Friction properties of in vivo human skin from visualized friction testing.

Investigations on mechanical behaviors of intravital human skin are of significance in various fields. However, due to the great complexity and the individual variation of human skin, traditional experimental mechanics often fails to work in such research objects. In this study, the friction property considering the skin-uplift effect of human skin was in vivo studied experimentally and theoretically. An in situ and noninvasive friction experiment was performed in vivo on human skin, where the projected contact morphology was captured through a novel specially developed optical system. According to the contact morphology, a model taking uplift resistance into account is proposed based on Greenwood model, in which the contact area was depicted as a combination of two ellipses to better characterize the skin deformation. Moreover, since the model degrades into Greenwood model in small deformation, it can be considered as an extension from the perspective of small deformation to large deformation. Based on the model, the adhesion friction and deformation friction have been separated according to the ratio of indentation depth to probe radius. The results show that the friction property of skin varies with the indentation depth changing, and the deformation friction is positively correlated with the ratio of indentation depth to probe radius.

In vivo adhesive behavior of human facial skin by a modified indentation test.

A better understanding of the adhesive behavior of human facial skin is important for dermatological or cosmetic applications. For their in vivo experimental characterization and analysis, the indentation test is an effective and widely used method. In this study, our independently developed transparent indenter and curved surface optical imaging technique are improved, by which the contact area of facial skin can be in vivo and in situ obtained during an indentation test. Thanks to the modified indentation technique, the real contact radii of human facial skin under different conditions (normal, as-moistened, moistened after 30 min) are obtained, and their adhesive behavior is studied. Moreover, we modify the classical elastic adhesion theory (JKR theory) based on the Neo-hookean model considering the fact that the hyperelastic model is usually more appropriate for skin research. It is evidenced that the adhesion properties highly influence the contact area as well as the adhesive force/energy, and our modified hyperelastic adhesion theoretical model shows a better agreement with the experimental values of contact radius under each condition.

[Clinical study of intensity modulated radiotherapy and three-dimensional conformal radiotherapy with three-dimensional brachytherapy and concurrent chemotherapy for patients with advanced cervical cancer].

Objective: To compare the dose, clinical efficacy and acute adverse reactions of intensity modulated radiotherapy (IMRT) and three-dimensional conformal radiotherapy (3D-CRT) combined with three-dimensional brachytherapy (3D-BT) in the treatment of concurrent radiotherapy and chemotherapy for advanced stage cervical cancer patients. Methods: Data collection was performed from January 2011 to November 2015 in Chinese PLA General Hospital and Inner Mongolia Cancer Hospital. All 89 patients with advanced stage (Ⅱ b-Ⅲ b) cervical cancer were treated by pelvic radiotherapy and concurrent chemotherapy, 46 cases of them received IMRT and 3D-BT (IMRT group) , 43 cases received 3D-CRT and 3D-BT (3D-CRT group) , along with cisplatin chemotherapy. The dose accumulation of external beam radiotherapy and 3D-BT was calculated by deformable image registration to analyze clinical efficacy, acute adverse reactions and prognosis of the two groups. Results: (1) Dose of radiotherapy: planning target volume (PTV) coverage of IMRT group and 3D-CRT group were respectively (95.4±4.7)% and (95.1±5.1)%, without significant differences (t=0.289, P=0.773). Compared with the patients treated with 3D-CRT, the volumn receiving at least 30 Gy (V(30)), V(50) of rectum, colon, bladder and small intestine and V(20) of bone marrow in the IMRT group were significantly decreased (P<0.05). Regarding the combined dose, the maximum dose (D(max)) and the minimum dose received by the most exposed 2 cm(3) volume of the analyzed organ (D(2CC)) of rectum, colon, bladder and small intestine of IMRT group were significantly lower than those of 3D-CRT group (P<0.05). (2) Short-term efficacy: the effective rate of IMRT and 3D-CRT group were respectively 93% (43/46) and 91% (39/43), with no significant differences (χ(2)=0.237, P=0.626). (3) Acute adverse reactions: compared with 3D-CRT, IMRT could significantly reduce grade 1-2 acute toxicity in gastrointestinal [63%(29/46) vs 84%(36/43)], genitourinary [17%(8/46) vs 37%(16/43)] and hematologic [57%(26/46) vs 79%(34/43)] system (all P<0.05). There were no significant differences of grade 3 acute adverse reactions of gastrointestinal, genitourinary and hematologic system between two groups (all P>0.05). No grade 4 acute adverse reactions were observed. (4) Prognosis: the overall survival rate at 1, 2-year of IMRT and 3D-CRT group were respectively 95.6%, 89.1% and 93.1%, 86.1%. The progression-free survival rateat 1, 2-year of IMRT and 3D-CRT group were 91.1%, 89.1% and 88.4%, 86.1%, respectively. There were no significant differences in overall survival rate and progression-free survival rate between two groups (P>0.05). Conclusions: Compared with 3D-CRT, IMRT combined with 3D-BT has dosimetry advantages based on dose accumulation algorithms by deformable image registration. IMRT could ensure clinical efficacy and significantly reduce the incidence rate of acute toxicities.

[Clinical application of robotic plat form in the treatment of early ovarian cancer].

Objectives: To evaluate the feasibility and safety of robotic system in early ovarian cancer surgery. Methods: The clinical data of 131 patients with early ovarian cancer undergoing surgical treatment from November 2014 to November 2015 were reviewed retrospectively. There were 27 cases of early ovarian cancer, of which 9 cases of robotic group, 10 cases of laparoscopic group, 8 cases of laparotomy group. Age, Body Mass Index (BMI), preoperative neoadjuvant chemotherapy, operating time, operating method, intraoperative blood loss, intraoperative and postoperative complications, pathological type, lymph node dissection, postoperative exhaust time and postoperative hospital stay of all the patients were analyzed. Results: In the robot group, the mean operating time was( 251.4±58.7) minutes, the intraoperative blood loss was (208.9±202.7) ml, and the number of the main abdominal and pelvic lymph nodes was 27.8±8.9. The mean postoperative hospital stay was (11.1±3.5) days, and the mean postoperative hospital stay was( 2.0±0.5) days. All the patients were followed up for 12-24 months. There was no differences were observed among the three groups for operating time, complications, the blood loss, the number of lymph nodes, the hospital stay and survival time (P≥0.05). Conclusion: A robotic approach for the early ovarian cancer is feasible and effective. Compared with traditional laparoscopic surgery and laparotomy, there is no significant difference in operative effect and tumor-free survival. The robotic approach provides a new method for surgical treatment of early ovarian cancer.

Effect of weaning age on cortisol release in piglets.

The effect of weaning age on the adrenal cortex, which plays a vital role in the stress response, is currently unknown. Therefore, plasma adrenocorticotropic hormone (ACTH) and cortisol levels, weights and relative weights of adrenal glands, and steroidogenesis-related protein and enzyme expression levels in piglets weaned on different days were determined. Piglets weaned at 35 days had significantly lower ACTH levels than those weaned at 14 or 21 days, and cortisol levels of piglets weaned at 21, 28, and 35 days were significantly lower than those of piglets weaned on day 14. Adrenal gland weights of piglets weaned at 28 and 35 days and relative adrenal gland weights of piglets weaned at 35 days were significantly lower than those of piglets weaned at 14 days. However, no significant difference was detected in the expression of melanocortin-type 2 receptor mRNA, which is associated with weaning age. Steroidogenic acute-regulatory (StAR) mRNA and cholesterol side-chain cleavage cytochrome P450 mRNA expression levels in piglets weaned at 28 and 35 days were significantly lower than in those weaned at 14 or 21 days, and P450 11ß mRNA expression levels in piglets weaned at 28 and 35 days were significantly lower than in those weaned at 14 days. Therefore, early-weaned piglets exhibited increased adrenal gland weights and StAR and steroidogenic enzyme expression, all of which contributed to high cortisol levels. The high plasma ACTH and cortisol levels in early-weaned piglets indicate that these animals would be greatly affected by stress.

p16 expression in patients with cervical cancer and its prognostic significance: meta-analysis of published literature.

OBJECTIVES: p16, a tumour suppressor, is unable to express its suppressive effects following interaction with E7-retinoblastoma protein. Previous reports have suggested that p16 immunostaining allows precise identification of cervical intra-epithelial neoplasia and cervical cancer lesions in biopsies. The prognostic value of p16 expression in cervical cancers has been evaluated for several years, but the results remain controversial. As such, the authors undertook a systematic review and meta-analysis of studies assessing the impact of p16 expression on overall survival and disease-free survival. STUDY DESIGN: Medline, Embase and China National Knowledge Infrastructures were searched to identify studies on the prognostic impact of p16 expression in patients with cervical cancer. In total, 1070 patients from 10 eligible studies were included in the analysis. Pooled risk ratios (RRs) with 95% confidence intervals (95% CI) were calculated. RESULTS: A significant association was found between p16 expression and increased disease-free survival (RR 0.60; 95% CI 0.44-0.82; p=0.001). However, no significant association was found between p16 and overall survival. CONCLUSION: p16 expression may be predictive of a favourable prognosis in patients with cervical cancer. However, large-scale, multicentre and well-matched cohort studies are warranted to confirm this finding.

Statistical measures of DNA sequence dissimilarity under Markov chain models of base composition.

In molecular biology, the issue of quantifying the similarity between two biological sequences is very important. Past research has shown that word-based search tools are computationally efficient and can find some new functional similarities or dissimilarities invisible to other algorithms like FASTA. Recently, under the independent model of base composition, Wu, Burke, and Davison (1997, Biometrics 53, 1431 1439) characterized a family of word-based dissimilarity measures that defined distance between two sequences by simultaneously comparing the frequencies of all subsequences of n adjacent letters (i.e., n-words) in the two sequences. Specifically, they introduced the use of Mahalanobis distance and standardized Euclidean distance into the study of DNA sequence dissimilarity. They showed that both distances had better sensitivity and selectivity than the commonly used Euclidean distance. The purpose of this article is to extend Mahalanobis and standardized Euclidean distances to Markov chain models of base composition. In addition, a new dissimilarity measure based on Kullback-Leibler discrepancy between frequencies of all n-words in the two sequences is introduced. Applications to real data demonstrate that Kullback-Leibler discrepancy gives a better performance than Euclidean distance. Moreover, under a Markov chain model of order kQ for base composition, where kQ is the estimated order based on the query sequence, standardized Euclidean distance performs very well. Under such a model, it performs as well as Mahalanobis distance and better than Kullback-Leibler discrepancy and Euclidean distance. Since standardized Euclidean distance is drastically faster to compute than Mahalanobis distance, in a usual workstation/PC computing environment, the use of standardized Euclidean distance under the Markov chain model of order kQ of base composition is generally recommended. However, if the user is very concerned with computational efficiency, then the use of Kullback-Leibler discrepancy, which can be computed as fast as Euclidean distance, is recommended. This can significantly enhance the current technology in comparing large datasets of DNA sequences.

[Diagnostic tactics in localized fibroadenomatosis of the breast]. / Diagnosticheskaia taktika pri lokalizovannom fibroadenomatoze molochnoi zhelezy.

Results of the examination and treatment of 203 patients with localized fibroadenomatosis of the mammary gland are described. The authors give an estimation of diagnostic algorithms used when detecting the physical signs of the disease. It was shown that the examination of patients with the palpation signs of nodular mastopathy should necessarily include mammography which can eliminate unwarranted risk of hypodiagnosing carcinoma of the mammary gland and determine the group of patients in whom the emergency operation is not necessary.

[How often is breast fibroadenomatosis asymptomatic?]. / Kak chasto fibroadenomatoz molochnykh zhelez imeet bessimptomnoe techenie?

The results of clinico-morphological examinations of 386 women having no complains of discomfort in the mammary glands are presented. Methods of palpation, mammography and morphological investigation have detected fibroadenomatosis without subjective symptoms of the disease in 38%, 67% and 78% of the patients correspondingly. This variant of the disease is called asymptomatic since the woman can not notice it and so it is out of the field of attention of oncologists. High incidence of asymptomatic fibroadenomatosis requires a revision of the current assessment of it as a disease because it does not take into account a variant of the disease when the patient has no complains of painful indurations in the mammary glands.

Function of steroidogenic factor 1 domains in nuclear localization, transactivation, and interaction with transcription factor TFIIB and c-Jun.

Normal endocrine development and function require nuclear hormone receptor SF-1 (steroidogenic factor 1). To understand the molecular mechanism of SF-1 action, we have investigated its domain function by mutagenesis and functional analyses. Our mutant studies show that the putative AF2 (activation function 2) helix located at the C-terminal end is indispensable for gene activation. SF-1 does not have an N-terminal AF1 domain. Instead, it contains a unique FP region, composed of the Ftz-F1 box and the proline cluster, after the zinc finger motif. The FP region interacts with transcription factor IIB (TFIIB) in vitro. This interaction requires residues 178-201 of TFIIB, a domain capable of binding several transcription factors. The FP region also mediates physical interaction with c-Jun, and this interaction greatly enhances SF-1 activity. The putative SF-1 ligand, 25-hydroxycholesterol, has no effects on these bindings. In addition, the Ftz-F1 box contains a bipartite nuclear localization signal (NLS). Removing the basic residues at either end of the key nuclear localization sequence NLS2.2 abolishes the nuclear transport. Expression of mutants containing only the FP region or lacking the AF2 domain blocks wild-type SF-1 activity in cells. By contrast, the mutant having a truncated nuclear localization signal lacks this dominant negative effect. These results delineate the importance of the FP and AF2 regions in nuclear localization, protein-protein interaction, and transcriptional activation.

Inactivation of the monocistronic rca gene in Anabaena variabilis suggests a physiological ribulose bisphosphate carboxylase/oxygenase activase-like function in heterocystous cyanobacteria.

There was no discernible effect after incubating recombinant Anabaena Rubisco and carboxyarabinitol 1-phosphate with the product of the Anabaena rca gene. Since the unactivated cyanobacterial Rubisco is not readily inhibited by ribulose 1,5-bisphosphate and fallover is not observed, a genetic basis for the function of the Rubisco activase-like gene (rca) was sought. The monocistronic rca gene was inactivated in vivo and resulting mutant strains of A. variabilis were found to be incapable of synthesizing immunologically detected RCA protein. The requirement for the product of the rca gene in the light was further examined by measuring Rubisco activity in permeabilized whole cells of wild-type and rca mutant strains at different light intensities. In a 1% CO2-air atmosphere, inactivation of rca reduced the ability of A. variabilis to elevate Rubisco activity under high light (73 micromol quanta m(-2) s(-1)), but had little effect under low light (8 micromol m(-2) s(-1)). For air-grown cultures, differences in the rates exhibited by the wild-type and rca mutant to fully activate Rubisco during a whole-cell assay were enhanced by increases in light intensity. The significance of the rca mutation was underlined by effects on growth as, unlike the wild-type, growth rates did not increase after cells transferred from low to high light intensities. Higher exogenous CO2 concentrations (1%) were required to sustain a normal growth rate for the A. variabilis rca mutant. When grown in air levels of CO2, the rca mutant not only needed longer times to double in cell density but also exhibited greatly diminished Rubisco activity compared with the wild-type strain. Despite the unusual properties of cyanobacterial Rubisco, these results suggest a physiological role for the product of the rca gene in maximizing the activity of Rubisco in heterocystous cyanobacteria.

Identification of heparin-binding EGF-like growth factor as a target in intercellular regulation of epidermal basal cell growth by suprabasal retinoic acid receptors.

The role of retinoic acid receptors (RARs) in intercellular regulation of cell growth was assessed by targeting a dominant-negative RARalpha mutant (dnRARalpha) to differentiated suprabasal cells of mouse epidermis. dnRARalpha lacks transcriptional activation but not DNA-binding and receptor dimerization functions. Analysis of transgenic mice revealed that dnRARalpha dose-dependently impaired induction of basal cell proliferation and epidermal hyperplasia by all-trans RA (tRA). dnRARalpha formed heterodimers with endogenous retinoid X receptor-alpha (RXRalpha) over RA response elements in competition with remaining endogenous RARgamma-RXRalpha heterodimers, and dose-dependently impaired retinoid-dependent gene transcription. To identify genes regulated by retinoid receptors and involved in cell growth control, we analyzed the retinoid effects on expression of the epidermal growth factor (EGF) receptor, EGF, transforming growth factor-alpha, heparin-binding EGF-like growth factor (HB-EGF) and amphiregulin genes. In normal epidermis, tRA rapidly and selectively induced expression of HB-EGF but not the others. This induction occurred exclusively in suprabasal cells. In transgenic epidermis, dnRARalpha dose-dependently inhibited tRA induction of suprabasal HB-EGF and subsequent basal cell hyperproliferation. Together, our observations suggest that retinoid receptor heterodimers located in differentiated suprabasal cells mediate retinoid induction of HB-EGF, which in turn stimulates basal cell growth via intercellular signaling. These events may underlie retinoid action in epidermal regeneration during wound healing.

Function of steroidogenic factor 1 (SF1) ligand-binding domain in gene activation and interaction with AP1.

The nuclear receptor SF1 is an essential mediator in ventromedial hypothalamus-pituitary-gonadal development. As with other nuclear receptors, SF1 possesses a DNA-binding domain composed of two zinc fingers and a ligand-binding domain containing a ligand-dependent activation sequence termed AF2. To dissect the domain function of SF1, we examined various SF1 mutants in mouse adrenocortical Y1 cells and human placental JEG3 cells. Destruction of the AF2 structure removed 73-90% transactivation activity, suggesting that AF2 is indispensable for transactivation. Mutants carrying the DNA-binding domain but lacking the AF2 or the ligand-binding domain blocked the activity of normal SF1. Disrupting the zinc finger diminished the dominant negative effect of mutant. Cotransfection of SF1 with AP1 showed that the two transcription factors cooperated to activate gene expression. Some mutants lost the synergistic action with AP1, while some retained partial activity. These experiments delineate the functional domains of SF1.

[Does a sector resection of the breast cure nodal mastopathy?]. / Izlechivaet li sektoral'naia rezektsiia molochnoi zhelezy uzlovuiu mastopatiiu?

Results of the clinico-morphological investigation of 265 patients with localized mastopathy who were submitted to sectorial resection showed that in the margins of the operative wound there were morphological signs of mastopathy in 252 (95.1%) patients. The results obtained confirm the opinion that structural alterations of the tissues known to be the essential feature of fibroadenomatosis can not be local, they are of diffuse character. So, the sectorial resection performed for localized mastopathy can not be radical and is of no therapeutic significance. The indication to surgical intervention must be determined not so much by the necessary treatment as by the real risk of hypo-diagnosis of breast cancer. So, there is no need to fulfil the sectorial resection for localized mastopathy. It is enough to make operation of less volume (excision biopsy).

Maximum activity of recombinant ribulose 1,5-bisphosphate carboxylase/oxygenase of Anabaena sp. strain CA requires the product of the rbcX gene.

Filamentous cyanobacteria of the genus Anabaena contain a unique open reading frame, rbcX, which is juxtaposed and cotranscribed with the genes (rbcL and rbcS) encoding form I ribulose 1,5-bisphosphate carboxylase/oxygenase (RubisCO). Plasmid constructions containing the genes from Anabaena sp. strain CA were prepared, and expression studies in Escherichia coli indicated that the product of the rbcX gene mimicked the ability of chaperonin proteins to facilitate the proper folding of recombinant RubisCO proteins. The purified recombinant Anabaena sp. strain CA RubisCO, much like the RubisCO enzymes from other cyanobacteria, was shown not to undergo inhibition of activity during a time course experiment, and the properties of this chaperoned recombinant protein appear to be consistent with those of the enzyme isolated from the native organism.

Temperature extremes and mortality from coronary heart disease and cerebral infarction in elderly Chinese.

We studied the relation between outdoor temperature and mortality rates from cardiovascular disease in Taiwan from 1981 to 1991. In 11 years, there were 30,085, 21,750, and 39,818 deaths from coronary artery disease, cerebral infarction, and cerebral haemorrhage, respectively, among 7.6 million residents aged 25 and over in selected areas where climate was recorded. A temperature-mortality relation was especially apparent in the elderly. A U-shaped relation was observed between temperature and mortality from coronary artery disease and cerebral infarction. The range corresponding to least deaths from coronary artery disease (26-29 degrees C) and cerebral infarction (27-29 degrees C) was higher than that in countries with colder climates. In the elderly, the risk of cerebral infarction at 32 degrees C was 66% higher than that at 27-29 degrees C; the risk increased by 3.0% per 1 degree C reduction from 27-29 degrees C. The risk of coronary artery disease at 32 degrees C was 22% higher than that at 26-29 degrees C; below 26-29 degrees C, the risk increased by 2.8% per 1 degree C reduction. Mortality from cerebral haemorrhage decreased with increasing temperature at a rate of 3.3% per 1 degree C. These results imply a pathophysiological difference between thromboembolic and haemorrhagic cardiovascular diseases. Poor thermoregulation in older people may precipitate cardiovascular disease events.

Transcription control of ribulose bisphosphate carboxylase/oxygenase activase and adjacent genes in Anabaena species.

The gene encoding ribulose 1,5-bisphosphate carboxylase/oxygenase (RubisCO) activase (rca) was uniformly localized downstream from the genes encoding the large and small subunits of RubisCO (rbcL and rbcS) in three strains of Anabaena species. However, two open reading frames (ORF1 and ORF2), situated between rbcS and rca in Anabaena sp. strain CA, were not found in the intergenic region of Anabaena variabilis and Anabaena sp. strain PCC 7120. During autotrophic growth of Anabaena cells, rca and rbc transcripts accumulated in the light and diminished in the dark; light-dependent expression of these genes was not affected by the nitrogen source and the concentration of exogenous CO2 supplied to the cells. When grown on fructose, rca- and rbc-specific transcripts accumulated in A. variabilis regardless of whether the cells were illuminated. Transcript levels, however, were much lower in dark-grown heterotrophic cultures than in photoheterotrophic cultures. In photoheterotrophic cultures, the expression of the rca and rbc genes was similar to that in cultures grown with CO2 as the sole source of carbon. Although the rbcL-rbcS and rca genes are linked and are in the same transcriptional orientation in Anabaena strains, hybridization of rbc and rca to distinct transcripts suggested that these genes are not cotranscribed, consistent with the results of primer extension and secondary structure analysis of the nucleotide sequence. Transcription from ORF1 and ORF2 was not detected under the conditions examined, and the function of these putative genes remains unknown.

The Rubisco activase (rca) gene is located downstream from rbcS in Anabaena sp. strain CA and is detected in other Anabaena/Nostoc strains.

A gene encoding ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) activase (rca) was found downstream from the rbcLrbcS operon in the heterocystous cyanobacterium Anabaena sp. strain CA. Two unknown open reading frames were shown to be located between rbcS and rca in strain CA and all the genes, rbcLrbcS, ORF1, ORF2, and rca were in the same transcriptional orientation. The deduced amino acid sequence of the Anabaena Rubisco activase showed both similarities and differences to the plant enzyme with considerable differences at the carboxy and amino termini. Proposed ATP-binding sites were conserved in the cyanobacterial protein. Recombinant cyanobacterial Rubisco activase, however, reacted with antisera to spinach Rubisco activase. Hybridization studies, using the Anabaena sp. strain CA rca gene as a heterologous probe, detected homologous sequences in heterocystous Anabaena/Nostoc strains but not in unicellular or nonheterocystous filamentous cyanobacteria, suggestive of a close evolutionary relationship of chloroplasts and heterocystous cyanobacteria.

No significant effect of calcium and vitamin D supplementation on blood pressure and calcium metabolism in elderly Chinese.

To examine the effects of calcium and vitamin D supplementation on blood pressure and calcium metabolism, we conducted a randomized, double-blind, 2 x 2 factorial intervention study in 58 institutionalized elderly persons. The subjects were randomly allocated into four groups to receive: (1) calcium (800 mg/day) + vitamin D3 placebo, (2) vitamin D3 (5 micrograms/day) + calcium placebo, (3) calcium + vitamin D3, or (4) placebo treatment. Blood pressure was measured and a 24-h urine specimen and an 8-h fasting blood sample were collected at the time of recruitment before treatment and after 2 and 11 weeks of treatment. The changes in urinary calcium levels and plasma vitamin D concentrations were highly correlated with the corresponding treatments in each group, indicating good compliance. Mean systolic blood pressure decreased slightly during intervention in the group given calcium supplements, but increased slightly in the group given calcium + vitamin D. The data suggest that oral supplements of 800 mg calcium or 5 micrograms vitamin D daily produce no significant effect on blood pressure in the elderly in 11 weeks.

Direct effects of thymopentin (Arg-Lys-Asp-Val-Tyr) on cholinergic agonist-induced slow inactivation of nicotinic acetylcholine receptor function.

The effects of thymopentin (TP-5) on the cholinergic agonist-induced inactivation of function (desensitization) of the nicotinic acetylcholine receptor (nAChR) were explored using two systems, 1) Torpedo californica electroplax nAchR reconstituted into phospholipid vesicles and 2) T. californica nAChR expressed, in Xenopus laevis oocytes, from in vitro synthesized RNA transcripts. The pentapeptide did not modify the equilibrium binding of 125I-alpha-bungarotoxin, but toxin rate binding assays in the presence of the cholinergic agonist carbamylcholine (Carb) revealed that it shortened the time course of the Carb-induced nAchR transition to the high affinity, desensitized state. Thymopentin (but not thymosins alpha 1 and beta 4) accelerated the slow inactivation of nAchR-mediated 86Rb+ influx, as measured by the first-order decrease in the Carb-induced 86Rb+ transport into the reconstituted vesicles. The decay of the acetylcholine-induced current from Torpedo receptor expressed in oocytes was also accelerated by TP-5. The pentapeptide had no ion channel-blocking or agonist activity of its own and exhibited a requirement for Ca2+ to express its effects. On the basis of these results, it is proposed that TP-5 has a direct effect on the nAChR, resembling that of noncompetitive blockers, as opposed to an indirect mechanism of action via the activation of specific metabolic pathways.