HYPOPHYSEAL MORPHOLOGY 



229 



system in any one species (Adamson, Engel, 

 van Dyke, Schmidt-Neilsen and Schmidt- 

 Neilsen, 1956) . In the camel the ratio vaso- 

 is 2.6, the ratio in the paraventricular nu- 

 pressin: oxytocin in the supraotic nucleus 

 cleus is 0.26. The ratios of vasopressin to 

 oxytocin in the supraoptic and paraventric- 

 ular nuclei of the dog are approximately 10 

 times those in the camel. 



A simple explanation of these variations 

 would be provided by the hypothesis that 

 the two hormones are formed in different 

 cells. One advantage of such an hypothesis 

 is that it provides the only simple explana- 

 tion of the ability to secrete the hormones 

 separately (Smith, 1951). The fact that two 

 types of neurosecretory cells have not been 

 demonstrated in the supraoptic and para- 

 ventricular nuclei by staining reactions is no 

 objection to this hypothesis; the staining re- 

 actions at present used to demonstrate 

 neurosecretion would not be expected to 

 differentiate cells whose secretions are so 

 closely related chemically. 



F. INFERENCES CONCERNING RATE OF SECRE- 

 TION FROM CYTOLOGIC AND HISTO- 

 CHEMICAL STUDIES 



The staining of neurosecretion in sections 

 allows an estimate of the hormone content 

 and a demonstration of changes in hor- 

 mone content of different parts of the hypo- 

 thalamo-neurohypophyseal system to be 

 made, but does not demonstrate the rate of 

 formation or release of neurosecretion. The 

 demonstration by Sloper (1957) that S^^- 

 labeled cystine is incorporated into the 

 neurosecretion suggests a method by which 

 the rate of turnover as distinct from the 

 content may be investigated. 



The neurosecretion must be formed by 

 the ribonucleic acid-containing material in 

 the perikaryon which in nerve cells is called 

 Nissl substance. The marked accumulation 

 of neurosecretion in some neurones of old 

 animals of certain species which eventually 

 fills the axon, the dendrites, and a large 

 part of the perikaryon, is apparently the 

 result of an aging process which makes 

 it difficult for such cells to release their 

 secretion. That there is a stagnation in such 

 cells in indicated by the fact that the 

 amount of Nissl substance in such cells is 

 much reduced (Hild, 1956). 



It is the cells which do not show such 

 marked accumulations of neurosecretion, 

 except at their axone terminals, and have 

 large amounts of Nissl substance in their 

 perikarya, that are presumably responsible 

 for most of the secretory function of the 

 system. There does not seem, therefore, to 

 be any relation between the accumulations 

 of neurosecretion in the cells of the hypo- 

 thalamus and the secretory function; in 

 particular there is no reason to think that 

 the accumulation of neurosecretion in the 

 hypothalamus is related more directly to 

 alterations in adenohypophyseal than to a 

 disturbance of neurohypophyseal function. 



Pepler and Pearse (1957) observed hyper- 

 trophy of the cells of the supraoptic and 

 paraventricular nuclei in rats given 2.5 per 

 cent NaCl in the drinking water and also in 

 lactating rats. In both groups there was an 

 increase in the amount of specific acetyl- 

 choline esterase in the hypertrophied cells. 

 From these observations it may be inferred 

 that the reduction both of hormone content 

 and stainable neurosecretion observed by 

 Rennels (1958) in the neurohypophyses of 

 lactating rats was accompanied by an in- 

 creased production of neurosecretion and 

 was therefore the result of an increased rate 

 of discharge of this material. It would ap- 

 pear that the demonstration of the content 

 of specific enzymes by methods which are 

 capable of giving a cytologic localization 

 may prove to be a valuable method of 

 estimating the rate of secretion by endocrine 

 cells. Such methods are badly needed to 

 complement the information obtained from 

 the staining of specific granules which indi- 

 cates only the hormone content. 



XVI. References 



Adams. C. W. M., .'^nd Sloper, J. C. 1955. The 

 liypothalamic elaboration of posterior pituitary 

 principles in man, the rat and dog : histochemi- 

 cal evidence derived from a performic acid- 

 Alcian bhie reaction for cystine. J. Endocrinol., 

 13, 221-228. 



Ad.^ms, C. W. M., and Swettenh.^m, K. V. 1958. 

 The histochemical identification of two types 

 of basophil cell in the normal human adenohy- 

 pophysis. J. Path. & Bact., 75, 95-103. 



Adamson, K., Engel, S. L., v.^n Dyke, H. B., 

 Schmidt-Nielsen, B., and Schmidt-Nielsen, 

 K. 1956. The distribution of oxytocin and 

 vasopressin (antidiuretic hormone) in the neu- 

 rohvpophvsis of the camel. Endocrinology, 58, 

 272-278. 



