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Biomedical subjects

R Nielsen

Publications and source records attributed to R Nielsen.

At least 127 records · Page 7Linked to original sources
PubMed1987

Prostaglandin E2-stimulated glandular ion and water secretion in isolated frog skin (Rana esculenta).

Prostaglandins are known to stimulate the active sodium absorption in frog skin. In this paper it is shown that prostaglandin E2 (PGE2) stimulates an active secretion of Cl-, Na+, and K+ from the skin glands in Rana esculenta. The active Cl secretion is enhanced more than the Na and K secretion. Therefore, in skins where the Na absorption is inhibited by amiloride, the addition of PGE2 results in an increase in the short-circuit current (SCC). The PGE2-stimulated Cl secretion could be inhibited by the presence of ouabain or furosemide in the basolateral solution or diphenylamine-2-carboxylate in the apical solution. The PGE2-stimulated Cl secretion was enhanced by the phosphodiesterase inhibitor, theophylline, indicating that the effect of PGE2 was caused by an increase in the intracellular cAMP level in the gland cells. The calcium ionophore A23187, which increases the PGE2 synthesis in frog skin, stimulated the glandular Cl secretion. This secretion could be blocked by the prostaglandin synthesis inhibitor indomethacin, indicating that A23187 acts by increasing the prostaglandin synthesis and not by a direct action of Ca2+ ions per se. The net water flow (Jw) and the Cl secretion were measured simultaneously under the conditions outlined above. The stimulation, inhibition, and the time-course of the outward-directed Jw were similar to the change observed for the Cl secretion. These results show that PGE2 stimulates a glandular secretion of Cl and water in frog skin, probably by increasing the cAMP level in the gland cells.

Amiloride↗
PubMed1987

The effect of temperature and humidity levels in a protective mask on user acceptability during exercise.

Subjective and physiological responses were obtained from six subjects wearing a ventilated face mask while exercising (3.8 met) for 15 min on a bicycle ergometer. Different combinations of ambient air temperatures (7 degrees, 16 degrees, 25 degrees C) and mask air temperatures (22 degrees, 27 degrees, 33 degrees C) were studied together with two different air humidities inside the mask (61% and 86% RH). Control experiments were performed without the mask at the same ambient temperatures. Skin temperatures, heart rates and skin wettedness were monitored during exercise. The subject's acceptance of the mask and thermal environment, thermal sensation, sensations of discomfort, sweating and skin wettedness, and their judgment of the work of breathing were assessed at the end of the 15 min exercise period. The acceptance of both the ambient thermal environment and of the thermal microclimate in the mask primarily was determined by the ambient air temperature, but it was influenced by the air temperature and humidity inside the mask. At ambient temperatures of 7 degrees C and 25 degrees C, the acceptance of the thermal work conditions decreased. In the warm environment a mask air temperature less than or equal to 27 degrees C was 100% acceptable and increased the acceptance of thermal environment. In the cool environment, a mask air temperature greater than or equal to 27 degrees C was 100% acceptable. The humidity content of the mask air was only important when the mask air was warm. Warm humid air significantly decreased acceptance of the mask conditions.

Adult↗
PubMed1987

Effect of Ba2+ and furosemide on K+ and Rb+ secretion and absorption in isolated frog skin.

The aim of the present investigation was to explore whether in isolated frog skin there should be different pathways for K+ absorption and secretion. Therefore, the unidirectional fluxes of 42K+ and the K+-like isotope 86Rb+ were measured. By using various transport inhibitors, separate pathways for active K+ absorption and secretion were detected. The data obtained indicate that the transepithelial K+ and Rb+ transport across isolated frog skin is made up of four different components: one passive and three active. One of the active components is directed from the apical to the basolateral solution, whereas the other two are in the opposite direction. The direction of the net K+ transport depends on the activities of these three active transport components. The active uptake mechanism, which is present in the epithelial cells, discriminates between K+ and Rb+. The ratio between the K+ and Rb+ influxes, K/Rb, is about 3. The presence of Ba2+, furosemide or ouabain in the apical solution had no effect on the K+ influx. The active secretion of K+ takes place via two different pathways, namely the skin glands and the epithelial cells. The K+ secretion via the glands is inhibited by furosemide (basolateral), but is unaffected by Ba2+ (apical) and does not discriminate between K+ and Rb+. The active K+ secretion via the epithelial cells is blocked by apical Ba2+, and it discriminates between K+ and Rb+. The ratio between the K+ and Rb+ effluxes is about 2. The data presented show that the K+ channels in the apical and the basolateral membrane of the epithelial cells discriminate between K+ and Rb+.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Clothing and thermal environments. Field studies on industrial work in cool conditions.

Thermal environmental factors, heart rate, skin temperatures and thermal sensation votes were recorded in 19 workers in different types of cool environment industries. 45 workers from the same workplaces completed questionnaires. Transient thermal conditions were prevalent. After exercise chill, progressive cooling of the body during the working day, and cooling of hands and feet were general problems. Local cooling of certain body areas was found to be a trade-specific problem. Commonly used work clothing was insufficient for thermal comfort. Proposals for a more suitable choice of work clothing are given.

Journal Article↗
PubMed1986

Trifluoperazine stimulated sodium transport by increased prostaglandin E2 synthesis in isolated frog skin (Rana esculenta).

Addition of trifluoperazine (TFP) to the inside bathing solution of the isolated frog skin resulted in a biphasic increase in the short-circuit current (SCC). The Na+-flux measurements showed that the TFP-induced increase of SCC was accounted for by active sodium transport. The intracellular voltage in short circuited skins changed after addition of TFP (100 microM) from a control value of -80.9 +/- 0.8 to -66.2 +/- 1.0 mV (n = 8). This depolarization indicates that TFP acts by increasing the Na+-permeability of the apical membrane. The biphasic increase in SCC is due to different mechanisms. The primary activation could be abolished by the calcium ionophore A23187, whereas the secondary activation could be abolished by the prostaglandin synthesis inhibitor indomethacin, PGE2 or A23187. Stimulation of the SCC by TFP and theophylline or antidiuretic hormone (AVT) was additive. Furthermore, TFP did not increase the cAMP level of isolated epithelia or theophylline-stimulated epithelia. These results indicate that the TFP-induced change in the Na+-permeability was not due to an enhanced cAMP level. The TFP simulated SCC requires Ca2+ in the inside bathing solution. Addition of TFP resulted in an increase in prostaglandin E2 release to the inside bathing solution from a control value of 0.31 +/- 0.04 to 5.4 +/- 1.4 pmol PGE2 h-1 cm-2 (n = 8). It is suggested that TFP induces a Ca2+-dependent PGE2 synthesis, leading to an increase in the intracellular PGE2 concentration which might increase the Na+-permeability of the apical membrane.

Animals↗
PubMed1985

Cryopreservation of osteo-chondral grafts in rabbits.

To study the cryopreservation of osteoarticular allografts, a lateral femoral condyle of the rabbit was transplanted fresh, after uncontrolled freezing to -80 degrees C with 4 weeks preservation, and after freezing 1 degree C per min to -100 degrees C in 10 per cent dimethylsulphoxide medium with 4-week storage in liquid nitrogen. Autografts were used as controls. After 3 months, the incorporation of the grafted bone was good in all technically successful cases. The NADH2 diaphorase activity and 35S sulphate uptake indicated well-functioning chondrocytes in all autografts. In the allografts, areas lacking enzyme activity and lacking 35S uptake were observed in cartilages with otherwise normally functioning chondrocytes. No differences were found between the three allograft groups. We conclude that freezing permits reasonably good short-term bank preservation of cartilage. We found no difference between conventional freezing and controlled slow freezing with preservative.

Animals↗
PubMed1984

Influence of skin temperature distribution on thermal sensation in a cool environment.

Thermal sensation and distribution of skin temperatures in persons exercising at 36.5 W on a bicycle ergometer and resting in a cool environment (10 degrees C) in two different clothings, one with the insulation mainly over the trunk (1.22 clo), and one with well insulated limbs (1.67 clo), were studied. Their general thermal sensations varied from slightly warm to slightly cool. The placing of the insulation had a decisive influence on skin temperature distribution, so that skin temperature was always high in well-insulated areas. When the insulation was placed over the limbs, a greater amount of heat was lost than if a similar insulation was placed on the trunk. Neither Tsk nor skin temperature distribution correlated with general thermal sensation. Instead, mean body temperature seemed to be the determinant of general thermal sensation in these conditions. The best prediction of general thermal sensation was obtained by adding Tre with a weighting factor of 0.8-0.9 and Tsk with a weighting factor of 0.1-0.2.

Adolescent↗
PubMed1984

Measurement of mean skin temperature of clothed persons in cool environments.

The precision with which mean skin temperature could be estimated from some few points on clothed persons in a cool environment was studied. The skin temperature data were obtained from experiments on 10 clothed persons who were resting and working at an environmental temperature of 10 degrees C. With these data, eleven calculation formulas in current use were compared to a "reference mean skin temperature" based on a weighting formula involving 13 local skin temperatures. It was concluded that no formula including less than seven points gave a reasonably accurate mean skin temperature in this cool environment. In addition, a stepwise correlation analysis involving linear regression was performed on the data. This gave 12 new calculation formulas, which were evaluated for accuracy in estimating mean skin temperature. Among these, a weighting formula involving only four local skin temperatures was selected to be recommended for use in field investigations: Tsk = 9.429 + 0.137 X Tforehead + 0.102 X Thand + 0.290 X Tlower back + 0.173 X Tlower leg.

Adolescent↗
PubMed1984

Correlation between cAMP in isolated frog skin epithelium and stimulation of sodium transport and osmotic water flow by antidiuretic hormone and phosphodiesterase inhibitors.

The cAMP level in isolated frog skin epithelia was stimulated by a range of concentrations of the antidiuretic hormone arginine vasotocin (AVT) and compared to active sodium transport measured as short-circuit current (SCC). The response of SCC and osmotic water flow (OWF) to AVT was investigated in a separate series. SCC was approximately three times more sensitive to AVT than OWF. Measurable increments of cAMP above the basal level were found only with AVT concentrations eliciting half-maximal response or more of SCC. Two models are offered to explain the findings: (A) Total SCC depends on epithelial cAMP with a sigmoidal relationship. (B) Epithelial cAMP exists in two separate pools of which only one is accessible to AVT, and SCC stimulation depends on cAMP in the AVT-controlled pool in a simple saturable fashion. Correlation between cAMP and SCC after stimulation with theophylline resembled that after AVT. Papaverine (10 microM) induced only small changes in SCC inspite of a substantial increase in cAMP level. Higher concentrations of papaverine inhibited both basal and AVT-stimulated SCC, while the cAMP level was further increased. This effect of papaverine may be due to a simultaneous block of another rate-determining process. Papaverine had no effect on basal or AVT-stimulated OWF despite a marked stimulation of the cAMP level. Thus, the role of cAMP as mediator of the hydroosmotic action of AVT must be questioned.

3',5'-Cyclic-AMP Phosphodiesterases↗