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At least 343 records · Page 19Linked to original sources
PubMed1986

Altered spectrum of nitroglycerin action in long-term treatment: nitroglycerin-specific venous tolerance with maintenance of arterial vasodepressor potency.

The study of venodilator tolerance to nitroglycerin has been complicated by reflex compensation and by problems in analyzing venous tone in the presence of multiple determinants of venous pressure. We assessed venous tone as total effective vascular compliance (TEVC) under autonomic blockade in six dogs, in the nontolerant state, and during a 5 day infusion of nitroglycerin (1.5 micrograms/kg/min). Under long-term treatment, baseline TEVC was unaffected and the nitroglycerin dose-response relationship for TEVC was shifted to greater than 10-fold higher doses, whereas baseline mean arterial pressure (MAP) was lowered by 17 +/- 3 mm Hg without any shift in nitroglycerin responsiveness. This lowering of MAP was observed only after autonomic blockade. In six additional dogs instrumented with aortic flow probes, nitroglycerin (1.5 micrograms/kg/min) induced a 15 +/- 1% decline in peripheral vascular resistance (PVR) under autonomic blockade, but with reflexes intact these dogs showed no change in PVR and a 21 +/- 10% increase in norepinephrine release rate. We conclude that modest long-term exposure to nitroglycerin results in tolerance to its venodilating effects, whereas arteriolar action is maintained. This tolerance-induced shift in action from venous toward arteriolar dilation is normally masked by compensatory reflexes.

Animals↗
PubMed1983

Hypothalamic and pituitary sites of action of oxytocin to alter prolactin secretion in the rat.

To determine whether oxytocin (OT) could alter the release of PRL and other hormones from the anterior pituitary gland, the effects of OT were examined in two in vitro and two in vivo test systems. Cells dispersed from anterior pituitary glands of intact adult male rats were incubated in medium containing OT at doses of 10(-8), 10(-7), 10(-6), and 10(-5) M in two trials. OT stimulated PRL release 1.5-fold (P less than 0.01) and 2- to 3-fold (P less than 0.001) above control levels at 10(-8) and 10(-7) M doses, respectively, thus indicating a dose-dependent relationship. Higher doses did not produce a further elevation above that obtained with 10(-7) M OT. Arginine vasopressin (AVP) caused a slight decrease in PRL release from dispersed cells while TRH produced a small (25%), significant, but nondose-related increase in PRL release. Hemipituitary glands from adult male rats, incubated with 10(-6) and 10(-5) M OT, released twice as much PRL (P less than 0.01) into the medium as paired controls, but 10(-7) M OT was ineffective. The iv injection of 1 or 10 micrograms OT into conscious male rats elevated plasma PRL by 50% (P less than 0.05) or 500% (P less than 0.001), respectively, above basal values at 5 min only. Vehicle or 0.1 microgram OT were without effect. When 0.1 microgram OT was microinjected into the third ventricle (3V) of conscious male rats, it paradoxically reduced plasma PRL by 40% at 30 min (P less than 0.05), whereas 1 microgram OT significantly lowered PRL at 5-60 min, with the maximum suppression (60%, P less than 0.001) occurring at 30 min. These latter findings may indicate that an ultrashort loop feedback mechanism exists whereby exogenous OT decreases hypothalamic OT secretion, thereby reducing the OT stimulus for PRL release. The specificity of the OT effect on PRL was attested to by the failure of OT to alter significantly FSH, LH, and TSH in each system. GH was unchanged except that 3V-injected OT (1 microgram only) elevated (P less than 0.001) plasma GH at 15-30 min. These results support the view that OT acts directly on the cells of the anterior pituitary gland at low to high doses to release PRL specifically and in a dose-related fashion. In contrast, 3V injection of OT reduces PRL secretion, thereby suggesting that OT may decrease its own neurosecretion by ultrashort loop feedback and thus reduce an OT stimulus for PRL release.

Animals↗
PubMed2003

Mechanisms of the age-associated deterioration in glucose tolerance: contribution of alterations in insulin secretion, action, and clearance.

Glucose tolerance decreases with age. For determining the cause of this decrease, 67 elderly and 21 young (70.1 +/- 0.7 vs. 23.7 +/- 0.8 years) participants ingested a mixed meal and received an intravenous injection of glucose. Fasting glucose and the glycemic response above basal were higher in the elderly than in the young participants after either meal ingestion (P < 0.001) or glucose injection (P < 0.01). Insulin action (Si), measured with the meal and intravenous glucose tolerance test models, was highly correlated (r = 0.72; P < 0.001) and lower (P <or= 0.002) in the elderly than in the young participants. However, when adjusted for differences in percentage body fat and visceral fat, Si no longer differed between groups. When considered in light of the degree of insulin resistance, all indexes of insulin secretion were lower (P < 0.01) in the elderly participants, indicating impaired beta-cell function. Hepatic insulin clearance was increased (P < 0.002), whereas total insulin clearance was decreased (P < 0.002) in the elderly subjects. Multivariate analysis (r = 0.70; P < 0.001) indicated that indexes of insulin action (Si) and secretion (Phi(total)) but not age, peak oxygen uptake, fasting glucose, degree of fatness, or hepatic insulin clearance predicted the postprandial glycemic response. We conclude that the deterioration in glucose tolerance that occurs in healthy elderly subjects is due to a decrease in both insulin secretion and action with the severity of the defect in insulin action being explained by the degree of fatness rather than age per se.

Adult↗
PubMedDate not supplied

Effect of argon laser stapedotomy on cochlear potentials. II. Alteration of the compound action potential (CAP).

The influence of the argon laser on inner-ear function during and after laser stapedotomy was investigated in guinea pigs, using the compound action potential (CAP) as parameter. With the onset of the argon laser impact, the CAP is depressed or even extinguished up to 10 s. The temporal course of subsequent CAP recovery is similar to that of endocochlear temperature recovery after laser stapedotomy, so that a direct influence of temperature increase and CAP decrease is probable. No permanent attenuation of CAP amplitude was found after a single laser perforation of the stapes footplate.

Action Potentials↗
PubMed1988

[Possible mechanism of the alteration in the therapeutic action of cyclophosphane in mice with hemocytoblastosis La against a background of artificial hyperglycemia].

The concentration of reactive cyclophosphamide metabolites (CP) and the time of their circulation in blood plasma of mice increase during artificial hyperglycemia (HG). Intensification of the antitumor CP activity against a background of HG in C57Bl/6 mice with hemocytoblastosis La may be a result of changes in the drug pharmacokinetics. An inhibitory action of HG on the CP-metabolizing system of the liver monooxygenases is shown.

Animals↗
PubMed1987

Altered glucocorticoid binding and action in response to epidermal growth factor in HBL100 cells.

Incubation of adherent human breast epithelial HBL100 cells with epidermal growth factor (EGF) decreased [3H]dexamethasone binding by 35% with no effect on affinity. Maximal inhibition was obtained at 3 nM EGF and the 50% effective dose was 0.2 nM EGF. Decreased dexamethasone binding induced by 3 nM EGF was maximal by 5 min of treatment and, in the continuous presence of EGF, persisted at a constant level over 4 days. The action of EGF was antagonized by 12-O-tetradecanoylphorbol-13-acetate, which did not inhibit dexamethasone binding significantly, and by concanavalin A. In homogenates of EGF-treated cells, decreased dexamethasone binding was observed only in the cytosolic fraction. Saturation dexamethasone binding inhibited the growth rate of HBL100 cells by approximately 50%, but concurrent treatment with EGF overcame this inhibition. The effect of EGF on dexamethasone-inhibited cell growth also was antagonized by 12-O-tetradecanoylphorbol-13-acetate.

Breast↗
PubMed1995

Structural alterations induced by photodynamic action of hematoporphyrin derivative (HpD) in plasma membrane of glioblastoma (U-87MG) cells: time dependent fluorescence spectroscopic study.

Photodynamic action of hematoporphyrin derivative (HpD) on the plasma membrane of human glioblastoma U-87MG cells was investigated using lipid and protein specific fluorescent probes trimethylammonium-1,6-diphenyl 1,3,5-hexatriene (TMA-DPH) and N-(1-pyrene)-maleimide (PM) respectively. Steady state anisotropy, decay time and time dependent anisotropy of these probes in U-87MG cells were measured. Light irradiation caused an increase in the steady state anisotropy of TMA-DPH in cells treated with HpD; however, no change in decay time was observed. Time dependent anisotropy measurements were performed and the data were analyzed using wobbling in cone model. A decrease in the rotational relaxation time (phi) as well as the cone angle (theta(c)) and an increase in the order parameter (S) of TMA-DPH were observed on photosensitization of cells. A decrease in the order parameter (S) of TMA-DPH were observed on photosensitization of cells. A decrease in the steady rate anisotropy and the rotational relaxation time (phi) of PM and enhancement in the lipid peroxidation were also observed. Our results show that the photodynamic action of HpD increases the order in the lipid bilayer and the mobility of the proteins in the plasma membrane of cells.

Antineoplastic Agents↗
PubMed1998

Verapamil and TTX inhibit +Vmax but differentially alter the duration of action potential of adult chicken ventricular myocardium.

Verapamil, a Ca2+ channel blocker, is also reported to block Na+ channels in mammalian heart and to modulate the repolarisation phase of cardiac action potential (AP). The Na+ channel blocking activity of verapamil and its implication to changes in repolarisation were studied on chicken ventricular strips where upstroke is due to highly TTX sensitive Na+ channels. At low doses verapamil (0.5-5 micro M) and TTX (0.1-0.5 nM) did not cause any significant effect on resting membrane potential (Em), maximal upstroke velocity (+Vmax) or AP duration (ADP). Higher concentrations of both verapamil (10-320 micro M) and TTX (1-40 nM) caused dose-dependent decrease in +Vmax and overshoot (Eov) without any change in Em. EC50 for the inhibitory effect of verapamil and TTX on +Vmax was 140 microM and 14 nM respectively. Na+ channels in adult chicken ventricular myocardium, therefore, seem to be more sensitive to TTX than their mammalian counterpart. Higher dosage of verapamil are needed to block Na+ channels in adult avian heart as reported for mammalian myocardium. Both verapamil and TTX caused dose-dependent changes in APD at-20 mV (ADP20) and at 90% repolarisation (APD90). TTX (1-40 nM) produced a decrease of 5-13% in APD20 and 4-12% in APD90 indicating a uniform hastening of the repolarisation process. Verapamil (10-320 micro M), however, induced 6-38% decrease in APD20 but 5-12% increase in APD90. Regression analysis of the relationship between changes in +Vmax and APD20 and APD90 in presence of TTX and verapamil exhibit significant linear correlation r for APD20 and APD90, being +0.965 for TTX and +0.978 and-0.898 for verapamil respectively. A linear correlation between inhibition of +Vmax and reduction in APD for TTX indicates the possibility that Na+ channel linked mechanism(s) underlie repolarisation process. Verapamil induced decrease in APD20 and increase in APD90 could be explained by the block of Na+/Ca2+ and K+ channels respectively.

Action Potentials↗
PubMed1978

Potassium efflux in heart muscle during activity: extracellular accumulation and its implications.

1. Extracellular K+ activity and transmembrane potential were simultaneously monitored with a K+-selective micro-electrode placed in the extracellular space and a standard KCl-filled micro-electrode in the intracellular space of the frog ventricular muscle. 2. K+ was found to accumulate during activity and had the approximate magnitude and time course to account for the measured membrane depolarization. 3. The magnitude of the K+ accumulation depended on the frequency of stimulation, diameter of the muscle and temperature of the bathing solution. 4. The time constants of accumulation and decay were dependent only on the diameter and the temperature of the strip. A Q10 of 2 was measured for the decay of accumulated K+. 5. Double barrelled K+-electrodes were used to monitor the change in K+ activity accompanying a single action potential, since the reference barrel allowed for rapid compensation of the electrical potential fluctuations encountered in the subendothelial space. 6. K+ accumulated continuously during the plateau to a level which increased external K concentration by about 1 mM. This increase in the subendothelial space corresponds to about 1-3 muA/cm2 or 10-30 pmole/cm2-sec-1 of net K+ efflux. These values are at least an order of magnitude larger than required to discharge the membrane capacitance. 7. There is no direct relation between action potential duration and rate of development or magnitude of K+ accumulation during that action potential. 8. Increase in the external K concentration, while shortening the action potential and depolarizing the membrane, does not lead to an increased rate of accumulation of K+. The presence of Ni2+, on the other hand, prolongs the action potential and decreases the rate of K+ accumulation. 9. The results suggest that there is a substantial and continuous efflux of K+ during the action potential, which sums during rapid beating, resulting in membrane depolarization and alteration of action potential duration. The change in action potential duration in response to rate may be caused by alteration of EK in the local micro-environments.

Action Potentials↗
PubMed1999

Asymmetry of hindlimb muscle activity and cutaneous reflexes after tendon transfers in kittens.

The mechanical actions of various ankle muscles were changed by surgically crossing or transferring the tendons in kittens. After the kittens grew to adults, both hindlimbs were implanted with multiple electromyogram (EMG) recording and cutaneous nerve stimulation electrodes to compare the activity of altered and normal muscles. The tendon transfers showed a remarkable tendency to regrow toward normal or only slightly altered mechanical action. In these animals and in the sham-operation controls, the patterns of muscle activity and reflexes were symmetrical in corresponding muscles of the two legs, although they could differ substantially between animals, particularly for the cutaneous reflexes. Eleven animals had at least some persistent alterations in muscle action. Their cutaneous reflex patterns tended to be asymmetric, in some cases quite markedly. EMG activity during unperturbed locomotion and paw-shaking was more symmetrical, but there were some changes in altered muscles and their synergists. The central pattern generators for locomotion and paw-shaking and particularly for cutaneous reflexes during locomotion appear to be at least partially malleable rather than entirely hardwired. This may provide a tool for studying their development and spinal plasticity in general.

Animals↗
PubMed1993

Mechanisms of action for an androgen-mediated autoregulatory process in rat thecal-interstitial cells.

In rat thecal-interstitial cells (TIC), treatment with the synthetic androgen mibolerone has led to the documentation of an autoregulatory process for androgen production. In the present study, accumulated evidence has provided insight into the mechanisms of mibolerone action that control this process. Investigations using the nonsteroidal antiandrogen hydroxyflutamide were conducted to characterize mibolerone's mode of action. Hydroxyflutamide had differential effects on hCG action, the 1-microM dose stimulating hCG-induced androsterone synthesis by 27% and the 10-microM concentration decreasing the androgen levels by 84%. In addition, treatment with 1 microM hydroxyflutamide was effective in partially reversing the inhibitory action of mibolerone on hCG-stimulated androsterone production. Thus, the data indicated that mibolerone's mode of action may be mediated, at least in part, via the androgen receptor. The possibility that mibolerone had multiple sites of action prompted studies on the effectiveness of this androgen to alter various signaling pathways. Treatment with increasing concentrations (0.01-100 nM) of the phorbol ester 12-0-tetradecanoylphorbol 13-acetate (TPA), which activates protein kinase C, resulted in a 75% decrease in hCG-stimulated androgen production at a dose of 100 nM TPA. Treatment with mibolerone (100 nM) was unable to alter the action of TPA on androgen synthesis when doses of 1 and 10 nM TPA were employed. It was also found that Ca2+ can serve as a mediator of mibolerone action. Treatment with a 0.01-microM dose of A23187, a Ca2+ ionophore known to increase intracellular Ca2+, was ineffective in altering hCG-stimulated androsterone synthesis. The concurrent treatment of mibolerone (100 nM) and A23187 (0.01 microM) resulted in the potentiation of mibolerone's inhibitory effects on hCG-stimulated androgen production, thereby suggesting that mibolerone can stimulate Ca2+ influx. Additional studies revealed that the administration of a 1-microM dose of the L-type Ca2+ channel blocker verapamil to TIC cultures was able to partially block the inhibitory effect of mibolerone on androgen synthesis. Evidence for an additional site of mibolerone action was revealed through an analysis of the mRNA levels of P450scc and P450(17) alpha enzymes. Although hCG and insulin-like growth factor I treatment resulted in 20- and 32-fold increases in the amount of P450scc and P450(17) alpha mRNA, respectively, the addition of mibolerone (100 nM) reduced only P450(17) alpha mRNA levels by 91%. Overall, the evidence indicates that mibolerone has multiple sites of action in exerting its regulatory effect on androgen synthesis.

Androgens↗
PubMed2026

The potential clinical benefit of routine comprehensive genomic profiling in non-small cell lung cancer for the detection of prognostic co-mutations - A multicenter next generation sequencing study.

INTRODUCTION: Non-driver mutations such as TP53, STK11 and KEAP1 are clinically relevant in determining immunotherapy efficacy in patients with non-small cell lung cancer (NSCLC). The aim of this study is to determine the prevalence and clinical relevance of variations in TP53, STK11 and KEAP1 in patients in the analysis of NSCLC, using targeted next-generation sequencing. METHODS: This real-life prospective multicenter cohort study from July 2022 until October 2023 utilized samples of patients in the analysis of NSCLC. The samples were subjected to a targeted DNA NGS panel and, if indicated, RNA sequencing. The outcome of the molecular diagnostics was retrieved, including driver alterations and more in-depth analysis of TP53, STK11 and KEAP1. RESULTS: In 134 of the 437 samples an actionable genomic alteration (AGA) was detected. Of the remaining samples, 213 carried a mutation in either TP53, STK11 and/or KEAP1, while 90 harbored either variants of unknown significance (VUS) (16) or no variant (74). In-depth analysis showed 77 alterations of STK11, with 56 pathogenic and 21 VUS. Most STK11 variants were identified in exon 1, which is hypothesized to be correlated to an oncogenic isoform. Moreover, variants in KEAP1 were mostly VUS, with 48 VUS and 24 mutations. Lastly, 264 TP53 alterations, of which 249 pathogenic and 15 VUS, occurred, with an even spread in the DNA-binding domain. CONCLUSION: This study demonstrated the broad spectrum of variants in STK11, KEAP1 and TP53 in routine panel-based DNA NGS, with 70.3% of the samples without AGA showing a potential clinically relevant mutation in TP53, STK11 and/or KEAP1.

Humans↗
PubMed1992

Electrophysiological effects of CRE-1087 in guinea-pig ventricular muscles.

1. The electrophysiological effects of CRE-1087, a new antiarrhythmic drug, were studied in guinea-pig papillary muscles. 2. CRE-1087 (10(-7) M-10(-4) M) produced a concentration-dependent decrease in the action potential amplitude and Vmax of the upstroke without altering the action potential duration or the resting membrane potential. 3. At 5 x 10(-6) M, CRE-1087 produced a 5.0 +/- 1.0% tonic Vmax block and this value was not modified at the different rates of stimulation tested. In the presence of CRE-1087, trains of stimuli at rates between 0.5 and 3 Hz led to an exponential decline in Vmax (frequency-dependent Vmax block) which augmented at higher rates of stimulation. At 2 Hz the onset kinetics of the frequency-dependent Vmax block was fitted by a monoexponential function being the K value 0.099 +/- 0.012 AP-1. The time constant for the recovery of Vmax from the frequency-dependent block was prolonged to 18.3 +/- 1.5 s. 4. CRE-1087 (5 x 10(-6) M) did not shift the membrane responsiveness curve. 5. CRE-1087 had no effect on the characteristics of the slow action potentials elicited by isoprenaline in ventricular fibres depolarized by 27 mM KCl, which suggested that CRE-1087 did not exhibit class IV (Ca antagonist) antiarrhythmic actions. 6. The slow onset and the slow offset kinetics of frequency-dependent Vmax block during repetitive activity suggested that in guinea-pig ventricular muscle fibres CRE-1087 exhibited class Ic antiarrhythmic actions.

Action Potentials↗
PubMed1987

The effect of ethanol and temperature on calcium-dependent sensory neuron action potentials.

The ability of ethanol to decrease the duration of sensory neuron action potentials was evaluated at different temperatures. Intracellular stimulation and recordings were made as the drug was perfused onto dorsal root ganglion neurons in vitro. The cells were bathed in a medium which caused the evoked action potentials to have long durations which were calcium dependent. Ethanol decreased the duration of the action potentials in a dose-dependent manner, without altering amplitude, rate of rise, or resting potential. Furthermore, the potency of the drug varied directly with the temperature of the bathing medium. The recovery time for the reversal of ethanol's effect was also found to be temperature dependent. However, moderate temperature changes alone did not significantly alter the action potential waveform. These data are compatible with a boundary lipid or direct effect on the calcium channel for the mechanism of ethanol's action.

Action Potentials↗
PubMed1996

[Pharmacodynamic changes in the elderly subject].

Age-related physiological changes alter drug responsiveness in the elderly. The changes of pharmacokinetics are widely known but they do not explain completely the altered drug action in the elderly. In this work the authors deal with the alterations of pharmacodynamics which could be responsible for the different pharmacological action and the high frequency of side effects which can be found in old age.

Aged↗