Macroscopic Description of the Coronary Arteries in Swiss Albino Mice (mus Musculus)

INTRODUCTION The course and distribution of the coronary arteries of laboratory animals

Adana Veterinary Control and Research Institute Experimentation Ethics Committee.

RESULTS
The vascularisation of the heart was provided by the branches of the left and right coronary arteries and it was observed that the left coronary artery was dominant.
The left coronary artery arose from the sinus of the aorta, coursed left and distally between the pulmonary trunk and left auricle just after its origin and gave rise to 1-2 branches to the left atrium.Passing underneath the left auricle, the left coronary artery was observed to course in the sulcus interventricularis paraconalis, which was not evident (Figs 1A, B/1, 3A, B/1, 4A, B/3).
The ramus interventricularis paraconalis was the continuation of the left coronary artery which coursed in the paraconal interventricular groove.The terminal branches of this artery proceeded to the apex cordis and arrived at the atrial surface of the heart.Generally, the branches of this vessel course within the myocardium but in mice it was determined that this vessel ran subendocardially for the first 1/3 of its course (Fig. 1A, B/2, 3A, B/2).
This study indicated that the paraconal interventricular branch was the strongest artery to supply the heart.
The ramus coni arteriosi arose from the paraconal interventricular ramus and coursed subepicardially in the direction of the pulmonary trunk.This vessel was divided into terminal branches at the region of the conus arteriosus and in 10 specimens, anastomosed with same branches of the right coronary artery (Fig. 1A, B originated from the paraconal interventricular ramus and after its origin it coursed on the wall of the left ventricle to arrive caudal to the border of the interventricular septum.In its course this vessel gave off branches which supply the wall of the left ventricle and caudal region of the interventricular septum.The terminal branches of this vessel were observed to reach the right ventricle where they anastomosed with the septal branches of the right coronary artery.This vessel and its branches were seen intramyocardially for their entire course (Fig. 1A, B/3).
The ramus collateralis sinister distalis stemmed from the distal half of the paraconal interventricular ramus.It ran parallel to the ramus collateralis sinister proximalis on the left ventricle and almost reached the apex of the heart.Along its course, the vessel gave off branches to supply the distal third of the left ventricle and caudal region of the interventricular septum.In addition, the terminal branches were seen to supply the apex of the heart (Fig. 1A, B/4).
The rami septales were observed to arise from the medial margin throughout the paraconal interventricular ramus.These septal branches ran distally after their origin and their diameters were small.Terminal branches of these vessels were dispersed to the cranial region of the interventricular septum and mm.papillaris, supplying these areas (Fig. 3A, B/3).
The ramus circumflexus sinister arose from the left coronary artery at the level of the left auricle and coursed intramyocardially, below the left auricle, towards the margo ventricularis sinister (Fig. 1A, B/5).
The ramus proximalis atrii sinistri usually arose just after the origin of the left circumflex ramus generally (21 of 25), but in 4 mice it stemmed directly from the dorsal wall of the left coronary artery.After its origin, it coursed proximally and reached the free margin of the left auricle.In this area the vessel was observed to divide into terminal branches and in addition to these branches, it was determined that the ramus proximalis atrii sinistri gave off some branches to supply the medial surface of the right auricle and left ventricle (Fig. 1A, B/6).
The ramus intermedius atrii sinistri was seen to branch from the left circumflex ramus, run towards the left auricle and disperse to the medial and lateral surface of the left auricle.Along its course, on the wall of the left ventricle, a few branches started from the ramus intermedius atrii sinistri at the level of the left atrioventricular ostium to supply the left ventricle (Fig. 1A, B/7).
The ramus distalis atrii sinistri stemmed from the cranial edge of the left circumflex ramus on the left ventricle.This vessel and its terminal branches were dispersed to the medial region of the left atrium and auricle (Fig. 1A, B/8).
The ramus proximalis ventriculi sinistri was the strongest branch to arise from the left circumflex ramus and supply the left ventricle.After its origin, the vessel ran obliquely on the wall of the left ventricle and then coursed caudally towards the sulcus interventricularis subsinuosus.The terminal branches of this vessel were observed to supply the mm.papillares in the left ventricle (Fig. 1A, B/9).
The arteria coronaria dextra arose from the aorta at the level of the sinus aorta, but in 2 cadavers it originated with the left coronary artery from a common root, which stemmed from the aorta.Just after its origin, the right coronary artery gave off the ramus septalis and then coursed caudally towards the right ventricle, between the pulmonary trunk and right auricle (Fig. 2A, B/1, 3A, B/4, 4A, B/1).
The ramus circumflexus dexter was the continuation of the right coronary artery and coursed onto the atrioventricular border.It terminated close to the sulcus interventricularis subsinuosus and gave off branches which anastomosed with terminal branches of the ramus proximalis ventriculi sinistri (Fig. 2A, B/3, 3A, B/5).
The ramus proximalis atrii dextri was seen to branch from the right coronary artery just opposite to the ramus proximalis ventriculi dexter.It was observed that this branch was the strongest vessel supplying the right auricle.After its origin, this branch reached the free edge of the right auricle and divided into 2 branches, of which the 1st dispersed on the free edge of the right auricle and the 2nd dispersed on the medial and lateral wall of the right auricle (Fig. 2A, B/4).
The ramus coni arteriosi started from the right coronary artery as 1 root in 22 mice.However, in 3 mice this branch sprang from the right coronary artery as 2 branches, close to one another.It coursed subendocardially towards the conus arteriosus and ended in this area after giving off terminal branches (Fig. 2A, B/2).
The ramus proximalis ventriculi dextri was the 1st branch of the right coronary artery to the right ventricle, which ran intramyocardially.While it coursed distally, it gave off 2-3 branches in the directions of the sulcus interventricularis paraconalis.After that, the ramus proximalis ventriculi dextri was observed to course towards the apex cordis and gave off terminal branches which ended at the distal region of the left ventricle (Fig. 2A, B/5).
The ramus marginis ventriculi dextri arose the from the right circumflex ramus just after the point of origin of the ramus proximalis ventriculi dextri.It was the strongest branch that started from the right circumflex ramus to supply the right ventricle.After its origin, this vessel ran obliquely on the ventricular wall and divided into terminal branches which vascularised the apex cordis.Before giving off the terminal branches this vessel coursed intramyocardially, but the terminal branches ran subepicardially in the area of the apex.(Fig. 2A, B/6).
The ramus distalis ventriculi dextri originated from the right circumflex artery after passing the margo ventricularis dexter.This thin branch was observed to course obliquely on the wall of the right ventricle.It was also recorded that this branch arose from the ramus marginis ventriculi dexter in 2 mice (Fig. 2.A, B/7).
The ramus septalis was seen to branch from close to the point of origin of the right coronary artery in 20 mice (Fig. 3A, B/6), but in 2 mice it arose from the left coronary artery and in 3 mice it originated directly from aorta (Fig. 4A, B/2).Just after its origin, the vessel was seen to enter the interventricular septum at the level of the right semilunar valve.While it coursed caudoventrally, the ramus septalis gave off a few branches.Some of these branches reached the mm.papillares and the others, which coursed caudally, ended at the wall of the left ventricle and had anastomoses with ventricular branches of the left coronary artery.
Originating from the aorta, the left and right coronary arteries ran subepicardialy before entering the myocardium.Primary and secondary branches of the left coronary artery ran intramyocardially on the wall of the left ventricle but the secondary branches of the right coronary artery coursed subendocardially.However, the atrial branches coursed subepicardially.interventricularis paraconalis or right coronary artery to supply the septum.
Although several authors stated that the ramus interventricularis subsinuosus originated from the ramus circumflexus sinister in ruminants 16,21 or from a. coronaria sinistra in the horse 21 , pig 21 and donkey 25 , some authors pointed out that this vessel originated from the ramus circumflexus sinister or ramus circumflexus dexter, or from both as a bilateral coronary type in the cat and dog 2,15,21 and that exceptionally it may not exist in the cat 15,21 .In this study the ramus interventricularis subsinuosus did not exist in the Swiss albino mice, as reported in Angora rabbit 4 , in other rabbits 2,8,13,27 and in rats 1 .
As reported in the dog 12 , cardiac muscle bands were seen that crossed the coronary arteries obliquely, especially when they were running in the sulci, but when they leave the sulci, the arteries course parallel to muscle fibres of the myocardium.
In conclusion, this study revealed that the ramus septalis, a branch from the a. coronaria dextra, is the main vessel responsible for supplying blood to the interventricular septum and the septal branches of the paraconal interventricular ramus are also involved.Additionally, the ramus interventricularis subsinuosis is absent in Swiss albino mice.It is hoped that the results of the present study will encourage further research in this field.