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Biomedical subjects

F Schaefer

Publications and source records attributed to F Schaefer.

At least 109 records · Page 6Linked to original sources
PubMed1991

Pulsatile immunoreactive and bioactive luteinizing hormone secretion in adolescents with chronic renal failure. The Cooperative Study Group on Pubertal Development in Chronic Renal Failure (CSPCRF).

Delayed or arrested pubertal development is common in children with chronic renal failure (CRF). Normal puberty is initiated by the onset of episodic nocturnal secretion of luteinizing hormone (LH) containing an increasing proportion of bioactive hormone. To test the functional integrity of the hypothalamo-pituitary axis in CRF we measured immunoreactive (i-LH) and bioactive (bio-LH) plasma LH concentrations at 15-min intervals from 2000 to 0700 hours in 65 pubertal patients aged 10-23 years [46 boys/19 girls; 20 on conservative treatment (CT), 13 on dialysis (D), 32 with transplants (TP)]. i-LH was determined by radio-immunoassay and bio-LH by a mouse Leydig cell assay. Peak detection was performed by the cluster analysis computer programme. The mean (+/- SD) number of i-LH (in both sexes) and bio-LH pulses (in boys) per profile, and the mean peak area of i-LH (in both sexes) and bio-LH (in girls) were higher in TP than in CT or D patients. The ratio of bio-LH to i-LH increased during puberty in CT (G1 vs G4/5, 0.3 +/- 0.5 vs 1.8 +/- 0.,4) and TP (0.6 +/- 0.7 vs 1.8 +/- 0.7) but remained low in male D patients (0.4 +/- 0.7 vs 1.1 +/- 0.8). The ratios were subnormal, however, even in mature TP patients compared with healthy adults. The bio-LH/i-LH ratio and the bio-LH peak area best predicted integrated nocturnal testosterone concentrations in TP but not in uraemic male patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1991

Pulsatile growth hormone secretion in peripubertal patients with chronic renal failure. Cooperative Study Group on Pubertal Development in Chronic Renal Failure.

The pubertal growth spurt has been associated with changes of physiologic pulsatile growth hormone (GH) secretion, and abnormalities of the central regulation of GH release have been found by pharmacologic testing in patients with chronic renal failure. To assess the characteristics of GH pulsatility in chronic renal failure and their relationship to pubertal growth, we studied spontaneous nighttime GH plasma profiles in 80 patients (61 boys) aged 10 to 20 years receiving conservative treatment (n = 29) or dialysis (n = 18) or after renal transplantation (n = 33). Tanner genital stages 1 to 4 in boys and breast stages 1 to 3 in girls were represented. Growth hormone pulse analysis was performed by the PULSAR algorithm. Growth hormone concentration profiles were pulsatile in each patient. Growth hormone mean and baseline levels and pulse amplitudes were higher in patients receiving conservative or dialysis treatment than in patients who had undergone renal transplantation. Peak frequency was similar in all treatment groups in boys but higher in girls who had undergone transplantation than in girls receiving conservative or dialysis treatment. Growth hormone peak amplitude and mean levels were lowest in patients in late puberty. The physiologic elevation of GH amplitudes around midpuberty was observed in boys receiving conservative and dialysis treatment but not after transplantation. Growth hormone mean and baseline levels were positively correlated with plasma androgen levels in boys. Growth hormone peak amplitude was correlated with 6-month height velocity after transplantation but not in patients receiving conservative treatment or dialysis. A strong inverse relationship was observed between GH peak amplitude and corticosteroid dosage in patients undergoing transplantation. The lack of relationship between circulating GH levels and growth in patients receiving conservative or dialysis treatment is compatible with end-organ hyporesponsiveness to GH. Pubertal growth failure despite successful transplantation appears to be related to steroid-induced GH hyposecretion.

Adolescent↗
PubMed1991

Growth hormone prevents steroid-induced growth depression in health and uremia.

Treatment with supraphysiological doses of corticosteroids results in protein wasting and impairment of growth, whereas exogenous growth hormone (GH) causes anabolism and improvement of growth. We wanted to know whether the growth depressing effects of methylprednisolone (MP) are more expressed in an organism which is chronically diseased and whether these effects can be counterbalanced by concomitant treatment with recombinant human growth hormone (rhGH). MP in doses from 1 to 9 mg/kg/day caused a dose dependent reduction of length gain, weight gain and weight gain/food intake ratio in 140 g healthy female Sprague-Dawley rats. Food intake was not affected by MP. This points to a change in food metabolism as a mechanism for growth impairment. In addition, treatment with MP inhibited endogenous GH secretion, documented by serum GH concentration profiles over seven hours, decreased IGF-1 serum concentration and disturbed growth cartilage plate architecture. Concomitant treatment with 2.5 to 20 IU/rhGH/kg/day prevented the negative effects of MP on growth in a dose dependent manner and normalized growth plate architecture. In uremic rats in which food efficiency and growth was already reduced, 6 mg MP/kg/day further decreased length gain and prevented weight gain completely by bringing the weight gain/food conversion ratio to the nadir. All effects of MP including reduction of muscle mass could be prevented by concomitant treatment with 10 IU rhGH/kg/day. The effects of MP and rhGH on food efficiency and growth in uremic animals were numerically nearly identical to those in pair fed ad libitum fed controls, but this may be more relevant in the diseased organism in which basal growth is already suppressed.

Animals↗
PubMed1990

Disturbance of growth hormone--insulin-like growth factor axis in uraemia. Implications for recombinant human growth hormone treatment.

The growth hormone/insulin-like growth factor (IGF) axis is disturbed in uraemia. Elevated plasma growth hormone (GH) levels despite diminished growth suggest GH resistance, which may be due in part to a decreased expression of the growth hormone receptor at the cell membrane. The hepatic production of IGFs under the control of GH is impaired. Furthermore, there is an excess of IGF-binding protein over total IGF as a consequence of reduced renal clearance of low-molecular-weight subunits of the IGF-binding protein (IGF-BP). This results in an absolute (diminished production) and a relative (low bioavailability) deficiency of IGF. Recombinant human growth hormone (rhGH) in doses of 4 IU/m2 per day is able to induce catch-up growth in children with preterminal and terminal renal failure. The growth stimulation of exogenous GH is attributed to its potency to increase the ratio of IGF-I to IGF-BP, followed by a normalization of IGF bioactivity. In renal transplanted children growth is not only disturbed by decreased renal function but also by steroid treatment. Corticosteroids are responsible for catabolism, for suppression of pituitary GH secretion and for inhibition of local production of IGFs. Exogenous rhGH is able to counteract these growth-inhibiting effects. However, it remains to be seen whether long-term GH treatment definitely improves final adult height.

Adolescent↗
PubMed1990

Calcium deposits develop in rat substantia nigra but not striatum several weeks after local ibotenic acid injection.

The excitotoxin ibotenic acid (IBO) was used to place local circumscript lesions in rat substantia nigra (SN). Four to six months after the injection we found in the neuron depleted SN basophilic deposits resembling calcium concretion. Additional experiments revealed that calcium deposits, as verified with the alizarin red stain, were first detectable after a delay of 4 weeks. They increased in number, size and extent over the following 12 weeks, but remained confined to the boundaries of SN. Injection of at least 3.5 micrograms IBO was necessary for induction of deposits. In striatum, 14 micrograms IBO did not cause clearly identifiable concretions. Thus, IBO-induced lesions are not stationary but mature, and the long-term effects can be different in different brain regions. These observations may have some relevance for considerations on the cause of the idiopathic nonarteriosclerotic calcifications.

Animals↗
PubMed1990

Assessment of gonadal maturation by evaluation of spermaturia.

The urinary excretion of spermatozoa (spermaturia) reflects the achievement of exocrine testis function during male puberty. In order to test the sensitivity and practicability of repetitive urine sampling, we analysed the sediments of 1160 first morning urine specimens obtained on successive days from 129 healthy schoolboys aged 10.1 to 17.8 years for the presence of spermatozoa. The proportion of subjects with sperm positive urines increased from pubic hair stage (PH) 1 (6%) to PH 5 (92%) with a steep rise between PH 2 and 3. Estimated median age of first positive spermaturia ('spermarche') was 14.1 years. While at PH 1 to 4 all positive samples were found within the first five days of collection, at PH 5 cumulative frequency of spermaturia increased up to day 8. We conclude that repetitive morning urine sampling is a useful tool in assessing spermaturia and may be helpful to screen for testicular damage in epidemiological surveys.

Adolescent↗
PubMed1990

Pubertal growth in chronic renal failure.

We evaluated the growth records of 15 boys and 14 girls who developed end-stage renal failure before or during puberty and who were regularly followed from the onset to the end of their pubertal growth spurt. Height data were smoothed by using the kernel estimation method. Mean values for age, height, and height velocity at defined points of the pubertal growth period were compared with those of normal children entering puberty both at an average and late age. The start of the pubertal growth spurt was delayed by 2.5 y in both sexes. Its duration and intensity were significantly reduced. Mean pubertal height gain was 17.3 cm in boys and 13.9 cm in girls, i.e. 58 and 48% of that observed in the late maturing control group. Mean height at the onset of the pubertal spurt in the patients was the same as that in the late maturing healthy girls and 1.0 SD below that of corresponding boys. During the pubertal growth spurt, mean height declined to -2.9 SD in boys and -2.3 SD in girls. Although skeletal maturation was increasingly retarded, we did not observe accelerated growth velocity during late puberty. Our data indicate that most patients reaching end-stage renal failure before or during puberty irreversibly lose growth potential during this period. Renal transplantation did not consistently improve pubertal growth.

Adolescent↗
PubMed1990

[Effects of waiting times within simple problems: an analogy to waiting times in human-computer interaction].

The impact of forced intra-task waiting periods was evaluated in a laboratory study designed in analogy to forced waiting periods in human-computer interaction. Each task consisted of two lines of grouped capital letters (so-called Sterzinger lines) that had to be processed individually, separated by the experimental waiting period. The final response to both lines was taken after removal of the second line. The experiment was conducted according to a within-subjects design with the order of the two factors "duration" (2 s vs. 8 s) and "variability of the waiting periods" (constant vs. variable) controlled. The dependent variables were performance indices, heart rate, electrodermal activity, and subjective measures of mood and physical complaints. The results showed effects of the duration of waiting periods for the performance and the physiological variables, and effects of the variability factor for the subjective variables. Shorter waiting periods were associated with higher scores of heart rate and skin resistance responses, variable waiting periods seemed to confuse the subjects more than constant ones. The results are discussed with respect to the effects of the two experimental factors. With respect to dialog structures in human-computer interaction, the results lead to the conclusion that response interference could be avoided by giving the user the possibility to immediately input problem solutions. Partial and preliminary inputs should be permanently kept visible during the whole task cycle by the software.

Adult↗
PubMed1989

Low-dose cyclosporin A therapy in cadaver renal transplantation in children.

Fifty-one pediatric patients undergoing a first cadaveric kidney transplantation were followed for at least 2 years after grafting. They were divided into two groups: those treated with methylprednisolone plus azathioprine (AZA) and those treated with methylprednisolone plus low-dose cyclosporin A (CyA; median dose 109 mg/m2 per day = 3.4 mg/kg per day after 1 year). The steroid dosage given was significantly lower in the second group. The 4-year graft survival rate was 68% for the AZA group and 78% for the CyA group. Renal function did not differ significantly in the two groups; after 1, 2, and 3 years, the median 24-h creatinine clearance was 79, 69, and 51 ml/min/1.73 m2, respectively, for the AZA group and 78, 63, and 68 ml/min/1.73 m2, respectively, for the CyA group. Linear growth was similar in the two groups. We conclude that in pediatric patients the results of low-dose CyA immunosuppression do not differ significantly from those obtained with AZA in terms of graft survival, renal function, or growth.

Adolescent↗
PubMed1989

Continuous recordings of impedance and phase angle during electrodermal reactions and the locus of impedance change.

The relatively few studies that use alternating current (AC) in exosomatic electrodermal recording techniques focus on tonic measurement but not on phasic measures. AC methods of phasic measurement, however, are most useful in testing electrical models of the electrodermal response. Problems arising from AC recording of fast electrodermal changes are discussed, and an appropriate measurement concept for continuous recording of impedance and phase angle is developed. This enables tonic values of both parameters to be offset in order to sufficiently amplify small changes. An AC frequency of 100 Hz was used in recording electrodermal activity in 10 subjects during an habituation series of 80dB 1000 Hz tones. Comparison of transformed curves showed that the main component of electrical changes accompanying electrodermal response is a shift in conductance while susceptance shows only small fluctuations. According to a widely accepted simple electrical model of skin, these results indicate that electrodermal responses take place mainly in the resistive element which parallels the capacitance associated with the stratum corneum, but that other components may be involved too.

Adult↗
PubMed1989

Reactivation of peptidoglycan synthesis in ether-permeabilized Escherichia coli after inhibition by beta-lactam antibiotics.

The recovery of peptidoglycan-synthesizing activity after inhibition by beta-lactam antibiotics was investigated in ether-permeabilized cells of Escherichia coli B. Such cells synthesize sodium dodecyl sulfate-insoluble peptidoglycan when provided with UDP-linked precursors and Mg2+. The ability of beta-lactam antibiotics to inhibit the synthesis of peptidoglycan was correlated with their affinity for penicillin-binding proteins 1A and 1Bs. Penicillin-binding protein 1Bs is thought to be the major peptidoglycan synthetase in E. coli and is a major lethal target for beta-lactam antibiotics. Ether-treated bacteria were preincubated with concentrations of beta-lactams sufficient to completely inhibit peptidoglycan synthesis and then treated with beta-lactamases to inactivate free antibiotic prior to measurement of peptidoglycan synthesis. At 40 min after beta-lactamase treatment, the rate of peptidoglycan synthesis was about 74% of the control rate in cells pretreated with ampicillin, but only 15% of the control in cells pretreated with penicillin G or azlocillin. Reversal of inhibition by several other antibiotics fell between these extremes. When cross-linking of peptidoglycan was measured specifically, reversal of inhibition by ampicillin also occurred more readily than that by penicillin G. Reactivation of peptidoglycan synthesis was not due to de novo synthesis of penicillin-binding proteins since it occurred under conditions that did not allow incorporation of [14C]leucine. We conclude that there is considerable variation in the stability of the inactive acyl enzymes formed between various beta-lactams and penicillin-binding protein 1Bs, with those formed by penicillin G being relatively long-lived.

Anti-Bacterial Agents↗
PubMed1989

Pulsatile gonadotropin secretion in pubertal children with chronic renal failure.

We have examined physiological nocturnal secretion of gonadotropins in 6 boys and 2 girls with end-stage renal disease, who had either delayed or disturbed puberty. The 5 patients treated by dialysis had reduced gonadotropin pulsatility for their stage of pubertal maturation, whereas the 3 patients with successful kidney grafts demonstrated a higher nocturnal rise and increased amplitude of gonadotropin pulsatility. It is suggested that the improved gonadotropin pulsatility of transplanted patients is due to their restored renal function.

Adolescent↗
PubMed1989

[Recovery of galvanoplastic die-models--actual level and prospective development].

In contrast to the conventional methods of making galvanoplastic die-models a new technology of electrotype with copper is described. The important differences are the new mechanical arrangement of the electrolyticall cell, the using of a high constant current-density and the using of an open system with a continuous flowrate of the electrolyte and its constant temperature. With the new technology it is possible to get galvanoplastic dies from negativs with small diameter and with a high value of depth. The time of the electrochemical process is decreasing from 8 to 10 hours of only 40 minutes and the surface hardness is increasing from MHV 80 to MHV 160.

Copper↗
PubMed1989

[The effect of temporal distribution in relation to constant frequency of stimuli on habituation of the orienting reaction].

The lack of empirical evidence for faster habituation with the regular presentation of stimuli suggests that it is not the constancy of presentation of stimuli, but rather the rate of stimulation--defined as the reciprocal of the harmonic mean of the interstimulus intervals--that determines the speed of habituation. Using alternation of 10-70 and 30-50 sec and a constant sequence of 40 sec, three different rates of stimulation were realized. The hypothesis of faster habituation of skin conductance reactions with higher rates of stimulation was not confirmed. However, a consistent pattern of skin conductance reactions, with an increase in reaction after long intervals and a decrease after short intervals, was found, especially in the group with alternating intervals of 10 and 70 sec. The analysis of an additional group with a random sequence of intervals showed that the response pattern did not result simply from the expired time since last stimulus, i.e., a simple mechanical effect. The possibility of anticipating the stimuli and differing information content of the stimuli are discussed as possible determining factors.

Adult↗