Resistance of rabbits and guinea pigs to the diabetogenic effect of streptozotocin

Experimental animal models of coronary microvascular dysfunction

Coronary microvascular dysfunction (CMD) is commonly present in patients with metabolic derangements and is increasingly recognized as an important contributor to myocardial ischaemia, both in the presence and absence of epicardial coronary atherosclerosis. The latter condition is termed 'ischaemia and no obstructive coronary artery disease' (INOCA). Notwithstanding the high prevalence of INOCA, effective treatment remains elusive. Although to date there is no animal model for INOCA, animal models of CMD, one of the hallmarks of INOCA, offer excellent test models for enhancing our understanding of the pathophysiology of CMD and for investigating novel therapies. This article presents an overview of currently available experimental models of CMD-with an emphasis on metabolic derangements as risk factors-in dogs, swine, rabbits, rats, and mice. In all available animal models, metabolic derangements are most often induced by a high-fat diet (HFD) and/or diabetes mellitus via injection of alloxan or streptozotocin, but there is also a wide variety of spontaneous as well as transgenic animal models which develop metabolic derangements. Depending on the number, severity, and duration of exposure to risk factors-all these animal models show perturbations in coronary microvascular (endothelial) function and structure, similar to what has been observed in patients with INOCA and comorbid conditions. The use of these animal models will be instrumental in identifying novel therapeutic targets and for the subsequent development and testing of novel therapeutic interventions to combat ischaemic heart disease, the number one cause of death worldwide.

WTC rat has unique characteristics such as resistant to streptozotocin

Because we found that WTC rats might be resistant to streptozotocin (STZ), we have elucidated the mechanisms of resistant to the diabetogenic effects of STZ in the WTC rats. Dose response to STZ was evaluated with glucose levels. No significant changes in glucose level to STZ administration were observed in WTC rats. Insulin secretion by suppling glucose was preserved in WTC rats even after STZ administration. Although there was no significant difference in gene expression of both GLUT2 and Kir6.2, which were involved in STZ resistance, between WTC rats and Wistar rats, the expression of metallothionein 2a in pancreas and liver to STZ administration of WTC rats was significantly higher than that of Wistar rats. Moreover, alloxan did not induce diabetes in WTC rats as same as STZ. These results suggest that WTC rats might have powerful antioxidant property to protect β cells in pancreas. Because the STZ-resistant property is very close characteristics to human beings, WTC rats will become a useful animal model in diabetic researches.

A model of type 2 diabetes in the guinea pig using sequential diet-induced glucose intolerance and streptozotocin treatment

Type 2 diabetes is a leading cause of morbidity and mortality among noncommunicable diseases, and additional animal models that more closely replicate the pathogenesis of human type 2 diabetes are needed. The goal of this study was to develop a model of type 2 diabetes in guinea pigs, in which diet-induced glucose intolerance precedes β-cell cytotoxicity, two processes that are crucial to the development of human type 2 diabetes. Guinea pigs developed impaired glucose tolerance after 8 weeks of feeding on a high-fat, high-carbohydrate diet, as determined by oral glucose challenge. Diet-induced glucose intolerance was accompanied by β-cell hyperplasia, compensatory hyperinsulinemia, and dyslipidemia with hepatocellular steatosis. Streptozotocin (STZ) treatment alone was ineffective at inducing diabetic hyperglycemia in guinea pigs, which failed to develop sustained glucose intolerance or fasting hyperglycemia and returned to euglycemia within 21 days after treatment. However, when high-fat, high-carbohydrate diet-fed guinea pigs were treated with STZ, glucose intolerance and fasting hyperglycemia persisted beyond 21 days post-STZ treatment. Guinea pigs with diet-induced glucose intolerance subsequently treated with STZ demonstrated an insulin-secretory capacity consistent with insulin-independent diabetes. This insulin-independent state was confirmed by response to oral antihyperglycemic drugs, metformin and glipizide, which resolved glucose intolerance and extended survival compared with guinea pigs with uncontrolled diabetes. In this study, we have developed a model of sequential glucose intolerance and β-cell loss, through high-fat, high-carbohydrate diet and extensive optimization of STZ treatment in the guinea pig, which closely resembles human type 2 diabetes. This model will prove useful in the study of insulin-independent diabetes pathogenesis with or without comorbidities, where the guinea pig serves as a relevant model species.

Problems in Predicting Drug Effects across Species Lines

During the course of drug development, there are many instances where extrapolation of data from animals to man is difficult because the toxicologic and metabolic responses induced by drugs may be significantly different between the laboratory species. In cases where the drug in question has a potentially major therapeutic use in man, it is suggested that the data be evaluated on the basis of a pragmatic benefit-to-risk ratio, rather than zero-toxicity. In this way, we may provide drug therapy for those patients for whom adequate treatment does not exist, as well as protect those individuals who may be exposed to some hazard from the use of medicines.

Mechanisms and outcomes of drug- and toxicant-induced liver toxicity in diabetes

Increase dincidences of hepatotoxicity have been observed in diabetic patients receiving drug therapies. Neither the mechanisms nor the predisposing factors underlying hepatotoxicity in diabetics are clearly understood. Animal studies designed to examine the mechanisms of diabetes-modulated hepatotoxicity have traditionally focused only on bioactivation/detoxification of drugs and toxicants. It is becoming clear that once injury is initiated, additional events determine the final outcome of liver injury. Foremost among them are two leading mechanisms: first, biochemical mechanisms that lead to progression or regression of injury; and second, whether or not timely and adequate liver tissue repair occurs to mitigate injury and restore liver function. The liver has a remarkable ability to repair and restore its structure and function after physical or chemical-induced damage. The dynamic interaction between biotransformation-based liver injury and compensatory tissue repair plays a pivotal role in determining the ultimate outcome of hepatotoxicity initiated by drugs or toxicants. In this review, mechanisms underlying altered hepatotoxicity in diabetes with emphasis on both altered bioactivation and liver tissue repair are discussed. Animal models of both marked sensitivity (diabetic rats) and equally marked protection (diabetic mice) from drug-induced hepatotoxicity are described. These examples represent a remarkable species difference. Availability of the rodent diabetic models offers a unique opportunity to uncover mechanisms of clinical interest in averting human diabetic sensitivity to drug-induced hepatotoxicities. While the rat diabetic models appear to be suitable, the diabetic mouse models might not be suitable in preclinical testing for potential hepatotoxic effects of drugs or toxicants, because regardless of type 1 or type2 diabetes, mice are resistant to acute drug-or toxicant-induced toxicities.

Lipid and exocrine pancreatic ultrastructural changes due to experimental diabetes

The aim of this study was to establish if the changes in the ultrastructure of the exocrine part of the pancreas are correlated with changes in serum glucose, cholesterol and lipoprotein fractions during the progression of diabetes in rabbits. Diabetes mellitus was induced in male New Zealand rabbits by a single injection of alloxan into the auricular vein. On the day 7th the glucose level in the whole blood was measured and this day was designated as the first day of diabetes. Rabbits were divided into 5 groups: untreated control, 21-day diabetes, 42-day diabetes, 90-day diabetes and 180-day diabetes. The cholesterol, HDL (high-density lipoprotein) and LDL (low-density lipoprotein) levels were examined in the serum. The total pancreatic lipase activity was measured spectrophotometrically in the pancreatic homogenate. Histological specimens were examined under an electron microscopy. The glucose level increased significantly in all of the alloxan exposed animals. The significant elevation of cholesterol level was observed on day 21 and 180. The HDL level was increased (P<0.05) only on the day 21st. The LDL level and the total activity of pancreatic lysosomal lipase increased significantly on day 21, 42 and 90. Further dilation of granular endoplasmic reticular ducts and decrease in the number of zymogen granules were observed amongst exocrine cells. Fragmented mitochondrial and translucent matrix were also seen. Intensification of the pancreatic fibrosis was found on day 90. Microvascular changes were reported in exocrine cells after 180 days. Their nuclei were smaller with large bulges on the nuclear membrane, and the number of heterogeneous electron granules of zymogen further declined. We concluded that the intensification of ultrastructural changes of the exocrine part of the pancreas correlated with the changes of the pancreatic lipase activity, and glucose and lipoprotein levels.

Control of hyperglycaemia in diabetic rabbits by a combination of implants

Insulin demand varies with meal intake and physical activity. In this study the feasibility of using two implants to meet varying insulin demands was tested in rabbits with alloxan-induced diabetes. One group of severely diabetic rabbits was maintained on a basal dose released by a 50-mg implant made of a compressed admixture of 15% insulin in palmitic acid. The other group of mildly diabetic rabbits required no basal dose implant, but displayed a transient hyperglycaemia as well upon challenge. The supplemental dose was provided by another silicone implant with reservoirs containing 6 mg of compressed insulin. Serous fluid entered the 100 microliters internal volume of the silicone implant slowly through an orifice, and dissolved some of the solid insulin. When required, sideways compression of this second implant over the abdominal skin fold of the rabbit delivered the supplemental dose. Typically, a severely diabetic rabbit on a basal dose implant exhibited a transient hyperglycaemia after drinking sweetened water, which raised the blood glucose from 5.4 +/- 1.3 mmol l-1 to 14.0 +/- 0.5 mmol l-1 for 3 to 4.5 h. In the three test runs, the supplemental bolus of insulin from the silicone implant interrupted the expected rise in blood glucose at 6.1 +/- 2.2 mmol l-1 within 1 to 2 h, which then decreased to 3.0 +/- 0.2 mmol l-1 for 4 to 5 h before returning to the basal level. A mildly diabetic rabbit showed a blood glucose level of 10.5 +/- 1.9 mmol l-1 without the basal dose implant.(ABSTRACT TRUNCATED AT 250 WORDS)

Correlations between blood glucose levels and bromodeoxyuridine labelling indices of pancreatic islet cells following streptozotocin administration to pregnant Syrian golden hamsters

Eighteen timed-pregnant Syrian golden hamsters were injected subcutaneously with streptozotocin (STZ, 60 mg/kg bw) early on gestational day 10. The response varied widely, and based on changes in blood glucose levels during gestational days 11 to 15, the hamsters were categorized into four groups: 1) no change; 2) mild diabetes (200-250 mg/dl), which reverted; 3) moderate diabetes (greater than 300 mg/dl), which reverted; and 4) moderate to severe diabetes (300-500 mg/dl), which was sustained. Two hours before sacrifice, a 25 mg tablet of bromodeoxyuridine (BrdU) was implanted subcutaneously into each experimental hamster and into 17 control pregnant hamsters that had not received STZ. BrdU-labelling was demonstrated immunochemically in the pancreatic islet cells. In control hamsters, the mean labelling index (LI) of the islet cells was 0.07% and did not exceed 0.2% in any hamster. Following injection of STZ, islet cell LI's remained low (0.13%) if the blood glucose levels were not altered by the diabetogenic drug. However, LI's were increased in islet cells of hamsters which showed a mild to moderate diabetes which rapidly reverted; the highest LI's (5% +/- 2.1) occurred in four hamsters that were killed 2 days after receiving STZ. The LI's were moderately increased (1.4% +/- 0.42) in two hamsters with moderate diabetes killed 2 days after STZ, but LI's were low (0.12% +/- 0.04) in six hamsters with moderate to severe diabetes killed 3, 4, and 5 days after STZ. Reversion of hyperglycemia to normoglycemia correlated closely with increased DNA synthesis in the islet cells of the pregnant hamsters. These observations strongly suggest that following mild cytotoxic injury induced by STZ, the B cells regenerated and insulin production was restored sufficiently to maintain normoglycemia.

N-methyl antitumour agents. A distinct class of anticancer drugs?

This article reviews the structure-activity characteristics, mode of action, pharmacokinetics and clinical utility of a group of chemically dissimilar antitumour agents which have as a common structural feature the N-methyl moiety. The importance of this feature is shown by the fact that molecules without a substituent on the nitrogen or compounds with N-alkyl groups other than methyl are usually inactive in experimental systems. This observation is supported by structure-activity studies with N-alkyl derivatives of s-triazines, triazenes, formamides, hydrazines and nitrosoureas. Representatives of these structural types which have found clinical application are, respectively, hexamethylmelamine, dacarbazine, N-methylformamide, procarbazine and streptozotocin. Mode of action studies have shown that dacarbazine, procarbazine and streptozotocin can give rise to species capable of methylating nucleic acid. This may be the lesion which produces antitumour activity. The mechanism of action of N-methylmelamines and N-methylformamide remains unclear. There is good evidence that, with the exception of N-methylnitrosoureas, host metabolism is prerequisite for activity with these agents. Although not pronounced, the clinical activity of N-methyl antitumour agents is useful, particularly as activity is not associated with severe haematological toxicity. Furthermore, responses may be observed in patients resistant to bifunctional alkylating agents. It is concluded that the drugs reviewed herein show a degree of coincidence in terms of their biological properties which may warrant a common classification. The term N-methyl antitumour agent is proposed.

Biochemical and functional changes in hearts from rabbits with diabetes

Biochemical and myocardial functional changes were determined in rabbits made diabetic with alloxan (100 mg/kg, intravenously, two injections 24 h apart). Alloxan-induced diabetes was characterized by a state of hypoinsulinaemia and hyperglycaemia. After 10 weeks of diabetes, significant decreases in heart and left ventricular weights as well as increased serum and heart triglycerides and cholesterol were observed in the diabetic animals (p less than 0.05). In addition, left ventricular pressure, heart rate and rate of left ventricular pressure development were all decreased in the animals. The diabetic state was also associated with a slight elevation in myocardial calcium and a significant decrease in magnesium levels (p less than 0.05). Subcellular fractionation of diabetic hearts indicated the presence of alterations in myofibrillar and sarcoplasmic reticulum marker enzymes (p less than 0.05). Among the lysosomal enzymes, measured, N-acetyl-beta-glucosaminidase activity was significantly increased in the homogenates of diabetic left ventricles (p less than 0.05). These alterations in hearts of diabetic rabbits may be responsible for some aspects of diabetic cardiomyopathy.

Drug metabolism in spontaneously diabetic guinea pigs

Both sexes of spontaneously diabetic guinea pigs exhibit hyperinsulinemia (greater than 4-fold normal). This diabetic state is associated with the inhibition of hepatic drug metabolism in males but not females.

Effects of streptozotocin in the male guinea pig: a potential animal model for studying diabetes

The effects of acutely administered streptozotocin in the male guinea pig were studied for a period of 18 days following treatment. A single intracardiac injection of streptozotocin (150 mg/kg) was administered on Day 0. On Day 2, plasma glucose concentrations were not significantly different from control levels. On Day 7 and 18, an oral glucose tolerance test was performed with streptozotocin-treated animals receiving an acute injection of either insulin (18 U/kg, i.m.) or saline 90 minutes prior to glucose loading. On Day 7, streptozotocin-treated animals receiving saline had significantly elevated plasma and urine glucose concentrations at 3 hours after glucose loading when compared to controls. Streptozotocin-treated animals receiving insulin however, had significantly lower plasma glucose concentrations at 3 hours while urinary glucose was equal to control values. The second glucose tolerance test performed on Day 18 yielded similar results. Necropsies were performed on animals that died after Day 6. Lesions found in the streptozotocin-treated animals included: small and irregular pancreatic islets, pyknotic nuclei and degranulation of beta cells, renal proximal tubule swelling and vacuolization, adrenal cortical hyperplasia, hepatocyte vacuolization, and visceral fat atrophy. Animals surviving until Day 18 were sacrificed and found to have significantly elevated kidney and adrenal weights compared to controls. These changes illustrate the effectiveness of streptozotocin in the acute chemical induction of diabetes in an animal model (guinea pig) which, like humans, requires a dietary source of ascorbic acid.

Early glomerular changes in streptozotocin diabetes of the guinea pig

This work was to study--using morphometric methods--whether glomerular alterations are demonstrable in the guinea pig kidney even in streptozotocin diabetes of only short duration. In 25, 50, 100 and 150-days diabetes was investigated the blood sugar, the glucose tolerance test, histological and morphometric studies. Storage of glycogen in the kidney was to be found in numerous treated animals whereby it was evident that the cells of the macula densa showed no storage. The morphometric studies performed under blind conditions have shown that with a duration of diabetes of 50 and 100 days the number of cells in the mesangium is increased and that an increase of the mesangial matrix is demonstrable. Hence the mesangium is in the foreground of the initial alterations in diabetes mellitus.