Effect of Immobilization and Concurrent Exposure to a Pulse-Modulated Microwave Field

Stagg RB, Hawel LH III, Pastorian K, Cain C, Adey WR, Byus CV,

Radiat Res 155(4):584-592, 2001

Effect of Immobilization and Concurrent Exposure to a Pulse-Modulated Microwave Field on Core Body Temperature, Plasma ACTH and Corticosteroid, and Brain Ornithine Decarboxylase, Fos and Jun mRNA.

Exposure of humans and rodents to radiofrequency (RF) cell phone fields has been reported to alter a number of stress- related parameters. To study this potential relationship in more detail, tube-restrained immobilized Fischer 344 rats were exposed in the near field in a dose-dependent manner to pulse-modulated (11 packets/s) digital cell phone microwave fields at 1.6 GHz in accordance with the Iridium protocol.

Core body temperatures, plasma levels of the stress-induced hormones adrenocorticotrophic hormone (ACTH) and corticosterone, and brain levels of ornithine decarboxylase (Odc), Fos and Jun mRNAs were measured as potential markers of stress responses mediated by RF radiation.

We tested the effects of the loose-tube immobilization with and without prior conditioning throughout a 2-h period (required for near-field head exposure to RF fields), on core body temperature, plasma ACTH and corticosteroids. Core body temperature increased transiently (+/-0.3 degrees C) during the initial 30 min of loose- tube restraint in conditioned animals. When conditioned/tube- trained animals were followed as a function of time after immobilization, both the ACTH and corticosterone levels were increased by nearly 10-fold. For example, within 2-3 min, ACTH increased to 83.2 +/- 31.0 pg/dl, compared to 28.1 +/- 7.7 pg/dl for cage controls, reaching a maximum at 15-30 min (254.6 +/- 46.8 pg/dl) before returning to near resting levels by 120 min (31.2 +/- 10.2 pg/dl).

However, when non-tube-trained animals were submitted to loose-tube immobilization, these animals demonstrated significantly higher (3-10-fold greater) hormone levels at 120 min than their tube-trained counterparts (313.5 +/- 54.8 compared to 31.2 +/- 10.2 pg/dl; corticosterone, 12.2 +/- 6.2 ?g/dl compared to 37.1 +/- 6.4 ?g/dl).

Hormone levels in exposed animals were also compared to those in swim-stressed animals. Swimming stress also resulted in marked elevation in both ACTH and corticosterone levels, which were 10-20 fold higher (541.8 compared to 27.2-59.1 pg/dl for ACTH) and 2-5 fold higher (45.7 compared to 8.4- 20.0 ?g/dl for corticosteroids) than the cage control animals.

Three time-averaged brain SAR levels of 0.16, 1.6 and 5 W/ kg were tested in a single 2-h RF-field exposure to the Iridium cell phone field. When RF-exposed and sham-exposed (immobilized) animals were compared, no differences were seen in core body temperature, corticosterone or ACTH that could be attributed to near-field RF radiation.

Levels of Odc, Fos and Jun mRNA were also monitored in brains of animals exposed to the RF field for 2 h, and they showed no differences from sham-exposed (loose-tube immobilized) animals that were due to RF-field exposure.

These data suggest that a significant stress response, indicated by a transient increase in core body temperature, ACTH and corticosterone, occurred in animals placed in even the mild loose-tube immobilization required for near-field RF exposure employed here and in our other studies. Failure to adequately characterize and control this immobilization response with appropriate cage control animals, as described previously, could significantly mask any potential effects mediated by the RF field on these and other stress-related parameters.

We conclude that the pulse-modulated digital Iridium RF field at SARs up to 5 W/kg is incapable of altering these stress-related responses. This conclusion is further supported by our use of an RF-field exposure apparatus that minimized immobilization stress; the use of conditioned/tube-trained animals and the measurement of hormonal and molecular markers after 2 h RF-field exposure when the stress-mediated effects were complete further support our conclusion.