The Adrenal Cortex
The adrenal corticoid response to EMF stimulation is highly time-dependent (7). When groups of rats were exposed to 500, I000, 2000 and 5000 v/m at 50 Hz, the average urine-corticoid level of the latter two groups changed similarly during the 4-month exposure period (7): approximately the same maximum value was achieved in both groups and they exhibited increased corticoid levels as compared to the controls. The Iooo-v/m group, however, exhibited lower corticoid levels for the first 2 months of the exposure period followed by a rise above the control level during the last half of the exposure period; at 500 v/m the pattern of corticoid excretion was identical to that of the controls. The biological response was reversible in the sense that when the hela was removed, the corticoid level returned to normal within 2 months.
One of the important factors governing the time course of the corticoid level-and hence the dynamics of the pituitary-adrenal response-is the ratio of the exposure period to the nonexposure period. This was established by Udinstev who exposed groups of rats to 200 gauss, 50 Hz, intermittently for 6.5 hours/day, for 1, 3, 5, and 7 days, and, continuously for I and 7 days (9) (Table 6.2). The corticoid level in the continuously exposed rats was significantly greater than in the controls: following intermittent exposure, however, the corticoid response was considerably different. After 4 days-the total cumulative exposure was 26 hours-it was significantly lower in the exposed rats, and this trend continued after 5 and 7 days of intermittent exposure.
Table 6.2. SERUM CORTICOID LEVELS IN RATS FOLLOWING EXPOSURE TO CONTINUOUS AND INTERMITTENT (6.5 hr/day) 50-HZ MAGNETIC FIELDS
At 3 GHz, rats exposed to 5-10, µW/cm2, 8 hours/day, had elevated levels of excreted corticoids after I-3 months of exposure (10). At 60 GHz, 15 minutes/day, rats exhibited depressed levels of serum corticoids after 2 months (11). In such high-frequency EMF studies it is usually impractical to continuously expose the animals, because the fields can interfere with norrnal feeding and watering practices, thereby introducing artifacts. Thus, judging from the Udinstev studies, the intermittent exposure aspect of high-frequency studies is an additional factor-along with the characteristics of the EMFs and the physiological state of the organism- that will affect the time course of the corticoid response.
Changes in the gross weight of the adrenal gland reflect changes in its activity. Demokidova showed that I hour/day EMF exposure of rats produced changes in adrenal weight that were both time and frequency dependent (12-14). After 2 weeks, exposure at 3 GHz, the adrenals of the exposed rats were significantly larger than those of the sham-irradiated group: after 5 months, however, there were no adrenal-weight differences. At 70 MHz, adrenal weights, in the exposed animals were elevated after 1 week's and 1 month's exposure, but following 3 months' exposure they were depressed. After 8 months' exposure at I5 MHz, adrenal weights were similarly depressed below the corresponding control weight. There are two reports of EMF-induced histological changes in adrenal tissue (14, 15). The relative size of the innermost or reticular zone of the adrenal cortex was decreased following 3 months' exposure at 70 GHz (14). Exposure to I 30 gauss, 50 Hz, (4 hours/day) for I month resulted in changes in the blood vessels in the reticular zone along with some hemorrhage and dystrophic cellular changes (15). Four months' exposure to 5000 v/m, 50 Hz, produced no histological changes and no change in gross adrenal weight (7).