant decrease in the frequency of HLA-DR6 antigen was observed in both TBII-positive atrophic autoimmune thyroiditis (0% vs. 32%; chi 2 = 8.4; Pc = 0.03) and goitrous autoimmune thyroiditis (0% vs. 32%; chi 2 = 23.2; Pc < 0.001) patients. The frequency of the HLA-Cw1 antigen was significantly increased in all patient groups. We conclude that TRBab-positive atrophic autoimmune thyroiditis is immunogenetically different from both goitrous autoimmune thyroiditis and TRBab-negative atrophic autoimmune thyroiditis. It is possible that HLA-DR8 and/or DQB1*0302 may be related to the susceptibility genes involved in the production of TRBab in Koreans.

A 5' element of the chicken beta-globin domain serves as an insulator in human erythroid cells and protects against position effect in Drosophila

We have characterized an element near the 5' boundary of the chicken beta-globin domain that insulates a reporter gene from the activating effects of a nearby beta-globin locus control region (5'HS2) when assayed in the human erythroid cell line K562. We show that the insulation mechanism is directional, that it operates at the level of transcription, and that it involves the alteration of chromatin structure over the promoter of the gene. The insulator has no significant stimulatory or inhibitory effects of its own. In transgenic Drosophila, the insulator protects the white minigene from position effects. The action of the insulator thus is not restricted to erythroid or mammalian cells, suggesting that such elements may serve an important and widely distributed function in the organization of chromatin structure.

Effects of vitamin K1 and menadione on ethanol metabolism and toxicity

The effect of administration of two exogenous quinones on in vivo ethanol metabolism and ethanol-induced toxicity has been investigated. Menadione (vitamin K3; 50 mg/kg) or vitamin K1 (250 mg/kg) were given subcutaneously (sc) to male Sprague Dawley rats 1 hour before oral administration of ethanol (4 gm/kg). Menadione, a good quinone reductase substrate, increased the elimination rate of orally administered ethanol thereby decreasing its bioavailability (as measured by the area under the curve (AUC) relating blood level to time) and its induced hepatic triglyceride accumulation. On the other hand, closely related structural analog, vitamin K1, which was proven to be a poor substrate for quinone reductase, failed to show any significant effect. Thus, these results suggest that quinone reductase appear to play a role in in vivo ethanol metabolism and toxicity.

Brazilin protects cultured rat hepatocytes from BrCCl3-induced toxicity

Brazilin, the main constituent of Caesalpinia sappan, is an antioxidative substance that has catechol moiety in its chemical structure. Considering the antioxidant-activity of brazilin, it was expected to have protective effects on the toxicities of radical generating chemicals. The incubation of rat hepatocytes with BrCCl3 resulted in significant increase in lipid peroxidation, leakage of cytoplasmic enzymes and cytoplasmic glutathione depletion. The BrCCl3-induced toxicities on hepatocytes were reduced by the treatment of brazilin. Brazilin has been also proved to have a protective effect on the BrCCl3-induced depression of microsomal calcium sequestration activity. These results indicate that brazilin plays a protective role in BrCCl3-induced hepatocyte injury of the rat.

Relationship between activities of cytochrome P-450 monooxygenases in human placental microsomes and binding of benzo(a)pyrene metabolites to calf thymus DNA

Benzo(a)pyrene metabolism in human placental microsomes from smokers was studied. Benzo(a)pyrene metabolites were separated using high pressure liquid chromatographic technique. Reaction of benzo(a)pyrene with a microsomal fraction of placenta from individuals who smoke cigarettes during pregnancy yields 7,8 dihydroxy benzo(a)pyrene as a major metabolite, while 3'-hydroxy benzo(a)pyrene, 4,5 dihydroxy benzo(a)pyrene and quinones constitute minor metabolites. The activities of arylhydrocarbon hydroxylase and 7-ethoxycoumarin deethylase exhibited much higher activities in smokers than in nonsmokers. Examination of specific binding of monoclonal antibodies to cytochrome P-450 isozymes in placental microsomes revealed that cigarette smoking specifically enhanced the level of cytochrome P-450 c and d isozymes in human placental microsomes. Coincubation of 3H-benzo(a)pyrene and calf thymus DNA with placental microsomes yielded acid insoluble 3H-B(a)P from smokers, suggesting that cigarette smoking may induce placental enzymes which convert benzo(a)pyrene into ultimate metabolites to form carcinogen-DNA adducts.

The effect of an intermediate dose of labetalol on heart rate and blood pressure responses to laryngoscopy and intubation

STUDY OBJECTIVE

To evaluate the efficacy of an intermediate dose of labetalol (0.4 mg/kg) for attenuation of heart rate (HR) and blood pressure (BP) responses to laryngoscopy and intubation.

DESIGN

Randomized, double-blind, placebo-controlled study.

SETTING

Inpatient gynecology service at a university medical center.

PATIENTS

Two groups of 18 patients each undergoing elective surgery under general anesthesia.

INTERVENTIONS

Patients received either 0.4 mg/kg of labetalol or an equal volume of normal saline 5 minutes prior to laryngoscopy and intubation.

MEASUREMENTS AND MAIN RESULTS

HR and BP were measured upon arrival in the operating room (OR) (baseline) and at 1 minute intervals thereafter for 4 minutes prior to intubation and through 10 minutes following intubation. The labetalol group had a significantly lower HR from induction through 1 minute following intubation. Intragroup differences in HR were greatest immediately following laryngoscopy and intubation (33% increase above baseline for the placebo group vs 1% for the labetalol group, p less than 0.05). At the same time, a significant increase in mean arterial pressure (MAP) from baseline was noted in both groups (29% for the placebo group vs 23% for the labetalol group), but the difference between the groups was not significant.

CONCLUSIONS

An intermediate dose of labetalol blunted the HR response to laryngoscopy and intubation during rapid-sequence induction in healthy patients but had a minimal effect on BP.

Comparison of epidurally administered sufentanil, morphine, and sufentanil-morphine combination for postoperative analgesia

Postoperative analgesia provided by epidurally administered sufentanil and/or morphine was evaluated in 45 patients recovering from major gynecologic surgery. At the first complaint of pain in the Postanesthesia Care Unit, patients received a single epidural bolus of 30 micrograms sufentanil (group A), 5 mg morphine (group B), or 30 micrograms sufentanil plus 3 mg morphine (group C) in a randomized blinded fashion. Analgesic efficacy was assessed throughout the 24-h study period with 10-cm visual analog scales. The need for additional postoperative analgesia (patient-controlled analgesia, 1 mg of morphine every 6 min as necessary) and the incidence of adverse effects were also assessed. Patients receiving sufentanil (groups A and C) had significantly faster onset of analgesia than did patients given morphine alone (group B, P less than 0.05). Group B subjects experienced the longest duration of analgesia (B vs A and C, P less than 0.05) and required significantly less patient-controlled analgesia (morphine) than patients in group A (P less than 0.05). No patient developed clinically significant respiratory depression or excessive sedation, and there were no intergroup differences in incidence of pruritus or nausea (P value not significant). The data indicate that a mixture of sufentanil and morphine provides either a more rapid onset of epidural analgesia or reduced patient-controlled analgesia narcotic requirement than respective doses of each agent administered alone.

Effect of pyridoxine on rifampicin toxicity

The effects of pyridoxine (PN) on rifampicin (RMF) toxicity were investigated by both in vivo and in vitro methods. RMF (30 mg/kg) was injected intraperitoneally and PN(150 mg/kg) was administered orally to rats for 10 consecutive days. After treatment, clinical chemistry and hematologic profiles were measured. RMF and PN plus RMF did not show any adverse effects at this in vivo experimental condition. Thymidine incorporations of mice bone marrow cells were examined in vitro. RMF showed a decrease in thymidine uptake in a dose-dependent manner, but PN showed a reversal of the thymidine uptake suppression caused by RMF (p < 0.01). On the other hand, PN showed a decrease in thymidine uptake at a high concentration level.

Microradiographical determination of the dry mass density in the rat retina

A method for the quantitative measurement of the dry mass density in retinal tissue is presented. Cryosections of rat retinas were freeze-dried and exposed to soft X-rays together with a reference system. The section thickness was measured optically. The X-ray energy absorbed by the retinal tissue was recorded photographically and the microradiographs were evaluated photometrically. These measurements were used to estimate the dry mass density for each retinal layer. Sources of variation were evaluated. The precision was found adequate. The present method allows a localized determination of the dry mass density and of the hydration in the retina at a microscopic resolution.

Healing of rabbit corneal alkali wounds in vitro

The repair process of rabbit corneal alkali wounds was examined for 3 weeks in organ culture. The initial wound was inflicted by applying a round filter paper, 5.5 mm in diameter, soaked in 1 N NaOH, for 60 s on the central cornea--the same procedure as used in previous in vivo studies. Epithelial and endothelial healing were determined morphometrically by utilizing a standardized photographic procedure following alizarin red/trypan blue staining. A one-phase healing was discerned both in the epithelium and in the endothelium. The epithelial resurfacing of the wound was completed by 5 days and then remained intact. However, the endothelial defect did not heal completely during the observation period of 21 days. The defect area was, however, consistently reduced in size during the first four days. The present results were compared with previous in vivo findings in rabbit eyes. The advantages of using an in vitro model for initial therapeutic trials are described.

Corneal alkali wound healing in the monkey

Healing of a corneal alkali wound was followed in the monkey eye (Macaca fascicularis) for 4 months. A corneal alkali wound was inflicted in one eye in each of 30 monkeys under general anesthesia. A round filter paper, 5.5 mm in diameter, soaked in 1 N NaOH was put centrally on the cornea for 60 seconds. The alkali wounded all layers in the cornea underlying the filter paper, including the endothelium. Epithelial and endothelial healing was assessed morphometrically from photographs and micrographs, respectively. Stromal healing was documented using quantitative microradiography. During the observation period the wounds regained complete transparency. The epithelium showed few complications after primary healing during the first three days. The stroma regained normal thickness and dry mass content within one week. The endothelium resurfaced within one week and then remained intact. The role of the endothelial healing behaviour for the wound healing process is emphasized.

Hyaluronate in healing of corneal alkali wound in the rabbit

The effect of topically applied 1% and 2% sodium hyaluronate was studied on the healing of a standardized rabbit corneal alkali wound. The healing of the epithelium, the stroma, and the endothelium was evaluated separately by applying quantitative methods. The healing was followed for 8 weeks. Both 1% and 2% sodium hyaluronate have a statistically significant positive influence on the epithelial re-surfacing, especially during the late healing phase. Furthermore, sodium hyaluronate has a positive healing influence on the stromal healing at a certain time interval during the observation period. This was reflected as a better maintained stromal dry mass level compared to control. The stromal healing was parallel to a faster re-surfacing of the endothelium.

A comparison of morphine, meperidine, and oxymorphone as utilized in patient-controlled analgesia following cesarean delivery

Seventy-five patients (n = 75) undergoing elective cesarean delivery during epidural anesthesia were randomly assigned to receive one of three opioid analgesics via patient-controlled analgesia (PCA) when they first complained of pain in the recovery room. Following administration of an analgesic loading dose, patients were allowed to self-administer morphine 1.8 mg, meperidine 18 mg, or oxymorphone 0.3 mg iv every 8 min as required. Data collected during the 24-h observation period included visual analog scale (VAS) pain scores at rest and during movement, VAS patient satisfaction scores, total drug administered, the ratio of attempts/injections, and the incidence of nausea/vomiting, sedation, and pruritus. After adjusting for narcotic potency, no differences in 24-h dose requirements were noted between treatment groups (NS). All patients achieved an excellent level of analgesia at rest (NS); however, onset was most rapid with oxymorphone (P less than 0.05). The percentage of patients reporting severe pain during movement was highest in the meperidine group (P less than 0.05). Oxymorphone was associated with the highest incidence of nausea and vomiting (P less than 0.05), whereas increased sedation and pruritus were noted with morphine. Patient satisfaction with drug effect demonstrated significant negative correlations with resting pain scores and degree of sedation. Whereas morphine is a more commonly utilized PCA analgesic, the excellent analgesia, low incidence of sedation, and high patient satisfaction provided by meperidine and oxymorphone suggested useful alternatives.

Dry mass and water content in the corneal epithelium and superficial stroma during healing of corneal alkali wounds

The dry mass contents of the rabbit corneal epithelium and of the superficial stroma were determined during healing of a standardized corneal alkali wound. Quantitative microradiography was applied to freeze-sectioned corneal specimens. This method allows a morphological resolution of the order of 1 micron and quantitative dry mass determinations in volumes down to about 100 microns 3. For comparison, the epithelial morphology was studied using Toluidine Blue stained sections. Flat epithelial cells covered the wound surface during the first day, the dry mass content being equivalent to that of the normal wing cells. The dry mass content in the epithelium and, indirectly, the water content, followed the hydration state of the superficial stroma. A progressive thickening of the epithelium and a varying morphological picture were found during the first 2 months following initial damage. Normal thickness and cytoarchitecture were found after 6 months. Generally, the dry mass content of the epithelium was reduced compared with physiological values for 2 months. Later, the cells close to the stroma regained normal values. Cells in the middle zone and the superficial zone reached normal values after 6 months. The significance of the endothelial damage for the hydration state of the epithelium was discussed.

Two-step activation of valproic acid (VPA) by hepatic cytochrome P-450

There is now considerable evidence that the unsaturated metabolite of VPA, delta 4-VPA, may be responsible for VPA-induced hepatic injury. It is proposed that VPA is activated to a hepatotoxic species by a two-step cytochrome P-450-mediated mechanism consisting of 1) desaturation and 2) unknown activation, possibly by epoxide formation, involving one or more P-450 isozymes with subsequent covalent binding to cellular macromolecules. In vivo and in vitro experimental protocols are indicated for testing the proposed hypothesis.

Endothelial healing in rabbit corneal alkali wounds

The healing of rabbit corneal endothelium was studied following a standardized corneal alkali burn. The excised corneas were stained and examined, flat mount, endothelial side up, in the light microscope. Morphometric determinations were performed during the healing process by flat mount technique, and endothelial cell morphology was studied by both histological and flat mount techniques. The decrease of the endothelial wound diameter was linear, in the order of 18 micron/h, during the first 5 days. By one week the wound was almost completely covered by endothelial cells. Subsequently, the endothelium broke down in the central wound area during the second week. Endothelial healing resumed after the secondary break down although at a slow pace. The healing was often interfered with by invading fibroblast-like cells. The endothelial wound was not completely covered by endothelial cells even 6 months after trauma. The interrelation of the damage in different layers of the cornea was discussed.

The behaviour of corneal epithelium following a standardized alkali wound

The short and long-term healing of the rabbit corneal epithelium was studied after a standardized alkali wound. The wound was inflicted by applying a round filter paper, 5.5 mm in diameter, soaked in 1 N NaOH, for 60 seconds on the central cornea. The wound size and intensity was chosen not to cause melting and perforation, and not to cause vascular ingrowth. n-Heptanol corneal wounds of the same size were used as control. The eyes were followed for 8 weeks. Two phases of epithelial healing were discerned. The initial healing phase lasted 48 h during which the would was completely resurfaced. In spite of the more extensive tissue damage caused by alkali, the initial epithelial healing rate was faster than in n-heptanol wounds. The late healing phase consisted of recurrent epithelial break down, sometimes seen preceded by epithelial blister formation. Four weeks after trauma the state of epithelial healing was at its worst.

Stromal reaction and repair after corneal alkali wound in the rabbit: a quantitative microradiographic study

The corneal stromal reaction and repair were studied after alkali wound in the rabbit. The wound was followed for 6 months. The size and opacity of the wound were followed in the slit lamp and photographically. Morphology and dry mass or water content were studied using quantitative microradiography. The size of the wound opacity diminished throughout the observation period. The density of the opacity varied with the stromal water content. An increased water content as well as large variation in water content caused increased opacity. The corneal edema, determined already after 1 hr, was not detectable by 1 week using quantitative microradiography. Subsequently, an extensive edema developed, water accumulation being most marked in the posterior part of the cornea. After 8 weeks, an increase in interlamellar dry mass content could be determined as a sign of a stromal healing process. Stromal thickness and dry mass content had returned to normal values by 6 months.

RecA-independent recombination between direct repeats of IS50

Recombination between the IS50 sequences that flank Tn5 has been found to occur readily after the transformation of E. coli recA strains with a plasmid that contains direct repeats of these sequences. Analysis of mutants of IS50 indicates that the polypeptide encoded by IS50 that is required for transposition is also required for the recombination. Surprisingly, the mechanism of recombination appears to be similar to general homologous recombination rather than site-specific recombination. This IS50 recombination system may be responsible for resolving transient cointegrate structures containing direct repeats of IS50 or Tn5 during the transposition of IS50 and Tn5.

Nucleotide sequence analysis of in vivo recombinants between bacteriophage lambda DNA and pBR322

The nucleotide sequences involved in the illegitimate recombination of four recombinants between bacteriophage lambda DNA and pBR322 in E. coli (lambda TA6, lambda KA3, lambda TA1R, and lambda KA7) were determined. Each resulted from recombination between regions of homology of 10 to 13 base pairs. The presence of a recA+ allele was found to stimulate recombination between lambda DNA and pBR322 approximately 10-fold. Lambda TA6, lambda KA3, and lambda KA7 were isolated in the presence of a recA+ allele and therefore, may have been generated by the recA recombination system. However, lambda TA1R was isolated in a recA mutant, and was presumably generated by a different recombination system. The possibility that it was generated by DNA gyrase is discussed. Two recombination events were required to form lambda KA7, which may indicate that it also was generated by DNA gyrase.