Transplantation of Nonvascularized Kidney Tissue Fragments into the Rat Liver with the Aim of Preserving Renal Function

For research in regenerative medicine, not only the study of cellular pluripotency but also knowledge of the reorganization of tissue structure is crucial. However, the latter will probably be more difficult to acquire. When small fragments of kidney (approx. 1 × 1 mm) were implanted in the liver of syngeneic LEW rats, the tissue survived at least 2 weeks with retention of normal structure including glomeruli and tubules. In contrast, no kidney structure survived when transplanted to subcutaneous sites, omentum, or spleen. Molecules involved in renal tubular function, such as megalin and glut2 transporter protein, were detectable in the implanted tissue by immunohistochemistry, suggesting that the cells were biologically active. Survival of cortex, medulla, and calyx tissues was then compared. All three components were still detectable 8 weeks after transplantation but cortex and medulla were replaced by granuloma at 6 months. Only calyx tissue survived for up to 12 months after transplantation. There was no marked difference in tissue survival, either when the recipient liver was partially resected or when infantile donor kidney was implanted instead of adult kidney. The present method opens new avenues in the development of regenerative medicine (i.e., tissue transplantation) as an intermediate modus between organ transplantation and cell transplantation.

Factors affecting the ability of the renal medulla to exert an antihypertensive function

To examine whether changes in renomedullary osmolality and the activity of the renin-angiotensin system may influence the ability of the renal medulla to exert an antihypertensive function, rats were exposed to several manoeuvers. These affected either the medullary osmolality or the renin-angiotensin system (salt or saccharose load, salt depletion, treatment with captopril alone or in combination with salt depletion). A comparison of the antihypertensive capacity of the renal medulla was studied by transplanting renal medullae from the various groups into one-kidney one-clip hypertensive rats. A significant and quantitatively similar reduction in blood pressure was observed in hypertensive rats that received transplants of the medullae from control, salt or saccharose loaded rats and captopril treated rats. In contrast, medullae from salt depleted rats did not affect blood pressure when transplanted into hypertensive animals. The addition of captopril restored the antihypertensive function of renal medulla in salt depleted rats. The results do not support the view that osmolality of the renal medulla regulates its antihypertensive capacity, and suggest that angiotensin II may restrain renomedullary antihypertensive function.

The mechanism of renomedullary antihypertensive action: haemodynamic studies in hydronephrotic rats with one-kidney renal-clip hypertension

1. The protective action of the renal medulla was studied in one-kidney renal-clip hypertension in rats with unilateral hereditary hydronephrosis and almost complete atrophy of the medulla of the affected kidney. 2. Rats were unilaterally nephrectomized. The first group had a normal kidney remaining, and the animals from the second and third groups were left with a hydronephrotic kidney and received renomedullary and renocortical autotransplants respectively. Two weeks later all rats were made hypertensive by placing a silver clip (0.2 mm) on the renal artery. 3. From the fourth day after clipping until the end of the experiment blood pressure was found to be significantly (P less than 0.01) lower in rats with medullary transplants than in the other groups. No differences in renal excretory function, plasma volume and plasma renin activity were found between the groups either before or during development of hypertension (5 and 21 days after clipping). Early in the course of hypertension (5 days) cardiac output was significantly (P less than 0.05) lower in the rats with medullary transplants than in the other groups, although an increase in plasma volume was noted in all three groups. At that time no difference in total peripheral resistance was found between the groups. 4. The results are consistent with the hypothesis that the renomedullary antihypertensive substance(s) mitigates hypertension by preventing a hypertensive haemodynamic response to sodium/volume overload.

Reversal of hypertension by transplants and lipid extracts of cultured renomedullary interstitial cells

Transplants and lipid extracts of the same monolayer tissue culture of renomedullary interstitial cells from murine renal medulla exerted a similar antihypertensive action in rats having hypertension of the sodium-volume-dependent-type. The antihypertensive action resembled that caused by lipid extracts of rabbit renal medulla and extracts of lapine renomedullary interstitial cells grown in tissue culture. The recession of the arterial pressure of the hypertensive animals usually occurred slowly and steadily to a maximum within 6 to 12 hours. On occasions, a substantial acute depressor effect preceded the slow and steady decline of the pressure. As the pressure was lowered, there was either minimal or no change in the pulse rate. The lowering of the hypertensive pressure before there was vascularization of the transplant appears to support the view that the transplanted cells secreted and/or liberated an antihypertensive substance(s) that seeped out and was absorbed by nearby capillaries and/or lymphatics and circulated and acted in the manner of a hormone. The extracted and purified lipid from the same cells as used for transplantation is proposed as a candidate for such hormonal action. Evidence is presented that minimizes the possibility of the classic renomedullary prostaglandins as this antihypertensive lipid. The findings add support to the concept that the kidney exerts a hormonal antihypertensive action that opposes the well known hormonal prohypertensive renal actions.

Anti-hypertensive lipid tissue from culture of renomedullary interstitial cells of the rat

1. Allogenic transplants of cultured renomedullary interstitial cells exert a powerful anti-hypertensive action. The blood pressure of hypertensive animals usually drops slowly over 8-12 h whereas the pulse is unchanged or reduced. 2. Lipids derived from the cultured cells exert a similar anti-hypertensive action. 3. The anti-hypertensive action of transplanted cultured cells almost certainly results from the secretion of a substance(s) that acts in the manner of a hormone. The tissue culture lipid is a prime candidate hormone. 4. The relationship of the kidney to the hypertensive state is considered to entail pro- and anti-hypertensive actions. The pro-hypertensive actions include (a) activation of the renal pressor system (mainly renin-angiotensin), (b) failure to prevent sodium and fluid overloading because of either an injured or absent kidney or the excessive action of mineralocorticoids (mainly aldosterone). The antihypertensive actions of the kidney include (a) the relief of sodium and fluid overloading through diuresis-natriuresis and (b) the action of the reno-medullary interstitial cell hormone (the antihypertensive renomedullary hormone).

The renal medulla and mechanisms of hypertension in the spontaneously hypertensive rat

A significant number of offspring from brother-sister matings of NIH-Okamoto-Aoki spontaneously hypertensive rats (SHRs) were found to be normotensive at 20 weeks of age. Over 20% of the animals that were hypertensive at this age had mild-to-moderate unilateral hydronephrosis at the time of sacrifice. In over 90% of the rats that did not develop hypertension spontaneously, ligation of one ureter raised blood pressure above 150 mm Hg within 2 weeks. In those rats made hypertensive by obstructing one ureter and in those that developed hypertension with accompanying naturally occurring hydronephrosis, subcutaneous implants of fragmented renal medulla from unrelated normal rats decreased blood pressure to normotensive levels. In contrast, medullary implants had no significant effect in rats developing hypertension spontaneously without hydronephrosis. Renal inner medullary plasma flow was low in the obstructed kidneys of hydronephrotic hypertensive SHRs but was elevated in the kidneys of nonhydronephrotic hypertensive SHRs. The hypertension in hydronephrotic SHRs appears to be related to an impairment of the antihypertensive function of the renal medulla. Such an impairment of medullary antihypertensive function does not appear to play a significant role in the hypertension in SHRs without hydronephrosis.

Salt-induced hypertension in rats with hereditary hydronephrosis: the effect of renomedullary transplantation

The antihypertensive action of renomedullary autotransplantation was investigated in rats with unilateral hereditary hydronephrosis showing extensive destruction of the medulla of the affected kidney. All rats were divided into three groups and unilaterally nephrectomized. The first group consisted of rats with a normal kidney remaining. The second and third groups had the hydronephrotic kidney remaining and received renomedullary and renocortical autotransplants, respectively. After completion of baseline studies, all rats were given 1 per cent saline solution instead of drinking water, and relevant parameters were re-examined 14 days later. Significant increase in blood pressure (greater than 150 mm. Hg), extracellular fluid volume, and plasma volume were found in group 3 while no changes were detected in groups 1 and 2. After administration of aspirin (and presumed blockade of prostaglandin synthesis) significant increases in plasma and extracellular fluid volumes were detected in groups 1 and 2, but no change in blood pressure was found. The results show that renomedullary transplantation protects against salt-induced hypertension and further indicate that the renomedullary prostaglandins are not a likely mediator of the antihypertensive action of the renal medulla.

Antihypertensive and hypertensive effects of the kidney. Elucidated by treatment with medullary transplants and with blockade either of the reninangiotensin-system or of the prostaglandin biosynthesis

After subcutaneous isotransplantation of renal medulla either from normal donors or from the ischaemic kidney of renal two-kidney hypertensive rats, the blood pressure of the renal two-kidney hypertensive recipients was lowered-but not to normal levels. After i.v. injection of the converting enzyme inhibitor SQ 20,881, the blood pressure was further decreased to, or close to, normal blood pressure. A complete normalization of the blood pressure was obtained by the combined treatment with medullary transplants and infusions of the angiotensin II inhibitor Saralasin. The difference between the effects of these two blockers was probably caused by differences in the doses used. Administration of indomethacin, an inhibitor of the prostaglandin biosynthesis, to renal two-kidney hypertensive rats with or without renomedullary transplants failed to provoke a rise in blood pressure. This indicates that the anti-hypertensive activity of renomedullary transplants is not due to the group of prostaglandins, the synthesis of which is inhibited by indomethacin, and furthermore that these prostaglandins are not of importance to the blood pressure level in renal two-kidney hypertensive rats.

Experimental oliguric acute renal failure: protective effects of renomedullary autotransplants

An acute circulatory renal failure (ARF) was induced in 18 rabbits by temporary ischemia of the remaining kidney 8 days after unilateral nephrectomy and subcuteaneous autotransplantation of renomedullary tissue.--Mortality in the postischemic course was 50% in treated animals but 100% in the control group (n = 18) without autotransplantation. In the postischemic period plasma urea concentration was significantly lower (p smaller than 0.005) in the surviving transplanted animals and excretion of sodium and water significantly higher (p smaller than 0.005) as compared with the control group. Plasma renin values which were significantly lower than thos of the control(p smaller than 0.005) had decreased significantly even as compared with the initial values. These results indicate that hormonal substances are produced in interstitial cells of renomedullary autotransplants exerting a distinct protective effect against experimental acute renal failure. Decreased plasma renin activity may point to an inhibition of circulating and/or intrarenal renin by lipids originating from the transplants. Changes in sodium and water excretion indicate effects of circulating prostaglandins

Angiotensin-salt hypertension

1. Experimental hypertension could be induced in rats by injecting angiotensin I or II subcutaneously.

2. Such hypertension lasted for about 1 h after injection.

3. Angiotensin-induced hypertension was enhanced and sustained by salt loading and diminished by salt restriction or spironolactone.

4. Angiotensin-salt hypertension is reversed by transplants of compatible renal medulla subcutaneously.