Reference Protocol to Assess Analytical Performance of Higher Order Structural Analysis Measurements: Results from an Interlaboratory Comparison

Measurements of protein higher order structure (HOS) provide important information on stability, potency, efficacy, immunogenicity, and biosimilarity of biopharmaceuticals, with a significant number of techniques and methods available to perform these measurements. The comparison of the analytical performance of HOS methods and the standardization of the results is, however, not a trivial task, due to the lack of reference protocols and reference measurement procedures. Here, we developed a protocol to structurally alter and compare samples of somatropin, a recombinant biotherapeutic, and describe the results obtained by using a number of techniques, methods and in different laboratories. This, with the final aim to provide tools and generate a pool of data to compare and benchmark analytical platforms and define method sensitivity to structural changes. Changes in somatropin HOS, induced by the presence of zinc at increasing concentrations, were observed, both globally and at more localized resolution, across many of the methods utilized in this study and with different sensitivities, suggesting the suitability of the protocol to improve understanding of inter- and cross-platform measurement comparability and assess analytical performance as appropriate.

Chromatographic characterisation, under highly aqueous conditions, of a molecularly imprinted polymer binding the herbicide 2,4-dichlorophenoxyacetic acid

The affinity of a 2,4-dichlorophenoxyacetic acid (2,4-D) molecularly imprinted polymer (MIP), which was synthesised directly in an aqueous organic solvent, for its template (2,4-D) was studied and compared with the affinity exhibited by two other reference (control) polymers, NIPA and NIPB, for the same analyte. Zonal chromatography was performed to establish the optimal selectivity, expressed as imprinting factor (IF), under chromatographic conditions more aqueous than those described so far in the literature. Frontal analysis (FA) was performed on columns packed with these polymers, using an optimized mobile phase composed of methanol/phosphate buffer (50/50, v/v), to extract adsorption isotherm data and retrieve binding parameters from the best isotherm model. Surprisingly, the template had comparable and strong affinity for both MIP (K = 3.8x10(4) M(-1)) and NIPA (K = 1.9x10(4) M(-1)), although there was a marked difference in the saturation capacities of selective and non-selective sites, as one would expect for an imprinted polymer. NIPB acts as a true control polymer in the sense that it has relatively low affinity for the template (K = 8.0x10(2) M(-1)). This work provides the first frontal chromatographic characterization of such a polymer in a water-rich environment over a wide concentration range. The significance of this work stems from the fact that the chromatographic approach used is generic and can be applied readily to other analytes, but also because there is an increasing demand for well-characterised imprinted materials that function effectively in aqueous media and are thus well-suited for analytical science applications involving, for example, biofluids and environmental water samples.

Validation of a RP-LC method for the simultaneous determination of isoniazid, pyrazinamide and rifampicin in a pharmaceutical formulation

A simple and accurate liquid chromatographic method was developed and validated for estimation of isoniazid (ISN), pyrazinamide (PYR) and rifampicin (RIF) in combined dosage forms. Drugs were chromatographed on a reverse phase C18 column using a mobile phase gradient and monitored at the corresponding maximum of each compounds. Peaks were identified with retention time as compared with standards and confirmed with characteristic spectra using diode-array detector. Solution concentrations were measured on a weight basis to avoid the use of an internal standard. The method does not require any specific sample preparation except the use of a guard column. The method is linear (r(2)>0.999), precise (RSD%: 0.50% for ISN, 0.12% for PYR and 0.98% for RIF), accurate (overall average recovery yields: 98.55% for ISN, 98.51 for PYR and 98.56% for RIF) and selective. Due to its simplicity and accuracy the method is suitable for routine quality control analysis of antitubercolosis combination dosage form.

A partially structured species of beta 2-microglobulin is significantly populated under physiological conditions and involved in fibrillogenesis

The folding of beta(2)-microglobulin (beta(2)-m), the protein forming amyloid deposits in dialysis-related amyloidosis, involves formation of a partially folded conformation named I(2), which slowly converts into the native fold, N. Here we show that the partially folded species I(2) can be separated from N by capillary electrophoresis. Data obtained with this technique and analysis of kinetic data obtained with intrinsic fluorescence indicate that the I(2) conformation is populated to approximately 14 +/- 8% at equilibrium under conditions of pH and temperature close to physiological. In the presence of fibrils extracted from patients, the I(2) conformer has a 5-fold higher propensity to aggregate than N, as indicated by the thioflavine T test and light scattering measurements. A mechanism of aggregation of beta(2)-m in vivo involving the association of the preformed fibrils with the fraction of I(2) existing at equilibrium is proposed from these results. The possibility of isolating and quantifying a partially folded conformer of beta(2)-m involved in the amyloidogenesis process provides new opportunities to monitor hemodialytic procedures aimed at the reduction of such species from the pool of circulating beta(2)-m but also to design new pharmaceutical approaches that consider such species as a putative molecular target.

Immobilized penicillin G acylase as reactor and chiral selector in liquid chromatography

In this paper, the use of penicillin G acylase (PGA) as a biocatalyst and as a chiral selector is described. Penicillin G-acylase is an interesting enzyme used in the manufacture of semisynthetic antibiotics and, in particular, in the production of 6-APA by hydrolysis of penicillin G. Five PGA-based HPLC columns have been prepared by using two different silica supports by employing two immobilization methods, namely "in situ" and "in batch". The effects of the immobilization techniques and of different silica pore size on the catalytic properties of the enzyme as well as the applicability of the PGA-bonded stationary phases as chiral selectors for a number of chiral drugs have been investigated. The HPLC columns based on immobilized PGA combine the hydrolytic activity and the chiral recognition properties of PGA, therefore they have been used for the development of a combined reaction-separation system for chiral and achiral substrates.

Chiral capillary electrophoresis and nuclear magnetic resonance investigation on the structure-enantioselectivity relationship in synthetic cyclopeptides as chiral selectors

In the present work, synthetic cyclohexa- and cycloheptapeptides previously singled out by a combinatorial chemistry approach have been evaluated as chiral selectors in capillary electrophoresis. By applying the countercurrent migration technique and employing a new adsorbed coating, a series of dinitrophenyl amino acids as well as some chiral compounds of pharmaceutical interest have been evaluated for enantiorecognition. The results thus obtained led to a deeper investigation of the chiral discrimination process, by carrying out nuclear magnetic resonance (NMR) studies on selected cyclopeptide-analyte complexes. These studies shed light on the chemical groups involved in the analyte-selector interaction and provided useful information for a wider application of these cyclopeptides in the separation of other drug enantiomers.

Target analogue imprinted polymers with affinity for folic acid and related compounds

Two approaches to synthesize molecularly imprinted polymers with affinity for folic acid and other substituted pteridines have been compared. In the first approach, the folic acid analogue methotrexate was used as template and functional monomers capable of generating selective binding sites were searched in a miniaturized screening system based on binding assessment in the batch mode. Highest selectivity was seen using 2-vinylpyridine as functional monomer, which was confirmed in the chromatographic mode for a batch synthesized on a gram scale. However, the retentivity and selectivity of this phase were insufficient for anticipated applications. In a second approach, using methacrylic acid as the functional monomer, organic soluble inhibitors for the enzyme dihydrofolate reductase were used to develop sites complementary toward the pteridine substructure. This resulted in materials showing enhanced selectivity for substituted pteridines when evaluated by HPLC. Thus, methotrexate and leucovorine were selectively retained in mobile phases of either low or high aqueous content, thus showing the typical bimodal retention behavior of previously reported MIPs. In organic mobile-phase systems, the inhibitor used as template had an influence on the retentivity and selectivity of the MIP. The polymer imprinted with trimethoprim retained all folic acid analogues strongly and showed the highest selectivity among the MIPs in an organic mobile-phase system. This was supported by Scatchard analysis resulting in biphasic plots and a quantitative yield of high-energy binding sites. All templates were shown to associate strongly with MAA in CDCl(3), the strength of association correlating roughly with the template basicity and the selectivity observed in chromatography. Nonparallel complexation-induced shifts indicated formation of 1:2 template monomer complexes at concentrations corresponding to those of the prepolymerization solutions.

Properties of a stationary phase based on immobilised chicken liver basic fatty acid-binding protein

The fatty acid-binding proteins (FABPs) are a class of low-molecular-mass proteins that bind fatty acids and are thought to be involved in their intracellular transport. FABPs have been isolated and studied from several tissues, but their precise function and mechanism of action are still not clear. Chicken liver (basic) fatty acid-binding protein (bFABP) was immobilised on aminopropyl silica and the developed stationary phase was used to examine the enantioselective properties of this protein and to study the binding of drugs to bFABP. The retention and enantioselectivity of the new column for a large number of chiral drugs was investigated. The enantiomers of basic and neutral compounds were poorly retained and not resolved by the bFABP column. On the contrary the resolution of the enantiomers of some acidic compounds was obtained. Therefore the influence of the mobile phase pH and organic modifier on the chromatographic performance of acidic compounds was studied. In order to clarify the retention mechanism, competitive displacement studies were also carried out by adding short-chain fatty acids to the mobile phase as displacing agents and preliminary quantitative structure-retention relationship correlations were developed to describe the nature of the interactions between the chemical structures of the analytes and the observed chromatographic results.

Affinity capillary electrophoresis is a powerful tool to identify transthyretin binding drugs for potential therapeutic use in amyloidosis

In this work we used affinity capillary electrophoresis (ACE) to investigate the extent of interaction between a pool of drugs and wild-type transthyretin. After qualitative preliminary screening, attention was focused on the most promising molecules, flufenamic acid and flurbiprofen, which underwent a further stage of investigation, the determination of the binding constants, and, when possible, the assessment of the number of binding sites by ACE, frontal analysis (FA) capillary electrophoresis (CE) and parallel ultrafiltration (UF) experiments. Furthermore, our data demonstrate that FA CE is a suitable technique for identifying fibril ligands. This represents a novel CE application of pharmaceutical interest.

Evaluation of new adsorbed coatings in chiral capillary electrophoresis and the partial filling technique

When using chiral selectors and the partial filling technique in capillary electrophoresis, a suitable and reproducible suppression of the electroosmotic flow is still a challenging issue, and there are a number of reasons to find alternatives to the use of covalently coated capillaries for such a particular application. In this paper, new achiral, neutral, and water-soluble polymers are evaluated as adsorbed polymers for the suppression of electroosmotic flow (EOF) when employing chiral capillary electrophoresis and the partial filling technique. Four chiral selectors, namely a cationic cyclopeptide, vancomycin, human serum albumin and riboflavin binding protein have been chosen for this study and some analytes such as derivatized amino acids, promethazine and prilocaine have been used as test compounds. Reproducibility of migration times, resolution, and selectivity as well as efficiency are reported to critically evaluate the performance of the adsorbed coatings. Results are compared to parallel data obtained with fused-silica and polyvinyl alcohol-coated capillaries.

Chromatographic investigation on the binding site characteristics of quail egg-white riboflavin binding protein as a chiral stationary phase

Recently we described the use of riboflavin binding protein extracted from quail egg-white, as a new HPLC chiral stationary phase. In this study we show the further results obtained with the use of high-performance affinity chromatography to provide a better understanding of the chiral recognition mechanism for the observed enantioselectivity and to gain a deeper knowledge into the binding site that has been recently characterised by X-ray crystallography for chicken egg-white. High-performance affinity chromatography provides information on the potential protein structural changes occurring upon its immobilisation and enables competitive binding studies as well as the assessment of binding constants through frontal analysis experiments.

Evaluation of quail egg white riboflavin binding protein as a chiral selector in capillary electrophoresis by applying a modified partial filling technique

A preliminary evaluation of the enantioselective properties of quail egg yolk riboflavin binding protein (qRfBP) was carried out in capillary electrophoresis by using the complete filling technique. The most promising results obtained by this screening of nineteen chiral drugs were singled out with the aim of optimizing enantiomer separations by applying the partial filling technique, which allows operating at much higher protein concentrations without detection problems. The building of the separation zone in the partial filling technique has been modified in order to enable on-line monitoring, before each run, of the actual protein plug application velocity and, consequently, the building of a plug of the desired length. The electrophoretic conditions chosen gave opposite migration directions for the chiral selector and the analytes, with qRfBP migrating away from the detector. A polyvinyl alcohol-coated capillary was first totally filled with protein and the optimal plug length was obtained by further applying negative pressure together with positive voltage for the time needed. Separations of basic drugs were optimized by using protein concentrations ranging from 200 microM up to 900 microM and different plug lengths, while the running buffer pH (6.0), temperature (25 degrees C) and operating voltage (+20 kV) were kept constant. The enantioresolution of all solutes was affected by both the chiral selector concentration and protein plug length. Baseline separations were obtained for oxprenolol, prilocaine and bupivacaine.

The impact of capillary electrophoresis in drug analysis and bioanalysis

Capillary electrophoresis (CE) has penetrated a wide variety of areas of separation science during the last ten years. The relative strengths and weaknesses of this technique are here overviewed, by citing the most recent literature and updated Medline search, keeping an eye on technology news, as technology and the development of CE and its applicability progress in parallel. The issues discussed include micellar electrokinetic chromatography (MEKC), which permits non-ionic solutes to be solubilized and separated. Enantioselective applications in CE exploit addition to the run buffer of cyclodextrins, macrocyclic antibiotics and proteins for analysis of chiral drugs and the state of the art of this field will be emphasized. CE has significant potential for drug metabolism studies, especially coupled with MS for high sensitivity detection and structural characterisation. Strategies for the analysis of drugs and metabolites in body fluids include on-capillary methods of sample concentration and single-step analyses with direct injection of body fluids on-column, where detection techniques other than conventional UV are essential to achieve adequate sensitivity. The potential contribution of the hybrid technique of capillary electrochromatography (CEC), which couples the separating power of reversed-phase HPLC and the high efficiency of CE, has recently attracted growing interest and is therefore discussed. Finally, validation issues which are peculiar to CE are illustrated.

Evaluation of beta-lactoglobulin as a stationary phase in high-performance liquid chromatography and as a buffer additive in capillary electrophoresis: observation of a surprising lack of stereoselectivity

Previous studies have reported that alpha1-acid glycoprotein is quite similar in amino acid sequence and disulfide bond arrangements to members of a group of proteins which include beta-lactoglobulin (BLG). Since generally homologous proteins retain some similarity in function at the molecular level, we decided to evaluate the enantioselective properties of BLG as an high-performance liquid chromatographic chiral stationary phase (HPLC-CSP), and as an additive in capillary electrophoresis (CE). Two columns with differences in internal diameter and method of immobilisation on epoxide silica were prepared. Chiral acidic, basic and uncharged drugs were chromatographed and mobile phase parameters, namely pH and type of organic modifier, were varied in order to test the column performance. The CE approach has some advantages in that there is no need for immobilisation and only a small amount of protein is required. BLG was therefore tested as a CE buffer additive, using the same analytes as in the HPLC study. Although one would expect that a protein would display some enantioselectivity, BLG did not show any enantioselectivity whatsoever in either system; the protein has fairly weak interaction with the majority of the test solutes, as indicated by both techniques.

Selectivity in capillary electrophoresis: the use of proteins

Proteins, by their very diverse nature, provide a wide variety of options for generating selectivity in capillary electrophoresis (CE). Their use in different modes of CE will be considered in this review. Proteins added in solution to the background electrolyte allow separations to be made in a similar fashion to other electrokinetic chromatography methods, e.g., micellar separations. Alternatively, different immobilization schemes can be used to secure proteins within the capillary; these have included capillary electrochromatography with the protein grafted onto a silica support, or immobilization of the protein within a gel structure. Compounds varying in size from small inorganic ions to biopolymers may be bound by proteins. There is the potential for any sort of intermolecular interaction to play a role in the binding process (e.g., hydrophobic interactions, electrostatic interactions, etc.). Very specific high-affinity binding often occurs, but also there is often weaker, non-selective binding. Frequently the interactions of chiral compounds with proteins are stereoselective. Obtaining chiral selectivity has been one of the main applications of protein selectors in CE, and this use will be emphasized here in a discussion structured by type of protein. As well as utilizing the selectivity of proteins to develop separations, the role of CE in investigating ligand-protein interactions will be emphasized.

Comparison of drug binding sites on rat and human serum albumins using immobilized-protein stationary phases as a tool for the selection of suitable animal models in pharmacological studies

Immobilized serum albumins (rat and human) HPLC stationary phases have been used to investigate and to compare the binding sites of a number of analytes of pharmaceutical interest assessing the retention time as the chromatographic parameter which correlates the percentage of drug-binding of the corresponding free protein. Anti-inflammatory drugs with different molecular structure were chromatographed and the k' values were determined with a mobile phase based on 100 mM sodium phosphate buffer (pH 6.9) containing 6% n-propanol (v/v). The effect of the addition to the mobile phase of octanoic, decanoic and dodecanoic acids on the k' values enabled to elucidate the site of interaction between the solutes and the two albumins. The results indicate that there are some structural differences in the binding sites of the two albumins and also some quantitative differences with respect to the extent of drug-binding. Moreover the different stereoselective behaviour of the two albumins was studied by analysing some chiral anti-inflammatory drugs much as aryl-propionic acids.

Design of chiral LC separations for calcium antagonists on alpha 1-acid glycoprotein and ovomucoid columns

Three chiral calcium antagonist drugs, gallopamil and two dihydropyridine derivatives, have been successfully separated within short retention times using both the alpha 1-acid glycoprotein chiral stationary phase (Chiral-AGP) and the ovomucoid column (Ultron ES-OVM). Aqueous buffer at defined pH is modified by the addition of an organic component, in order to modulate the retention properties of each system. Optimization of pH and organic modifier is carried out using the modified simplex method, with Kaiser's peak separation function as a criterion. The influence of pH and percentage of organic modifier on retention, selectivity, resolution and column performance are discussed for the two dihydropyridines analysed on Chiral-AGP and Ultron ES-OVM stationary phases. A new method is proposed as a new chiral system suitability test for these protein-based phases, utilizing a racemic mixture of closely eluting verapamil enantiomers as a probe.

High-performance liquid chromatographic determination of alpha-tocopheryl nicotinate in cosmetic preparations

alpha-Tocopheryl nicotinate (alpha-TN) accelerates blood circulation and stimulates hair follicle cells, hence it is an active ingredient in a broad range of cosmetic products. A reversed-phase high-performance liquid chromatographic method was developed to determine alpha-TN in cosmetic preparations with alpha-tocopheryl acetate as internal standard. The method was found to be rapid, precise and specific.

High-performance liquid chromatography post-column derivatization with fluorescence detection to study the influence of ambroxol on dipalmitoylphosphatidylcholine levels in rabbit eustachian tube washings

In this work an appropriate high-performance liquid chromatography method was set up to guarantee specificity, sensitivity, precision and accuracy in analyzing dipalmitoylphosphatidylcholine (DPPC) in rabbit eustachian tube washings, as well as to determine its varying levels after administration of ambroxol chloride. The procedure is based on a post-column derivatization with fluorescence detection using 1,6-diphenyl-1,3,5-hexatriene which exhibits increased fluorescence in a lipid environment. DPPC was chromatographed on a Hypersil C18. The mobile phase for the isocratic elution consisted of 40 mmol/l choline chloride in methanol-tetrahydrofuran (97:3). Ambroxol was given to a group of New Zealand white rabbits at a dose of 30 mg/kg. A second group receiving vehicle only acted as controls.

[Evaluation in experimental animals of a mathematical model of foreseeing variations in values of stable glycosylated hemoglobin]

Assay of glycosylated hemoglobin provides reliable information on metabolic control in diabetes mellitus over a period of about 90 days. This is why it is currently used as a parameter of blood glucose control in diabetic patients. However, at present little is known about the kinetics of stable glycosylated hemoglobin variations as a result of circadian changes in blood glucose level. The authors describe a mathematical model which allows to foresee glycosylated hemoglobin variability as a result of alterations of blood glucose equilibrium.

[Evaluation of the changes in glycosylated hemoglobin in a sample of hospitalized diabetic patients. Significance and limitations of this diagnostic method]

Stable glycosylated hemoglobin measurement provides an index for plasma glucose control over an average three month period. It is not clear whether stable HbA1C can undergo rapid changes induced by short-term variations in glucose concentration. The present study was aimed at investigating whether variation of total HbA1C in response to changes in blood glucose, over a short period can be detected by routine methods of determination. Our result show that due to the sensitivity of the methods, stable HbA1C has to be considered only as an index of glucose control over long period of time.

[Therapeutic use of glutathione]

Liver pathology is very frequent in western countries. The numerous therapeutic approaches suggested so far for the prevention or limitation of liver damage in the course of hepatic diseases have often had disappointing results. Considering that at least part of the liver injury is caused by free radicals, the authors have tried an antioxidant, glutathione, as a hepatoprotective agent. Although particularly brilliant results were not achieved, clinical conditions and laboratory findings were improved in hall patients treated with glutathione.

[Clinical experience with a new antibiotic: cefmetazole]

Cefmetazole is a new semisynthetic derivative with a broad antibacterial spectrum as shown by data from 34 research institutes in Japan. It has antibacterial action against various species of Gram+ and Gram- bacteria and is extremely stable for beta-lactamase because it has a 7-alpha-methoxy group. In addition, it has excellent antibacterial activity against indole-positive Proteus strains against which conventional Cephalosporins are ineffective. Results of clinical trials carried out on urinary tract, respiratory tract and cutaneous infections are reported. A total of 30 patients were examined; the route of administration was intravenous, the most frequent daily-dose was 2 g. Clinical and bacteriological effectiveness of cefmetazole was 80% with excellent activity against E. coli, Proteus, S. aureus and K. pneumoniae. No serious side effect was observed. The above results indicate that CMZ is largely effective and useful for infections due to Gram+ cocci and Gram- bacilli.

Latent abnormalities of sinus node function in patients with organic heart disease and normal sinus node on clinical basis

Sinus node (SN) function was analyzed in 22 patients (mean age: 46.2 +/- 12.9 years) with organic heart disease and normal SN on clinical basis (group I) and in 20 normal subjects (mean age: 43.9 +/- 15.6 years), (control group). Sinus cycle length (SCL), corrected sinus node recovery time (CSRT) and sinoatrial conduction time (SACT) were analyzed. After the control study, autonomic blockade (AB) was induced by i.v. propranolol (0.2 mg/Kg) and atropine (0.04 mg/Kg). Measurements of SCL, CSRT and SACT were then repeated. The mean SCL values were very similar in the two groups during the control state and after AB. There were no significant differences in SACTs between the two groups during the control state or after AB. On the contrary, the CSRT of group I was significantly longer than that of control group during the control state (344.8 +/- 78.9 versus 262.2 +/- 46.3 msec, P less than 0.001) and after AB (238.9 +/- 72.8 versus 166.8 +/- 39.3 msec, P less than 0.001). The analysis of real depression of SN automaticity (CSRT minus SACT) in the two groups shows that prolongation of CSRT in group I during the control study and after AB is related to an intrinsic abnormality of SN automaticity; on the contrary, no dysfunctions of the autonomic nervous system appear. These data indicate that the intrinsic abnormality of SN automaticity represents the earliest involvement of the SN in subjects with organic heart disease and normal SN on clinical basis, although this conclusion is speculative and requires experimental verification.

Slight middle slurring in V1-V2 without bundle branch block. An electrocardiographic and follow-up study

A slight middle slurring in V1 and/or V2 with rS morphology (R less than S) in these leads, without right or left bundle branch block is a nearly ignored electrocardiographic finding. The purpose of this work is to provide a prospective and electrocardiographic analysis of this finding. We followed 200 subjects with middle slurring in V1 and/or V2, in the absence of bundle branch block (study group), (age: 41.5 +/- 19 years, follow-up period: 5.7 +/- 2.5 years) and 200 subjects with rS morphology in V1-V2 without the middle slurring (control group), (age: 39.8 +/- 20 years, follow-up period: 5.2 +/- 2 years). The age, sex, prevalence of organic heart disease, QRS duration and follow-up period did not show significant differences between the two group. In the study group there was a higher prevalence of vertical axis (P less than 0.001), of S1S2S3 morphology (P less than 0.001) and of terminal r wave in a VR (P less than 0.05) compared to control group. During the follow-up period, a right bundle branch block appeared in 19 subjects of study group (incomplete in 15 and complete in 4) and in 2 (complete) of control group (P less than 0.001). A left bundle branch block appeared only in one patient of study group and in one of control group. We conclude that the isolated slight middle slurring in V1-V2 expresses an initial involvement of the right bundle branch system and increases the likelihood of appearance of right bundle branch block.

The role of the autonomic nervous system on sinus node function in patients with intermittent sinoatrial block

Sinus node (SN) function was analyzed with and without autonomic blockade (AB) in 31 patients (mean age: 57.6 +/- 12.8) with intermittent sinoatrial block. Twenty-one patients had organic heart disease; in the remaining ten signs of underlying heart disease were not present. Nineteen patients had dizziness or syncope. Sinus cycle length, sinus rate, corrected sinus node recovery time (CSRT) and sinoatrial conduction time (SACT) were analyzed. After control measurements, AB was produced by i.v. propranolol (0.2 mg/Kg) and atropine (0.04 mg/Kg). Measurements of electrophysiological parameters were then repeated. After AB sinus rate and CSRT did not show statistically significant differences, whereas SACT decreased significantly (P less than 0.001). When intrinsic heart rate (IHR) was abnormal (11 cases), intrinsic CSRT was always abnormal, whereas when IHR was normal, intrinsic CSRT was normal in 11 patients and abnormal in nine. In several cases, when sinus rate increased after AB, CSRT decreased and vice-versa. The parameters of intrinsic SN function were normal in 80% of patients with a normal heart and only in 14.2% of patients with organic heart disease. These data indicate that: (1) during the control period SACT is mainly conditioned by the vagal tone; (2) abnormalities in control CSRT are not uniformly abolished after AB in patients with normal IHR; (3) AB has a differential effect on the two variables of SN automaticity; i.e. sinus rate and CSRT; and (4) in patients without underlying heart disease, the SN dysfunction is almost exclusively related to alterations of the autonomic nervous system.