When the temperatures rise, our heat-sensitive tissues would be at serious risk if it were not for a suite of stress responses that protect us. One of the main hormones that regulates these protective responses is corticotropin,which in turn stimulates the adrenal gland to produce other stress hormones;so investigating the relationship between the stress hormone and the gland `is of great importance' say Vesna Koko and colleagues. The team decided to investigate the effects of heat stress exposure on the structure of rat adrenal glands (p. 4225).
Exposing rats to a heat wave of 38°C for an hour, the team found that,as expected, the animals' corticotropin levels had risen in response to the dangerous heat. When they looked at the adrenal gland, it seemed to have shrunk, with the glucocorticoid-producing Zona fasculata shrinking the most. However, the cells in one region, the Zona glomerulosa, seemed slightly enlarged in response to corticotropin, although there were fewer of them and the region had shrunk over all. Koko explains that the Zona glomerulosa produces aldosterone, a hormone that helps retain salt, and could protect the mammal from salt loss as it perspires and salivates in an attempt to keep its temperature down.