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Biomedical subjects

H Opitz

Publications and source records attributed to H Opitz.

At least 37 records · Page 2Linked to original sources
PubMed1986

Influence of varying afterload upon left ventricular contractility.

In open-chest rabbits under pentobarbitone anaesthesia the left ventricular afterload was varied by occlusion of the carotid arteries, descending aorta and both of them together in alternating sequence when the aortic nerves and cardiac vagal nerves were cut. Ascending aortic flow AF was recorded by means of a flow probe around the aortic root, the left ventricular pressure LVP by direct canulating of the heart and the aortic blood pressure AP via catheter through the left subclavian artery. From the LVP the systolic and diastolic values LVSP and LVEDP, the contractility index CI = (dp/dt/p)max and from the AF the stroke volume SV and strokework W were evaluated. At mild afterload elevation (carotid or aortic occlusion alone) the CI appears to be enhanced, SV diminished, LVEDP only little raised, and W improved. At combined occlusions a drastical rise of LVEDP, decrease of SV and impairment of W is observed whereas the CI remains elevated and the LVSP increases with AP. From the pump function diagram ensues that at mild afterload increase the operational point is shifted towards the strokework optimum whereas at high afterload it is far away. After discharge of the ventricle all alterations are rapidly and completely restituted.

Animals↗
PubMed1986

Comparative investigations of right and left ventricular contractility in the rabbit.

In pentobarbitone-anaesthetized open-chest rabbits the left and right ventricular pressures were measured. The contractilities of the left and right ventricle were expressed by the contractility index CI = (dp/dt/p)max. Evaluation of left and right ventricular systolic pressure and CIs was done before and at aortic nerve stimulation as well as with pacing and without pacing of the heart. Pressures and CIs appear to be four times greater in the left ventricle than in the right one. The values of the pressure ratio LVSP/RVSP resp. CI ratio CILV/CIRV are adequate before and after aortic nerve stimulation. Any effect difference between the left and the right aortic nerve stimulation does not exist. In the paced heart the left and right ventricular pressure and the left ventricular CI are lower than without pacing. The effect time courses of the left and right ventricle appear to be adequate. Hence is follows that the left rabbit ventricle predominates in contraction development.

Animals↗
PubMed1985

Cloning of hexokinase structural genes from Saccharomyces cerevisiae mutants with regulatory mutations responsible for glucose repression.

The regulatory hexokinase PII mutants isolated previously (K.-D. Entian and K.-U. Fröhlich, J. Bacteriol. 158:29-35, 1984) were characterized further. These mutants were defective in glucose repression. The mutation was thought to be in the hexokinase PII structural gene, but it did not affect the catalytic activity of the enzyme. Hence, a regulatory domain for glucose repression was postulated. For further understanding of this regulatory system, the mutationally altered hexokinase PII proteins were isolated from five mutants obtained independently and characterized by their catalytic constants and bisubstrate kinetics. None of these characteristics differed from those of the wild type, so the catalytic center of the mutant enzymes remained unchanged. The only noticeable difference observed was that the in vivo modified form of hexokinase PII, PIIM, which has been described recently (K.-D. Entian and E. Kopetzki, Eur. J. Biochem. 146:657-662, 1985), was absent from one of these mutants. It is possible that the PIIM modification is directly connected with the triggering of glucose repression. To establish with certainty that the mutation is located in the hexokinase PII structural gene, the genes of these mutants were isolated after transforming a hexokinaseless mutant strain and selecting for concomitant complementation of the nuclear function. Unlike hexokinase PII wild-type transformants, glucose repression was not restored in the hexokinase PII mutant transformants. In addition mating experiments with these transformants followed by tetrad analysis of sporulated diploids gave clear evidence of allelism to the hexokinase PII structural gene.

Cloning, Molecular↗
PubMed1985

Interactions between aortic pressure and inotropic responses in the carotid sinus baroreflex of the rabbit.

The isolated left carotid sinus of rabbit was stimulated with 20 kPa pressure steps. By means of an intraaortic balloon catheter the arterial blood pressure could be either fixed against reflex changes (pressure clamp) or adjusted to any value desired. The passive pressure dependence of the left ventricular systolic pressure LVSP is observed to be linear, and the enddiastolic pressure LVEDP is hardly affected. The LV contractility index CI = (d log P/dt)max has a nonlinear dependence on the aortic pressure. Its slope, the so-called coefficient of pressure-induced inotropy CPI, is high in the lower pressure range and vice versa. In the paced heart inotropic reflex responses to 20 kPa intrasinus pressure steps, expressed in percent attenuation of the CI, were firstly elicited at freely variable arterial pressure and, thereupon, at pressure clamp conditions. In the latter case the inotropic effects are significantly lower (14.5%) than at free running pressure (34.6%). A mean of CPI = 2.32% . kPa-1 is obtained from the inotropic effect differences and the concomitant pressure drops. When subdividing the effects with respect to initial diastolic pressure, we could obtain a CPI = 3.7% . kPa-1 in the pressure range below 14.5 kPa, and a CPI = 1.53% . kPa-1 for higher pressures. The primary inotropic effects at pressure clamp conditions do not depend on the arterial pressure.

Animals↗
PubMed1983

Interaction of baroreflex bradycardia and inotropy in the rabbit.

In urethane-anaesthetized, closed-chest rabbits negative inotropic reflex responses from the left ventricle were elicited by aortic nerve (AoN) and carotid sinus nerve (CSN) stimulation in the paced and spontaneously beating heart and characterized as percent decrease of the contractility index (d log p/dt)max. The negative inotropic reflex action upon the left ventricle is, at freely changing heart rate, masked by the concomitant reflex bradycardia, in dependence on the prestimulation spontaneous heart rate. Therefore, inotropic reflex responses to AoN and CSN stimulation, as well as before and after vagotomy are comparable only on the condition of paced heart. In hearts with a prestimulation rate below 245 beats/min the negative reflex inotropy at freely changing rate is higher than under pacing, and at rates above 245 beats/min vice versa. It is assumed that at lower rates the nervous inotropy is augmented by negative rate-dependent inotropy (Bowditch staircase), at higher rates counteracted by a positive staircase, caused by reflex bradycardia. This nonuniform interaction can be explained by the strength-interval relation of the left ventricle which has an optimum at 245 ms (= 245 beats/min). The inotropic effect differences between stimulations at freely changing and paced heart rate are correlated to the effective heart intervals; the regression lines both for AoN and for CSN stimulation show equal intercepts with the abscissa at 245 ms. This is further evidence that at high heart rate the negative nervous inotropy counteracts, and at low rate cooperate with the rate-dependent inotropy.

Afferent Pathways↗
PubMed1982

Interactions of adaptation and masking in the guinea pig cochlea.

Fast cochlear adaptation and masking phenomena, expressed as percent inhibition of the summed action potential, are studied from the guinea pig cochlea responses to click trains and tone bursts given previously or simultaneously to the click sequence. After preceding tone bursts, the click responses are superposed by inhibitory aftereffects dependent on the tone frequency. With interposed tone bursts, the click sequence response is masked, dependent on tone frequency.

Adaptation, Physiological↗
PubMed1981

Cochlear responses to dynamic click patterns in the guinea pig.

Fast cochlear adaptation, expressed as percent inhibition of the summed action potential, is studied from the guinea pig cochlea responses to click trains, ramps, and steps in both directions. The transition time function of adaptation to constant click trains does not depend on click strength, but rather on click interval. On the background of steady state adaptation, click steps produce only transient changes of the adaptive state, opposite to step direction. Compared to constant train stimulation, adaptation is enhanced by descending click ramps, and diminished or reversed (near threshold) by ascending ramps.

Acoustic Stimulation↗
PubMed1980

[Dynamics of rhythm-dependent potentiation in the guinea pig heart].

In strip preparations from the right ventricle of the guinea pig heart, potentiation phenomena due to varied pacing rate (frequency potentiation FP) or paired stimulation (paired pulse potentiation PPP) are studied with respect to contractile strength and dynamics. Heart rate or interstimulus interval of paired stimulation were modulated both stepwise and sinusoidally. Steady state characteristics of FP as well as PPP prove to be linear in a broad range. FP is enhanced by increasing rate, whereas PPP is diminished by increasing interval. Paired stimulation is always more effective than single stimulation at double rate. Effects upon action potential are negligible. The response of PPP to interval steps are first order transients, whereas rate steps produce on/off response of FP, opposite to step direction, with subsequent staircase. Frequency response characteristics of FP and PPP yield in first order transfer functions: for PPP with dead time, and for FP with negative derivative action. After substitution of Ca++ by Sr++ ions, the negative derivative term of FP disappears, whereas positive staircase remains. By means of a compartment hypothesis of electromechanical coupling in the mammalian myocardium the mode of action of the potentiation phenomena and their differences are interpreted, and the obtained dynamic parameters are attributed to presumably underlying Ca transport processes within the cell.

Action Potentials↗
PubMed1975

[Biocybernetic studies on reflectory heart modification in the rabbit].

In rabbits the depressor nerves and cardiac vagal branches were stimulated. Their actions on heart rate, atrio-ventricular conduction time, myocardial action potential and mean central blood pressure were recorded. The frequency-effect characteristics of the chronotropic, dromotropic and electrotropic actions on the heart, resulting from afferent and efferent nerve stimulation, are compared. The participation of each of the depressor nerves in their total effects on heart rate and blood pressure is studied. Time courses of heart rate and blood pressure decrease by afferent and efferent nerve stimulation with sinusoidally modulated pulse rates are presented. The results are discussed with respect to the different dynamics of blood pressure and heart rate control. It is concluded that at least two mechanisms are involved in blood pressure control by the depressor nerves: 1. Decrease of vascular resistance by lowering the sympathetic tone. 2. Decrease of heart rate by enhancing the cardiac vagal activity. It is suggested that the parasympathetic control unit compensates rapid disturbances, whereas the slow-acting sympathetic vascular mechanism exerts a long-time pressure control of high efficiency.

Action Potentials↗
PubMedDate not supplied

Dynamic contrast enhancement of intracranial tumors with snapshot-FLASH MR imaging.

PURPOSE: To investigate whether exact evaluation of the dynamic contrast enhancement pattern within intracranial tumors can help to classify tumor histology and vascularity. METHOD: Forty-nine patients suffering from different intra- and extraaxial intracranial tumors underwent MR-examination in a 1.5-T superconductive whole body system. After rapid injection of Gd-DTPA, 48 images were acquired during the first 1.5 to 2 minutes of contrast enhancement within the tumors. A fast snapshot-FLASH imaging technique allowed measurement times of 1 second per image. Appearance of Gd-DTPA in a venous sinus served as a temporal reference point. Transformation of 48 discrete measurement points (mean signal values of the enhancing tumor region) into a continuous curve, using a cubic spline approximation, allowed calculation of the time of maximum signal increase (Tm1) and the following time of half maximum increase (Tm2). These time parameters were compared to histopathologic findings, especially the degree of tumor vascularization. RESULTS: Significantly different dynamic patterns of the early enhancement period were found for the different tumors. All eight neurinomas, typically less vascularized than most meningiomas, showed a characteristically prolonged contrast enhancement with a long Tm2. Histopathologic findings concerning the degree of vascularization showed two subtypes in meningiomas (n = 17) as well as in pituitary macroadenomas (n = 7). This was confirmed by dynamic evaluation in all cases, in the sense that short Tm1 and Tm2 were found in cases with higher degrees of vascularization. Negatives values of Tm1 were measured in two glomus jugulare tumors, reflecting the arterialization of these vascular tumors. In neuroepithelial tumors (n = 15), the glioblastomas (n = 7) showed very short Tm1 compared to the lower grade gliomas (n = 8). This is explained by histologic findings of pathologic vessels with arteriovenous shunts. CONCLUSION: The evaluated dynamic time parameters can be used to narrow differential diagnostic possibilities and to infer the degree of vascularization of intracranial tumors.

Adenoma↗
PubMedDate not supplied

Demonstration of mercury in the human brain and other organs 17 years after metallic mercury exposure.

A male subject became exposed to metallic mercury vapor at work in 1973. He excreted 1,850 mg Hg/l urine initially. Controls of urine mercury excretion after D-penicillamine administration led to the assumption of a total body clearance of mercury latest since 1976. Subsequently he developed an organic psychosyndrome without detectable signs of classical mercurialism. He never returned to work again and died of lung cancer in 1990. In different organs (brain, kidney, and lung) which were sampled at autopsy elevated levels of mercury were documented by atomic absorption analysis. Histological examination of the tissue by the Danscher and Schroder method, which is specific for mercury, showed a highly positive staining in the majority of nerve cells and cells of other organs. Ultrastructurally mercury could be demonstrated by elemental x-ray analysis within lipofuscin deposits. The lipofuscin content was increased in the mercury positive nerve cells as demonstrated by a strong positive autofluorescence.

Cerebellar Cortex↗