The study aimed to investigate the effect of an external stressor (magnetic field) and an internal stressor (ischemia) on the two main stress‐responsive neuroendocrine systems: the hypothalamus‐pituitary‐adrenal and hypothalamus‐pituitary‐thyroid axes.
Gerbils were divided into the following groups: 1) magnetic field exposure (n=11), 2) ischemia (submitted to occlusion of both carotid arteries for 10 min) (n=11); 3) ischemia + magnetic field co-exposure (n=11), 4) sham exposure (n=6), 5) sham surgery (n=6); 6) control group (n=3). To evaluate the immediate and delayed effects of the treatments, one‐half of the animals from each group (except control group) were sacrificed 7 days and the other half 14 days after onset of the experiment.
As there were no significant differences between or within the sham exposure (group 4), sham surgery (group 5) and control group (group 6), all parameters of the treatment groups were compared to a single control value only.
|Chamber||Cages with 3-4 gerbils|
|Setup||Electromagnet with a regular laminated transformer core and pole diameter of 9.5 cm producing a gradient magnetic field; magnetic force lines were parallel to the horizontal component of the local geomagnetic field; two cages with gerbils were simultaneously placed one on each side of the electromagnet; their centers were 20 cm away from the electromagnetic poles; with the electromagnet turned on, the temperature increased slightly in the cages (up to 0.3°C); to prevent the transfer of mechanical vibrations to the animal cages, they were placed at a sufficient distance from the electromagnet, fixed on foam sponges and covered with perforated plexiglas plates; the gerbils moved freely within the cages; exposure was performed in an isolated room under identical standard conditions (temperature, humidity, light intensity and cycle) as in the animal facility where the animals were reared|
|Sham exposure||A sham exposure was conducted.|
Exposure to the magnetic field (group 1) and ischemia (group 2) and particularly the co-exposure (group 3) significantly decreased the volume density of ACTH cells after 7 days compared to the control. Moreover, intracellular ACTH content and plasma ACTH concentration were significantly increased after 7 days in group 3 compared to the control. Serum TSH concentration was significantly increased on day 7 in group 1 and after 14 days in group 2 and intracellular TSH content was significantly increased on day 14 in groups 1 and 3 compared to the control.
The authors conclude that exposure of gerbils to a 50 Hz magnetic field and cerebral ischemia could induce immediate and delayed stimulation of pituitary ACTH and TSH synthesis and secretion.