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Biomedical subjects

M Weiss

Publications and source records attributed to M Weiss.

At least 703 records · Page 39Linked to original sources
PubMed1980

Pharmacokinetics of prostaglandins: prediction of steady-state concentrations during intravenous infusion.

A pharmacokinetic model useful for compounds with high pulmonary clearance is presented which defines the interrelationships of extraction ratios and cardiac output in determining the steady-state plasma concentration during continuous intravenous infusion. Under the assumption of a dose-independent kinetics, the single pass and the recirculating system are treated with linear system theory. The analysis of data from the literature suggests that the model adequately describes the disposition of prostaglandin F2 alpha (PGF2 alpha) in man.

Biological Availability↗
PubMed1980

Relationship between the pharmacokinetics of a short-acting antiarrhythmic drug and its effects: studies with Falirytmin.

Pharmacokinetics, and the effect on cardiac conduction times were studied in ten patients after intravenous infusion (50 mg) of the new antiarrhythmic N,N'-Bis-[3-(2'-aethoxyphenoxy)-2-hydroxypropyl]-aethylendiamin (Falirytmin). The change of the PA, AH and HV interval induced by the drug was measured by the His-bundle electrogram technique. The results were compared with those of a previous study where the atrioventricular conduction time (PQ-interval) had been measured non-invasively. A 2-compartment open model was fitted to the measured blood concentrations. A total body clearance close to 1500 ml/min was calculated in both studies. An average biological half-life of 18.2 and 13.9 min, respectively, was found. The significant delay which was observed between the time course of blood concentration and response vanished if the change in conduction time was set in comparison to the theoretical drug amount in the peripheral compartment of the model.

Adult↗
PubMed1979

[Effects of juxtafastigial stimulation on the rhythmic activity of Purkinje cells in harmaline-treated rats].

In the anaesthetized rat, harmaline induces an olivary activation which results in rhythmic complex-spike (CS) discharges of Purkinje cells (4--8/sec) in the vermian cortex. The temporal organization of the rhythmic CS activity was studied. While some Purkinje cells present long periods of continuous rhythmic activity, the rhythmic CS discharge of other cells is modulated by periodical suppression of activity, with a total cycle length of about 10 sec. This organization can be modified by electrical stimulation of the juxtafastigial region (JF). During periods without spontaneous rhythmical CS firing, single JF shocks produce a late reflex response (200--300 msec) of the Purkinje cells, which appears as a repetitive sequence of CS (up to 30) at the harmaline-like induced frequency. The response obtained is the same whether the electrical stimulus is single or given in succession at regular intervals; however, in order to obtain such an effect, the frequency of the JF stimulation has to be inferior to the rhythmic CS frequency produced by the drug. At a higher stimulation rate (10 c/sec, 3 sec) the JF-induced response of Purkinje cells is abolished and we observe the suppression--4 to 8 sec following stimulation - of any rhythmic CS activity. This experimental modulation of rhythmic activity of the Purkinje cells (inducement or suppression of the CS firing), controlled indirectly by the olivary system, reproduces the spontaneous fluctuations of the thythmicity under harmaline. A neurophysiological model is presented and the functional significance of the results is discussed.

Alkaloids↗
PubMed1979

The effects of ACTH on adrenal steroidogenesis and blood corticosteroid levels in the echidna (Tachyglossus aculeatus).

1. The effects of short-term (S.T., 30 min) and long-term (L.T., 4 days) administration of ACTH on peripheral blood corticosteroid levels and on in vitro steroidogenesis were investigated. 2. Control levels of cortisol, corticosterone and aldosterone were 58 +/- 12, 130 +/- 26 and 10 +/- 6 (SEM) ng/100 ml respectively. 3. Corticosterone was 70% higher after S.T. and 150% higher after L.T., when cortisol was 800% higher. 4. Adrenal homogenates from control echidnas converted [14C]progesterone predominantly to 11-deoxycorticosterone (45%) and 11-deoxycortisol (12%). 5. After L.T. the principal product was corticosterone (25%), but S.T. had no effect. 6. In control echidnas the Km and V for 11 beta-hydroxylation of 11-deoxycorticosterone were 20 microM and 2.8 rho mol/min/mg respectively. After L.T. V increased to 10 rho mol/min/mg.

Adrenal Cortex Hormones↗
PubMed1979

Relaxin and collagen metabolism.

The influence of the peptide hormone relaxin on collagen metabolism was studied in the symphysis pubis of the mouse. In the tissue the content of water and of acid soluble collagen in relation to total collagen is increased by hormonal treatment. Total collagen calculated in relation to the dry weight is decreased. Collagenase which was also detected in the symphyses of the controls is slightly enhanced. In serum collagen peptidase and collagen peptidase inhibitor as well as cyclic AMP exhibit distinctly increased levels. The effects can be suppressed by administration of relaxin-specific antisera. The data make clear that in the symphysis relaxin activates the collagenolytic system.

Animals↗
PubMed1979

Electrostimulation of the median nerve in tetraplegics by means of implanted stimulators.

Since 1971 we studied on the possibility of utilization of implanted stimulators in tetraplegics caused by spinal cord injury of the cervical segment. Restoration to tetraplegic patients of the ability to perform some grasping functions of the hand may make them recover some independence and reduce the degree of disability. The examination conducted so far supplied much valuable information regarding reactions of a neuromuscular system at implanted stimulators as well the influence of systematic stimulation training on functions of the hand. This was not observed by other authors using transcutaneous stimulation. The examinations we performed revealed a several-fold increase in the force and prolongation of the period of maintenance of the maximal moment developed by the stimulation as well as the result of the stimulation training. Another observation we made was the possibility of active influence of the patient on the stimulation results. It consists in the possibility of active increase by the patient of the value of forces developed by the stimulated, previously paralysed muscles. The effect on the stimulation level, and on the extent of the "stimulation base" was found. The effect of active "support" of stimulation by the patient is the more effective, the lower the stimulation base is. We believe that our observations may have practical significance. Perfection of control over the stimulators' activity from inner sources will probably permit in many instances to utilize functionally tetraplegics' paralysed hand.

Electric Stimulation↗
PubMed1979

Synthesis of steroids by echidna (Tachyglossus aculeatus) testis and the effects of gonadotrophin administration.

After administration of hCG and PMSG to male echidnas (in non-breeding state) the testis to body weight ratio increased 3-fold and the diameter of the seminiferous tubules doubled, but spermatogenesis was not induced. The major conversion product of testicular homogenate with [4-14C]progesterone as substrate was 17 alpha-hydroxyprogesterone (4% in untreated and 29% in treated echidnas). Testosterone (5%), androstenedione (16%) and 17 alpha,20 beta-dihydroxypregn-4-en-3-one (7%) were also obtained in gonadotrophin-treated animals. In untreated animals these steroids were present in minor amounts (less than 1%).

Androstenedione↗
PubMed1979

[The diagnostic value of various stiffness indices in the evaluation of the diastolic properties of the left ventricle].

The results are presented of simulated calculations obtained with the aid of a continuum model of the left ventricle in a passive state on the basis of a nonlinear elasticity theory. Various empirical indexes of left ventricular rigidity are calculated from modelled diastolic pressure/volume curves, and are compared with myocardial elasticity indicators. With respect to sensitivity and specificity, as the best there were found the volume-standardized Diamond index (d[lnP]/dV)V0 and the Laird index d(lnP)/d/lnV). The indexes are calculated from two parts of enddiastolic pressure/volume values. An analysis of clinically measured values confirmed the model predictions.

Blood Pressure↗