Cardiac catecholamine and serotonin contents and responses to these amines in various species of animals.
Accumulate evidence indicates that catecholamines are normally synthesized, stored and degraded within the myocardium and it has been also well documented that the store of catecholamine in the myocardium is involved in maintaining normal cardiac functions. Lee and Shideman(1959) observed that depletion of myocardial catecholamines resulted in depression of cardiac contractility and suggeste that the cardiac stores of these amines are important in maintaining normal contractility, In addition, Lee et al.(1966) demonostrated that the increased cardiac function from pretreatment with thyroxine is largely dependent upon its
capacity to cause an increase in concentration of cardiac catecholamines.
The present experiment was undertaken to examine and compare the concentrations and distributions of myocardial catecholamines among various species of animals. The serotonin content in hearts of these animals was also determined.
Animals employe din this experiment were the cat, dog, pig and rabbit(Mammalia), chicken and duck(Aves), turtle (Reptilia), frog(Amphibia), fish(Pisces) and clam(Mollusca). The animals, except cows and pigs, were sacrificed by decapitationg or by a blow on the head and then the heart rapidly removed. The catecholamine and serotonin contents were determined by spectrophotofluorometric procedure described by Shore and Olin(1958), and by Bogdanski et al.(1956), respectively.
1. Mammalian hearts:
Examination of myocardial catecholamines showed that th total catecholamine contents in hearts of cats, dogs, rat and rabbits were within the range of 1.5 and 2.0 μg/g and of these contents, norepinephrine occupied over 90%, whereas epinephrine was 10% or liess. The hearts of pigs and cows, however, contained approximately 1,0μg/g of total catecholamines and of these animes, epinephrine constituted 20-30%.
Examination of the regional distribution of catecholamines in these mammalian hearts showed that the content of the auricle was generally higher than that of the septum and considerably than that of the ventricle. Concerning the serotonin contents, all mammalian hearts studied contained uniformly very small amounts.
Furthermore, serotonin was found to fail to produce any effect on the isolated auricles of these animals, wherea; catecholamines produced a marked cardiostimulant action.
2. Avian hearts:
The total myocardial catecholamine content in fowls and ducks were one-third to one-fourth of those observed in the mammalian hearts. Of these amines norepinephrine constituted approximately 20% in the chicken hearts, similar to the mammalian gearts, but it constituted over 50% in duck hearts.
Examination of the regional distribution of catecholamines in these avian hearts showed that the auricle contained a higher concentration than the ventricle. In contrast to mammalinan hearts, however, the content of septums was generally less than that of ventricles. The serotonin contents in chicker and duck hearts were very small, similar to those observed in the mammalina hearts. However, serotonin exerted a significant stimulant action on the isolated atria of these aves in contrast to mammals.
3. Reptile, amphibian and piscine hearts:
The heart of the turtle, frog and snake-fish generally contained fairly small amounts of catecholamines compared to those observed in hearts of aves and mammals. It is interesting to note that the total myocardial catecholamines of these cold-blooded vertebrate animals were constituted largely by epinephine rather than by norepinephrine.
The hearts of these animals contained a significantly larger amount of serotonin than those of aves of mammals and serotonin exerted a marked stimulant action on the isolated atria of these cold-blooded vertebrate animals.
4. Molluscan hearts:
Clam hearts contained negligibly small amount of catecholamines but very large amount of serotonin (40μg/g). Furthermore, catecholamines failed to produce any effects but serotonin produced a marked cardiostimulant action on the isolated heart of clams.
From the above results, it appears that larger amount o catecholamines are contained in hearts of animals as they progress more towards the higher animals. Thus, a neligibly small amount was present in hearts of a non-verterate, the clam, and among vertebrate animals, warm-blooded animals contained more catecholamines in their hearts than cold-blooded animals. Among warm blooded animals, mammals contained more myocardial catecholamines than aves. The ratio of norepinephrine to epinephrine in total myoardial catecholamines also seems to be greater as the animals progressed to the higher animals.
I contrast to catecholamines the highest concentration of serotonin was contained in hearts of the clam, a non-vertebrate animal, among all the animals studied, and there was less in hearts of vertebrates which had progressed towards the higher animals.