I020 



HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY II 



penic response to operative trauma or injection of 

 epinephrine. However since a detailed histological 

 study was not made the author concluded: ''It can- 

 not be conclusively stated that the hypophysial 

 vessels had not regrown." De Groot & Harris (72) 

 observed that electrolytic lesions placed in the path 

 of the portal vessels (in the zona tuberalis of the 

 pituitary gland of the rabbit) abolished the lympho- 

 penia that follows emotional stress, although lesions 

 of a similar nature in the center of the gland had no 

 effect. In a further study on stalk-sectioned mice de 

 Groot (71) found that those animals in which portal 

 vessel regeneration occurred showed a return of the 

 stress response after operation, whereas the animals in 

 which a plate had been placed between the ends of the 

 stalk showed loss of the adrenal response to stress for 

 the duration of the experiment and adrenal atrophy. 

 McCann (233) reported that the eosinopenia induced 

 i)y epinephrine and the adrenal ascorbic acid response 

 to unilateral adrenalectomy were prevented in the 

 rat by extensive electrolytic destruction of the pitui- 

 tary stalk. Donovan & Harris (81) studied the adrenal 

 weights of ferrets with cut stalks imder normal en- 

 vironmental conditions. Animals in which portal 

 vessel regeneration had been prevented showed a sig- 

 nificant loss of adrenal weight, whereas animals in 

 which vascular regeneration occurred across the site 

 of section showed no adrenal atrophy. This finding 

 was taken to indicate a reduction in the basal rate of 

 ACTH secretion under nonstress conditions following 

 interruption of the portal vessels. In the study of 

 Fortier et al. (107) on the rabbit, marked adrenal 

 atrophy was found to follow stalk section (although 

 not to the extent seen in hypophysectomized controls), 

 whether portal vessel regeneration occurred or not. 

 The responses to stressful stimuli were however dlfTer- 

 ent in the two groups in that the animals in which 

 vascular regeneration was prevented failed to respond 

 to stimuli calculated to give rise to predominantly 

 nervous or emotional excitation (restraint, exposure 

 to cold), although they did respond to stimuli involv- 

 ing tissue trauma or metabolic disturbances (lapa- 

 rotomy, injection of epinephrine). Recently Hume 

 (186) has made observations on the monkey in which 

 the pituitary stalk had been cut and a film of polythene 

 placed between the hypothalamus and pituitary 

 gland. In these animals the release of ACTH in re- 

 sponse to operative trauma i to 3 mo. after stalk sec- 

 tion was markedly decreased though not entireh' 

 prevented. 



The results of studies utilizing the method of pitui- 

 tar)' transplantation are more clear-cm than those 



using pituitary stalk section, perhaps because the com- 

 plete absence of hypophysial portal vessel regeneration 

 can be established with more certainty. As a prelim- 

 inary to the data mentioned below, it may be said 

 that if pituitary tissue is grafted in the hypophysec- 

 tomized rat under the median eminence of the tuber 

 cinereum, then adrenal glands within the normal 

 weight range are maintained (161). These pituitary 

 grafts were found to be vascularized by vessels de- 

 rived from the primary plexus of the hypophysial 

 portal system. In contrast to this finding are the 

 results of studies in which pituitary tissue is trans- 

 planted to a site outside the reach of the portal vessels. 

 Such grafts have been found by many dififerent 

 workers (54, 105, 161, 237, 238, 260, 306, 353) to be 

 incapable of maintaining nonnal adrenal weights, 

 and in most reports the adrenals are markedly 

 atrophic although slightly larger than in hypophysec- 

 tomized controls. The ACTH response of pituitary 

 transplants to the effect of stress stimuli has been 

 studied by many groups. Cheng et al. (54) showed 

 that the combined stress of unilateral adrenalectomy 

 and histamine injection resulted in a fall in adrenal 

 ascorbic acid concentration in pituitary transplanted 

 rats. Fortier & Selye (108) obtained the same result 

 in rats following unilateral adrenalectomy and expo- 

 sure to cold. The subcutaneous injection of epineph- 

 rine, or even of hypertonic saline, was reputed to 

 produce a significant fall of the blood eosinophiles in 

 pituitary transplanted animals (237). In 1951 Fortier 

 (105) made the significant observation that the ability 

 of transplants to release ACTH in response to stressful 

 stimuli depended on the type of stimulation used. He 

 found that hypophysectomized rats bearing intra- 

 ocular transplants, while still showing an eosinopenic 

 response to so-called systemic stimuli (cold, adminis- 

 tration of epinephrine or histamine), failed to give 

 any evidence of ACTH release in response to neuro- 

 tropic stimuli (ner\ous or emotional stimuli, such as 

 intense sound or immobilization on a board). It was 

 suggested that the hypothalamohypophysial path- 

 ways are required for pituitary activation in response 

 to stimuli acting via the central nervous system, 

 whereas the corticotrophic efTect of systemic stress is 

 mediated through changes in the composition of the 

 blood in the general circulation, acting either inde- 

 pendently or concurrently on the pituitary to elicit 

 the discharge of ACTH. 



'fhyrfltroplnc Secretion After Pituitary Stalk Section or 

 Transplantaiion. Pituitary stalk-sectioned rats were 

 found l)y Uotila (y^-^) to possess thyroid glands that 

 were histologicalK normal. However, lack of good 



