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Biomedical subjects

H Hoppe

Publications and source records attributed to H Hoppe.

At least 55 records · Page 3Linked to original sources
PubMed1994

Involvement of endogenous opioids in the regulation of LH and testosterone release in the male horse.

To investigate the involvement of endogenous opioids in the regulation of gonadotrophin release in male horses, effects of the opioid antagonist naloxone (0.5 mg kg-1 i.v.) on plasma LH and testosterone concentrations and the possible influence of season and of gonadal steroids were investigated. To determine quantitative as well as qualitative changes in gonadotrophin release, LH concentrations were measured by radioimmunoassay and by an in vitro bioassay. Experiments were performed in May, August and December. In stallions, basal LH secretion in May and August was significantly higher than in December (May versus December: P < 0.01; August versus December: P < 0.05); plasma testosterone concentrations were highest in August (August versus May: P < 0.05, August versus December: P < 0.001). The basal bioactive LH concentration and the ratio of bioactive:immunoreactive LH in stallions were highest in May. Therefore, in addition to seasonal changes in quantitative LH secretion, the bioactivity of LH in the circulation also undergoes seasonal variations. Bioactive LH concentrations and the bioactive:immunoreactive ratio in geldings were higher than in stallions. Naloxone caused a significant increase in LH release in stallions in August and December (P < 0.001); no significant increase was found in May (P = 0.06). In geldings, naloxone did not induce any changes in LH secretion; in stallions, a highly significant correlation was observed between basal testosterone concentrations and the LH increment after injection of naloxone (P < 0.001). In August and December, the bioactive:immunoreactive ratio increased significantly (P < 0.05) after injection of naloxone in stallions, indicating a preferential release of LH molecules with high bioactivity. The bioactive:immunoreactive ratio did not change after naloxone injection in May. The naloxone-induced LH release was followed by a significant increase in plasma testosterone concentrations in stallions in August (P < 0.001) and December (P < 0.05). In conclusion, endogenous opioid systems are involved in the regulation of LH and testosterone secretion in stallions. These mechanisms undergo seasonal changes: their activity is increased during winter and decreased during the breeding season. By affecting LH release, endogenous opioids, at least in part, regulate seasonal changes in reproductive activity in the stallion.

Animals↗
PubMed1994

Effects of the opioid antagonist naloxone on release of luteinizing hormone in mares during the anovulatory season.

To investigate an involvement of endogenous opioids in the regulation of circannual changes in reproductive activity, effects of the opioid antagonist naloxone on the concentration of immunoreactive and bioactive luteinizing hormone (LH) in plasma were measured in mares during the anovulatory season. Naloxone (0.5 mg/kg i.v.) caused a significant increase (P < 0.05) in immunoreactive as well as bioactive LH concentration in plasma. The amplitude of the increase in LH concentrations measured with an in vitro bioassay was more pronounced than the amplitude of the increase in LH secretion determined by radioimmunoassay. This indicates that although in seasonal anovulatory mares the bioactivity of LH in plasma is low, highly bioactive LH is present in the anterior pituitary and can be released by naloxone. The LH response to naloxone did not depend on the degree of ovarian follicular activity. It can be concluded that a tonic opioid inhibition of LH release is present in mares during at least part of the anovulatory season and that endogenous opioids seem to be involved in the regulation of seasonal reproductive activity in the horse. In contrast to the situation during the breeding season, the opioid systems regulating LH release are activated independently of luteal progesterone.

Animals↗
PubMed1993

Multiwavelength photometry of thermochromic indicator solutions for temperature determination in multicuvettes.

If buffer/indicator systems are used as optical thermometers in multicuvettes, the temperature resolution is limited by errors of optical measurements produced mainly by variations of pathlength and blank transmittance of the wells. Theoretical and practical approaches show that, in multicuvettes, a between-well temperature resolution of < 0.05 degrees C can be achieved by multiwavelength photometry with use of the Tris/cresol red indicator system. Using up to three absorbances (A0, A1, A2) measured in the same well at different wavelengths for calculation of differences, quotients, and quotients of differences, we found the optimum temperature signal to be In(A1/A2), with equal-ranking absorbances changing with temperature in opposite directions. We have used the method successfully to measure the temperature profiles and temporal dynamics of temperatures at all positions in two types of multicuvettes under controlled conditions, or not controlled thermostatically.

Indicators and Reagents↗
PubMed1992

Growth factors produced by human embryonic kidney cells that influence megakaryopoiesis include erythropoietin, interleukin 6, and transforming growth factor-beta.

Partially purified protein preparations containing megakaryocyte growth factor activity were prepared from human embryonic kidney (HEK) cell conditioned medium using ammonium sulfate precipitation, Cibicron blue affinity chromatography, and wheatgerm lectin affinity chromatography. Treatment of these preparations with neutralizing antibodies directed against erythropoietin (EPO) and interleukin 6 (IL6) resulted in a dramatic reduction in their capacity to stimulate megakaryocyte maturation in vitro. The presence of EPO in these preparations was confirmed by both immunoblotting and use of a mouse spleen erythroid progenitor cell proliferation assay routinely used to quantitate EPO activity in vitro. Northern blot analysis of HEK cell-derived mRNA with IL6 DNA probes revealed the presence of an IL6 transcript with a molecular size of 1.3 kb. Analysis of the HEK cell-derived preparation by ELISA confirmed the presence of immunologically reactive IL6. In addition, it was shown that purified recombinant human EPO and IL6 stimulated megakaryocyte maturation in the in vitro assay used in this study. These data indicate that the activity in HEK cell conditioned medium that stimulates megakaryocyte maturation in vitro is predominantly due to the presence of IL6 and EPO. Immunoneutralization studies of another HEK cell-derived preparation, which was inhibitory in the megakaryocyte maturation assay, demonstrated that it contained transforming growth factor beta (TGF beta), a potent inhibitor of megakaryocyte maturation. Taken together, these studies indicate that HEK cell conditioned medium, which has previously been reported to contain megakaryocyte growth factor activity, is comprised of a complex mixture of growth and differentiation factors, some of which promote and others that inhibit the process of megakaryopoiesis.

Biological Assay↗
PubMed1987

Ultramicro-ELISA for calmodulin and anticalmodulin.

A non-competitive ELISA-technique for the determination of anticalmodulin as well as a sensitive competitive ELISA for calmodulin in 10 microliters samples has been developed. The assay for calmodulin has an inter-assay and intra-assay variability of 18% and 17%, respectively; the limit of detection is 20 pg per assay. The corresponding values for the assay of anticalmodulin are less than 6%, less than 6% and 35 pg, respectively. The methods for the purification of calmodulin and the production of anticalmodulin are also described.

Animals↗
PubMed1986

Turnover of phosphomonoester groups and compartmentation of polyphosphoinositides in human erythrocytes.

The turnover of phosphomonoester groups of phosphatidylinositol 4-phosphate (PtdIns4P) and phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2] was investigated in human erythrocytes by short-term labelling with [32P]Pi. The procedure applied ensured a quantitative extraction of erythrocyte polyphosphoinositides as well as their reliable separation for the determinations of pool sizes and specific radioactivities. The pool sizes of phosphatidylinositol (PtdIns), PtdIns4P and PtdIns(4,5)P2 are 25, 11 and 44 nmol/ml of cells respectively. Under steady-state conditions, the phosphorylation fluxes from [gamma-32P]ATP into PtdIns4P and PtdIns(4,5)P2 are in the ranges 14-22 and 46-94 nmol X h-1 X ml of cells-1 respectively. Only 25-60% of total PtdIns4P and 6-10% of total PtdIns(4,5)P2 take part in the rapid tracer exchange, i.e. are compartmentalized. In isolated erythrocyte ghosts, the turnover of PtdIns4P approximately corresponds to that in intact erythrocytes, although any compartmentation can be excluded in this preparation. Under the conditions of incubation employed, the turnover of PtdIns(4,5)P2 is more than one order of magnitude smaller in isolated ghosts than that obtained for intact erythrocytes.

Adenosine Triphosphate↗
PubMed1986

Hepatic elimination kinetics of organic anions in rats: developmental aspects and influence of phenobarbital.

Maturation and phenobarbital inducibility of hepatic uptake of the organic anions indocyanine green (ICG) and eosine were studied in rats of different ages. Bile duct ligation reduced the ICG and eosine liver concentration in young rats. Therefore, bile duct ligation cannot be recommended for uptake investigations in rats of different ages. The longest elimination half life time (12.4 min) was found in 10-day-old rats within the first 15 min after i.v. administration of 38 mumol ICG/kg. In 20-day-old rats the ICG half life was significantly shorter than in adult 110-day-old rats (5.8 versus 9.6 min). Phenobarbital pretreatment did not alter the ICG elimination half lives in 10-, 20- and 110-day-old rats. The shortest elimination half life time of eosine was found in 60-day-old rats (33.0 min versus 80.3 min in 10-day-old rats and 62.4 min in 240-day-old ones). Phenobarbital pretreatment did not influence eosine serum concentrations. Our results indicate for ICG that uptake comes to maturity earlier than biliary excretion. Differences between ICG and eosine in maturation of the two transport steps support the assumption of more than one carrier for exogenous organic anions. Dye uptake was not altered after phenobarbital and, consequently, cannot be responsible for enhanced biliary dye excretion in differently aged rats.

Aging↗
PubMed1986

Two-stage median-based methods for characterizing enzyme inhibition.

Non-parametric linear regression is used for inhibition diagnostics and parameter estimation based on the velocity equation v = sKsV/(1 + sKS + iKI + isKIS) = sV(i)/(K(i) + s) = W(s)/(L(s) + i). From velocities measured as a function of inhibitor level i at different constant substrate levels s, median-based estimates of 1/W(s) and L(s)/W(s) are derived. Different diagnostic secondary plots are introduced, which take special shapes at limiting inhibition types. Two-stage median-based methods are presented for fitting the four-parameter equation to the observed velocities. These methods cause only little computational effort in contrast to one-stage median-based estimation which requires medians to be taken of solutions of impracticably large numbers of linear equation systems. Performance of the new methods is compared with that of the least-squares fit by application to simulated velocity data. For velocity data containing outliers, the median-based estimates are superior to the least-squares ones, whereas for normally distributed data the reverse is true.

Enzyme Inhibitors↗
PubMed1980

Effect of magnesium-dependent cell membrane alterations on the transport of K+ in Ehrlich ascites tumour cells.

Mg-deficiency or Mg-loading of tumour cells changes the permeability of the cell membrane. The influence of this change on the K+ transport across the membrane was investigated using 86Rb+ and K+ analog. The time course of the influx and efflux rates were estimated by means of a mathematical approach for a two-compartment system with inconstant pool sizes. The comparison of the two states of the cells demonstrates that in Mg-deficient cells the passive K+ efflux is significantly enhanced (40%). This in turn stimulates the active counter transport mediated by the (Na+-K+)-ATPase, raising the ATP consumption by about 30%. However, the enzyme is not able to maintain the cellular K+ content under these conditions. After a short transient increase due to the initially enhanced influx the passive net efflux prevails. Differences in the electrophoretic mobility of the two states of the cells confirm Mg-dependent changes of the cell membrane structure.

Animals↗
PubMed1980

[Calcium oxalate activity products and discriminant analysis of urinary parameters as basis for a calcium oxalate screening program (author's transl)].

The values of 7 urinary parameters in divided urine collections were measured in 20 patients with calcium oxalate stones and ten normal persons. On this basis the thermodynamic stone formation risk was calculated for the different urine collections. Stone formation risk in the 0-6 a.m. urine fractions appeared to be the most important. The risk of stone formation is significantly increased in the time from midnight to 6 a.m. To detect the risk situation the determination of oxalic acid, calcium, potassium and inorganic sulfate in night urine is adequate.

Calcium↗
PubMed1980

Improvements of the chamber analysis.

Improvements of the chamber analysis directed to increase the sensitivity by introduction of fluorescence assays, to facilitate the handling of the procedure and to increase the accuracy by introduction of automatic data processing and partially automatized volume dispensing for 50 microliter volumes simultaneously are described. The method is used for measuring of enzyme activities and substrate concentrations in 2--30 microliter sample volumes with final assay volumes lower than 100 microliter. Two variants of the procedure are presented. With variant I all steps of the analysis including start of the reaction by mixing, incubation and measuring are carried out in the measuring chamber. With variant II the measuring chamber is used for the measuring process only, the other steps are performed outside in special chambers. Application examples from biochemical and clinical chemical analysis are demonstrated.

Acetylglucosaminidase↗
PubMed1979

The effect of changes in cardiac frequency on left and right ventricular dP/dt max at different contractile states of the myocardium.

In 17 canine heart-lung preparations the dependence of frequency potentiation of the right and left ventricular myocardium on the basic inotropic state of the heart was investigated. The effect of unipolar stimulation of the right atrium on dP/dt max in both ventricles was measured. The aortic pressure was maintained constant. Shortly after isolation of the heart, a stepwise increase of rate from 140 to 200 beats/min only had a very weak influence on left ventricular dP/dt max. With deterioration of the myocardium the frequency potentiation of dP/dt max increased considerably. End-diastolic pressure regularly decreased with rising cardiac frequency. Since the real positive inotropic effect is masked by the concomitant fall in diastolic loading, the end-diastolic pressure was maintained constant in a second group of 8 hearts during rate variation. The most pronounced inotropic effect was now found shortly after isolation of the heart. A rate increase of 30 beats/min resulted in a 20% rise of dP/dt max. The frequency potentiation decreased with deterioration of the heart resulting in a 12% dP/dt max increase at an estimated inotropic state of 50% of control. When the contractile state of the heart was improved above the control state by calcium application the frequency potentiation of the myocardium decreased. In the right ventricle similar results were obtained except for the fact that no significant correlation between the steepness of the frequency characteristics and the contractile state of the heart could be found when the end-diastolic pressure was kept constant.

Animals↗
PubMed1979

Direct effects of dopamine, orciprenaline and norepinephrine on the right and left ventricle of isolated canine hearts.

In 31 canine heart-lung preparations the direct cardiac effects of dopamine were compared to those of norepinephrine and orciprenaline. All three agents increased heart rate by 50-60% to a maximum of 240-250 beats/min. The inotropic effects of the three drugs were not significantly different. Even with the highest doses cardiac arrhythmias were rarely observed. To achieve maximal chronotropic and inotropic effects, dopamine required four times higher doses than norepinephrine and orciprenaline. All three drugs increased right ventricular dP/dt max by about twice as much as left ventricular dP/dt max. Peak systolic pressure (P max) in the right ventricle was increased 4-5 times more than P max in the left ventricle while mean aortic pressure was elevated by 12-16 mm Hg and mean pulmonary pressure by 6-14 mm Hg. The positive inotropic effect of all three sympathomimetics and of CaCl2 was substantially more pronounced on the right than on the left ventricle.

Animals↗
PubMed1979

Concentration-dependent mutation by alkylating agents in human lymphoblasts and Salmonella typhimurium: N-methyl-N-nitrosourethane and beta-propiolactone.

The toxic and mutagenic effects of the alkylating agents N-methyl-N-nitrosourethane (MNUT) and beta-propiolactone (BPL) were quantitatively measured in human lymphoblasts and Salmonella typhimurium. Forward mutation to 6-thioguanine resistance was measured in the human lymphoblasts, and forward mutation to 8-azaguanine resistance was measured in the bacterial cells after equigenerational (1.5 doubling times) exposures. In both systems, the induced mutant fraction rose linearly as a function of concentration for BPL and was biphasic for MNUT. The responses of the two assay systems to eight alkylating agents were compared. The exposure of the cells to each alkylating agent was calculated as exposure concentration multiplied by the time of exposure, and allowance was made for the decomposition of the alkylating agents during exposure (integral exposure). Human cells were 2.5--13 times more sensitive than was S. typhimurium to the alkylating agents methyl methanesulfonate, ethyl methanesulfonate, propyl methanesulfonate, N-methyl-N'-nitro-N-nitrosoguanidine, methylnitrosourea, and MNUT. S. typhimurium cells were three times more sensitive to butyl methanesulfonate and 25 times more sensitive to BPL than were human cells.

Alkylating Agents↗
PubMed1978

Phenotypic lag and mutation to 6-thioguanine resistance in diploid human lymphoblasts.

Mutants of a diploid human lymphoblast line resistant to 6-thioguanine (6TG) appear 6--16 generations after treatment with any of a diverse group of mutagents: methylnitrosourea (MNU), methylnitrosoguanidine (MNNG), ICR-191, 5-bromodeoxyuridine (BUdR). A hypothesis is advanced that expression of the 6-thioguanine-resistant state may require the removal of essentially all pre-existing hypoxanthine--guanine phosphoribosyl transferase (HGPRT) molecules via division, dilution, and protein turnover. Design of protocols for quantitative mutation assays requires attention to this phenomenon.

Bromodeoxyuridine↗