As one of the main uses of ginseng is as an antistress agent, it is necessary to consider the mechanism of stress reaction. In the living body such reaction is controlled by
1) the hypothalamus, which is embedded in the lower or "visceral" part of the brain and has an important automatic regulatory role concerning the internal environment of the body e.g. water balance, food intake, mammalian body temperature, hormone release via the pituitary gland, as well as responding to signals from the conscious or thinking areas of the brain,
2) the pituitary gland which controls the other endocrine or ductless glands and is a pea-shaped endocrine structure also in the brain and connected to the hypothalamus by the infundibulum, and
3) the adrenal or suprarenal glands which are located one above each kidney and yield the steroid hormones and catecholamines.
The hypothalamus receives signals from higher centres of the brain indicating a stress situation; such stimulation causes release of chemical messengers called peptide neurohormones into the blood stream prompting the activation of the pituitary gland with the release of signals to the adrenal glands via the adrenocorticotrophin hormone (ACTH). Responding to ACTH stimulation the adrenal cortex, the outer area of the adrenal gland, secretes corticosteroids (glucocorticoids e.g. hydrocortisone or cortisol) which rapidly mobilise the body's carbohydrate, protein and fat reserves. In man hydrocortisone forms 95 per cent of the total glucosteroids formed in the adrenal cortex. Production and distribution of glucosteroid stress hormones is increased under stress although limited in the body at rest even when ginseng is administered. Ginseng encourages adrenal gland response in stress situations and also facilitates a rapid shutdown when the stress is removed. If the stress is prolonged the adrenal glands conserve their reserves and do not release so much hormone i.e. there is a greater sensitivity to stress. Significantly ginseng saponins, despite their triterpenoid structure which closely resembles steroid structure, have little effect on normal organisms although effective in stressed, injured or impaired animals by stimulation of the pituitary-adrenocortical system.
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