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Evidence for a New Mammalian Organ: A Preliminary Report
Vol. 116, September
THE JOURNAL OF UROLOGY
Printed in U.S.A.
Copyright © 1976 by The Williams & Wilkins Co.
EVIDENCE FOR A NEW MAMMALIAN ORGAN: A PRELIMINARY REPORT OTTO M. LILIEN From the Department of Urology, Upstate Medical Center, State University Hospital, Syracuse, New York
ABSTRACT
During an investigation on the mechanisms by which mannitol increases renal blood flow, using an in vitro perfused rat kidney preparation, it was observed that an osmotic challenge (320 mOsm.) was followed by the accumulation of chloride and calcium ions in the renal medulla. Although the chloride was derivyd from the perfusate, the source of calcium appeared to be localized in the renal sinus fatty tissue. A morphologic study of this area reveals the existence of a tissue complex, having the characteristics of a hitherto unrecognized organ or gland communicating with the renal parenchyma via a portal vascular system. The possible physiologic significance of this complex is discussed. During experiments to investigate the mechanisms by which mannitol increases renal blood flow a series of observations was made, leading to the possible discovery of a previously unrecognized organ or gland in the region of the renal sinus. To test the hypothesis that mannitol has a direct effect on renal blood vessels an isolated perfused rat kidney preparation was developed. This system has been described previously in detail. 1 Briefly, the right kidney of young adult male rats was approached transabdominally, a 20-gauge cannula was placed into the renal artery, and the kidney and surrounding fat were excised en bloc and placed in the perfusion apparatus after 2 minutes of ischemia. The kidneys were perfused with a gassed, acellular Krebs-Henseleit buffer solution at constant pressure. 2 Venous effluent fluid was collected at 4-minute intervals with calculation of perfusion rates. During a 1-minute period 4 ml. volumes of varied concentrations of mannitol were introduced into the perfusion system by means of a Harvard pump. Intravascular osmolalities varied from approximately 290 through 370 mOsm. As previously reported' each dose of mannitol tested produced significant and reproducible changes in perfusion rates, indicating a response of vascular smooth muscle to the osmotic signal. The specimen was removed from the perfusion apparatus 20 minutes after the completion of each injection of mannitol, and the cortex and medulla were separated and analyzed for ionic content. Comparison between perfused and non-perfused kidneys indicated that a significant movement of ions (specifically calcium) occurred from the renal sinus and perihilar tissues into the renal medulla. This phenomenon was most evident after injections of mannitol, approximating an intravascular osmolality of 320 mOsm. This enigmatic finding, suggesting the possible existence of a portal system connecting the renal sinus tissues and the renal medulla, caused us to focus our attention on a study of the renal sinus fat pad. A morphologic investigation of this region constitutes the basis for this report. On dissection of kidneys from young adult (300 to 400 gm.) Sprague-Dawley male rats, the renal sinus fat pad weighs approximately 100 mg. Its gross appearance is that of adipose tissue in which white and brown components can be distinguished. It appears to have a rich vascular supply with islands of brown fat concentrated in the region of the renal artery branches. Histologic studies of this tissue, using 40 mµ. formalin fixed
sections stained with hematoxylin and eosin demonstrate lobules or islands· of tissue, similar in appearance to brown or hibernating fat distributed in an intimate relationship to arterial branches arising from the renal artery or its interlobar branches (fig. 1). On higher magnification, the afferent arterioles supplying the islands of brown fat are seen to arise directly from the interlobar branches of the renal artery (fig. 2). Using the injection of microspheres of various sizes, we have been able to determine that the afferent arterioles have a proximal diameter of about 25 mµ. The islands or lobules of brown fat appear glandular. They are composed of large, polygonal, basophilic staining cells whose cytoplasm appears engorged with a colloid-like granular material. Cell walls are distinct and arranged in a honeycomb or bubble pattern. Each lobule is supplied by branching end arterioles, which arise directly from main branches of the renal artery (fig. 3). An extremely rich capillary network permeates the lobules. Electron photomicrographs of the brown fat islands reveal an ultrastructural complex of impressive biological potential. The intimate relationship between the rich capillary network and the surrounding cells is evident. A profusion of mitochondria with transverse cristae crowd the cytoplasm between lipid-like droplets. Pinocytotic vesicles are evident in the capillary wall as well as in the adjacent cytoplasm of the juxtaposed brown fat cell, suggesting an active exchange of materials between the two (figs. 4 to 6). In an attempt to demonstrate the efferent vessels or portal system joining the renal sinus tissue and the parenchyma, india ink injection studies were done. These studies revealed efferent post-capillary vessels directed towards the outer surface of the renal pelvis, where they form a meshwork of marginal vessels. These vessels course along the renal pelvis towards its junction with the renal parenchyma at a narrow junctional zone, where the peripelvic marginal vessels converge to enter the parenchyma. Continuing as marginal vessels they give rise to branches that join the ascending limbs of the vasa rectae as described by Fourman and Moffat, 3 and Hill (fig. 7). • The ectopic glomerulus seen in figure 8 has been a frequent finding in our studies. Although the existence of these structures has been noted previously 2 their significance is not yet known.
Accepted for publication February 6, 1976. Supported in part by the National Institutes of Health Grant 5-ROl-12520-01. 277
DISCUSSION
From the preceding observations we are able to propose the existence of an organ complex, as represented in figure 9. The existence of a hitherto unsuspected, highly organized tissue complex interposed between a rich arterial supply arising from
278
LILIEN
FIG. 1. Formalin fixed sagittal section (40 mµ.) of male rat kidney. 1, papilla. 2, pelvis. 3, cortex. 4, renal vein. 5, branches of renal artery. 6, afferent arterioles supplying brown fat islands. 7, brown fat islands. 8, ureter.
FIG. 2. Formalin fixed sagittal section (40 mµ.) of male rat kidney. 5, interlobar branch of renal artery. 6, afferent arteriole.
FIG. 3. Formalin fixed section (40 mµ.) of male rat kidney. 3, cortex. 6, afferent arteriole. 7, lobule or island.
EVIDENCE FOR NEW MAMMALIAN ORGAN
279
FIG. 4. Electron photomicrograph of gluteraldehyde fixed male rat renal sinus. C, capillary. L, lipid droplet. M, mitochondria, R, red blood cell. Reduced from x3,200.
L
of gluteraldehyde fixed rna.le rat spc-;c~. L, droplet, R,enncea horn 1
renal sinus. C) cytotis vesicle.
cau11w1v
FIG. 7. Formalin fixed sagittal section (20 mµ.) of male rat kidney after india ink injection. 1, papilla. 2, pelvis. d, efferent peripelvic marginal vessels.
FIG. 8. Formalin fixed sagittal section of male rat kidney after india ink injection. 1, papilla. 2, pelvis. 3, cortex. 4, renal vein. a, efferent peripelvic marginal vessels. b, parenchymal marginal vessels. 9, ectopic glomerulus. 280
EVIDENCE FOR NEW MAMMALIAN ORGAN
previously unrecognized organ or gland playing a potentially vital role in renal physiology. Many unresolved problems regarding the regulation of renal function and abnormalities thereof could be re-examined in the light of the potential function of such a metabolically promising structure. The existence of a portal circulatory pathway connecting this structure with the renal parenchyma lenrls strong support to the validity of such a concept. Thus, physiologic signals, such as changes in plasma osmolality, variations in blood electrolytes, fluctuations in hormone levels, blood volume alterations and changes in blood pressure, are anatomically presented to this pre-renal region before reaching the kidney proper. Sensing such signals, appropriate organ responses in the form of calcium ion liberation and/or hormonal secretion could be transmitted to the renal parenchyma, where appropriate readjustments take place. Such a system possesses the virtue of an ideally situated servomechanism monitoring arterial blood and readjusting the renal vasculature appropriately.
Mr. Christel Manke provided technical assistance, Dr. Gerald B. Gordon and the Medical Illustration Department of the Syracuse Veterans Administration Hospital provided the electron photomicrographs and Profs. I. Weiner and W. Westerfeld provided sound advice. REFERENCES
1. Lilien, 0. M.: The paradoxical reaction of renal vasculature to mannitol. Invest. Urol., 10: 346, 1973.
Fm. 9. Schematic representation of organ complex interposed between branches of renal artery and renal parenchyma. RA, renal artery branch. BF, brown fat lobule. WF, white fat. MV, efferent marginal vessels. RV, renal vein. RP, renal pelvis. P, papilla. C, cortex.
the main branches of the renal artery and efferent vessels that drain into the renal parenchyma, suggests the existence of a
2. Krebs, H. A. and Henseleit, K.: Untersuchungen iiber die Harnstoffbildung im Tierkorper. Hoppe-Seylers Z. Physiol. Chem., 210: 33, 1932. 3. Fourman, J. and Moffat, D. B.: The Blood Vessels of the Kidney. Oxford: Blackwell Scientific Publications, 1971. 4. Hill, G. S.: Experimental pyelonephritis: compensatory vascular alterations and their relation to the development of papillary necrosis. Bull. Hopkins Hosp., 119: 100, 1966.
THE JOURNAL OF UROLOGY
Printed in U.S.A.
Copyright © 1976 by The Williams & Wilkins Co.
EVIDENCE FOR A NEW MAMMALIAN ORGAN: A PRELIMINARY REPORT OTTO M. LILIEN From the Department of Urology, Upstate Medical Center, State University Hospital, Syracuse, New York
ABSTRACT
During an investigation on the mechanisms by which mannitol increases renal blood flow, using an in vitro perfused rat kidney preparation, it was observed that an osmotic challenge (320 mOsm.) was followed by the accumulation of chloride and calcium ions in the renal medulla. Although the chloride was derivyd from the perfusate, the source of calcium appeared to be localized in the renal sinus fatty tissue. A morphologic study of this area reveals the existence of a tissue complex, having the characteristics of a hitherto unrecognized organ or gland communicating with the renal parenchyma via a portal vascular system. The possible physiologic significance of this complex is discussed. During experiments to investigate the mechanisms by which mannitol increases renal blood flow a series of observations was made, leading to the possible discovery of a previously unrecognized organ or gland in the region of the renal sinus. To test the hypothesis that mannitol has a direct effect on renal blood vessels an isolated perfused rat kidney preparation was developed. This system has been described previously in detail. 1 Briefly, the right kidney of young adult male rats was approached transabdominally, a 20-gauge cannula was placed into the renal artery, and the kidney and surrounding fat were excised en bloc and placed in the perfusion apparatus after 2 minutes of ischemia. The kidneys were perfused with a gassed, acellular Krebs-Henseleit buffer solution at constant pressure. 2 Venous effluent fluid was collected at 4-minute intervals with calculation of perfusion rates. During a 1-minute period 4 ml. volumes of varied concentrations of mannitol were introduced into the perfusion system by means of a Harvard pump. Intravascular osmolalities varied from approximately 290 through 370 mOsm. As previously reported' each dose of mannitol tested produced significant and reproducible changes in perfusion rates, indicating a response of vascular smooth muscle to the osmotic signal. The specimen was removed from the perfusion apparatus 20 minutes after the completion of each injection of mannitol, and the cortex and medulla were separated and analyzed for ionic content. Comparison between perfused and non-perfused kidneys indicated that a significant movement of ions (specifically calcium) occurred from the renal sinus and perihilar tissues into the renal medulla. This phenomenon was most evident after injections of mannitol, approximating an intravascular osmolality of 320 mOsm. This enigmatic finding, suggesting the possible existence of a portal system connecting the renal sinus tissues and the renal medulla, caused us to focus our attention on a study of the renal sinus fat pad. A morphologic investigation of this region constitutes the basis for this report. On dissection of kidneys from young adult (300 to 400 gm.) Sprague-Dawley male rats, the renal sinus fat pad weighs approximately 100 mg. Its gross appearance is that of adipose tissue in which white and brown components can be distinguished. It appears to have a rich vascular supply with islands of brown fat concentrated in the region of the renal artery branches. Histologic studies of this tissue, using 40 mµ. formalin fixed
sections stained with hematoxylin and eosin demonstrate lobules or islands· of tissue, similar in appearance to brown or hibernating fat distributed in an intimate relationship to arterial branches arising from the renal artery or its interlobar branches (fig. 1). On higher magnification, the afferent arterioles supplying the islands of brown fat are seen to arise directly from the interlobar branches of the renal artery (fig. 2). Using the injection of microspheres of various sizes, we have been able to determine that the afferent arterioles have a proximal diameter of about 25 mµ. The islands or lobules of brown fat appear glandular. They are composed of large, polygonal, basophilic staining cells whose cytoplasm appears engorged with a colloid-like granular material. Cell walls are distinct and arranged in a honeycomb or bubble pattern. Each lobule is supplied by branching end arterioles, which arise directly from main branches of the renal artery (fig. 3). An extremely rich capillary network permeates the lobules. Electron photomicrographs of the brown fat islands reveal an ultrastructural complex of impressive biological potential. The intimate relationship between the rich capillary network and the surrounding cells is evident. A profusion of mitochondria with transverse cristae crowd the cytoplasm between lipid-like droplets. Pinocytotic vesicles are evident in the capillary wall as well as in the adjacent cytoplasm of the juxtaposed brown fat cell, suggesting an active exchange of materials between the two (figs. 4 to 6). In an attempt to demonstrate the efferent vessels or portal system joining the renal sinus tissue and the parenchyma, india ink injection studies were done. These studies revealed efferent post-capillary vessels directed towards the outer surface of the renal pelvis, where they form a meshwork of marginal vessels. These vessels course along the renal pelvis towards its junction with the renal parenchyma at a narrow junctional zone, where the peripelvic marginal vessels converge to enter the parenchyma. Continuing as marginal vessels they give rise to branches that join the ascending limbs of the vasa rectae as described by Fourman and Moffat, 3 and Hill (fig. 7). • The ectopic glomerulus seen in figure 8 has been a frequent finding in our studies. Although the existence of these structures has been noted previously 2 their significance is not yet known.
Accepted for publication February 6, 1976. Supported in part by the National Institutes of Health Grant 5-ROl-12520-01. 277
DISCUSSION
From the preceding observations we are able to propose the existence of an organ complex, as represented in figure 9. The existence of a hitherto unsuspected, highly organized tissue complex interposed between a rich arterial supply arising from
278
LILIEN
FIG. 1. Formalin fixed sagittal section (40 mµ.) of male rat kidney. 1, papilla. 2, pelvis. 3, cortex. 4, renal vein. 5, branches of renal artery. 6, afferent arterioles supplying brown fat islands. 7, brown fat islands. 8, ureter.
FIG. 2. Formalin fixed sagittal section (40 mµ.) of male rat kidney. 5, interlobar branch of renal artery. 6, afferent arteriole.
FIG. 3. Formalin fixed section (40 mµ.) of male rat kidney. 3, cortex. 6, afferent arteriole. 7, lobule or island.
EVIDENCE FOR NEW MAMMALIAN ORGAN
279
FIG. 4. Electron photomicrograph of gluteraldehyde fixed male rat renal sinus. C, capillary. L, lipid droplet. M, mitochondria, R, red blood cell. Reduced from x3,200.
L
of gluteraldehyde fixed rna.le rat spc-;c~. L, droplet, R,enncea horn 1
renal sinus. C) cytotis vesicle.
cau11w1v
FIG. 7. Formalin fixed sagittal section (20 mµ.) of male rat kidney after india ink injection. 1, papilla. 2, pelvis. d, efferent peripelvic marginal vessels.
FIG. 8. Formalin fixed sagittal section of male rat kidney after india ink injection. 1, papilla. 2, pelvis. 3, cortex. 4, renal vein. a, efferent peripelvic marginal vessels. b, parenchymal marginal vessels. 9, ectopic glomerulus. 280
EVIDENCE FOR NEW MAMMALIAN ORGAN
previously unrecognized organ or gland playing a potentially vital role in renal physiology. Many unresolved problems regarding the regulation of renal function and abnormalities thereof could be re-examined in the light of the potential function of such a metabolically promising structure. The existence of a portal circulatory pathway connecting this structure with the renal parenchyma lenrls strong support to the validity of such a concept. Thus, physiologic signals, such as changes in plasma osmolality, variations in blood electrolytes, fluctuations in hormone levels, blood volume alterations and changes in blood pressure, are anatomically presented to this pre-renal region before reaching the kidney proper. Sensing such signals, appropriate organ responses in the form of calcium ion liberation and/or hormonal secretion could be transmitted to the renal parenchyma, where appropriate readjustments take place. Such a system possesses the virtue of an ideally situated servomechanism monitoring arterial blood and readjusting the renal vasculature appropriately.
Mr. Christel Manke provided technical assistance, Dr. Gerald B. Gordon and the Medical Illustration Department of the Syracuse Veterans Administration Hospital provided the electron photomicrographs and Profs. I. Weiner and W. Westerfeld provided sound advice. REFERENCES
1. Lilien, 0. M.: The paradoxical reaction of renal vasculature to mannitol. Invest. Urol., 10: 346, 1973.
Fm. 9. Schematic representation of organ complex interposed between branches of renal artery and renal parenchyma. RA, renal artery branch. BF, brown fat lobule. WF, white fat. MV, efferent marginal vessels. RV, renal vein. RP, renal pelvis. P, papilla. C, cortex.
the main branches of the renal artery and efferent vessels that drain into the renal parenchyma, suggests the existence of a
2. Krebs, H. A. and Henseleit, K.: Untersuchungen iiber die Harnstoffbildung im Tierkorper. Hoppe-Seylers Z. Physiol. Chem., 210: 33, 1932. 3. Fourman, J. and Moffat, D. B.: The Blood Vessels of the Kidney. Oxford: Blackwell Scientific Publications, 1971. 4. Hill, G. S.: Experimental pyelonephritis: compensatory vascular alterations and their relation to the development of papillary necrosis. Bull. Hopkins Hosp., 119: 100, 1966.