ioi6 



HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY II 



possible to estimate the degree to which endocrine 

 function is dependent on the central nervous system. 



ENDOCRINE ACTIVITY AFTER HYPOPHYSECTOMY. It haS 



long been known that hypophysectomized animals 

 survive for longer periods than adrenalectomized, a 

 fact which indicates some adrenal cortical activity on 

 the part of the hypophysectomized preparation. Re- 

 cent ineasurements (277) of adrenal activity in the 

 hypophy.sectomized dog have shown the rate of 

 secretion of aldosterone to be 66 per cent that of 

 control animals, while for 1 7-hydroxycorticosterone, 

 corticosterone and i i-desoxy-i 7-hydro.\ycorticos- 

 terone it was only 10 per cent. The thyroid gland 

 retains some slight activity in the absence of the 

 pituitary for the thyroid of the hypophysectomized 

 rat (2, 273) and rabbit (48) still accumulates radio- 

 active iodine and discharges r'"-labeled hormone into 

 the blood, although at a low rate. The ovaries and 

 testes appear more wholly dependent on the presence 

 of an intact pituitar)-, although in some species, such 

 as the rat, the initial stages of oogenesis and spermato- 

 genesis still occur after hypophysectomy (320). 



The slight autonomous activity of the adrenal cor- 

 tex and thyroid shown by the hypophysectomized 

 animal is probably independent of the blood level of 

 adrenal cortical and thvroid hormones. This has been 

 shown for the adrenal cortex by Sayers & Sayers 

 (301) who found the effect of administration of ex- 

 ogenous ACTH on the ascorbic acid concentration of 

 the gland was not modified by administration of 

 adrenal cortical extracts. In the case of the thyroid 

 the position is not so clear. In the hypophysectomized 

 rabbit thyroxine does not affect the rate of release of 

 radioactive hormone from the thyroid (47) nor the 

 response of the gland to administration of exogenous 

 TSH (47, 344). In the hypophysectomized rat thy- 

 roxine administration was found (88) to produce no 

 change in thyroid weight, but it has been observed 

 {58) to reduce the thyroid response to exogenous TSH 

 as judged by the criteria of mean thyroid acinar cell 

 heights and the percentage of uptake of I"'. How- 

 ever, it is felt that the rate of secretion of radioactive 

 hormone gives a more direct ineasure of thyroid 

 activity than histological or I "'-uptake measurements. 



There is no evidence that environmental stimuli 

 can effect the activity of the gonads, adrenal cortex or 

 thyroid in the hypophysectomized animal. It should 

 perhaps be pointed out that the factors regulating the 

 release of aldosterone from the adrenal are not well 

 known. There is evidence that the secretion of this 

 hormone in the dos and rat is not controlled to the 



same degree by the anterior pituitary as is the secre- 

 tion of glucocorticoids (96, 97, 277, 286, 316) but 

 may be affected separately by the ionic balance of 

 the blood (286, 317, 342). Another recent view is 

 that aldosterone secretion is controlled by a hormone 

 liberated from the central nervous system and carried 

 to the adrenal in the general circulation (276). It is 

 possible that the release of this hormone could be 

 affected in the absence of the pituitary. 



.i^NTERlOR PITUITARY ACTIVITY AFTER PITUITARY STALK 



SECTION OR TRANSPLANT.4TION. Section of the pituitary 

 stalk interrupts the hypophysial portal blood vessels. 

 It has now been established that after simple stalk 

 section this s\stem of vessels regenerates across the 

 site of section in the majority of animals [mouse (71), 

 rat (153, 160), rabbit (47, 50, 107, 189), ferret (81, 

 329) and monkey (162)]. Further, if stalk section with 

 plate insertion is performed, a capillary plexus may 

 in some cases form in the fibrous capsule of the plate 

 and so re-establish at least slight vascular continuity 

 between the median eminence and adenohypophysis 

 (107, 345). If the plate is slighth' misplaced then 

 larger vessels may rejoin the stalk ends around the 

 borders of the plate (81, 153). 



Most workers are agreed that section of the hy- 

 pophysial stalk interferes with anterior pituitary func- 

 tion in a large number of cases. Two views have been 

 put forward in explanation. First, that stalk section 

 decreases the blood supply of the anterior pituitary to 

 a sufficient extent to result in ischemic atrophy and 

 thereby loss of function of the gland. Second, that 

 stalk section deprives the anterior lobe of some specific 

 physiological stimulus, emanating from the hypo- 

 thalamus and transmitted through the portal vessels, 

 which is necessary for the normal activity of the gland. 



To estimate the significance of adenohypophysial 

 atrophy after cutting the stalk it is necessary to meas- 

 ure the \olume of tlie pars distalis rather than that of 

 the whole pituitary. Section of the pituitary stalk in 

 the rat is followed by a slight and variai:)le area of 

 necrosis in the center of the pars distalis. This butter- 

 fly-shaped (in transverse section) area has been 

 ob.scrved after extensive electrolytic lesions in the 

 median eminence (Dumont, S., personal communica- 

 tion) and has been depicted and described after stalk 

 section (354) and after cautery of the portal vessels of 

 the rat pituitary stalk (67). Similar central necrosis 

 has been obser\'ed in amphibians (207), birds (22, 

 315), sheep (68) and humans (288; Ehni, G., per- 

 sonal communication). Some figures are av'ailable for 

 the amount of pars distalis tissue, well vascularized 



