The Pituitary Stalk and Ovulation 65 



for as short a time as three minutes, whereas stimuli appHed to the pituitary 

 stalk (below the level of the median eminence) or to the pars distalis of the 

 gland, for periods of up to 1\ hours, were not followed by any ovarian 

 response. Both Markee, Sawyer and Hollinshead (65) and Harris (44) 

 suggested that the failure of the anterior pituitary to respond to electrical 

 stimulation might be due to the fact that the hypothalamus normally regulates 

 the activity of this gland by a humoral mechanism rather than by a direct 

 nerve supply. Such a suggestion had been tentatively put forward by various 

 workers previously (56, 43, 1 2) in an attempt to explain the absence of a well- 

 marked nerve supply to the pars distalis. 



Anatomical Pathway from Hypothalamus to Pituitary 



The anatomical pathway by which the hypothalamus influences the adeno- 

 hypophysis has been discussed many times (for recent and detailed reviews, 

 see 46, 5, 20). Data relating to the various suggested pathways may be 

 summarized, for the present purpose, as follows : 



(1) Direct nerve supply 



{a) Cervical sympathetic supply carried to the gland via the carotid plexus. 

 But, ovulation still follows sterile coitus in the partially or completely 

 sympathectomized rabbit (49, 10). 



{b) Parasympathetic supply carried to the gland via the greater superficial 

 petrosal nerves. However, ovulation still follows coitus after bilateral 

 avulsion of the facial nerve and geniculate ganglion, or after destruction of 

 the petrosal nerves at the geniculate ganglion (41, 82). 



(c) A nerve supply passing to the gland via the pituitary stalk. However, 

 prolonged electrical stimulation of the pituitary stalk at a level below the 

 median eminence does not evoke ovulation (44). Section of the pituitary 

 stalk in the rabbit (35) may be followed by a normal ovulation reflex if 

 vascular regeneration has occurred across the cut. All available evidence 

 indicates that hypothalamic nerve fibers do not regenerate across the site of 

 pituitary stalk section. 



Histological studies, although unable to prove a negative finding, give very 

 strong indication that the pars distalis of the anterior pituitary receives a 

 very scanty nerve supply, if any at all (77, 38, 87). 



(2) Vascular path 



{a) General systemic circulation. There are no data that the hypothalamus 

 regulates the anterior pituitary release of FSH or LH through the general 

 circulation. Unlike the ovary, testis, adrenal cortex and thyroid, the pituitary 

 gland does not maintain normal internal secretory activity if transplanted to 

 a distant site in the body. General ovarian and folHcular atrophy have been 

 repeatedly observed in well-controlled studies of pituitary transplants. 



{b) Hypophysial portal circulation. This system of vessels, first described 

 by Popa and Fielding (75, 76) in man, has now been extensively studied. 



