Psychosocial stress causes endothelial injury in cynomolgus monkeys via beta1-adrenoceptor activation.

Current evidence links psychosocial factors to exacerbation of diet-induced atherosclerosis in monkeys via activation of the sympathetic nervous system. However, it is uncertain whether these factors can potentiate initial lesion formation, and do so even in the absence of dietary provocation, and whether any such effects can be prevented by beta-adrenergic blockade. As endothelial injury has been considered an initiating event in atherogenesis, we studied the effect of psychosocial stress on endothelial integrity in 48 adult male cynomolgus monkeys (Macaca fascicularis). All animals were housed in 12 social groups of four monkeys each for 11 weeks. The monkeys in half of the groups were exposed to a socially unstable ('stressed') condition for 72 h and received saline (n = 8), a lipophilic beta1-blocker (metoprolol, 0.30 mg/kg per h; n = 8), or hydrophillic beta1-blocker (atenolol, 0.15 mg/kg per h; n = 8). The remaining six social groups were assigned to the socially stable (non-stressed) condition; for 72 h these animals all remained in their social groups and were similarly treated with saline (n = 8), metoprolol (n = 8), or atenolol (n = 8). The frequency of IgG-positive (injured) endothelial cells was estimated on en face (Häutchen) preparations from the thoracic aorta and coronary arteries. Psychosocial stress caused a significant increase in the number of injured endothelial cells in the circumostial areas of the descending thoracic aorta in the placebo group (0.3 vs. 0.8%, P < 0.02), an effect that had not been demonstrated previously. Moreover, beta-blockade significantly (P < 0.01) inhibited the stress effect, with no differences between the two beta-blocking agents. The number of injured endothelial cells in the non-branched portions of the aorta and coronary arteries were low and indistinguishable among groups; irregularities in the size and location of branching points in the coronary arteries precluded analysis of these sites. This study demonstrated that psychosocial stress induces endothelial injury, and that this effect is mediated via beta1-adrenoceptor activation.

Characterization, standardization and experiences with KONE ISE for Mg2+.

The principles of a fully automated potentiometric determination of ionized magnesium in human blood serum are presented. By incorporating a magnesium selective electrode, into a commercially available six channel electrolyte analyzer (Microlyte 6, KONE Instruments, Finland), determination of the biologically-active, ionized fraction of magnesium has been made possible. In this paper, the analytical performance of the measurement system is presented and determination of ionized magnesium in real patient samples is discussed with special attention to the significance of this new parameter.

On the bias caused by regression toward the mean in studying the relation between change and initial value.

In studies of treatment effects in clinical trials and longitudinal followup investigations, it is not unusual to inquire as to whether a relationship exists between the change of a variable and its initial value, for example pocket depth Such studies must be carried out with great care, since the results are biassed by the regression towards the mean (RTM) effect. Examples are presented, the magnitude of the RTM effect is estimated and means of dealing with the RTM problem are discussed. RTM also appears as a selection phenomenon, emphasizing the need to include control groups in order to make possible adjustments for the bias caused by RTM.

On the choice of computational unit in statistical analysis.

It is stated that in trials where experimental units on different levels (sites, patients, etc.) are employed, the highest level unit should be used as computational unit when computing standard errors and in statistical inference. Using a lower level unit will underestimate the standard error and the level of significance (P-value). A numerical illustration is presented.

Analysis of change--are base-line measurements needed? Some statistical comments on a common experimental design.

In experiments where the treatment effect is defined as the change of a variable during treatment, one may, under certain circumstances, obtain a higher precision by basing the statistical analysis on the after-treatment measurements alone instead of the change during treatment. The conditions for this are derived and an empirical illustration involving bacterial counts is presented. In the case of a cross-over trial it is found in this particular case that not using the base-line measurements reduces the number of patients needed by approximately 40%. In the case of a completely randomized design, about the same precision is obtained whether or not one utilizes the base-line values.

Sampling of subgingival microbiota for dark-field microscopy.

The aim of the present investigation was to study the validity of 2 different methods of sampling the subgingival microbiota. The composition of the flora was estimated using the dark-field microscope. Subgingival samples were obtained using either a curette or a Hamilton microsyringe for a subgingival washing. The method of determination of the composition of the subgingival microorganisms was found to be very reproducible when the same investigator performed the counting. Samples obtained by the washing technique had a slight but significantly higher proportion of coccoid cells when compared to samples obtained by curette. The calculation of the reproducibility of the washing technique as assessed in 6 immediately repeated samples from the same sites yielded a coefficient of variation of 40% for spirochetes and motile rods. When 9 repeated samples from each of 28 sites (14 with a curette, 14 with washing) were studied over a period of 32 days, no systemic alterations were observed in the % of spirochetes and motile rods. The variation within each individual site was high. For curette samples and washing samples, the coefficients of variation for spirochetes and motile rods were 85% and 63%, respectively. The present investigation clearly demonstrated that care should be taken in the interpretation of single samples of subgingival microbiota. A more relevant picture of the actual situation is achieved when trends of repeated samples over time are studied.

Effect of increasing bronchodilatation on the single breath nitrogen test.

To determine if and how changes of the slope of phase III of the N2 test reflect drug-induced bronchodilatation, we studied patients with moderate to severe reversible airflow limitation who inhaled increasing doses of salbutamol. The bronchodilating response on each dose level was monitored both by the N2 test and dynamic spirometry. The study shows that the slope of phase III is related to drug-induced bronchodilatation in a dose-dependent way. Furthermore, the decrease of the slope of phase III mirrors the concomitant increase of FEV1. These results are consistent with bronchomotor tone as a determinant of the slope of phase III. Alternatively, the decrease of the slope of phase III may be independent of bronchomotor tonus per se and be explained by a decrease in residual volume as reflected by the observed dose-dependent increase in vital capacity.

A new method for investigating the relation between change and initial value in longitudinal blood pressure data. I. Description and application of the method.

The relation between change and initial value is of great interest in longitudinal studies. With variables containing random errors (short-term intra-individual variations and measurement errors) the directly computed relation is however, biased by the regression towards the mean phenomenon. Earlier proposed solutions of the problem are unsatisfactory. In this paper the regression towards the mean phenomenon is described and a new method is proposed by which the error caused by the regression towards the mean is avoided. The method is applied to a set of longitudinal blood pressure data. It is shown that the observed, biased relation in this case is significantly negative, while the correct relation obtained with this method is significantly positive. Since random errors are present in most biological variables, similar erroneous conclusions may easily be drawn also in other cases if the regression towards the mean phenomenon is not corrected for. In this analysis, random errors constitute 65--80% of the observed blood pressure change. To reduce this dominance, recommendations about study design for future studies of change/initial value relationships are given.

A new method for investigating the relation between change and initial value in longitudinal blood pressure data. II. Comparison with other methods.

Whether initial value affects blood pressure change or not is of interest in longitudinal blood pressure studies. The change/initial value relationship is, however, biased by the regression towards the mean phenomenon, as blood pressure measurements contain random errors (short-term intra-individual variation and measurement errors). Two methods (here called C and D) of avoiding this bias have earlier been proposed and used in population studies in South Wales and Framingham, with conflicting results. In the preceding paper a new method of avoiding the bias has been presented. In the present paper a comparison of the new method with the two earlier is made by applying them to the same data set. Method C indicates, as in South Wales, a highly significant positive relationship, while method D (as in Framingham) and the new method give a regression coefficient close to zero. The structure of the three methods is analysed. Method C is shown to be valid only under very restricted conditions and is best avoided. Method D gives a fairly accurate result, but underestimates the coefficient by approximately 30% in this case. The new method proposed seems to be the best method hitherto for this kind of analysis.

Application of a method for correcting an observed regression between change and initial value for the bias caused by random errors in the initial value.

When studying the correlation between the change of a variable during treatment and the value before treatment, random errors (errors of measurement as well as intra-individual biological variation) may yield seriously biased results. In the present work a method to adjust for this bias is presented. The method was applied to data from blood coagulation factor and plasma protein analyses in chronic alcoholics before and after one week of abstinence. It was found that many of the significant correlations were lost when the data were adjusted.

No inhibition by Li+ of thyroxine monodeiodination to 3,5,3'-triiodothyronine and 3,3',5'-triiodothyronine (reverse triiodothyronine).

The possibility that lithium affects the conversion of thyroxine to 3,5,3"-triiodothyronine and 3,3',5'-triiodothyronine (reverse triiodothyronine) was studied by measurement of the serum concentractions of these parameters in five patients during the first week of lithium therapy. In three patients there was a decrease in serum thyroxine concentration and a slightly less pronounced decrease in that of serum 3,5,3'-triiodothyronine. In two patients, who also received L-tryptophan or flupentixol, no change was noted in the concentrations of these compounds. There was no increase in serum 3,3',5'-triiodothyronine concentration in any of the patients. No systematic change was found in the serum concentrations of thyrotropin or unsaturated thyroid-hormone binding proteins. The results obtained do not support the contention that lithium should inhibit the monodeiodenation of thyroxine to its active and inactive metabolites.