Does the magnetic field of a magnetic stirrer in an optical aggregometer affect concurrent platelet aggregation?

Platelets are subjected to extremely low frequency electromagnetic fields during standard aggregometry measurements owing to the use of a magnetic stir bar in the instrument. This study evaluates the effects of this magnetic field exposure on platelet aggregation by comparing the results obtained in a modified aggregometer. Blood samples from healthy volunteers were anticoagulated using citrate or heparin. Platelet-rich plasma (PRP) samples were prepared. A mechanical stirring device was attached to the aggregometer instead of the magnetic stir bar system. The PRP samples were stirred using a stirring rod tip that did not produce any magnetic fields in one channel of the aggregometer; in the other channel, a stirring rod carrying a small magnet at its tip was used. As a result, a magnetic field in the extremely low frequency range and in the amplitude range of 1.9-65 mT was applied to the platelets assigned to the channel where the magnetic stirring rod tip was used. Aggregation was induced using adenosine diphosphate (ADP), collagen, or epinephrine. The slopes, maximum aggregation values, and areas under the aggregation curves were compared between the magnetic and neutral stirring rod tip groups. For samples stirred with the magnetic stirring rod tip, a significant decrease was observed in 12 of the 14 parameters evaluated for aggregations induced with ADP or collagen compared to the neutral stirring rod tip, regardless of the method used for anticoagulation. This observation indicates that the magnetic stir bars used in standard aggregometry may significantly alter aggregation parameters and platelets may be possible targets of electromagnetic fields.

Investigation of the effects of 50 Hz magnetic fields on platelet aggregation using a modified aggregometer.

PURPOSE: Electromagnetic fields have various effects on intracellular calcium levels, free oxygen radicals and various enzymes. The platelet activation pathway involves an increase in intracellular calcium levels and protein kinase C activation; and free oxygen radicals play a mediating role in this pathway. This study investigated whether 1 mT and 6 mT, 50 Hz magnetic fields had any effects on platelet aggregation. MATERIALS AND METHODS: Blood from healthy volunteers was anticoagulated with either citrate or heparin. Each sample was divided in half and assigned to exposure and control groups. Platelet rich plasma samples in the exposure group were exposed to a 1 mT or a 6 mT, 50 Hz magnetic field for 1.5 or 1 h, respectively. The samples from both exposure and control groups were simultaneously evaluated using a modified optical aggregometer. Adenosine-diphosphate, collagen, and epinephrine were used as inducing agents. The slopes of the aggregation curve, the maximum values and the areas under the curves were recorded and compared. RESULTS: A significant effect was observed only in the 1 mT-citrate group. It was found that magnetic field exposure significantly increased the maximum values and slopes of the collagen-induced aggregations. CONCLUSIONS: It was found that magnetic field exposure has an activating effect on platelet aggregation.

Early menopause association with employment, smoking, divorced marital status and low leptin levels.

AIMS: The aims of this study were (1) to investigate the determining risk factors related to early menopause and (2) to compare the relationships between demographic characteristics and hormonal status and leptin levels in subjects with early (no surgical) and natural menopause. STUDY DESIGN: The prospective study was conducted on 500 women with early and 2700 women with natural menopause. Detailed information was collected about their employment status, past and present smoking habits, coffee and alcohol use, educational level and other factors relevant to health. Thirty participants with early menopause and 30 participants with natural menopause were evaluated for hormone and leptin levels. RESULTS: Employment status (OR: 1.94), current smoking (OR: 1.80) and divorced marital status (OR: 1.79) were found to be significant risk factors for early menopause. Mean levels of leptin in natural and early menopause were measured 11.40 ± 4.1 ng/ml and 8.01 ± 3.9 ng/ml, respectively (p = 0001). Leptin levels in the early (r = 0.765, p = 0.001) and natural (r = 0.750, p = 0.001) menopause subjects correlated positively with oestradiol (E2) levels. CONCLUSION: This study shows that early onset of menopause is correlated with smoking, employment status, divorced marital status and lower leptin levels.

A brain electrophysiological correlate of depth perception.

OBJECTIVE: To investigate brain electrical activity accompanying depth perception using random-dot stereograms. Additional experiments were conducted to ascertain the specificity of this potential to depth perception. METHODS: In the present study, we performed 3 different and independent experiments on 34 subjects to establish the relationship between depth perception and its cortical electrophysiological correlate. Visual evoked potentials in response to visual stimulation by random-dot stereograms were recorded. To achieve this goal, a data acquisition and analysis system, different from common visual evoked potential recording systems, consisting of 2 personal computers, was used. One of the computers was used to generate the visual stimulus patterns and the other to record and digitally average the potentials evoked by the stimuli. This study was carried out at the Department of Biophysics of Ege University Medical School, Izmir, Turkey, from April to December, 2006. RESULTS: A negative potential component, which is thought to arise in association with depth perception, was recorded from the occipital region from 30 of the 34 subjects. Typically, it had a mean latency of 211.46 ms and 6.40 uV amplitude. CONCLUSION: The negative potential is related to depth perception, as this component is present in the responses to stimulus, which carries disparity information but is absent when the stimulus is switched to no disparity information. Additional experiments also showed that the specificity of this component to depth perception becomes evident beyond doubt.