§ 3.115 VISCERAL MUSCLE 67 



3.115 Muscles of blood vessels 



No case of hormone control of muscular contraction in the 

 vascular system (vasoconstriction), apart from the contraction of 

 heart muscle, has been reported for any invertebrate except, 

 possibly, in the cephalopoda (p.416). 



Vertebrata. The arteries of vertebrates react to a number of 

 hormones: for instance, to vasopressin*, ADH, and to a lesser 

 extent to oxytocin, both from the neurohypophysis (§ 2.1 14). This 

 effect, v^hich may be merely pharmacological, can best be shown 

 by intravenous injection of vasopressin into any tetrapod after the 

 peripheral blood vessels have been expanded by hypophysectomy 

 (Buddenbrock, 1950). 



Certain doses of pure adrenaline dilate the peripheral blood 

 vessels when first injected into the rabbit's ear, whereas subsequent 

 injections of similar doses cause contractions (Fig. 3-8). This seems 

 to be unexplained. 



3.116 Other visceral muscles 



Vertebrata. Visceral muscles attached to the hair follicles in 

 mammahan skin cause erection of the hair (as on a dog's neck or 

 a cat's tail) in response either to sympathetic nerve stimulation or 

 to ADRENALINE sccrction. Thcsc also cause the radial muscles of 

 the iris of the eye to contract, thereby greatly enlarging the pupil. 

 The release of adrenaline into the circulation, as a result of fear, 

 shock or rage (cf. secretion in response to excitement, Fig. 3-3), 

 is therefore accompanied by at least the sensation of the hair 

 standing on end, and by the appearance of staring eyes with 

 expanded pupils, and blanching of the face, due to the contraction 

 of the peripheral blood vessels (§ 3.115). More useful features of 

 this "emergency" syndrome due to adrenaline are the increased 

 rate of heart beat (§ 3.111), and the enlarged blood flow bringing a 

 greater supply of sugars to the body muscles (§ 5.211), which 

 enable the animal to achieve a very high output of muscular effort 

 for a time— probably long enough to effect an escape from the 

 predicament causing the original fright. 



* This hormone would be better named antidiuretin from its main 

 action (§ 5.32). 



