Hexagonal Prisms Form in Water-Ice Clouds on Mars, Producing Halo Displays Seen by Perseverance Rover.

Observations by several cameras on the Perseverance rover showed a 22° scattering halo around the Sun over several hours during northern midsummer (solar longitude 142°). Such a halo has not previously been seen beyond Earth. The halo occurred during the aphelion cloud belt season and the cloudiest time yet observed from the Perseverance site. The halo required crystalline water-ice cloud particles in the form of hexagonal columns large enough for refraction to be significant, at least 11 µm in diameter and length. From a possible 40-50 km altitude, and over the 3.3 hr duration of the halo, particles could have fallen 3-12 km, causing downward transport of water and dust. Halo-forming clouds are likely rare due to the high supersaturation of water that is required but may be more common in northern subtropical regions during northern midsummer.

Dust, Sand, and Winds Within an Active Martian Storm in Jezero Crater.

Rovers and landers on Mars have experienced local, regional, and planetary-scale dust storms. However, in situ documentation of active lifting within storms has remained elusive. Over 5-11 January 2022 (LS 153°-156°), a dust storm passed over the Perseverance rover site. Peak visible optical depth was ∼2, and visibility across the crater was briefly reduced. Pressure amplitudes and temperatures responded to the storm. Winds up to 20 m s-1 rotated around the site before the wind sensor was damaged. The rover imaged 21 dust-lifting events-gusts and dust devils-in one 25-min period, and at least three events mobilized sediment near the rover. Rover tracks and drill cuttings were extensively modified, and debris was moved onto the rover deck. Migration of small ripples was seen, but there was no large-scale change in undisturbed areas. This work presents an overview of observations and initial results from the study of the storm.

Terminal 13p deletion in squirrel monkey (Saimiri sciureus) with differentiated phenotype.

BACKGROUND: The taxonomic classification of squirrel monkeys is often controversial issue offering many different information. The classification of captive animals is difficult due to the phenotypic similarities between the presented species, which is observed mainly in coat coloration. METHODS: The objective of this study was to analyze the chromosome pattern of one squirrel monkey with off standard physical characteristics, which is kept in the Laboratory Animals Breeding Center in Rio de Janeiro State, Brazil, and try to establish some correlations. Chromosomes were obtained using lymphocyte culture technique. RESULTS AND CONCLUSIONS: Evaluation of G bands showed a terminal deletion in one chromosome of pair 13. The association of the results found with the different phenotypic characteristics led us to classify it as a Saimiri sciureus specimen with a structural chromosomal change, possibly allowing the expression of hemizygous alleles.

Adaptation of antibiotic treatment to clinical practice guidelines in patients aged ⩾65 years hospitalised due to community-acquired pneumonia.

Early, conforming antibiotic treatment in elderly patients hospitalised for community-acquired pneumonia (CAP) is a key factor in the prognosis and mortality. The objective was to examine whether empirical antibiotic treatment was conforming according to the Spanish Society of Pulmonology and Thoracic Surgery guidelines in these patients. Multicentre study in patients aged ⩾65 years hospitalised due to CAP in the 2013-14 and 2014-15 influenza seasons. We collected socio-demographic information, comorbidities, influenza/pneumococcal vaccination history and antibiotics administered using a questionnaire and medical records. Bivariate analyses and multilevel logistic regression were made. In total, 1857 hospitalised patients were included, 82 of whom required intensive care unit (ICU) admission. Treatment was conforming in 51.4% (95% confidence interval (CI) 49.1-53.8%) of patients without ICU admission and was associated with absence of renal failure without haemodialysis (odds ratio (OR) 1.49, 95% CI 1.15-1.95) and no cognitive dysfunction (OR 1.71, 95% CI 1.25-2.35), when the effect of the autonomous community was controlled for. In patients with ICU admission, treatment was conforming in 45.1% (95% CI 34.1-56.1%) of patients and was associated with the hospital visits in the last year (<3 vs. ⩾3, OR 2.70, 95% CI 1.03-7.12) and there was some evidence that this was associated with season. Although the reference guidelines are national, wide variability between autonomous communities was found. In patients hospitalised due to CAP, health services should guarantee the administration of antibiotics in a consensual manner that is conforming according to clinical practice guidelines.

Suitability of multiple Mediterranean oak species as a food resource for Reticulitermes grassei Clément (Isoptera: Rhinotermitidae).

The subterranean termite Reticulitermes grassei Clément causes lesions in the trunk of Quercus suber L. by constructing feeding galleries, but no information is available regarding other Quercus species from the Mediterranean region. This work aimed to study the suitability of the other main oak species of Mediterranean forests as a food resource for R. grassei. Two experiments, choice and non-choice feeding, were conducted lasting for 15, 30, and 45 days each. In the non-choice experiment, termites were offered one of the following food types: Quercus suber, Quercus ilex L., Quercus faginea Lam, cork or Pinus pinea L., which was considered the control. The choice feeding experiment used all the same food types listed above, supplied simultaneously in the same container. Food selection was examined by analysing the relationships over time between surviving termites and food consumption. The results indicated that R. grassei could be considered a generalist species, as it consumed the cork and wood of all oak species, as well as displaying a clear preference for soft wood (pine). Correlation analysis indicated that consumption was not dependent on wood density. Survival of R. grassei was influenced by the time of exposure to different oak species, but a high survival rate was maintained over time in the pine treatment (upper 70% in the three experiments). Given these results, it can be concluded that all the oak species are a suitable food source for R. grassei.

Effectiveness of acellular pertussis vaccination during childhood (<7 years of age) for preventing pertussis in household contacts 1-9 years old in Catalonia and Navarra (Spain).

Pertussis vaccination with 4-5 doses of acellular vaccines is recommended in Spain to all children at 2 months to 6 years of age. The effectiveness of the acellular pertussis vaccination was assessed in this study by comparing the incidence of secondary pertussis in vaccinated (4-5 doses) and unvaccinated or partially vaccinated (0-3 doses) household contacts 1-9 years old of confirmed cases of pertussis in Spain in 2012-13. Eighty-five percent of contacts had been vaccinated with 4-5 doses of acellular pertussis vaccines. During the 2-year study period, 64 cases of secondary pertussis were detected among 405 household contacts 1-9 years old: 47 among vaccinated and 17 among unvaccinated or partially vaccinated contacts. The effectiveness for preventing secondary pertussis, calculated as 1 minus the relative risk (RR) of secondary pertussis in vaccinated vs. unvaccinated/partially vaccinated contacts, was 50 % [95 % confidence interval (CI): 19-69 %, p < 0.01] when household contacts were vaccinated using DTaP, Tdap, hexavalent or heptavalent vaccines, and it was 51.3 % (95 % CI: 21-70 %, p < 0.01) when they were vaccinated using DTaP or TdaP vaccines. The effectiveness adjusted for age, sex, pertussis chemotherapy and type of household contact was 58.6 % (95 % CI: 17-79 %, p < 0.05) when contacts were vaccinated using available acellular vaccines, and it was 59.6 % (95 % CI: 18-80 %, p < 0.01) when they were vaccinated using DTaP vaccines. Acellular pertussis vaccination during childhood was effective for preventing secondary pertussis in household contacts 1-9 years old of pertussis cases in Catalonia and Navarra, Spain.

Trends in hip fracture rates in spain from 2001 to 2018.

The present study includes the longest period of analysis with the highest number of hip fracture episodes (756,308) described in the literature for Spain. We found that the age-adjusted rates progressively decreased from 2005 to 2018. We believe that this is significant because it may mean that measures such as prevention and treatment of osteoporosis, or programs promoting healthy lifestyles, have had a positive impact on hip fracture rates. PURPOSE: To describe the evolution of cases and rates of hip fracture (HF) in patients 65 years or older in Spain from 2001 to 2018 and examine trends in adjusted rates. METHODS: Retrospective, observational study including patients ≥65 years with acute HF. Data from 2001 to 2018 were obtained from the Spanish National Record of the Minimum Basic Data Set of the Ministry of Health. We analysed cases of HF, crude incidence and age-adjusted rates by sex, length of hospital stay (LOS) and in-hospital mortality, and used joinpoint regression analysis to explore temporal trends. RESULTS: We identified 756,308 HF cases. Mean age increased 2.5 years, LOS decreased 4.5 days and in-hospital mortality was 5.5-6.5%. Cases of HF increased by 49%. Crude rate per 100,000 was 533.3 (95% confidence interval [CI], 532.1-534.5), increasing 14.0% (95%CI, 13.7-14.2). Age-adjusted HF incidence rate increased by 6.9% from 2001 (535.7; 95%CI, 529.9-541.5) to 2005 (572.4; 95%CI, 566.7-578.2), then decreased by 13.3% until 2017 (496.1, 95%CI, 491.7-500.6). Joinpoint regression analysis indicated a progressive increase in age-adjusted incidence rates of 1.9% per year from 2001 to 2005 and a progressive decrease of -1.1% per year from 2005 to 2018. A similar pattern was identified in both sexes. CONCLUSIONS: Crude incidence rates of HF in Spain in persons ≥65 years from 2001 to 2018 have gradually increased. Age-adjusted rates show a significant increase from 2001 to 2005 and a progressive decrease from 2005 to 2018.

Location also matters: The oxidative response of the intertidal purple mussel Perumytilus purpuratus during tidal cycle.

For sessile intertidal organisms, periods of low tide impose both cellular and physiological challenges that can determine bathymetric distribution. To understand how intertidal location influences the cellular response of the bivalve Perumytilus purpuratus during the tidal cycle (immersion-emersion-immersion), specimens from the upper intertidal (UI) and lower intertidal (LI) of bathymetric distribution were sampled every 2 h over a 10-h period during a summer tidal cycle. Parallelly, organisms from the UI and LI were reciprocally transplanted and sampled throughout the same tidal cycle. Levels of oxidative damage (lipid peroxidation and protein carbonyls) as well as total antioxidant capacity and total carotenoids were evaluated as cellular responses to variations in environmental conditions throughout the tidal cycle. The results indicate that both the location in the intertidal zone (UI/LI), the level of aerial exposure, and the interaction of both factors are determinants of oxidative levels and total antioxidant capacity of P. purpuratus. Although oxidative damage levels are triggered during the low tide period (aerial exposure), it is the UI specimens that induce higher levels of lipid peroxidation compared to those from the LI, which is consistent with the elevated levels of total antioxidant capacity. On the other hand, organisms from the LI transplanted to the UI increase the levels of lipid peroxidation but not the levels of protein carbonyls, a situation that is also reflected in higher levels of antioxidant response and total carotenoids than those from the UI transplanted to the LI. The bathymetric distribution of P. purpuratus in the intertidal zone implies differentiated responses between organisms of the lower and upper limits, influenced by their life history. A high phenotypic plasticity allows this mussel to adjust its metabolism to respond to abrupt changes in the surrounding environmental conditions.

Colorectal cancer risk after removal of polyps in fecal immunochemical test based screening.

Background: Colonoscopy surveillance intervals are based on the predicted risk of metachronous colorectal cancer (CRC) after polyp removal. However, risk estimation per polyp subtype is difficult due to the fact that many patients have multiple polyps. To enable risk estimation per polyp subtypes we examined the metachronous CRC risk of subgroups based on presence or absence of co-occurring findings. Methods: Using high-quality screening colonoscopies performed after a positive fecal immunochemical test between 2014 and 2020 within the Dutch CRC screening program, we applied Cox regression analysis to evaluate the association between findings at baseline colonoscopy and metachronous CRCs. For our primary outcome, we appointed each patient to unique subgroups based on removed polyp subtypes that were present or absent at baseline colonoscopy and used the groups without polyps as reference. High-risk subgroups were individuals with high-risk serrated polyps, defined as serrated polyp ≥10 mm, sessile serrated lesions with dysplasia, or traditional serrated adenomas, as well as high-risk adenomas, defined as adenoma ≥10 mm or containing high-grade dysplasia. Findings: In total 253,833 colonoscopies were included. Over a median follow-up of 36 months (IQR, 21-57), we identified 504 metachronous CRCs. Hazard ratios for metachronous CRC was 1.70 (95% CI, 1.07-2.69) for individuals with high-risk serrated polyps without high-risk adenomas, 1.22 (0.96-1.55) for individuals with high-risk adenomas without high-risk serrated polyps, and 2.00 (1.19-3.39) for individuals with high-risk serrated polyps and high-risk adenomas, compared to patients without polyps. Interpretation: Accounting for co-occurring findings, we observed an increased metachronous CRC risk for individuals that had high-risk serrated polyps with the presence of high-risk adenomas, or individuals with high-risk serrated polyps without high-risk adenomas. These findings could provide more evidence to support post-polypectomy surveillance guidelines. Funding: None.

Mars 2020 Perseverance Rover Studies of the Martian Atmosphere Over Jezero From Pressure Measurements.

The pressure sensors on Mars rover Perseverance measure the pressure field in the Jezero crater on regular hourly basis starting in sol 15 after landing. The present study extends up to sol 460 encompassing the range of solar longitudes from L s  âˆ¼ 13°-241° (Martian Year (MY) 36). The data show the changing daily pressure cycle, the sol-to-sol seasonal evolution of the mean pressure field driven by the CO2 sublimation and deposition cycle at the poles, the characterization of up to six components of the atmospheric tides and their relationship to dust content in the atmosphere. They also show the presence of wave disturbances with periods 2-5 sols, exploring their baroclinic nature, short period oscillations (mainly at night-time) in the range 8-24 min that we interpret as internal gravity waves, transient pressure drops with duration ∼1-150 s produced by vortices, and rapid turbulent fluctuations. We also analyze the effects on pressure measurements produced by a regional dust storm over Jezero at L s  âˆ¼ 155°.

Hazy Blue Worlds: A Holistic Aerosol Model for Uranus and Neptune, Including Dark Spots.

We present a reanalysis (using the Minnaert limb-darkening approximation) of visible/near-infrared (0.3-2.5 µm) observations of Uranus and Neptune made by several instruments. We find a common model of the vertical aerosol distribution i.e., consistent with the observed reflectivity spectra of both planets, consisting of: (a) a deep aerosol layer with a base pressure >5-7 bar, assumed to be composed of a mixture of H2S ice and photochemical haze; (b) a layer of photochemical haze/ice, coincident with a layer of high static stability at the methane condensation level at 1-2 bar; and (c) an extended layer of photochemical haze, likely mostly of the same composition as the 1-2-bar layer, extending from this level up through to the stratosphere, where the photochemical haze particles are thought to be produced. For Neptune, we find that we also need to add a thin layer of micron-sized methane ice particles at ∼0.2 bar to explain the enhanced reflection at longer methane-absorbing wavelengths. We suggest that methane condensing onto the haze particles at the base of the 1-2-bar aerosol layer forms ice/haze particles that grow very quickly to large size and immediately "snow out" (as predicted by Carlson et al. (1988), https://doi.org/10.1175/1520-0469(1988)045<2066:CMOTGP>2.0.CO;2), re-evaporating at deeper levels to release their core haze particles to act as condensation nuclei for H2S ice formation. In addition, we find that the spectral characteristics of "dark spots", such as the Voyager-2/ISS Great Dark Spot and the HST/WFC3 NDS-2018, are well modelled by a darkening or possibly clearing of the deep aerosol layer only.

Winds at the Mars 2020 Landing Site. 2. Wind Variability and Turbulence.

Wind speeds measured by the Mars 2020 Perseverance rover in Jezero crater were fitted as a Weibull distribution. InSight wind data acquired in Elysium Planitia were also used to contextualize observations. Jezero winds were found to be much calmer on average than in previous landing sites, despite the intense aeolian activity observed. However, a great influence of turbulence and wave activity was observed in the wind speed variations, thus driving the probability of reaching the highest wind speeds at Jezero, instead of sustained winds driven by local, regional, or large-scale circulation. The power spectral density of wind speed fluctuations follows a power-law, whose slope deviates depending on the time of day from that predicted considering homogeneous and isotropic turbulence. Daytime wave activity is related to convection cells and smaller eddies in the boundary layer, advected over the crater. The signature of convection cells was also found during dust storm conditions, when prevailing winds were consistent with a tidal drive. Nighttime fluctuations were also intense, suggesting strong mechanical turbulence. Convective vortices were usually involved in rapid wind fluctuations and extreme winds, with variations peaking at 9.2 times the background winds. Transient high wind events by vortex-passages, turbulence, and wave activity could be driving aeolian activity at Jezero. We report the detection of a strong dust cloud of 0.75-1.5 km in length passing over the rover. The observed aeolian activity had major implications for instrumentation, with the wind sensor suffering damage throughout the mission, probably due to flying debris advected by winds.

The sound of a Martian dust devil.

Dust devils (convective vortices loaded with dust) are common at the surface of Mars, particularly at Jezero crater, the landing site of the Perseverance rover. They are indicators of atmospheric turbulence and are an important lifting mechanism for the Martian dust cycle. Improving our understanding of dust lifting and atmospheric transport is key for accurate simulation of the dust cycle and for the prediction of dust storms, in addition to being important for future space exploration as grain impacts are implicated in the degradation of hardware on the surface of Mars. Here we describe the sound of a Martian dust devil as recorded by the SuperCam instrument on the Perseverance rover. The dust devil encounter was also simultaneously imaged by the Perseverance rover's Navigation Camera and observed by several sensors in the Mars Environmental Dynamics Analyzer instrument. Combining these unique multi-sensorial data with modelling, we show that the dust devil was around 25 m large, at least 118 m tall, and passed directly over the rover travelling at approximately 5 m s-1. Acoustic signals of grain impacts recorded during the vortex encounter provide quantitative information about the number density of particles in the vortex. The sound of a Martian dust devil was inaccessible until SuperCam microphone recordings. This chance dust devil encounter demonstrates the potential of acoustic data for resolving the rapid wind structure of the Martian atmosphere and for directly quantifying wind-blown grain fluxes on Mars.

Temporal and spatial control of the adenovirus proteinase by both a peptide and the viral DNA.

The adenovirus proteinase (AVP) uses both an 11-amino acid peptide (pVIc) and the viral DNA as cofactors to increase its catalytic rate constant 6000-fold. The crystal structure of an AVP-pVIc complex at 2.6-A resolution reveals a new protein fold of an enzyme that is the first member of a new class of cysteine proteinases, which arose via convergent evolution.

Possible Mechanisms of Hatching from Egg Capsules in the Gastropods Crepipatella dilatata and Crepipatella peruviana, Species with Different Modes of Early Development.

Many invertebrates enclose their embryos within egg capsules, from which the offspring hatch. In marine gastropods that brood their egg capsules, hatching could involve radular activity by the mother or by unhatched stages, increased osmotic concentration of the intracapsular fluid, or production of hatching enzymes. The present research sought to determine whether mechanical action by the brooding female or by the encapsulated embryos was involved in the hatching for two sympatric and closely related species of calyptraeid: Crepipatella dilatata, which exhibits direct development without free-living larvae, and Crepipatella peruviana, which releases free-living veliger larvae. We also considered the role that enzymatic action or osmotic changes in the intracapsular fluid might play in hatching. Using scanning electron micrograph analyses, we found no evidence that the well-developed, pre-hatching juvenile radula of C. dilatata played any role in the hatching process and that the radula of C. peruviana did not even develop until long after hatching; so there was no evidence of radular activity involved in the hatching of either species. For C. peruviana, the intracapsular fluid osmolality was always higher than that of the surrounding seawater, suggesting that there is a strong natural water inflow during development. Moreover, when egg capsules of C. peruviana were exposed to lower ambient salinities, the substantial entry of water correlated well with high percentages of hatching, particularly for egg capsules containing advanced veligers, suggesting that an osmotic mechanism may be involved in the hatching process of this species. In contrast, hatching in C. dilatata appeared to be enzymatically mediated.

Modulation of cell-associated plasminogen activator activity by cocultivation of a stem cell and its tumorigenic descendant.

The effect of the presence of one cell type on the plasminogen activator activity of another cell type was studied. The cell types, AC and D, were isolated from a rat neuroblastoma (I. Imada and N. Sueoka, Dev. Biol. 66:97-108, 1978). AC cells are stem cells capable of multipotential differentiation in vitro and have little or no cell-associated plasminogen activator activity. D cells are tumorigenic and have high levels of cell-associated plasminogen activator activity. When AC cells were cocultivated with D cells, the plasminogen activator activity of the D cells was dramatically inhibited. The presence of as few as 1,250 AC cells inhibited 70% of the plasminogen activator activity of 20,000 D cells, as determined by a highly quantitative assay. The amount of inhibition by AC cells was proportional to the number of AC cells present. At increasing numbers of AC cells and a constant number of D cells, the Vmax for the activation of plasminogen proportionately decreased and the Km remained constant, implying that AC cells did not alter the structure or concentration of plasminogen. Inhibition was not mediated by a soluble inhibitor secreted by AC cells. Rather, attachment of AC cells adjacent to D cells, i.e., cell-to-cell contact, seemed to be required for inhibition. The substratum-attached material of AC cells, that which remained on the microwell surface after removal of AC cells with EDTA, inhibited D cell plasminogen activator activity. If plasminogen activator activity is involved in metastasis, then regulation of the plasminogen activator activity of one cell type by another cell type may be involved in determining which cells in a tumor can metastasize and where secondary tumors can arise.

Theory and experimental method for determining individual kinetic constants of fast-acting, irreversible proteinase inhibitors.

A theory and experimental method are presented to characterize the kinetics of fast-acting, irreversible proteinase inhibitors. The theory is based upon formal analysis of the case of an irreversible inhibitor competing with a substrate for the active-site of a proteinase. From this theory, an experimental method is described by which the individual microscopic kinetic constants for the interaction of the inhibitor with the proteinase can be determined. These are, for a two-step inhibition reaction sequence, the equilibrium dissociation constant and the first-order rate constant for inhibition, and, for a one-step inhibition reaction sequence, the second-order rate constant for inhibition. The theory and experimental method were validated by an analysis of the inhibition of trypsin by the two-step synthetic inhibitor p-nitrophenyl p-guanidinobenzoate and the one-step protein inhibitor bovine pancreatic trypsin inhibitor. The substrate used in these experiments is a new, fluorogenic substrate for trypsin-like serine proteinases (Cbz-Ile-Pro-Arg-NH)2-Rhodamine, the synthesis and properties of which are described.

Different modes of inhibition of human adenovirus proteinase, probably a cysteine proteinase, by bovine pancreatic trypsin inhibitor.

The type of proteinase and the nature of the active site of the human adenovirus proteinase are unknown. For these reasons we produced an inhibitor profile of the enzyme. Enzyme activity in disrupted virions was inhibited by several serine-specific as well as cysteine-specific proteinase inhibitors. Of the inhibitors that worked, the most useful potentially in illuminating the nature of the active site was bovine pancreatic trypsin inhibitor (BPTI), and for this reason we extensively characterized the interaction with BPTI. In disrupted virions, the enzyme is irreversibly inhibited by BPTI with a Ki of 35 nM and a ki of 6.2 x 10(-4) s(-1). One reason enzyme activity is inhibited is that BPTI, a basic protein, precipitates the viral DNA, a cofactor of enzyme activity. In vitro with purified components, BPTI acts as a competitive inhibitor (Ki 2 microM) of the recombinant proteinase complexed with its 11-amino-acid cofactor pVIc. The recombinant endoproteinase is beat labile whereas its 11-amino-acid cofactor is heat stable. We estimate there are about 50 molecules of proteinase per virus particle.

Cellular delivery of functional peptides to block cytokine gene expression.

Advances in molecular and cellular biology have identified the cellular mediators that regulate many disease processes and have facilitated the development of new therapeutic agents that control these events. However, the size, complexity, and cellular inaccessibility of these therapeutic agents make their cellular delivery difficult. Here, we describe an efficient cellular delivery system that exploits the membrane-translocating ability of signal peptides to import functional peptides into cells. Molecular conjugates consisting of the signal import peptide (IP) and nuclear localization sequence (NLS) of the transcription factor NF-kappaB were synthesized. Electrophoretic mobility shift and enzyme-linked immunosorbent assays were used to assess the inhibitory effects of these synthetic peptides on agonist-induced NF-kappaB nuclear translocation and transcriptional activation. Our results indicated that the peptides were effective in inhibiting both the nuclear translocation and transcriptional activation of NF-kappaB. However, their effects required the presence of the IP moiety for efficient cellular entry of the NLS. Structural analysis of IP showed that the hydrophobic domain, and to a lesser extent the N-terminal domain, was responsible for the membrane translocating activity of IP.

The effect of lead on the eruption rates of incisor teeth in rats.

The effects of lead on the continuously erupting rat incisors under normo-, hyper- and hypofunctional conditions were investigated. Left lower incisors of 20 rats were rendered unimpeded (hypofunctional) by cutting them out of occlusion every 2 days; the right lower incisors of these rats were considered hyperfunctional. Measurements on normally growing teeth (normofunctional) were carried out in a group of ten rats whose teeth were not cut but only marked every 2 days. On day 7 of the experiment, half of the rats from these two groups were given a single intraperitoneal injection of lead acetate (40 mg/kg), and the other half received sodium acetate (22 mg/kg). Another group of 15 rats was used to obtain blood samples for lead determination 1 h, and 10, 20, and 30 days after lead administration. Animals were killed on day 32. Hypofunctional incisors from lead-treated rats erupted more slowly than control ones (P<0.05). These results show a previously unreported toxic effect of heavy metals.