§ 3.111 VISCERAL MUSCLE 59 



increase the amplitude and frequency of the heart beat (Fig. 3-1) 

 This action is beUeved to be due to an or^/zo-dihydroxytryptamine 

 and is closely similar to the action of adrenaline and noradrenaline, 

 which are chemically not widely dissimilar. 



Results on other species are rather contradictory, and different 

 doses are needed at different times of year to get similar results. 

 This may be compared with the effects that adrenaline and 

 noradrenaline have on vertebrates, where contraction or relaxa- 

 tion can be obtained, according to conditions in the organs 

 resulting from previous treatment, size of dose, etc. (Welsh, 1955). 



"It is assumed that the function of the pericardial organs in these 

 Crustacea consists in liberating, through fine neuropile-like 

 terminations of the nerve fibres, some hormone passing with 

 the blood into the heart and producing on it a stimulating effect" 

 (Alexandrowicz and Carlisle, 1953). Blood taken from the peri- 

 cardial cavity before reaching the heart gave the same reaction as 

 the extracts ; but that taken from the leg arteries after leaving the 

 heart did not, presumably because the chemical was destroyed 

 before it reached the legs. 



Earlier statements (e.g. Welsh, 1937) that the sinus glands of 

 Crustacea provided a heart- accelerating extract might have been 

 unreliable, because insufficient care was taken to avoid the presence 

 of histamines in the extracts (the same is probably true of extracts 

 of sub-neural glands of ascidians credited with similar activity). 

 A heart-accelerating hormone from sinus gland extracts has, 

 however, now been obtained from the freshwater shrimp, Paratya, 

 and also an inhibiting extract from the brain (Hara, 1952). They 

 are thought to be distinct from the chromactivators from the same 

 sources (§ 3.223). 



INSECTA. The frequency of beat of the isolated heart of the cock- 

 roach, Periplaneta americanay perfused with a suitable Ringer 

 solution, can be increased some 50 per cent above normal, and 

 the amplitude of the muscle contraction increased also, if an 

 aqueous extract of one pair of corpora cardiaca (§ 2.111) of the 

 same species is added to each 10 ml of the perfusate (Cameron, 

 1953). At concentrations one-tenth as strong, the amplitude is still 

 increased, but not the frequency. If the extract is separated by 

 paper chromatography, one spot at a time can be eluted and added 



