Prolactin, growth hormone and thyrotropin-thyroid hormone secretion during stress states in man

Changes in hormone secretion and/or metabolism almost constantly accompany stressful events. The hormonal response to stress is directly related to the intensity of the stimulus, and greatly depends on the individual's perception of potentially stressful situations. Hypoglycaemia, surgery and exercise represent physical, metabolic and psychological stressful events where the activation of the endocrine system plays a great role. These endocrine responses also include the secretion of GH and prolactin, but the response pattern varies with the stimulus. Hypoglycaemia, exercise and surgery are potent stimuli to GH and prolactin release, both in men and women. The available data suggest that prolactin is more responsive than GH to surgical stress, whereas physical exercise and hypoglycaemia preferentially stimulate GH secretion. Prolactin levels during hypoglycaemia rise solely when symptomatic neuroglycopenia is achieved. By contrast, prolactin and GH responses to purely psychological stress are rarely seen, although some forms of reproductive stress may potentiate prolactin release in women. A teleologically satisfactory rationale for the acute GH and prolactin rise in response to these stressful stimuli is not clearly apparent in man. No definite metabolic activity of prolactin on intermediate metabolism has been demonstrated, although prolactin is mildly diabetogenic. The known metabolic actions of GH do not appear to be critical during surgery or acute hypoglycaemia, although GH probably participates in the regulation of metabolic homeostasis during chronic hypoglycaemia and chronic exercise. Changes in secretion and/or metabolism of hypothalamic neurotransmitters can increase the secretion of GH by increasing the secretion of GHRH or by decreasing the secretion of somatostatin. The prolactin rise is brought about by either a decrease in dopamine activity, an increased secretion of a hypothetical PRF, or by both mechanisms. Since multiple neuronal pathways converge on the hypothalamus from many other parts of the brain, the pronounced effects of hypoglycaemia, exercise and surgery on the secretion of GH and prolactin also reflect the action of different and complex neural inputs on the activity of the hypothalamic-pituitary axis. However, the morpho-functional mapping of these excitatory pathways still remains incomplete. TSH secretion is tightly regulated by the negative feed-back mechanism exerted by thyroid hormones. The small changes in TSH level observed during surgery and physical exercise seem to reflect mainly alterations in peripheral T4 metabolism.(ABSTRACT TRUNCATED AT 400 WORDS)