228 



HYPOPHYSIS AND GONADOTROPHIC HORMONES 



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I II. 3.35. Electronmicrograph of neurohyp(M'li\ -1- "i i ii. ni w \i mi 

 .Mcii luiy material inside vesicular membrane.-, i.t.. liioplLi- ol m uiu^^ucietuiy .-ub.-iancc, ur 

 neurosecretory granules. Electronmicrograph by S. L. Palay, National Institutes of Health, 

 Bethesda. X 37,100. 



SO closely packed as to leave little room for 

 any other structure. 



Palay finds the neurosecretory granules 

 in the neurones of the supraoptic nucleus 

 and in the axones throughout their course. 

 There is a concentration of the granules in 

 the terminal part of the axons (Fig. 3.35) . 

 The terminations are blunt or bulbous and 

 end on a basement membrane separated 

 by connective tissue from the basement 

 membrane and endothelium of the adjacent 

 capillaries. There do not appear to be any 

 secretory granules in the pituicytes. Se- 

 cretory granules are not found outside the 

 axones in tissue spaces or in the lumen of 

 the capillaries. It appears that only the 

 soluble content of the granule is liberated 

 during secretion ; the complete granules are 

 not extruded. 



D. THE HORMONE CONTENT OF THE 

 NEUROSECRETORY GRANULES 



From hypophyseal tissue homogenized in 

 sucrose solution oxytocic and vasopressor 

 activity can be deposited by centrifugation 

 (Pardoe and Weatherall, 1955) and from 



this behavior it is inferred that the hor- 

 mones are contained in the granules and 

 that in sucrose solution the granules are 

 preserved with their hormone content in- 

 tact. Pardoe and Weatherall obtained evi- 

 dence that the oxytocin and vasopressor ac- 

 tivities were in particles of different size or 

 of different fragility because a partial sepa- 

 ration was obtained by differential centrifu- 

 gation. This behavior of these hormones in 

 tissue suspensions in sucrose solutions is 

 paralleled by that of the gonadotrophic 

 hormones, as found hv McShan and Mever 

 (1952). 



The stainable content of the neurosecre- 

 tory granules is released by agents which 

 destroy the membrane. It is removed in tis- 

 sue which has been perfused by buffers sat- 

 urated with ether. 



E. THE DISTRIBUTION OE OXYTOCIN 

 AND VASOPRESSIN 



Tlie ratio of vasopressin to oxytocin 

 varies markedly among different species of 

 mammals and also is variable in different 

 parts of the hypothalamo-neurohypophyseal 



