Hypotheses Concerning the Mechanism of Adenohypophyseal Hormone Release by Neurosecretory Material in Mammals
Emerson, Marcia Brackney
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Resolution of issue, as all the others discussed throughout this paper, awaits further research. The necessity to investigate the the link that certainly seemed to exist between the nervous and endocrine systems could not be denied. Research has established with a great degree of certainty the embryology, anatomy, and histology of the pituitary gland and the hypothalmus. The afferent nervous and humoral pathways leading to the hypothalmus have been fairly well established as has the release of the trophic hormones and their subsequent action upon their target organs. The question of what activity transpires in the hypothalamo-hypophysea1 system in the interval between hypothalamic stimulation and hypophyseal response has yet to be answered. Part of the enigma has been elucidated. Hypothalamic median eminence extracts have yielded individual release factors which have been shown to actively cause the release of their specific trophic hormones. The amino acid sequence of one on these release factors has already been found in its entirty. The others will probably be determined within the next two to three years of research. But questions as to the composition and function of the populations of vesicles and granules in hypothalmic nerve endings, or how the neurosecretory release factors are liberated from the neuronal endings to the capillaries will be answered only after much more research. Again experimental evidence has, shown that an activity does occur. but does not explain how it occurs. And the primary question still remains, How, by what mechanism, does the ISM act on the adenohyposeal cells? On this issue the experimental data are so new as to allow unrestrained hypothesizing. Hence a genetic induction and repression and a neurosecretory release factor addition model were proposed. Each is supported by small amounts of data and large amounts of hopefully logical supposition. What remains is for research to evaluate the adequacy of either of these hypotheses separately, or both functioning together.