Aortic arch in rabbits :-Morophological and istological study

:-The study aimed is to investigate the morphological and histological variations of the aortic arch of local breed rabbits ( Oryctylagus conniculus ) . knowledge of these variations is important for other basic sciences . Nine adult local rabbits were obtained to study the aortic arch(four animal for corrosion cast technique ,two injected with colored latex and three for histological study) all the rabbits were euthanized and exsanguinatd, for the cast of the aortic arch they injected by self polymerizing resin via the left ventricle of the heart and the specimens were macerated in( KOH %25) for two weeks and the cast of the aortic arch were prepared, two main branches identified from aortic arch(except in one cadaver has three branches ) ,the brachiocephalic trunk firstly and the left subclavian artery ,the two common carotid artery (right and left) and the right subclavian artery arising from brachiocephalic trunk, the right and left subclavian arteries gave the same branches :-(double vertebral arteries,costocervical trunk,cervical profund artery ,internal thoracic artery,external thoracic artery,superficial cervical artery,and continous as axillary artery). elastic fibers ,fibroblast cells, mast cellsvasavasorum ,, the aortic arch has alarge diameter (98±0.2019)µm and thickness of the wall is ( 18±0.0282)µm to convey the high blood pressure in aortic arch.the conclusion of this study, there is avariation in the branches of the aortic arch in different species of animals when the results compared with another studies and also,the diameter,thickness of the wall of aortic arch is variable from one animal to another.


Introduction:-
Aorta is the major elastic artery of circulatory system and the arteriesbranched from it which supply all tissues of organs in the body, aorta is divided into four segments according to the region , ascending aorta,aortic arch,descending thoracic and abdominal aorta (1,2) .
Aortic arch or arcus aortae is the convexity of aorta toward caudo-dorsal, exiting the heart . this segment of aorta was very important it gave several vessels which supplied head,neck,fore limbe and the proximal half of thoracic region like right and left common carotid arteries ,vertebral artery,axillary artery,internal thoracic,costocervical trunk and dorsal scapular artery respectively (3).
Histologically the wall of the aortic archconsist of three tunica from internal to external (intimea,media,adventitia). tunica intima is relatively thick and is lined by single layer of endothelial cells beneath it subendothelial layer which consist of loose connective tissue that contain elastic fibers and few smooth muscle cells.tunica media is the thickest layer which consist of numerous elastic laminae As asheet in a circular and oplique arrangment and between them ,there is a thin layer of connective tissue contain collagen fibers and smooth muscle cells,tunica intima and tunica media separated from each other by internal elastic lamina.
Tunica adventitia is the relatively A thin layer contain A bundles of collagen fibers and few elastic fibers,fibroblasts, mast cells and vasa vasorum. the aortic wall diameter and thickness of each layer of the wall is change in four segments of the aorta with the variation in variable species (10, 11) guinea pig and rat.
The research work aimed for study aortic arch in rabbitsin order to providing information for other basic science.

Materials and Methods :-
Nine adult local breed rabbits (Oryctylagus Conniculus) aged 6-12 months and weighted ( 1.5-2 Kg) wereused for morphological and histological study of the aortic arch, (four for preparing aortic cast ,two injected with colored latex and three for histological study).
All the animals were euthanized with(Ketamine 50 mg/k.g ml and Xylazine 10 mg/k.g),the thoracic cavity of all the animals were opened. A cannula was inserted into the left ventricle to exsanguinated the animals after that injected with normal salin 0.9% into the left ventricle to prevent formation of blood clotting .
For the cast technique we used the self polymerizing resin to study the aortic arch and the arteries arises from it ,repared resin rapiddly selfcuring powder( 5 mg) mixed with (15 ml) of self polymerizing liquid and injected into the left ventricle of the heart of cadaver by using the disposable syringe (50 ml) after that the rabbit left (24)hours and transferred into 25% KOH bath for two weeks for maceration. (13,14,15). The aortic arch give two main branches fig.6 (2,3) brachiocephalic trunk and left subclavian artery and this in agreement with researchers in another species like in ruminants,equine,pigs,carnivores and domestic mammals (3,4),red squirrels(18),(19) in ground squirrels (Spermophilus citellus), chinchilla(6) guinea pigs(7) and fox (8), while disagreement with other studies ( the aortic arch give arise to three branches ,brachiocephalic trunk ,left common carotid artery and left subclavin artery) in human(2o), rat (21) , porcupine(Hystrix Cristata) (22) , in mole-rats (Spalax Leucodon (23), and in Turkish spiny mice and in adult Cyprus spiny mice (24) ,but in some human cadavers showed variations in branching pattern some of them gave two branches , left subclavian artery and common trunk which gave brachiocephalic trunk , left common carotid artery and another give aris for four branched are brachiocephalic trunk,lef and rightt common carotid arteries and left vertebral artery (25).
Brachiocephalic trunk branched to left common carotid artery and common trunk from which the right common carotid and right subclavian artery arising fig. (4) and this result is corresponding with (7,18 and 19) in guinea pig, red and ground squirrels .right common carotid artery passing to right side of head and neck region, then the right subclavian artery give branches supply the right limb and right side of thoracic region,while the left subclavian artery passing to the left limb and left part of thoracic region and it respected with (3, and16) in domestic animals and human .
The branched ramified from the left and right subclavian arteries are :-two vertebral arteries, common trunk(costocervical trunk ,cervical profund artery ,internal thoracic artery) , external thoracic artery ,superficial thoracic artery and it continuous as axillary artery Fig,(4,5) and this noticed is similar to (6 and23) in the study of chinchilla and mole-rats, and differs with (7) in the study of guinea pig.

Histological study :-
The wall of the aortic arch is composed of three layers from internal to external is tunica intima,tunica media and tunica adventitia Fig. (6a) and this in agreement with(26,27,28).
Tunica intima is consist of single layer of flattened endothelial cells, few elastic fibers and few smooth muscle cells ,between tunica intima and tunic media there is internal elastic lamina, the thickness of tunica intima in aortic arch is (1±0.166 table)µm (1) Fig,(6b,6c) Tunica media is composed of elastic concentric laminea with circular arrangement and in the space between elastic laminae are thin layer of connective tissue contain collagen fibers,smooth muscle cells ,tunica media is the thickest layer ( 12±0.0149)µmm table (1) Fig.(6b,6c) Tunica adventitia (Fig.6b,6c) is relatively thin and contain bundles of collagen fibers and few elastic fibers ,also present of fibroblasts, mast cells ,smooth muscle cells and vasa vasorum. The thickness of Tunica Adventitia is(5±0.0166) µm table (1).the diameter of aortic arch is( 98±0.2019)µm and thickness of aortic arch wall is (18±0.0282 )µm so the aortic arch has a large diameter and thick wall to convey the high blood pressure of the blood that passing through it, our above result is differ from the result of (10,23) in the (guinea pig and rat) and spiny mice due to the nature of histological structure of aortic arch wall also in the study of hamster (28) they can observed ER stress on the aortic arch wall under normal condition