. The endocrine organs; an introduction to the study of internal secretion . -media and pars nervosa—and it has since been shown that it is yielded byextracts of either pars intermedia or pars nervosa alone, but rather moredistinctly by the pars nervosa than by the pars intermedia (Herring). Theeffect of the extract upon the blood-vessels is a direct one, and is notdue, as in the case of the suprarenal hormone, to its stimulant action onsympathetic endings. The effect on the heart was also shown by Howellto be different from that of adrenalin; for whereas—with the vagi cutor paralysed—adrenali
. The endocrine organs; an introduction to the study of internal secretion . -media and pars nervosa—and it has since been shown that it is yielded byextracts of either pars intermedia or pars nervosa alone, but rather moredistinctly by the pars nervosa than by the pars intermedia (Herring). Theeffect of the extract upon the blood-vessels is a direct one, and is notdue, as in the case of the suprarenal hormone, to its stimulant action onsympathetic endings. The effect on the heart was also shown by Howellto be different from that of adrenalin; for whereas—with the vagi cutor paralysed—adrenalin causes a marked acceleration of the heart (sym-pathetic stimulation), the pituitary autacoid causes slowing with increasein force of the individual beats. In the bird it augments both auricular o and ventricular contractions, whereas adrenalin affects the auricles only 84 Effects of Extracts of Posterior Lobe of Pituitary 85 (Noel Paton and Watson). Moreover, while adrenalin either produces noaction on the coronary vessels or, in some cases, causes them to dilate,. -e§ 9 •oc oo - I-H —• r, Ctt o S ,0 WJ fs O S n^ a o . - S -S s CO 5- O S O * e o .^ g-§ - w «§ H4) o -So I CO _J2 ^ ^ 3 ^3 Jj;^ •O 3O QJ o« n 83 00 .S -G co »o CO si11 § o rt o the autacoid of the pituitary constricts them as it does most other systemicarterioles; this is true also for the pulmonary vessels. The pressorhormone also has the peculiarity that the effect of a second dose admini-stered a short interval (thirty minutes or less) after the first usually causes 86 The Endocrine Organs no effect (tachyphylaxisl) ; or, if any, not a rise but a fall of blood-pressurewhich may or may not be followed by a slight rise (fig. 57). Frequently
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