A consistent model of insulin-dependent diabetes mellitus hypertension

A novel mouse model of diabetes mellitus using unilateral nephrectomy

Diabetes mellitus (DM) is a major cause of morbidity and mortality worldwide, and its complications are prominent public health issues. Many experimental models of streptozotocin (STZ)-induced and high-fat diet (HF)-induced DM have been used to study this disease. Studies have indicated that unilateral nephrectomy (UN) accelerates the development of diabetic nephropathy. We hypothesized that UN stimulates HF and STZ combination-induced DM in mice. Seventy-two female C57BL/6J mice were divided into four treatment groups: HF; HF + STZ120 (HF and STZ, 120 mg/kg); UN + HF + STZ120 (UN, HF and STZ, 120 mg/kg); and HF + STZ200 (HF and STZ, 200 mg/kg). Onset of DM, survival rate, blood pressure, urine glucose level, and pancreatic histology were investigated. Additionally, renal function was evaluated in the UN + HF + STZ120 group after STZ injection. DM was induced in the UN + HF + STZ120 and HF + STZ200 groups within one week. The UN + HF + STZ120 group had lower mortality than the HF + STZ200 group and greater pancreatic destruction than the HF and HF + STZ120 groups. Two weeks after STZ injection, blood pressure was not significantly different among the groups. Nephrotoxicity associated with the combination of UN and STZ was not observed. In conclusion, the combination of these three techniques – UN, HF and STZ induced DM rapidly and effectively.

Dietary NaCl-induced hypertension in uninephrectomized Wistar-Kyoto rats: role of kidney function

This study tests the hypothesis that combination of unilateral nephrectomy and a high sodium chloride (NaCl) diet causes hypertension in otherwise normotensive Wistar-Kyoto (WKY) rats and that this hypertensive response is due to a deficit in the remaining kidney's function. Four-week-old male WKY rats underwent either a right nephrectomy or a sham operation. Two weeks later, the groups either were switched to a high (8%) NaCl diet or remained on the basal (0.72%) NaCl diet. At ages 3 and 6 months, hemodynamic parameters and renal excretory responses were measured, in the conscious animals, before and after administration of a 30-min isotonic saline challenge (5% of body weight). The high-NaCl diet increased arterial pressure in the uninephrectomized but not in sham-operated rats; the development of hypertension was associated with increases in baseline renal excretion of fluid and sodium and diuretic and natriuretic responses to the isotonic saline challenge. The increased diuresis and natriuresis in the hypertensive WKY rats were related to a significant reduction in renal tubular reabsorption and an associated increase in fractional excretion of fluid and sodium. The high-NaCl diet also increased renal excretion of fluid and sodium in the sham-operated rats; however, the uninephrectomized animals excreted much more fluid and sodium than did sham-operated rats. These data suggest that the combination of unilateral nephrectomy and dietary NaCl excess causes hypertension in the normotensive WKY rats, but the hypertensive response is not likely due to a functional deficit in the remaining kidney.

Renal function in the noninsulin-dependent diabetic rat: effects of unilateral nephrectomy

A new model of noninsulin-dependent diabetic (NIDD) is described which exhibits more prominent defects in renal function than does the standard neonatal NIDD model. To produce this model, 2-day-old neonatal male Wistar Kyoto (WKY) rats were injected intraperitoneally with streptozotocin (90 mg/kg; NIDD), while their corresponding nondiabetic controls were administered vehicle (citrate buffer, pH: 4.5; control). At 3 weeks of age, the animals were weaned, and 1 week later, under ether anesthesia, the animals underwent a right nephrectomy or a sham operation. Diabetes was confirmed by intraperitoneal administration of a glucose load (2g/kg), which resulted in significantly higher blood glucose concentration in the NIDD, compared to the nondiabetic rats. Surgical reduction of renal mass had no effect on the glycemic response to a glucose tolerance test in either group. Intravenous administration of an isotonic saline load resulted in a similar pattern of enhanced sodium and fluid excretion in the two-kidney sham-operated nondiabetic and NIDD rats. These responses were significantly higher than those observed in their counterparts with one remaining kidney. Yet, the natriuretic and diuretic responses to the saline load were significantly lower in the nephrectomized NIDD, compared to the nephrectomized nondiabetic rats. The glomerular filtration rate was similar in the sham-operated (two kidneys) NIDD and nondiabetic rats. In contrast, both the basal and saline-stimulated glomerular filtration rate were lower in the nephrectomized NIDD rats compared to the nephrectomized nondiabetic group. Mean arterial pressure was similar between the two nephrectomized groups, thereby ruling out a significant contribution from the pressure-diuresis-natriuresis mechanism to the reduction in sodium and fluid excretion in the nephrectomized NIDD rats. Thus, unilateral nephrectomy is an effective method of accelerating the manifestation of NIDD-related renal alterations. The mild, but progressive, nature of diabetes in this model should facilitate the investigation of temporal changes in renal function in NIDDM.

Effect of administration of insulin on streptozotocin-induced diabetic hypertension in rat

We have reported that streptozotocin-induced insulin-dependent diabetes mellitus in 25% reduced renal mass rats is associated with low-renin, volume-expanded hypertension and that the development of the hypertension can be prevented with insulin. In this study we examined the effect of insulin after the animals had developed sustained hypertension. Normotensive 25% reduced renal mass rats were treated with streptozotocin and, as expected, developed insulin-dependent diabetes mellitus and hypertension. After 4 weeks of sustained hypertension, neutral protamine Hagedorn insulin (6 to 8 IU/d) was administered subcutaneously for 4 weeks. As expected, insulin treatment decreased plasma glucose and increased body weight gain relative to untreated diabetic rats. On the other hand, insulin treatment did not reverse the hypertension and albuminuria. It also did not normalize extracellular fluid volume and plasma renin activity. Furthermore, insulin treatment did not reverse the increase in plasma Na+,K(+)-ATPase inhibitory activity (determined by both radioimmunoassay and bioassay) and the inhibition of myocardial microsomal Na+,K(+)-ATPase activity observed in the untreated diabetic hypertensive rats. 5'-Nucleotidase, a membrane marker, was not different between insulin-treated and untreated diabetic rats. These results show that insulin, given as here described, does not reverse the insulin-dependent diabetes mellitus hypertension in 25% reduced renal mass rats once it is established, perhaps because it does not reverse the albuminuria, volume expansion, increase in endogenous digitalis-like substance, and inhibition of cardiovascular muscle cell Na+,K(+)-ATPase activity.