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Biomedical subjects

L R Monteiro

Publications and source records attributed to L R Monteiro.

11 recordsLinked to original sources
PubMed2001

Kinetics, dose--response, and excretion of methylmercury in free-living adult Cory's shearwaters.

We evaluated methylmercury (MHg) kinetics, dose--responses, and excretion in free-living adult Cory's shearwaters using a nondestructive multi-tissue approach. Elimination of MHg in blood comprised an initial fast phase, with half-time of 1 d, and a slow terminal phase with half-time between 44 and 65 d. Molt was a crucial factor in determining the rate of MHg elimination. Half-times were independent of dose. A relationship between steady-state blood concentrations and dietary intake of MHg was derived. Ratios between Hg concentrations in eggs or hatchlings' plumage and parental blood were independent of dose, with tissue--blood partition coefficients identical to those in controls. Dose--response relationships were linear. Females were subjected to Hg concentrations 18% higher than males but exhibited a 10% lower dose--response in blood. The difference is not fully accounted for by excretion into the egg and may be due to unidentified sex-related differences in physiology. Excretion rates into plumage showed no dose dependency but were higher (33% of intake) in birds exposed during molt than in birds dosed 2 months before the start of molt. Hg excretion through the skin in exfoliated epidermal cells that adsorb into plumage was estimated to represent 8% of the intake. The results of this study may be used in advanced modeling of the kinetics of MHg in adult birds to fill the current gap of a bioenergetic model for avian exposure to MHg.

Animals↗
PubMed2001

Kinetics, dose-response, excretion, and toxicity of methylmercury in free-living Cory's shearwater chicks.

Methylmercury (MHg) kinetics, dose-response, excretion, and toxicity were experimentally evaluated and compared between small (one to two weeks old) and large (six to seven weeks old), free-living Cory's shearwater chicks. The half-time for the terminal elimination phase of MHg in blood (5.7 d) and the average percentage of ingested MHg deposited in the blood volume (12%) were independent of the age at exposure. Therefore, these data were employed to derive a relationship between steady-state blood concentrations and dietary intake of MHg in bird chicks. Plumage:blood ratios were independent of dose and could be used as partition coefficients. Dose-response relationships in plumage and blood were linear over the wide range of exposures employed. Blood dose-responses of MHg in small and large chicks were similar. Excretion percentages into the final plumage varied between 42 and 60% of intake. The body condition of experimental chicks did not indicate sublethal toxicity of the doses administered; hence, the exposure levels provide maximum avian no-observed-adverse-effect levels for external symptoms in wild seabird chicks.

Administration, Oral↗
PubMed2000

Variation in mandible shape in Thrichomys apereoides (Mammalia: Rodentia): geometric analysis of a complex morphological structure.

The model of development and evolution of complex morphological structures conceived by Atchley and Hall in 1991 (Biol. Rev. 66:101-157), which establishes that changes at the macroscopic, morphogenetic level can be statistically detected as variation in skeletal units at distinct scales, was applied in combination with the formalism of geometric morphometrics to study variation in mandible shape among populations of the rodent species Thrichomys apereoides. The thin-plate spline technique produced geometric descriptors of shape derived from anatomical landmarks in the mandible, which we used with graphical and inferential approaches to partition the contribution of global and localized components to the observed differentiation in mandible shape. A major pattern of morphological differentiation in T. apereoides is attributable to localized components of shape at smaller geometric scales associated with specific morphogenetic units of the mandible. On the other hand, a clinical trend of variation is associated primarily with localized components of shape at larger geometric scales. Morphogenetic mechanisms assumed to be operating to produce the observed differentiation in the specific units of the mandible include mesenchymal condensation differentiation, muscle hypertrophy, and tooth growth. Perspectives for the application of models of morphological evolution and geometric morphometrics to morphologically based systematic biology are considered.

Animals↗
PubMed2000

Comparative analysis of cranial suture complexity in the genus Caiman (Crocodylia, Alligatoridae).

The variation in degrees of interdigitation (complexity) in cranial sutures among species of Caiman in different skull regions was studied by fractal analysis. Our findings show that there is a small species effect in the fractal dimension of cranial sutures, but most variation is accounted for by regional differentiation within the skull. There is also a significant interaction between species and cranial regions. The braincase sutures show higher fractal dimension than the facial skull sutures for all three species. The fractal dimension of nasal-maxilla suture is larger in Caiman latirostris than in the other species. The braincase sutures show higher fractal dimensions in C. sclerops than in the other species. The results suggest that different regions of the skull in caimans are under differential functional stress and the braincase sutures must counteract stronger disarticulation forces than the facial sutures. The larger fractal dimension shown by C. latirostris in facial sutures has probably a functional basis also. Caiman latirostris is known to have preferences for harder food items than the other species.

Alligators and Crocodiles↗
PubMed1999

Functional and historical determinants of shape in the scapula of Xenarthran mammals: evolution of a complex morphological structure.

The mammalian scapula is a complex morphological structure, composed of two ossification plates that fuse into a single structure. Most studies on morphological differentiation in the scapula have considered it to be a simple, spatially integrated structure, primarily influenced by the important locomotor function presented by this element. We used recently developed geometric morphometric techniques to test and quantify functional and phylogenetic influences on scapular shape variation in fossil and extant xenarthran mammals. The order Xenarthra is well represented in the fossil record and presents a stable phylogenetic hypothesis for its genealogical history. In addition, its species present a large variety of locomotor habits. Our results show that approximately half of the shape variation in the scapula is due to phylogenetic heritage. This is contrary to the view that the scapula is influenced only by functional demands. There are large-scale shape transformations that provide biomechanical adaptation for the several habits (arboreality, terrestriality, and digging), and small scale-shape transformations (mostly related to the coracoid process) that are not influenced by function. A nonlinear relationship between morphometric and phylogenetic distances indicates the presence of a complex mixture of evolutionary processes acting on shape differentiation of the scapula.

Animals↗
PubMed1996

Relationships between heavy metal and metallothionein concentrations in lesser black-backed gulls, Larus fuscus, and Cory's shearwater, Calonectris diomedea.

Metallothionein, cadmium, zinc, copper, and mercury concentrations were measured in adult lesser black-backed gulls, Larus fuscus; and metallothionein, cadmium, zinc, and copper concentrations were measured in fledgling Cory's shearwaters, Calonectris diomedea. In gulls, metallothionein was positively correlated with cadmium (kidney r = 0.83, liver r = 0.46), zinc (kidney r = 0.46, liver r = 0.37), and copper (kidney r = 0.28, liver r = 0.34). Mercury levels in lesser black-backed gulls showed no correlations with metallothionein or with any other metal. In shearwaters metallothionein was positively correlated with cadmium in the kidney (r = 0.41) but not in liver, zinc in kidney (r = 0.43) and liver (r = 0.52), and copper in kidney (r = 0.55) but not in liver. Cadmium levels were the most important factor determining tissue metallothionein concentrations in adult lesser black-backed gulls demonstrating the role of metallothionein in heavy metal detoxification. In fledgling Cory's shearwaters, the most important factor in determining metallothionein concentrations in kidney was copper concentrations, and in liver, zinc concentrations. During the latter phases of chick growth high levels of zinc are required for feather development, and at this time the binding of cadmium may be masked by the presence of a large amount of zinc- and copper-bound metallothionein. These results illustrate disparate roles of metallothionein, the levels of which will be in a state of flux both seasonally and annually.

Animals↗