CENTRAL AUTONOMIC MECHANISMS 



967 



thalamus (160). These functions arc undoubtedly 

 conjoint with the anterior pituitary, and Bogdanove 

 & Halmi (29) have shown that bilateral lesions in 

 the anterior part of the hypothalamus suppress the 

 formation of thyrotrophic hormone by the former and 

 block the goitrogenic effect of thiouracil. 



HYPOTHALAMICOHYPOPHYSIAL RELATIONSHIPS. It is 



certain that not all functions of the hypophysis are 

 under nervous control, especially those of the an- 

 terior lobe which is able to respond to chemical 

 feed-back mechanisms such as changes in blood 

 concentration of various hormones from other en- 

 docrine glands. It is also likely that such nervous 

 control as exists may vary in different animal forms. 

 There is, however, evidence of nervous participation 

 in the regulation of the functions of both of the chief 

 lobes. Chapter XXXIX of this work is de\oted to 

 this subject. 



a) The Posterior Lobe. The posterior loije is chiefly 

 concerned with water metabolism, although a sub- 

 stance which promotes contraction of smooth muscle 

 is also formed within it. An antidiuretic hormone 

 which promotes reabsorption of water in the distal 

 convoluted portion of the renal tubule against the 

 osmotic influences of the blood is formed and re- 

 leased in the posterior lobe and its stalk. Production 

 of this powerful substance depends upon the integrity 

 of nerve fibers which originate from the supraoptic 

 nucleus. There have been two theories concerning 

 the production of this hormone. The first proposes 

 that nerve impulses conveyed by fibers of the supra- 

 opticohypophysial tract bring about the production 

 and release of the antidiuretic hormone by the 

 pituicytcs which are glia-like cells peculiar to the 

 posterior lobe. Against this theory is the fact that 

 after degeneration of the supraopticohypophysial 

 tract there is no change in the characteristics of these 

 cells. 



Another theory, supported by Scharrer (147) and 

 others, proposes that the neurons and fibers of the 

 supraopticohypophysial tract actually form and 

 secrete the hormone. This theory is based in the 

 first place upon the occurrence of a stainable sub- 

 stance within the cell bodies and axons of these 

 neurons. This neurosecretory suiistance may be 

 a forerunner of the antidiuretic hormone, it may be a 

 carrier for the antidiuretic hormone or it may inter- 

 act with the pituicytes in the production of the anti- 

 diuretic hormone. This hormone has ijeen extracted 

 from the supraoptic region of the hypothalamus, and 

 sectioning or occlusion of the pituitary stalk produces a 

 damming back of the secretory material which ordi- 



narily is presumed to work its way out along the 

 axons to the fiber endings. While the neurosecretory 

 material has not been positively identified with the 

 antidiuretic hormone, some histochemical attempts 

 have been made to check this possibility. Barrnett 

 (17) found disulfide groups in the hypothalamico- 

 hypophysial fibers in the stalk and in the infimdibular 

 process in dogs and rats. In extracts of the neuro- 

 hypophysis, insoluble pituitrin also stained for di- 

 sulfides. Sloper (155) and Adams & Sloper (i) have 

 recently advanced histochemical evidence that the 

 neurosecretory material has a close similarity to the 

 cyclic octapeptides of du Vigneaud. While not com- 

 pletely proved, the neurosecretory theory is extremely 

 attractive and fits \ery well with modern ideas con- 

 cerning the regulation of urine output, including the 

 phenomena of diabetes insipidus. The subject is 

 further considered in Chapter XL of this work by 

 Ortmann. 



There is now ample evidence that diabetes in- 

 sipidus, which is characterized by excretion of large 

 quantities of dilute urine, is due to degeneration of 

 the supraopticohypophysial system, to interruption 

 of these ncr\'e fibers high in the pituitary stalk, or 

 to the destruction of the posterior lobe together with 

 the stalk (51). Experimental findings in aniinals have 

 been amply confirmed by observations on human 

 patients (67). If all sources of antidiuretic hormone 

 are completely eliminated, diabetes insipidus will 

 occur even if the anterior lobe of the pituitary is 

 absent; but polyuria is never maximal under these 

 circumstances. A maximal polyuria depends upon 

 normal levels of metabolic activity throughout the 

 body, and these depend upon normal anterior lobe 

 function. Diabetes insipidus in itself is probably not 

 associated with abnormalities of salt metabolism. 

 The latter may occur, however, with other types of 

 lesions of the hypothalamus which depress the ap- 

 petite for fluids. Application of the neurosecretory 

 theory to this condition accounts for the survival of 

 the pituicytes in otherwise degenerated infundibulo- 

 hypophysial structure. 



There is excellent evidence that the rate of pro- 

 duction of antidiuretic hormone varies in accord with 

 changes in osmotic pressure of the blood (161). 

 Increase in the osmotic pressure of the blood which 

 supplies the supraoptic nuclei increases the activity 

 of these neurons and increased amounts of anti- 

 diuretic hormone are released to ineet the need for 

 water conservation. It is interesting to note in this 

 connection that the paraventricular and supraoptic 

 nuclei have an exceedingly rich blood supply. Verney 

 has hypothecated the existence of osmoreceptors in 



