Study type: Medical/biological study (experimental study)

Effects of extremely low frequency electromagnetic fields on morphine analgesia and tolerance in rats. med./bio.

Published in: Gen Physiol Biophys 2017; 36 (4): 415–422

Aim of study (acc. to author)

To examine the effects of exposure to a 50 Hz magnetic field on morphine analgesia and tolerance in rats.

Background/further details

A total of 78 male rats were utilized. Rats were examined after 1, 4, 7, 11, and 15 days of exposure and at 30 min intervals after injection of morphine (time points of 0, 30, 60, 90, and 120 minutes).
In a first experiment, the analgesic effects of magnetic field exposure alone were examined in four groups (n=6 per group): 1.1) control group, 1.2) 1 mT magnetic field, 1.3) 5 mT magnetic field, and 1.4) 10 mT magnetic field.
In a second experiment, the ideal morphine concentration was determined to be 5 mg/kg body weight.
In a third experiment, the effect of the magnetic field on morphine analgesia was tested (n=6 per group): 3.1) saline solution, 3.2) magnetic field (5 mT), 3.3) morphine (5mg/kg), 3.4) magnetic field (5 mT) + morphine (5 mg/kg).
In a fourth experiment, the effect of the magnetic field on morphine tolerance was tested. Morphium tolerance was induced with high doses of morphine over three days (30 to 120 mg/kg). Four groups were utilized (n=6 per group): 4.1) saline solution, 4.2) morphine tolerant, 4.3) magnetic field (no magnetic flux density given), and 4.4) magnetic field + morphine tolerant.

Endpoint

Exposure

Exposure Parameters
Exposure 1: 50 Hz
Exposure duration: 120 minutes (intermittent 30 min on - 15 min off) per day for 15 days
experiment 1
Exposure 2: 50 Hz
Exposure duration: 120 minutes (intermittent 30 min on - 15 min off) per day for 15 days
experiment 3
Exposure 3: 50 Hz
Exposure duration: 120 minutes (intermittent 30 min on - 15 min off) per day for 15 days
experiment 4
  • no value given

Exposure 1

Main characteristics
Frequency 50 Hz
Type
Exposure duration 120 minutes (intermittent 30 min on - 15 min off) per day for 15 days
Additional info experiment 1
Exposure setup
Chamber rats were exposed in a plexiglass cage (40cm x 17cm x 13cm); three rats simultaneously
Setup plexiglass cage was placed in solenoid (length 500mm, diameter 210mm) with 1400 turns of insulated 1.4 mm copper wire; solenoid was in a north-south direction; temperature was kept constant at 22.0 ± 2°C
Sham exposure A sham exposure was conducted.
Parameters
Measurand Value Type Method Mass Remarks
magnetic flux density 1 mT - measured - -
magnetic flux density 5 mT - measured - -
magnetic flux density 10 mT - measured - -

Exposure 2

Main characteristics
Frequency 50 Hz
Type
Exposure duration 120 minutes (intermittent 30 min on - 15 min off) per day for 15 days
Additional info experiment 3
Exposure setup
Exposure source
Sham exposure A sham exposure was conducted.
Parameters
Measurand Value Type Method Mass Remarks
magnetic flux density 5 mT - measured - -

Exposure 3

Main characteristics
Frequency 50 Hz
Type
Exposure duration 120 minutes (intermittent 30 min on - 15 min off) per day for 15 days
Additional info experiment 4
Exposure setup
Exposure source
Sham exposure A sham exposure was conducted.
Parameters
Measurand Value Type Method Mass Remarks
magnetic flux density - - - - no value given

Exposed system:

Methods Endpoint/measurement parameters/methodology

Investigated system:
Investigated organ system:
Time of investigation:
  • after exposure

Main outcome of study (acc. to author)

Remark EMF-Portal: The results of the tail flick test and hot plate test were very similar, which is why the following text always refers to both tests.
In the first experiment, the analgesic effect of the magnetic field was shown. In all magnetic field exposed groups (groups 1.2-1.4), the latencies to the first sign of pain were significantly higher than in the control group (group 1.1). The highest latencies were found in the group exposed to a magnetic field of 5 mT (group 1.3) and after 90 minutes (probably after exposure was finished).
In the third experiment, both a magnetic field (group 3.2) and morphine (group 3.3) significantly increased the latencies compared to the saline solution (group 3.1). Furthermore, a combination of morphine and the magnetic field (group 3.4) increased again the latencies compared to morphine alone (group 3.3).
In the fourth experiment, it was shown that both a magnetic field (group 4.2) and morphine in morphine tolerant group (group 4.3) significantly increased the latencies compared to the saline solution (group 4.1). Furthermore, a combination of morphine and the magnetic field in morphine tolerant rats (group 3.4) increased again the latencies compared to morphine alone in morphine tolerant rats (group 3.3).
The authors conclude that a 50 Hz magnetic field increases morphine analgesia and reduces morphine tolerance in rats.

Study character:

Study funded by

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