Male Imai Rats Research Articles

Protein restriction and AST-120 improve lipoprotein lipase and VLDL receptor in focal glomerulosclerosis

Imai rats exhibit spontaneous focal glomerulosclerosis (FGS) with progressive proteinuria and hyperlipidemia leading to renal insufficiency by age 34 weeks. Recently, we reported marked down-regulations of skeletal muscle and adipose tissue lipoprotein lipase (LPL) and very low-density lipoprotein (VLDL) receptor in male Imai rats at 32 weeks of age. Dietary protein restriction and oral adsorbent AST-120 (AST) have been shown to slow progression of renal disease and attenuate hyperlipidemia in the Imai rats. This study tested the hypothesis that amelioration of proteinuria by protein restriction or use of oral adsorbent AST-120 beginning at 10 weeks of age may improve renal disease and LPL and VLDL receptor deficiencies in Imai rats. Ten-week-old male Imai rats were randomly assigned to those fed either a regular diet, low protein diet (LPD), or regular diet containing the adsorbent preparation, AST-120. Ten-week-old male Sprague-Dawley rats served as controls. The animals were observed for 24 weeks. Six rats were included in each group. All diets were prepared in powder form. The untreated 34-week-old Imai rats showed severe proteinuria, hypoalbuminemia, 50% reduction in creatinine clearance, hypercholesterolemia, hypertriglyceridemia, and elevated plasma VLDL concentration. This was associated with significant reductions in plasma post-heparin LPL activity, hepatic lipase activity, as well as adipose tissue and skeletal muscle immunodetectable LPL and VLDL receptor proteins. Protein restriction mitigated the decline in creatinine clearance, ameliorated proteinuria, hypoalbuminemia, hypertension, and hypercholesterolemia, lowered plasma VLDL, and improved plasma postheparin LPL activity, hepatic lipase activity, LPL, and VLDL receptor proteins in skeletal muscle and adipose tissue. Similar improvements were observed in all parameters with AST administration. Moderate protein restriction and use of oral adsorbent can slow progression of renal disease and, thereby, ameliorate LPL, hepatic lipase, and VLDL receptor deficiencies and the associated hyperlipidemia in rats with spontaneous FGS.

Effect of Soy Protein Added to Casein Diet on the Development of Glomerular Injury in Spontaneous Hypercholesterolemic Male Imai Rats

Background: We have already reported an attenuating effect of a semipurified alcohol extract of soy protein (mainly consisting of isoflavones) on glomerular injury. Therefore, in the present study, we investigated whether soy protein itself has an ability to attenuate glomerular injury when added to casein diet in male Imai rats of a spontaneous focal segmental glomerulosclerosis model. Method: Male Imai rats were used and allocated into five groups. Group A of control casein diet (Ca) was fed standard diets containing 24.5% casein as a protein source. Group B of control soy protein diet (SP) was fed soy protein diet containing 24.5% protein that substituted a soy protein isolate for casein. Groups C (Ca-SP10) and D (Ca-SP20) were fed a mixture diet of casein (24.5%) and SP (10%) or SP (20%). Group E (Ca-Ca) was fed high casein diet containing the same quantity in protein content (44.5% casein) as the Ca-SP20 diet. Body weight, urinary protein, serum constituents and systolic blood pressure were investigated every 4 weeks from 12 weeks through 24 weeks of age. At 24 weeks of age, rats were studied morphologically. Results: Animals fed control SP diet showed a significantly greater body growth than animals fed the other 4 test diets. No significant differences were found in body growth among the other 4 groups except for group E, which showed a stunt at the end of the experiment. Control SP diet significantly decreased proteinuria and serum cholesterol and attenuated glomerular injury and glomerular hypertrophy as compared with control casein diet. Added SP failed to attenuate glomerular injury, but when compared with high casein diet (group E), added SP resulted in less proteinuria, less hyperlipidemia, less hypoalbuminemia, less glomerular hypertrophy and less renal histological damage despite the quantity being the same in protein content. Conclusion: The present study indicates that soy protein added to conventional casein diet did not have the ability to attenuate glomerular injury, but soy protein is not as harmful as casein as a protein source when added to casein diet in the development of glomerular injury in the rat model of spontaneous focal glomerular sclerosis.

Attenuating effect of soy protein as compared with casein on glomerular injury in spontaneous hypercholesterolemic male Imai rats

SUMMARY: Soy protein has hypocholesterolemic and oestrogenic properties. Because the reno‐protective effect of both lipid‐lowering agents and oestrogen has been reported, we investigated whether soy protein has an ability to attenuate glomerular injury in male Imai rats in which hyperc‐holesterolemia, focal and segmental glomerulosclerosis (FSGS) and renal insufficiency occur spontaneously. Twenty male Imai rats were randomly divided into two groups and fed diets containing 20.0 g/100 g of either casein or soy protein. Each group was fed freely one of the respective test diets from when they were 8–26 weeks of age. Bodyweight, urinary protein, serum constituents and systolic blood pressure was investigated every 4 or 8 weeks from when rats were 10 weeks through to 26 weeks of age. At 26 weeks of age, rats were studied morphologically. Soy protein‐fed animals consumed larger amounts of diet and showed higher urinary urea excretion and a more rapid weight gain than the control casein diet‐fed animals. No significant differences were seen in blood pressure between the two groups. the soy protein diet did not influence absolute kidney or heart weight, but significantly reduced those organs to bodyweight ratios. Soy protein diet resulted in less proteinuria, less hyperlipidemia, less hypoalbuminemia, less renal functional impairment, less glomerular hypertrophy, and less renal histological damage as compared with the control casein diet. the soy protein diet tended to affect serum sex‐hormone levels with a trend toward lower levels of both testosterone and estradiol. the present study showed a beneficial effect of soy protein diet on glomerular disease in a spontaneous FSGS model, although the mechanisms remain to be determined.

Attenuating effect of a semipurified alcohol extract of soy protein on glomerular injury in spontaneous hypercholesterolemic male Imai rats

We investigated whether soy protein's alcohol-extractable components (SPEs; mainly consisting of isoflavones) have the ability to attenuate glomerular injury in male Imai rats of a spontaneous focal segmental glomerulosclerosis model. Male Imai rats were fed a casein-based diet with and without SPEs. Group 1 (Cont) was fed a standard diet without additional SPEs, and groups 2 (SPE-1) and 3 (SPE-2) were fed a standard diet supplemented with a semipurified alcohol extract of soy protein, 0.05 and 0.10 g/100 g of diet, respectively. Body weight, urinary protein level, serum constituents, and systolic blood pressure were evaluated every 4 weeks from 12 through 28 weeks of age. At 28 weeks of age, rats were studied morphologically. Growth rates were not different among the three groups throughout the experiment. SPE-supplemented diets resulted in less proteinuria and less hyperlipidemia. The decline in renal function shown by blood urea nitrogen and creatinine clearance was less marked in the animals fed the SPE-supplemented diets. Each SPE-supplemented diet equally induced less glomerular hypertrophy and less renal histological damage compared with nonsupplemented diets. The present study showed a beneficial effect of a semipurified alcohol extract of soy protein on glomerular disease.

Dual effect of estrogen on glomerular injury in hypercholesterolemic male Imai rats: its regulation by testosterone

Background. Hypercholesterolemic Imai rats, especially males, spontaneously develop proteinuria and glomerulosclerosis. We previously studied the effect of estrogen on the development of glomerular injury in this rat strain and found that estrogen treatment showed a sex difference in its effect on glomerular injury, exerting dual effect, an attenuating effect in males and an exacerbatory effect in females. Because this dual effect seemed to be related to and regulated by testosterone, in the present study, we investigated whether estrogen's effect on glomerular injury differed in the presence and absence of testosterone, using castrated male Imai rats in experiment 1 (Exp 1), and testosterone-replaced castrated Imai rats in Exp 2.

Combined Therapy with Estrogen and Testosterone Eliminates the Aggravating Effect of Estrogen Replacement Therapy on Glomerular Injury in Hypercholesterolemic Female Imai Rats

Hypercholesterolemic Imai rats spontaneously develop proteinuria and glomerulosclerosis, especially male animals. Ovariectomy aggravates glomerular injury in femal Imai rats. However, estrogen replacement therapy did not abolish this aggravating effect of ovariectomy and rather aggravated glomerular injury with an increase in serum levels of lipids and growth hormone (GH). Whereas we have already reported that treatment with testosterone in addition to estrogen reduces GH levels and attenuates glomerular injury as compared with estrogen alone in male Imai rats, in the present study, to investigate whether increased GH levels may contribute to an enhancing effect of estrogen on glomerular injury, we treated ovariectomized female Imai rats with estrogen puls testosterone. Group 1 was sham operated and group 2 was ovariectomized at 6 weeks of age. Groups 3, 4, and 5 were ovariectomized and received estrogen, testosterone, or estrogen plus testosterone, respectively. Body weight, urinary protein, and serum constituents were investigated every 4 weeks from 12 to 24 weeks of age. At 24 weeks of age, the rats were studied morphologically. Each treatment with estrogen or testosterone equally aggravated glomerular injury with an increase in both proteinuria and serum lipids with increased serum GH levels in estrogen–treated rats but without influencing GH levels in testosterone–treated rats; combined treatment with estrogen plus testosterone resulted in a reduction of both proteinuria and serum lipids to levels of the controls and attenuated glomerular injury to levels close to those of controls with a reduction of the elevated serum GH levels. These results suggest that increased GH levels may contribute to an enhancing effect of estrogen replacement therapy on glomerular injury and that testosterone, when administered to the estrogen–treated rats, seems to exert an attenuating effect on glomerular injury by suppressing GH levels.

Estrogen Replacement Therapy with Its Physiological Dose Does Not Eliminate the Aggravating Effect of Ovariectomy on Glomerular Injury in Hypercholesterolemic Female Imai Rats

Hypercholesterolemic Imai rats spontaneously develop proteinuria and glomerulosclerosis, especially in males. Estrogen administration attenuated glomerular injury in male Imai rats, and the aggravating effect of ovariectomy in female rats is found. To clarify whether this aggravating effect of ovariectomy is due to a lack of estrogen, we administered estrogen to ovariectomized female Imai rats. At 6 weeks of age, group 1 (control) was sham-operated and group 2 was ovariectomized. Groups 3 and 4 were ovariectomized and received estrogen replacement therapy (0.1 mg in group 3 and 0.2 mg in group 4 once a month subcutaneously). Body weight, urinary protein and serum constituents were investigated every month from 3 to 6 months of age. At 6 months of age, rats were studied morphologically. Estrogen replacement therapy increased serum estrogen to levels close to those of controls when 0.1 mg was used, or higher when 0.2 mg was used. Estrogen replacement therapy with 0.1 mg did not eliminate the aggravating effect of ovariectomy on glomerular injury and rather aggravated it, but conversely therapy with 0.2 mg attenuated glomerular injury and abolished the aggravating effect of ovariectomy. Estrogen replacement therapy markedly elevated serum GH levels dose-dependently. These results suggested that other hormones as well as estrogen may play a protective role of the ovary for the development of glomerular injury, and that estrogen seems to exert a dual effect on glomerular injury.

Testosterone does not eliminate the attenuating effect of estrogen on progressive glomerular injury in estrogen-treated hypercholesterolemic male Imai rats.

Hypercholesterolemic Imai rats spontaneously develop proteinuria and glomerulosclerosis, especially males. Estrogen attenuates the progressive glomerular injury in these male rats. To clarify whether this attenuating effect of estrogen depends on a reduction of testosterone and/or a reduction of the sex-related factors, we investigated whether testosterone administration eliminates the attenuating effect of estrogen on the development of glomerular injury in estrogen-treated male Imai rats. Estrogen significantly reduced sex-related low molecular weight protein excretion to undetectable levels; and treatment with estrogen and testosterone failed to increase these levels. Unexpectedly, treatment with estrogen and testosterone attenuated glomerular injury more than treatment with estrogen only. Estrogen significantly increased both levels of estrogen and growth hormone (GH), whereas it suppressed testosterone levels. Testosterone administration resulted in an increase in serum testosterone levels of about fivefold above the control levels, but reduced the elevated serum GH to the levels of the controls. These results suggest that estrogen appears to play a protective role by itself or in association with sex-related factors, independent of the levels of serum testosterone, and that testosterone does not exert its effect on augmenting glomerular injury and rather may act to attenuate glomerular injury associated with a reduction of GH levels.

Estrogen Attenuates Progressive Glomerular Injury in Hypercholesterolemic Male Imai Rats

Hypercholesterolemic Imai rats spontaneously develop proteinuria and glomerulosclerosis, especially in males. A sex difference in glomerular injury has been recognized, but the role of sex hormones in glomerular injury remains unclear. Therefore, we investigated whether estrogen administration influences the progressive glomerular injury in male Imai rats. Estrogen produced a significant decrease in body weight. Systolic blood pressure in estrogen-treated rats was significantly lower than that in controls. Estrogen attenuated the progression of glomerular injury by significantly reducing proteinuria and glomerular sclerosis. The glomerulosclerosis index was significantly higher in controls than in estrogen-treated rats. Estrogen suppressed serum testosterone levels, whereas it increased GH levels. Results suggest that estrogen appears to play an inhibitory role on the development of glomerular injury, by itself or in association with sex-related factors regulated by estrogen and testosterone.

Testosterone Eliminates the Attenuating Effect of Castration on the Progressive Glomerular Injury in Hypercholesterolemic Male Imai Rats

Hypercholesterolemic Imai rats, especially males, spontaneously develop proteinuria and glomerulosclerosis. We have shown that castration attenuated the progression of glomerular injury in male Imai rats. The present study was designed to investigate whether the attenuating effect of castration on glomerulosclerosis is eliminated by administration of testosterone. Testosterone propionate (TP) eliminated the attenuating effect of castration on the progression of glomerular injury by significantly and dose dependently increasing proteinuria and enhancing glomerular sclerosis. TP at 1 mg failed to reverse glomerulosclerosis to the control levels, despite a dose of TP sufficient to restore urinary protein excretion, serom testosterone level and glomerular growth. The results indicated that besides testosterone other sex-related hormones may be involved in the development of glomerulosclerosis in male Imai rats.

Castration Attenuates Proteinuria and Glomerular Injury in Hyperlipidemic Male Imai Rats

Hyperlipidemic Imai rats spontaneously develop proteinuria and glomerulosclerosis, especially in males. We investigated the effect of castration on spontaneous proteinuria and progressive renal injury in male Imai ats. Male Imai rats (n = 16) were castrated at 5 weeks of age. Body weight, blood pressure, urinary protein excretion and serum constituents were checked and compared with sham-operated control rats (n = 16) up to 24 weeks. Sham-operated group 1 (n = 5) and castrated group 2 (n = 6) underwent morphological study after 16 weeks of observation and sham-operated group 3 (n = 11) and castrated group 4 (n = 10) were followed for an additional 8 weeks and used for morphological study. Growth rate was significantly stunted in castrated rats as compared with the controls. Castration significantly reduced proteinuria almost throughout the experiment (167 +/- 84 vs. 46 +/- 24 mg/kg/day, p < 0.001, at 8 weeks and 688 +/- 211 vs. 458 +/- 97, p < 0.01, at 20 weeks). The glomerulosclerosis index was significantly higher in sham-operated control rats than in castrated rats (28.8 +/- 18.0 vs. 7.3 +/- 3.1, p < 0.01, at 16 weeks, and 92.1 +/- 35.5 vs. 39.5 +/- 8.9, p < 0.001, at 24 weeks). There were no significant differences in blood pressure, serum cholesterol, plasma renin activity, plasma somatomedin C levels between the two groups. These results raise the possibility that sex hormones may partly contribute to spontaneous proteinuria and progressive renal injury in male Imai rats.

Angiotensin-converting enzyme inhibition attenuates hypercholesterolemia and glomerular injury in hyperlipidemic Imai rats.

Hyperlipidemic Imai rats spontaneously develop hypercholesterolemia, proteinuria and glomerulosclerosis. We investigated the effect of enalapril, an angiotensin-converting enzyme (ACE) inhibitor, on spontaneous hypercholesterolemia and the progressive renal injury in this rat strain. Male Imai rats (n = 7) were treated with enalapril at a dose of 50 mg/l in drinking water starting at 6 weeks of age. Body weight, blood pressure, urinary protein excretion and serum constituents were checked and compared with untreated controls (n = 5) up to 38 weeks of age. Enalapril treatment significantly reduced hypercholesterolemia (247 +/- 41 vs. 102 +/- 13 mg/dl, p < 0.01, at 38 weeks) and proteinuria (766 +/- 290 vs. 206 +/- 119 mg/kg/day, p < 0.01, at 38 weeks). The glomerulosclerosis index (SI) was significantly higher in untreated control rats than in the enalapril-treated group (227 +/- 57 vs. 27 +/- 9, p < 0.01). Although we could not clarify whether hypercholesterolemia is a primary event or secondary to the nephrotic syndrome, these results indicate that the ACE inhibitor has the property to protect remnant glomeruli from glomerulosclerosis in male Imai rats as well as in other animal models in which focal and segmental glomerulosclerosis is believed to represent a common pathologic pattern. This rat strain represents a unique model of a spontaneous proteinuria which can provide an important information on the pathogenesis of human focal and segmental glomerulosclerosis.