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Results for “Natural variation”

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At least 181 records · Page 10Linked to original sources
PubMed1979

Effect of natural variations in PaCO2 on plasma [HCO3-] in dogs: a redefinition of normal.

Graded degrees of both chronic hyper- and hypocapnia are known to induce renal responses that significantly alter plasma bicarbonate concentration. These findings have raised the possibility that even normal variations in PaCO2 play an important role in determining the exact level of bicarbonate in plasma. To test this hypothesis, we examined the relationship between resting levels of PaCO2 and the plasma bicarbonate concentration in two groups of normal dogs, one ingesting a normal salt diet and the other a salt-restricted diet. The results indicate that values for bicarbonate within the normal range are highly dependent on the prevaling level of carbon dioxide tension ([HCO3-] = 0.35 PaCO2 + 9.0, r = 0.72). Accordingly, approximately 50% of the normal variance in bicarbonate concentration is explained simply by the variance in PaCO2. The joint confidence region for bicarbonate concentration and PaCO2, which can be derived from these data, provides a new and more rigorous definition of the normal range for acid-base values in the dog.

Acid-Base Equilibrium↗
PubMed2005

Tests for the replication of an association between Egfr and natural variation in Drosophila melanogaster wing morphology.

BACKGROUND: Quantitative differences between individuals stem from a combination of genetic and environmental factors, with the heritable variation being shaped by evolutionary forces. Drosophila wing shape has emerged as an attractive system for genetic dissection of multi-dimensional traits. We utilize several experimental genetic methods to validation of the contribution of several polymorphisms in the Epidermal growth factor receptor (Egfr) gene to wing shape and size, that were previously mapped in populations of Drosophila melanogaster from North Carolina (NC) and California (CA). This re-evaluation utilized different genetic testcrosses to generate heterozygous individuals with a variety of genetic backgrounds as well as sampling of new alleles from Kenyan stocks. RESULTS: Only one variant, in the Egfr promoter, had replicable effects in all new experiments. However, expanded genotyping of the initial sample of inbred lines rendered the association non-significant in the CA population, while it persisted in the NC sample, suggesting population specific modification of the quantitative trait nucleotide QTN effect. CONCLUSION: Dissection of quantitative trait variation to the nucleotide level can identify sites with replicable effects as small as one percent of the segregating genetic variation. However, the testcross approach to validate QTNs is both labor intensive and time-consuming, and is probably less useful than resampling of large independent sets of outbred individuals.

Animals↗
PubMed1984

Natural variations in brain phenylethanolamine-N-methyltransferase activity during different phases of the oestrous cycle: effect of chronic dexamethasone treatment.

The activity of phenylethanolamine-N-methyltransferase (PNMT) was studied in the hypothalamus, hypophysis, striatum and the rest of the brain during the four different phases of the oestrous cycle of the rat. The oestrous phase was marked by high level of enzyme activity in all the regions except the hypophysis. The hypophysis showed maximum increase in activity at the metoestrous phase of the oestrous cycle. Chronic treatment of rats with dexamethasone for 10 days led to decreased level of PNMT activity in the hypophysis, hypothalamus and the rest of brain. These decreases were important in the hypothalamus and the hypophysis which represented only 25 and 20% of the control activity after dexamethasone administration.

Animals↗
PubMed1999

Evidence that modifications of Lp(a) in vivo inhibit plasmin formation on fibrin--a study with individual plasmas presenting natural variations of Lp(a).

In the present study we have investigated the effect of individual variations in the concentration of Lp(a) on plasmin formation at the surface of fibrin. The plasma Lp(a) concentrations from 20 nephrotic children were high at flare-up of the disease (0.43+/-0.45 g/l) and decreased progressively with remission at both 6 weeks (0.28+/-0.24 g/l) and 6 months (0.24+/-0.288 g/l). In contrast, the concentration of plasminogen showed an inverse variation, with low values at flare-up (1.27+/-0.34 microM) and normal values at remission (1.66+/-0.17 microM at 6 weeks and 1.99+/-0.21 microM at 6 months). An increase in plasmin formation (from 0.62+/-0.49 to 0.73+/-0.61, and 0.84+/-0.75 pmol/well) and a decrease in apo(a) binding (from 5.45+/-2.42 to 4.54+/-2.12, and 3.93+/-1.51 fmol/well) on the surface of fibrin, were concomitantly observed from flare-up to remission at 6 weeks and at 6 months, respectively. Values for plasmin formation parallel the amount of plasminogen bound. The low concentration of plasminogen found at flare-up may also have contributed to the increased binding of Lp(a) as indicated by a decrease in the maximal amount of Lp(a) bound (Bmax) to fibrin as a function of plasma plasminogen concentrations. Bmax was 1.51 fmol in the absence of plasminogen and decreased to 1.1 fmol and 0.93 fmol at respectively 1 and 2 microM of plasminogen. Altogether, these data constitute the first quantitative evidence indicating that plasmin formed at the surface of fibrin may vary with modifications of the concentration of Lp(a) in vivo.

Adolescent↗
PubMed1985

Developmental arborization of sensory neurons in the leech Haementeria ghilianii. I. Origin of natural variations in the branching pattern.

The overall sizes, contours, and positions of the receptive fields maintained by different individual cells of the T, P, and N types of mechanosensory neurons in the segmental skin of the leech Haementeria ghilianii are not subject to wide variation. However, the locations and contours of the boundaries which separate the various compartments of the sensory field, namely, the major and minor fields, as well as their component subfields, do vary significantly. These variations are reflected in differences in the detailed pattern of arborization of the mechanosensory axon branches that innervate different parts of the receptive field. The appreciable variation in the kinetics of embryonic outgrowth of sensory axon branches, in conjunction with a mechanism of neuronal self-avoidance, is a probable source of this variability in adult receptive field structure. Thus, establishment of these sensory field components would seem to entail a first-come-first-served territorial exclusion between different axon branches extended by the same neuron.

Animals↗
PubMed1985

[Extent of natural variation of the longitudinal axis of the kidney collecting system].

Since the position of the longitudinal axis of the renal pelvis is of special significance in the diagnosis of the renal masses, the physiological range of the angle formed by this axis and the spine was determined by retrospective evaluation of 516 urograms. Up to the age of 11, in boys and girls the angle increases without side difference. In the adult, the position of the kidney is more transverse in men than in women, the left angle being smaller than the right one in both, male and female. The lateral contour of psoas muscle changes in similar fashion except for the side difference. Moreover, the decrease in size of the adrenal glands in early childhood is thought to be responsible for the rotation of the kidneys. Neither the kidney's shape nor its position respective to the spine proved significant for the position of the axis. The right kidney constantly being in a position nearly one vertebra lower than the left one, both sink caudad about 2/3 of a vertebra after the age of 50.

Adolescent↗