Okajimas Folia Anat. Jpn.. 69(1): 1-10, May, 1992 A Macroscopical Study of the Inferior Phrenic Artery of Female Rats, with Reference to the Embryological Background of Occurrence of the Genital Artery from this Artery By Shigeki MIZUKAMI, Shigenori TANAKA and Madoka MORIYA School of Nursing, Fukui Prefectural College, Oohatamachi 97-21-3, Fukui 910 Department of Anatomy, School of Medicine, Kanazawa University, Takaramachi 13-1, Kanazawa 920 -Received for Publication, December 24, 1991- Key Words: Inferior phrenic artery, Diaphragm, Genital branch. Pleuroperitoneal fold, Female rat Summary: The principal aim of this study was to elucidate the general features of the inferior phrenic artery (IPA) of female rats which retain the original embryonic configuration of this artery. The artery of the right side was found to be detached from the renal artery, while that of the left side arose from the aorta. Between these fellow arteries, however, no essential morphological differences were discernible. At some point not far from their origin, they were found to break up into the ascending, suprarenal, suprareno genital and descending arteries. The ascending artery of the right side coursed along with the phrenic nerve, and vascularized a greatest portion of the total area of the partes sternalis et costalis of the diaphragm. Furthermore, the artery was found to be intimately associated with the inferior caval vein. Thus, it could be assumed that this artery of adult rats has been embryologically related to the musculus diaphragmaticus, transverse septum, ventral pleuroperitoneal fold, and the caval venous mesentery. The suprarenal artery took its course along the superior margin of this gland to reach the lateroinferior part of the pars costalis of the diaphragm. Its course and destination strongly indicates that in its development the suprarenal artery has been intimately related to the formation of the ventral pleuroperitoneal fold. The suprarenogenital artery was characterized as giving off a genital branch which entered first the diaphragmogenital ligament, and then took a descending course toward the ovary, in a quite similar manner of origin and course to those of the aberrant gonadal (testicular and gonadal) arteries observed in Japanese human adults (Shinohara et al., 1990; Hanie, to be published). The descending artery was observed to be closely associated with the major splanclinic nerve and the celiac ganglion. The variability of arteries of the IPA of female rats and also of humans, seems to reflect dramatic changes which have occured in the early stages of development, and have influenced more or less the morphology of the uppermost abdominal anlages of the followings: transverse septum, musculus diaphragmaticus, dorsal and ventral pleuroperitoneal folds, suprarenal gland and celiac ganglion, urogenital organs, inferior caval vein in the caval venous mesentery. In conclusion, it could be said that the anatomy of female rats provide us valuable clues as to the essential configuration of the IPA of humans and the relationships of the IPA to structures which are thought to be directly involved in the development of this artery. The inferior phrenic artery (IPA) of human surrounding mesoderm both cause the gonads and beings is known to be distributed far more extensively the mesonephric tracts to descend from the initial than its name implies; this artery gives off branches location immediately below the diaphragm (Arey, not only to the diaphragm, but also to the suprarenal 1966; Patten, 1946); In the male, the testis courses gland, the celiac ganglion, the adiposal capsule of as far downward as the inguinal ligament by the the kidney, and to the inferior caval vein (Williams beginning of the third month and attains its final et al. 1989). This fact leads us to a supposition that position in the scrotum early in the ninth lunar the IPA's potential to supply blood to broad areas month (Arey, 1966). In the female, the ovary descends might be attributable to embryological situations in the same manner as the testis does. and reaches a under which the IPA of human embryos develops. point just inferior to the pelvic brim by the twelfth In this development the most substantially involved week of gestation (Moore, 1982). It is this descent of are the mesonephroi with the meso- or parameso- the gonads that renders it difficult for us to discern nephric ductus and the mesonephric ductuli; The with certainty the intimacy of the human IPA with progressive degeneration of mesonephroi and the the gonads and genital tracts in the anatomy of Correspondence should be addressed to: Prof. Shigcki Mizukami. School of Nursing. Fukui Prefectural College. 0ohatainachi 47-21-3 Fukui Japan 910. 1 2 S. Mizukamiet al. human adults, although this artery has been reported solution at 60 C° for 3 days to make casts of the to occasionally give origin to the testicular artery blood vessels. (Shinohara et al., 1990) or give off an aberrant 2) Four rats, after the initial perfusion with 200 ml branch toward the ovary (Horie, to be published). of normal saline containing heparin, were perfused In contrast to human beings, the female adult rats with an additional 20 ml of normal saline containing concerned with in this study fortunately provide ca. 1% of coloring matter (Sakura Poster color/ us good research material, because in this animal Japan), and finally with 40 ml of 10% (v/v) formalin the ovary and the ovarian tube are closely associ- solution also containing ca. 1 percent of the coloring ated with the diaphragm, being connected by the matter; the animals so perfused were postfixed in the diaphragmogonadal ligament to the latter. This same fixative for 2-3 days. After the fixation, the topography of the ovary of the full-grown female rat abdominal wall, together with the abdomnal viscera is almost the same as that of the embryo of this including the adrenal glands, the ovaries and the animal. Therefore, it could be said that the ovary uterine tubes, and branches of the IPA, were resected and the genital tracts of female rats retain the position out, dehydrated in graded series of ethyl alcohol, nearest to the diaphragm as observed in early stages and cleared in xylene for examination. This pro- of rat embryos (Ganotte, 1984), and that this animal cedure allowed us a substantially improved investig- provides for us quite beneficial anatomical findings ation of the fine branches of the IPA. to discern the essential relationship of the IPA to the The observations of the anatomical details of transverse septum, the musculus diaphragmaticus, the IPA were performed exclusively under a ster- the dorsal and ventral pleuroperiotoneal folds, the eomicroscope at a maginfication of between 4 and suprarenal gland, the celiac ganglion, the gonad, the 10 times. The working field was illuminated by mesonephroi and the inferior caval vein, all of which two fiber optical goose neck lamps (Nikon). In are known to be importantly involved in the devel- the intervals between observations, the materials, opment of the IPA. To our knowledge, however, when required, were photographed on Neopan SS the morphological features of the IPA of rats are far (6.2 x 8.8 cm2) films with a camera (Mamiya RB67), from having entirely elucidated, and in the literature and enlarged on projection paper (Hishicopy/ very little information is available. The present study Mitsubishi; 42.0 x 59.3 cm2) to about 5-6 times was therefore undertaken to provide a detailed the actual size, where each finding was noted. The description of the overall features of the IPA of findings in this study are based on the data recorded female rats in the hopes of obtaining clues for a on a total of 10 photoprojection papers. better understanding not only of the IPA of female rats, but also of human beings as well. Findings Materials and Methods The morphology of the paired IPA was found in For the purpose of this investigation, 6 Wistar principle to be the same for both. Therefore, for the female rats (weighing between 150-300 gm) were sake of simplicity, the following accounts will be used; the animals were anesthetized first with ether, given primarily for the right side, whilst descriptions and then with intraperitoneally injected solution of the left IPA will be confined to describing essential of urethane (sodium ethylcarbamate, 900 mg/kg). differences from the right side. When the rats were completely narcotized, the thoracic cavity was opened and the heart exposed The IPA of the right side. for cutting open the left ventricle, through which a The IPA of the right side was found to issue from catheter was retrogradely inserted into the ascending the right renal artery on its way to the renal porta, aorta. Perfusion was commenced with 200 ml of and to course in the subperitoneal areolar tissue normal saline containing heparin (10 IU/ml). Out- which covers the inferior (or abdominal) aspect of flow of perfusate was from the cut right auricle. the diaphragm (Figs. 1 and 2). At some point not far When the ouflow was quite free of blood, the rats from the origin of this artery, the IPA split into the were divided into two groups and posttreated in the following arteries: (1) the ascending artery; (2) the following way: suprarenal artery; (3) the suprarenogenital artery; and (4) the descending artery. The description of 1) In two rats, 30 ml of neoprene latex (Showadenko- these arteries follows. Dupon) was injected. The rats so injected were immersed for 3 hours in a 1% aqueous solution of Ascending artery periodide acid, allowing the neoprene latex injected The ascending artery was seen arising as the direct into blood vessels to harden. The rats were thereafter continuation of the IPA and played a role in vascu- subjected to digestion by a 1% protease aqueous Thc Inferior Phrenic Artery of Female Rats 3 larizing the greatest portion of the diaphragm — i.e., the pars costalis of the diaphragm, and inferiorly to pars sternalis and pars costalis of the diaphragm, the ovary and the uterine tube.