Discussions 189 



Chairman Hisaw: Does that satisfy your curiosity? 



Dr. Roy O. Creep: I should like to know whether he thinks the neural secretory material 

 has anything to do with it, particularly that which has been identified in the supra- 

 optico-hypophyseal tract. 



Dr. Geoffrey Harris: I am a little bit doubtful about that for various reasons. One 

 reason is that if the supraoptico-hypophyseal tract is stimulated electrically, ovulation 

 does not necessarily occur. I am rather hesitant, therefore, about accepting this tract, 

 or the innervation of the neurohypophysis, as being concerned in the neural 

 mechanism underlying LH release in the rabbit. However, I think a polypeptide 

 related to those known to be present in the neurohypophysis may well be concerned. 

 If such a polypeptide is liberated at nerve terminals in the median eminence, the 

 mechanism could I suppose be referred to as neurosecretory in type. 



Dr. Roy O. Creep : I do not know of any other fibre tracts where there is thought to be 

 movement of material. The idea of axial flow, of neurosecretory material in the tract, 

 is now being questioned rather seriously. 



There is another question I would like to ask Dr. Harris. Has he any evidence as 

 to whether the active extract of the median eminence yields positive results by any of 

 the classic tests for neurohypophyseal activity ? 



Dr. Ceoffrey Harris: I think it is almost certain that such principles would be present 

 in our extracts. The only thing I can say at the moment is that a rough calculation 

 based on the amount of hormone known to be present in the posterior pituitary glands 

 of rabbits and the proportion of the rabbit neurohypophysis formed by the median 

 eminence, would indicate that only small amounts, of the order of 100 m U posterior 

 pituitary hormone, would be present in the extract of one rabbit median eminence. 



Referring to the idea of neurosecretion, the nerve fibres innervating the posterior 

 pituitary would seem to be analogous to those presumed to exist on the present 

 hypothesis. Posterior pituitary hormone does apparently exist, in one form or another, 

 through the whole length of the neurons which innervate the posterior pituitary gland. 

 Whether this material is in fact moving centrifugally along the nerve fibre is doubted 

 by some workers, and it may be that what is liberated at the nerve terminal is actually 

 formed at the terminal. I don't know what the answer is to this particular point, but 

 it certainly seems as if the active material is present along the whole length of the fibre. 



Dr. William F. Canong: I should like to rise in defence of the median eminence. I admit 

 that I have a vested interest. However, if we could switch for a moment to the regulation 

 of ACTH secretion, the evidence here is that lesions in the mid-portion of the median 

 eminence are the only ones which will block ACTH release. In stimulation experiments, 

 ACTH secretion follows stimulation of the median eminence, the posterior tuberal 

 region and the orbital surface of the frontal lobes. According to Mason {Endocrinology 

 63, 403, 1958), stimulation behind the mammillary bodies, where the reticular fibres 

 sweep into the hypothalamus, is also effective. Therefore, my concept is one of 

 multiple inputs, coming down to a final, common pathway, the median eminence. 

 I should like to ask Dr. Harris the same question he was asked by Dr. Folley this 

 morning, but possibly with a slightly different emphasis. How do you feel about 

 putting materials which are vasoactive directly into the pituitary? You recall this 

 was a considerable problem some years ago, when people put materials directly on 

 anterior pituitary transplants in the eye. 



Dr. Ceoffrey Harris: The only thing I can say about that is that we have infused other 

 vasoactive materials into the pituitary without getting similar responses. 



Dr. Cregory Pincus: If there is a portal system present, can the blood flow back to the 

 median eminence from the pituitary ? 



Dr. Ceoffrey Harris: All the evidence indicates that blood flows only from the median 

 eminence to the pituitary gland. This may be taken as established. There is no evidence 

 that blood ever flows up the portal vessels to the median eminence. 



