Human Pituitary Hormones: Circadian and Episodic Variations

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During the last decade, circadian and episodic fluctuations of the plasma levels of pituitary hormones have been demon~ trated in man. The interest in the time dependence of the pituitary secretions partially originates from their close functional relation with the neuroendocrine mechanisms pre­ sumably responsible for the control of the circadian.rhyth­ micity in man. High frequency blood sampling techniques and specific radio­ immunoassays have allowed to describe in detail the varia­ tions over the 24-h cycle of the hormonal concentrations in healthy individuals under basal conditions as well as after manipulation of external synchronizers such as the sleep­ wake cycle, the dark-light cycle and the feeding schedule. Alterations in normal hormonal var~ions have been sugges­ ted to play a role in the etiopathogeny of several metabo­ lic and mental diseases, such as obesity or manic-depressio~ Important clinical implications regarding treatment and pre­ vention are expected to be developed in the near future. However, so far, data obtained in different groups are dif­ ficult to compare because different hormones were studied using different protocols and statistical methods. As a result, unclear or controversial issues are not uncommon.