Autacoids of Posterior Lobe of Pituitary 



97 



of the kidney we may be dealing with the action of a single autacoid 

 which acts as a chalone upon the blood-vessels of the organ, producing 

 inhibition of their tone, and as a hormone upon the secreting cells, stimu- 

 lating them to increased activity ; or two separate autacoids may be con- 

 cerned, one of which affects the blood-vessels and the other the cells of 

 the organ. The latter view was taken by Herring and myself, but was 

 combated by Dale, who adduces other examples of the action of drugs in 

 which the same active substance produces a double result. If Dale's con- 

 tention is correct, we are, so far as the action upon the kidney and its 

 vessels is concerned, dealing with a single autacoid capable of acting either 

 upon both tissues, viz., blood-vessels and secreting cells, or, under certain 



A B 



FIG. 67. A. Tracing showing the effect of extract of pars nervosa of ox pituitary on isolated 

 muscular tissue of rat's uterus. (Herring.) The strip was acted upon by the extract during 

 the period marked by the signal. B, this tracing was made from the same preparation 

 as that employed to obtain the last tracing. It shows the effect produced by an equivalent 

 amount of extract of pars intermedia. The resulting contraction is smaller and less prolonged. 



circumstances, upon one only. When its action is produced upon one only 

 this may be interpreted to mean that the other is temporarily insensitive 

 to its action : when, for example, in the action of pituitary upon the kidney 

 the diuretic action (upon the cells) fails to be produced whilst the vascular 

 effects are pronounced, or vice versa. But even if this were valid for the 

 kidney, there are strong reasons for the belief that the posterior lobe of 

 the pituitary yields more than one autacoid. For there is distinct evidence 

 that a specific hormone affects the secretion of milk ; quite possibly the 

 effect upon the uterus is due to another ; while there is very little doubt 

 that the fall of blood-pressure produced by a second dose of pituitary 

 extract is due to a chalonic agent entirely different from the hormone 

 causing the initial rise. Bayer and Peter have also produced evidence 

 that there are two autacoids which act upon intestinal muscle, one produc- 

 ino; inhibition and the other contraction. 



o 



Important observations bearing upon this question have been made 



7 



