Adrenocortical hormones are known to cause which of the following responses?

Adrenocortical hormones, particularly glucocorticoids like cortisol, play a vital role in glucose metabolism. When these hormones are released, they stimulate gluconeogenesis, which is the process of producing glucose from non-carbohydrate sources, primarily in the liver. This action is essential during times of stress, allowing the body to maintain adequate energy levels by increasing the availability of glucose in the bloodstream. By doing so, adrenocortical hormones provide the necessary energy for cells, especially those in the brain and muscles, to respond effectively to stressors.

In the context of the other options, a decrease in blood volume is typically associated with conditions that might be opposite to the action of adrenocortical hormones, which tend to promote water retention and consequently could lead to an increase in blood volume. An increase in immune system activity contradicts the known immunosuppressive effects of glucocorticoids; they actually tend to suppress inflammation and the immune response. Lastly, while adrenocortical hormones can influence protein metabolism, they do not primarily lead to an increase in protein production; instead, they can promote protein catabolism under certain conditions, particularly in the context of stress.