The data available suggest that there are two levels in the neural control of the anterior pituitary. The first level is situated in the medial basal hypothalamus. It is termed ‘hypophysiotrophic area’ (HTA). It seems likely that this region produces the hypothalamic releasing and inhibiting substances that regulate anterior pituitary function and are carried by the portal circulation to the pituitary cells. Probably, this area can maintain the basal secretion of the anterior lobe hormones by itself. Part of the feedback action of the peripheral hormones and of the trophic hormones, as well as the action of some other substances appear to be exerted on this region. The second control level comprises neural structures outside the HTA, such as other hypothalamic regions, the limbic system, the midbrain, etc. This level controls normal pituitary function, among others cyclic release of the trophic hormones. Environmental as well as internal neural stimuli influencing pituitary hormone secretion are integrated at this level. The neural elements of this system appear to be hormone-sensitive and thus might react to changes in the actual levels of peripheral hormones in the blood. The second control level exerts stimulatory as well as inhibitory effects on the adenohypophysis, presumably acting via the HTA.
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