THE PITUITARY BODY 



SUMMARY 



Only two active principles have been identified as char- 

 acteristic secretions of the pars neuralis: the oxytocic prin- 

 ciple and the vasopressor or diuresis-inhibiting principle. It 

 is not certain whether there is a third principle affecting car- 

 bohydrate metabolism. The oxytocic and vasopressor prin- 

 ciples have been markedly concentrated and nearly com- 

 pletely separated from each other but are not yet available 

 as pure substances. In both, an oxidation-reduction system 

 dependent upon the disulphide linkage appears to be present; 

 however, the state of this system seems to be much less im- 

 portant in determining activity than is true of insulin. 



The physiological importance of these hormones is dis- 

 cussed in chapter x. 



The oxytocic principle is usually more effective when the 

 uterus is under the influence of oestrogen. In the rabbit the 

 activity of the principle is markedly reduced if the condition 

 of the uterus corresponds to that of pregnancy (except near 

 term) and pseudopregnancy. However, this relationship is 

 not found in other animals, including, probably, man. The 

 important vascular effects of oxytocic principle appear to 

 be (i) a depressor effect in birds and (2) possibly a relaxing 

 effect on the coronary arteries. Recently it has been reported 

 that the principle can promote diuresis in the rat. 



The vasopressor principle is most important, not for its 

 pressor action, but because it brings about water retention 

 by facilitating the tubular reabsorption of water in the kid- 

 neys. It is difficult to describe the significance of its action 

 on mineral metabolism. The hormone usually increases the 

 rate of excretion of sodium chloride especially. Some evi- 

 dence suggests that actions on tissues other than the kidneys 

 are important; however, the findings so far are inconclusive. 

 Larger doses of the vasopressor hormone are required to 

 elicit a pressor effect, which initially may be masked by a 

 fall in blood pressure caused by coronary constriction, which 



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