Regolazione Della Secrezione Dell'ormone Somatotropo: Tentativo Di Interpretazione Unitaria [Regulation of somatotropin secretion: attempted unitary interpretation]

The various aspects of growth hormone secretion are considered: it is subject to the influence of the energy substrates, such as glucose, NEFA and proteins (metabolic regulation) and to catecholamine mechanisms (stress, vasopressin, pyrogens, L-dopa); there is also a rhythmic secretion of GH, the mechanism of which is as yet undefined, related to sleep (SWS). While metabolic stimulation can be inhibited by simultaneous glucose administration, this is not so for catecholamine- or sleep-related stimulation. On the basis of these premises and of the assumption that GH secretion is regulated at the diencephalic level, a comprehensive hypothesis interpreting the control mechanism of growth hormone secretion is set out. It is suggested that the metabolic signal and the catecholamine signal are picked up independently, or rather that the second acts at a lower level than the first, so that contrary to the first it cannot be influenced by hyperglycemia. In other words the existence of a chemoreceptor is postulated which would be sensitive to information concerning energy substrates and would transmit the signal by an adrenergic mechanism. Reception in the GH-RF-secreting cell would be by α-receptors. As to topographical distribution, it is suggested that metabolic control occurs in the middle-posterior diencephalon (ventromedial nucleus) and the stress-and sleep-related control in the anterior diencephalon (paraventricular nucleus)