Activation of the tubuloglomerular feedback mechanism in dehydrated rats

To study the influence of the tubuloglomerular feedback control (TGF) on the regulation of glomerular filtration rate (GFR) during dehydration, micropuncture experiments were performed on surface nephrons of dehydrated rats. Dehydration was achieved by withdrawal of food and water for 24 h. The urine flow rate decreased to 1.5 μl/min (controls 2.9 μl/min) and GFR decreased in these rats to 0.80 ml/min (controls 1.22). TGF was studied by two different micropuncture procedures. With the first technique the changes in proximal stop-flow pressure in response to changes of the late proximal microperfusion rate were measured. With this technique the perfusion rate necessary to induce a half maximal stop-flow pressure response, the turning point, was also determined. An increased TGF sensitivity was found in dehydrated rats, as indicated by increased stop-flow pressure responses (35 versus 26%) and decreased turning points (16 versus 21 nl/min). With the second micropuncture technique the single nephron GFR (SNGFR) was measured at distal and proximal tubular sites, in the same nephron. Distal SNGFR was decreased during dehydration to 32.2 nl/min, versus 42.7 nl/min in controls. A significant difference between paired SNGFR measurements in the same nephron was observed during dehydration, the proximal value being 5.3 nl/min higher than the distal, whereas this difference was not seen in control rats. This finding indicates that activation of the feedback mechanism takes place to reduce SNGFR. It is concluded that the decrease in whole kidney GFR is partly caused by the observed increase in feedback activity. The present results are also in agreement with our earlier hypothesis that the hydrostatic and oncotic pressure conditions within the interstitial space surrounding the macula densa cells modulate the sensitivity of the tubuloglomerular feedback mechanism.     

Bonding of restorative resins to dentin by means of methacryloylchloride and methacryloyl-R-isocyanate

Abstract – The bonding of restorative resins to dentin by means of an intermediary monomer containing a carboxylic acid chloride or an isocyanate group was investigated. Such intermediary monomers are supposed to react with the organic constituent of dentin. Bond strengths were enhanced by the use of the intermediary monomers, resulting in mean bond strengths of 0.13 kg/mm2. Bond strengths of this order of size are probably too low to be of clinical interest.     

Protective value of sympathectomy of the ear in noise

Noise-induced hearing loss was assessed in unilaterally sympathectomized rats exposed one month to 100 dB L_eq(lin) noise. The systolic blood pressure of these animals was in the range of 110–140 mmHg. Auditory sensitivity was determined electrophysiologically by brainstem response audiometry to 1/3-octave filtered clicks. The results showed that the loss of sensitivity was about 10 dB smaller (p<0.01) on the sympathectomized side. This observation may partially explain the individual differences in susceptibility to noise-induced hearing loss and point towards protective measures and therapeutic possibilities through manipulation of sympathetic activity in the inner ear.     

The Effect of Intravenous Injection of Purified Human Tissue Thromboplastin in Rats

As a background for the development and testing of phospholipase C in the therapy of post-traumatic and post-surgical intravascular coagulation, highly purified tissue thromboplastin was injected i.v. into rats. The levels of factor V, VII, VIII and blood platelets and the activity of the intrinsic coagulation pathway in general (the cephalin test) were followed. Histological examination of pulmonary, kidney and liver tissue was carried out. The dose-response was highly dependent on the injection rate. A marked activation of factor VII and a fall in the activities of factors V and VIII as well as in thrombocyte counts were observed. Very few or no thrombi were seen beyond the pulmonary circulation. The main changes (fibrin-containing thrombi and platelet aggregates) were observed in the lungs during the first 15 min after injection. After 15 min virtually no thrombi or platelet aggregates could be detected. The effect of tissue thromboplastin was counteracted by large doses of antithrombin III.     

A methodological study of errors in vertical measurements of edentulous ridge height on orthopantomographic radiograms

The purpose of this methodological investigation was to study the relative magnitude of the various errors in vertical ridge measurements from orthopantomograms of edentulous patients. The study was divided into two parts, Part I and Part II. Part I included eleven patients. Two standard orthopantomograms were taken of each patient. Part II included five of the eleven patients in Part I. Here, a third X-ray taken with the mouth open was added to the X-rays from Part I. The X-rays were traced by three dentists. Twelve vertical measurements in the maxilla and in the mandible were made. The variance produced by the patients (morphological variance) and those produced by the dentist, the X-ray, the interaction patient-dentist, the interaction dentist-X-ray and the random variance (methodological variances) were separately estimated on the basis of a three-way mixed analysis of variance model. In Part I, on the average, the sum of the methodological variances constituted 1·7 % and 2·5 % of the total variance in the maxilla and in the mandible respectively. The X-ray produced the greatest single variance component, averaging 1·1 % in both jaws. Although generally statistically significant, the remaining methodological variances were of low magnitude. The interaction patient-dentist, however, was not significant in most cases. In Part II, on the average, the sum of the methodological variances increased to 38·8 % in the maxilla and 4·6 % in the mandible, mainly caused by an increase in the variance produced by the X-ray.     

Analysis of antibody reactivities toward self antigens of IgM of patients with Waldenstrom's macroglobulinemia

By using a quantitative immunoblotting technique, we have analyzed the repertoires of antibody reactivities of IgM directed toward self antigens in the serum of patients with Waldenstrom's macroglobulinemia (WM) and in the serum of healthy adults. Monoclonal IgM of patients with WM expressed various degrees of polyreactivity and a high degree of heterogeneity with regard to the number and the nature of the protein bands that were recognized in homologous tissue extracts. Heterogeneous patterns of reactivity of WM IgM contrasted with the conserved profiles of reactivity of IgM in the serum of healthy blood donors. Protein bands that were recognized by WM IgM belonged to the restricted set of self antigens recognized in homologous tissues by normal polyclonal IgM, indicating the absence of a disease-specific reactivity profile of monoclonal WM IgM. Thus, monoclonal IgM that is present in large amounts in WM distorts the homogeneous pattern of reactivity of natural antibodies with self antigens which characterizes the natural antibody repertoire of healthy individuals.