Hypothalamus, adenohypophysis and adrenal cortex.

Abstract

The conviction that the hypothalamus has a regulatory influence over the adenohypophysis is strengthened by new experimental data, but unfor­ tunately the precise mechanism or mechanisms by which this regulatory control is mediated remains unsettled. We have assumed that there is a connecting link between the hypothalamus and adenohypophysis which represents a final common path for the great variety of stimuli which in­ duce ACTH release. A logical sequence of developments would call for def­ inition of this final common path before proceeding to the delineation of the paths which subserve various categories of stimuli. Work has already been initiated to elucidate the tracts from lower and higher centers of the nervous system which lead into the hypothalamus and terminate on the final com­ mon path. In anticipation of new developments in this field we have de­ voted a relatively large part of this review to the neuro-anatomical features of the hypothalamus and its connections. The available evidence justifies the popularity of acceptance of the thesis that the portal venous system carries a neurohumor from the median eminence to the adenohypophysis. However, in the absence of unequivocal data to support the thesis or to establish it as the sole or major mechanism of regulation, we have purposely set out a fairly exhaustive classification of mechanisms regardless of available experimental support. Finally, we have emphasized those contributions on the nature of the secretion of the adrenal cortex which are based on steroid analyses of adrenal vein blood. Quantitative analysis of adrenal vein steroids represents a most profitable approach to pituitary and extrapituitary regulation of steroid secretion. New insight into fundamental problems of the homeostatic con­ trol of electrolyte composition and volume of body fluids will undoubtedly be gained within the next year or two as a result of investigations in this area.