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Biomedical subjects

G Geiger

Publications and source records attributed to G Geiger.

At least 37 records · Page 2Linked to original sources
PubMed1990

[Conjunctival oxygen partial pressure, hemorheology and circulatory parameters in acute cerebral infarct before and following infusion of 6 percent low molecular hydroxyethyl starch].

A prospective clinical trial was performed on the effects of a three hour infusion of 500 ml 6% low-molecular-weight hydroxyethyl starch in patients with acute ischemic stroke. Hemorheology and conjunctival oxygen tension were found to be disturbed prior to treatment. After the infusion there was a marked improvement of the pertinent parameters, indicative of an increase in cerebral microcirculation and oxygen supply. Even 3 h later persistent significant effects were observed. The infusion was well tolerated. Blood pressure and cardiac index remained unchanged.

Blood Viscosity↗
PubMed1989

Sociobiology and the structural stability of behavior patterns.

A structural stability approach to population-genetic systems and to dynamic evolutionary games is attempted in order to examine the theoretical significance of sociobiological selection models. A criterion of weak selection is derived that is not restricted to differential reproduction in polymorphic systems but describes possible directions of evolutionary change in time scales governed by genetic mutation rates. The criterion applies to the problems of how the initial mutational basis of an adaptive trait may be established and how this may happen, for analogous traits, independently in different species. Two basic sociobiological concepts are reconsidered with reference to the criterion. It is shown that W. D. Hamilton's condition of increases in inclusive fitness due to altruistic interactions among kin expresses the structural instability of populations against the evolution of altruistic behavior. Using the dynamic approach to evolutionary game theory, it is demonstrated that if a behavioral phenotype is an evolutionarily stable strategy, it is structurally stable against perturbations of the fitness payoffs, provided selection is weak. These results are applied to material problems of the evolution of animal social behavior.

Animals↗
PubMed1988

Comparison of the beta-adrenoceptor affinity and selectivity of cetamolol, atenolol, betaxolol, and ICI-118,551.

The objective of the present study was to compare the quantitative differences in the beta 1- vs. beta 2-adrenoceptor affinity and selectivity of cetamolol and its enantiomers to the reference compounds atenolol, betaxolol, and ICI-118,551, using isolated tissues obtained from the dog, guinea pig, and rat. Cetamolol antagonized the beta-adrenoceptor-mediated responses induced by isoproterenol, epinephrine, norepinephrine, and salbutamol, in tissues from both the dog and guinea pig, in a concentration-dependent manner. For a given tissue, the beta-adrenoceptor antagonist activity of cetamolol (measured as a pA2 or pKB value) was independent of the agonist used. In the dog tissues, cetamolol was more potent at inhibiting responses in the coronary artery (beta 1-adrenoceptors) than in the saphenous vein (beta 2-adrenoceptors). In the guinea pig tissues, the potency of cetamolol was approximately the same in the trachea (mixed beta 1- and beta 2-adrenoceptors) and atria (predominately beta 1-adrenoceptors), but lower in the soleus muscle (beta 2-adrenoceptors). Studies with the S-(-) and R-(+) enantiomers of cetamolol demonstrated that the S-(-) enantiomer was approximately 100-fold more potent at beta 1-adrenoceptors than the R-(+) enantiomer. In rat brain, cetamolol displaced [3H]-dihydroalprenolol bound to homogenates of cortex (beta 1-adrenoceptor binding sites) and cerebellum (beta 2-adrenoceptor binding sites). The potency of cetamolol at beta 1-adrenoceptors was found to be similar to that of betaxolol but greater than that of atenolol. However, the magnitude of the beta 1-adrenoceptor selectivity displayed by atenolol and betaxolol was greater than that displayed by cetamolol. In contrast, ICI-118,551 was found to possess potent and selective affinity for beta 2-adrenoceptors.

Acetamides↗
PubMed1987

Peripheral vision in persons with dyslexia.

We compared persons with dyslexia and normal readers with respect to how well they identified letters and short strings of letters briefly presented in the peripheral visual field at the same time that a single letter was presented at the fixation point of gaze. We found that the dyslexic subjects had a markedly wider area in which correct identification occurred in the peripheral field than did the normal readers. However, the dyslexic subjects had a "masking" between letters in the foveal field and letters in the near periphery. It appears that dyslexic persons learn to read outside the foveal field and, more generally, that there are different learned strategies for task-directed vision. Among such strategies are different mutual interactions between foveal and peripheral vision.

Adolescent↗
PubMed1987

In vitro isolated tissue studies with atiprosin (AY-28,228): a new antihypertensive compound.

Using in vitro isolated tissue and binding studies we have defined a receptor activity profile for atiprosin. The most prominent action of the compound was significant alpha-adrenoceptor antagonist activity (pA2 = 8.11) that was less potent than prazosin (pA2 = 8.78) but more potent than either ketanserin (pA2 = 7.34) or indoramin (pA2 = 7.85). In addition, atiprosin was selective for alpha 1-adrenoceptors, since the compound was over 100-fold less potent as an antagonist at alpha 2-adrenoceptors (pA2 = 6.04). Atiprosin also displayed selective serotonin 5-HT2-receptor antagonist activity similar to that seen with ketanserin, but with a lesser potency (pA2 atiprosin, 6.87; ketanserin, 8.61). Although atiprosin also displayed significant histamine H1-antagonist activity (pA2 = 7.32), it was less potent as an H1-antagonist than as an alpha 1-adrenoceptor antagonist. In contrast, both indoramin and ketanserin displayed H1-antagonist activity (pA2 8.77 and 8.83, respectively) greater than their respective alpha 1-adrenoceptor antagonist activities. Atiprosin had little or no activity at either beta 1- or beta 2-adrenoceptors, muscarinic or histamine H2-receptors, nor any marked ability to produce smooth muscle relaxation either by a direct effect or via calcium entry blockade.

Adrenergic alpha-Antagonists↗
PubMed1987

Tissue-dependent alpha adrenoceptor activity of buspirone and related compounds.

The present organ chamber and receptor binding studies were designed to evaluate the alpha adrenoceptor subtype (alpha-1 vs. alpha-2) and tissue selectivity of buspirone and the related compounds, gepirone, isapirone and 1-(2-pyrimidinyl)-piperazine (a metabolite of buspirone). Buspirone, gepirone and isapirone were found to possess weak alpha-1 adrenoceptor affinity (relative to prazosin) but significant and selective alpha-1 adrenoceptor intrinsic efficacy (relative to norepinephrine, phenylephrine and ST-587), which was expressed in a tissue- and species-dependent manner. The rank order for alpha-1 adrenoceptor affinity (isapirone greater than buspirone approximately equal to gepirone) was different from the rank order for alpha-1 adrenoceptor intrinsic efficacy (buspirone greater than gepirone greater than isapirone). The tissues that were the most responsive to norepinephrine and ST-587 (i.e., rat and rabbit aorta) were the same tissues in which the intrinsic efficacy of buspirone was expressed. In contrast, 1-(2-pyrimidinyl)-piperazine was inactive at alpha-1 adrenoceptors. Although no alpha-2 adrenoceptor intrinsic efficacy was observed for any of the compounds, isapirone and 1-(2-pyrimidinyl)-piperazine displayed weak alpha-2 adrenoceptor affinity (relative to rauwolscine). Recent studies have shown buspirone to have an effect on central and peripheral monoaminergic mechanisms. The demonstration in the present study that buspirone and related compounds display significant alpha adrenoceptor activity suggests that alpha adrenoceptor involvement should be considered as a potential contributing factor in the central nervous system and/or peripheral activity of this class of compounds.

Animals↗
PubMed1986

Enhancing the perception of form in peripheral vision.

Experiments are reported which show that the tachistoscopic presentation of a figure at the point of fixation makes salient the same figure where it occurs elsewhere in the visual field during the same flash. This induced saliency operates in all directions from the axis of gaze. If the eccentric figure is alone on a blank field the phenomenon is termed 'eccentric enhancement'. The induced saliency of figures that are laterally masked within horizontal strings of figures that lie off the fixation point is termed 'demasking'.

Attention↗
PubMed1985

[Long-term study of women with biopsy-proven mastopathy].

Out of a total of 1306 women (average age 42 years) with a biopsy proven mastopathy, manifest ipsilateral carcinoma occurred in 13 during the following 6 years. Thus the incidence of carcinoma differed little from the expected number of new cases in women of a comparable age. However, subdivision of breast lesions into simple (n = 1052) and proliferative (n = 254) forms showed that the carcinoma risk is double in proliferative mastopathy and fourfold higher when mastopathy with atypical epithelial proliferation is considered. An association with contraceptive hormones was not seen.

Adult↗
PubMed1985

Autocatalysis in cultural ecology: model ecosystems and the dynamics of biocultural evolution.

Using a well-known mathematical model frequently applied in theoretical population dynamics, certain ecological mechanisms are investigated that are inherent in the organic evolution of cultural capacities in man. Culture is argued to involve ecological interactions exhibiting analogies to the interaction of chemical species in autocatalytic biomolecular reactions. In the model, biocultural evolution proceeds by more and more broadening ecological niches and, thus, releasing competitive selection pressure on the populations involved. This, in turn, facilitates the maintenance of polymorphism in these populations as well as the individual acquisition of organic traits through learning and cultural transmission. The result is that the genetic variance in phenotypic expressions decreases at an accelerated rate.

Cultural Evolution↗