Nondiabetic Dogs Research Articles

A comparison of anesthetic complications between diabetic and nondiabetic dogs undergoing phacoemulsification cataract surgery: a retrospective study

To compare the incidence of anesthetic complications in diabetic and nondiabetic dogs undergoing general anesthesia and phacoemulsification cataract surgery. The medical and anesthetic records of all dogs undergoing phacoemulsification cataract surgery at Davies Veterinary Specialists between 2005 and 2008 were reviewed. Anesthetic records were evaluated by an ECVAA Diplomate. Dogs for which records were incomplete were excluded. The anesthetic technique, including all drugs administered in the perioperative period, was recorded. The anesthetic complications investigated included hypotension (MAP (mmHg): >or=55 none/mild; <or=54 moderate/severe), bradycardia (<60 bpm associated with hypotension) and hypothermia (esophageal temperature <36.7 degrees C). Where hypotension was present, the method of and response to treatment was recorded. The incidence of severe hyperglycemia (blood glucose >13.75 mmol/L (250 mg/dL)) in the diabetic group was also assessed. 66 diabetic and 64 nondiabetic dogs were included in the study. Diabetic dogs were more likely to develop moderate and severe intraoperative hypotension than nondiabetic dogs. Forty-four percent of diabetic dogs had at least one episode of severe hyperglycemia whilst anesthetized. Diabetic dogs undergoing phacoemulsification are more likely to suffer the anesthetic complications of moderate and severe hypotension than nondiabetic dogs. The increased incidence and severity of hypotension in diabetic dogs may be explained by hypovolemia secondary to hyperglycemia and resultant osmotic diuresis.

Evolutionary history of DLA class II haplotypes in canine diabetes mellitus through single nucleotide polymorphism genotyping

Strong linkage disequilibrium (LD) is a characteristic of the major histocompatibility complex (MHC) region, as well as the genome in general in dogs as a consequence of demographic changes with domestication. Disease association studies of MHC haplotypes may be affected by high LD and the resultant shared genetic backgrounds of haplotypes giving associations with linked but non-causative mutations, and also by convergent haplotypes, in which combinations of alleles have arisen independently. This study provides preliminary tools for dog leukocyte antigen (DLA) class II haplotype analysis with 102 single nucleotide polymorphisms (SNPs) identified in 14.6 kb and genotyping of 20 of these SNPs to tag haplotypes in 60 dogs with diabetes mellitus and in 49 non-diabetic dogs. The pattern of LD and analysis of SNP patterns indicated combinations of exon 2 alleles have arisen through both recombination and convergence. For exon 2 haplotypes associated with susceptibility or protection from diabetes mellitus, a region of fixed differences in SNPs across the DQ region was observed, suggesting a region outside exon 2 may be implicated in disease association. Four new DQB1 promoter alleles restricted to diabetic dogs were identified, as well as a substitution difference in the X1 box of the DQB1 promoter that will potentially modify the effect of the protective haplotypes within diabetic dogs.

Análise da fórmula SRK/T no cálculo de lente intra-ocular em cães portadores de catarata

Foram utilizados 20 cães de raças e idades variadas, machos e fêmeas, portadores de catarata e não diabéticos, os quais foram submetidos ao exame oftálmico. Posteriormente, realizaram-se mensurações oculares empregando-se um ecobiômetro ultra-sônico (ultra-sonografia modo-A) para o cálculo do poder dióptrico da lente intra-ocular por meio da fórmula SRK/T. O comprimento axial médio foi de 19,94±1,12mm. Todos os animais foram submetidos à facoemulsificação extracapsular. A lente calculada foi implantada no transoperatório da cirurgia de catarata, obtendo-se média de 37,33±3,05D. A avaliação pós-cirúrgica do erro refracional aos 60 dias de pós-operatório, pela retinoscopia, com a utilização da esquiascopia, foi de 5,57±1,59D. A fórmula SRK/T não ofereceu bons resultados.

Anti‐Insulin Antibodies in Diabetic Dogs Before and After Treatment with Different Insulin Preparations

Anti-insulin antibodies (AIA) occur in diabetic dogs after insulin therapy, although their clinical significance is unclear. Treatment of diabetic dogs with heterologous insulin is more likely to stimulate production of AIA than is treatment with homologous insulin. Diabetic dogs sampled before insulin therapy (n = 40), diabetic dogs sampled following treatment with porcine (homologous) insulin (n = 100), bovine (heterologous) lente insulin (n = 100), or bovine protamine zinc (PZI) insulin (n = 20), and nondiabetic control dogs (n = 120). Prospective observational study. Sera were analyzed by ELISA for antibodies against porcine insulin, bovine insulin, insulin A, B, or C peptides, and control antigens; canine distemper virus (CDV) and canine thyroglobulin (TG). Canine isotype-specific antibodies were used to determine total and anti-insulin IgG1 : IgG2 ratios. There was no difference in CDV or TG reactivity among the groups. AIA were detected in 5 of 40 newly diagnosed (untreated) diabetic dogs. There was no significant difference in AIA (ELISA optical density reactivity) comparing control and porcine insulin-treated diabetic dogs (P > .05). Anti-insulin reactivity was most prevalent in bovine PZI insulin-treated dogs (90%; P < .01), and bovine lente insulin-treated dogs (56%; P < .01). AIA induced by treatment were enriched for the IgG1 isotype. This study indicates that bovine insulin is more immunogenic than porcine insulin when used for treatment of diabetic dogs.

Advanced glycation end products accumulate in vascular smooth muscle and modify vascular but not ventricular properties in elderly hypertensive canines.

Advanced glycation end products (AGEs) are believed to increase left ventricular (LV) and vascular stiffness, in part via cross-linking proteins. We determined whether and where AGEs were increased in elderly hypertensive nondiabetic dogs and whether an AGE cross-link breaker (ALT-711) improved vascular or ventricular function. Elderly dogs with experimental hypertension (old hypertensives [OH]) were randomized to receive ALT-711 (OH+ALT group; n=11; 1 mg/kg PO) or not (OH group; n=11) for 8 weeks. Conscious blood pressure measurements (weekly), echocardiography (week 8), and anesthetized study (week 8) with LV pressure-volume analysis and aortic pressure-dimension and pressure-flow assessment over a range of preloads and afterloads were performed. In LV and aorta from OH, OH+ALT, and young normal dogs, AGE content (immunohistochemistry and Western analysis for N(epsilon)-(carboxymethyl)lysine [CML]) was assessed. Aortic CML content was markedly increased in OH and OH+ALT dogs compared with young normal dogs. CML was localized to aortic and aortic vasa vasorum smooth muscle but not to collagen or elastin. CML was essentially undetectable in young normal, OH, or OH+ALT myocardium but was visible in large vessels in the LV. ALT-711 therapy was associated with lower blood pressure and pulse pressure, decreased systemic vascular resistance, increased aortic distensibility and arterial compliance, and, notably, significant aortic dilatation. Neither LV systolic nor diastolic function was different in OH+ALT versus OH dogs. In elderly hypertensive canines, AGE accumulation and AGE cross-link breaker effects were confined to the vasculature without evidence of myocardial accumulation or effects. The lack of AGE accumulation in collagen-rich areas suggests that the striking vascular effects may be mediated by mechanisms other than collagen cross-linking.

Diabetes mellitus-related morphoquantitative changes in the celiac ganglion neurons of the dog

Diabetes mellitus is the most common endocrine disturbance of domestic carnivores and can cause autonomic neurological disorders, although these are still poorly understood in veterinary medicine. There is little information available on the quantitative adaptation mechanisms of the sympathetic ganglia during diabetes mellitus in domestic mammals. By combining morphometric methods and NADPH-diaphorase staining (as a possible marker for nitric oxide producing neurons), type I diabetes mellitus-related morphoquantitative changes were investigated in the celiac ganglion neurons in dogs. Twelve left celiac ganglia from adult female German shepherd dogs were examined: six ganglia were from non-diabetic and six from diabetic subjects. Consistent hypertrophy of the ganglia was noted in diabetic animals with increase of 55% in length, 53% in width, and 61.5% in thickness. The ordinary microstructure of the ganglia was modified leading to an uneven distribution of the ganglionic units and a more evident distribution of axon fascicles. In contrast to non-diabetic dogs, there was a lack of NADPH-diaphorase perikarial labelling in the celiac ganglion neurons of diabetic animals. The morphometric study showed that both the neuronal and nuclear sizes were significantly larger in diabetic dogs (1.3 and 1.39 times, respectively). The profile density and area fraction of NADPH-diaphorase-reactive celiac ganglion neurons were significantly larger (1.35 and 1.48 times, respectively) in non-diabetic dogs compared to NADPH-diaphorase-non-reactive celiac ganglion neurons in diabetic dogs. Although this study suggests that diabetic neuropathy is associated with neuronal hypertrophy, controversy remains over the possibility of ongoing neuronal loss and the functional interrelationship between them. It is unclear whether neuronal hypertrophy could be a compensation mechanism for a putative neuronal loss during the diabetes mellitus.

Intramuscular Injection of Islet Neogenesis-Associated Protein Peptide Stimulates Pancreatic Islet Neogenesis in Healthy Dogs

Diabetes is a serious health problem. It has been proposed that islet neogenesis from pancreatic progenitor cells may restore insulin secretion in diabetic mammals. Islet neogenesis- associated protein (INGAP) stimulates islet neogenesis; therefore, we hypothesized that it would stimulate islet neogenesis in dogs. Forty nondiabetic beagle dogs were randomly divided into 4 groups. Group 1 received daily intramuscular injections of vehicle, whereas the other 3 groups received daily INGAP injections of 0.5, 1.5, or 10 mg/kg. After 30 days, pancreatic tissues were collected, and RNA and histological sections were analyzed. In dogs treated with 1.5 mg/kg INGAP, there was a significant (P < 0.001) increase in the percentage of insulin-positive cells (P < 0.001) and insulin gene expression. There was a trend to increased insulin-positive cells and gene expression with treatments of 0.5 and 10 mg/kg peptide. Protein gene product 9.5-positive cells were increased with treatment. These results indicate that INGAP stimulates cells in the pancreatic duct epithelium of healthy dogs (putative islet progenitor cells) to develop along a neuroendocrine pathway and form new islets in response to INGAP peptide. The INGAP might be an effective therapy for diabetes.

The effect of elective phacofragmentation on central corneal thickness in the dog

To characterize the short- and intermediate-term effects of elective phacofragmentation on central corneal thickness (CCT) in the dog. Forty-three dogs (66 eyes) undergoing elective phacofragmentation cataract surgery over an 8-month period at a single private ophthalmology referral clinic were enrolled in the study. Central corneal thickness was measured by ultrasonic pachymetry just prior to surgery, 1 day following surgery, 1 week postoperatively, 1 month postoperatively, and more than 2 months postoperatively. Statistical comparisons were made using descriptive and inferential statistical methods with a level of significance set at P < 0.05. The initial mean CCT of 611 microm increased dramatically to 741 microm 1 day postphacofragmentation. Mean CCT remained slightly elevated (666 microm) at 1 week postoperatively, but became indistinguishable from preoperative measurements by 1 month postsurgery (626 microm) and remained so at the > 2-month time period (618 microm). The change over time and trends remained statistically significant and remarkably similar, even when adjusted separately for age, gender, surgeon status, diabetic status, cataract type, and total surgery time (all P < 0.0001). Corneas of diabetic dogs were thicker than those of nondiabetic dogs at all time periods, and the overall effect of diabetic status was significant (P = 0.016). There was a sharper increase from the preoperative to 1-day postoperative CCT in the diabetic group compared to the nondiabetic group. The mean CCT of the pseudophakic group took longer to return to baseline than the aphakic group. The mean CCT of the foldable intraocular lens (IOL) group took longer to return to baseline than both the rigid IOL and aphakic groups. Dogs with documented in-hospital postoperative intraocular pressure spikes (> 25 mmHg) developed a greater 1-day postsurgical increase in CCT. It appears that there was a sharper decrease in mean CCT from 1 month to more than 2 months postoperatively in the postoperative hypertension group. Elective phacofragmentation cataract surgery results in an increase in CCT in dogs, but this increase is transient. Particular care may be indicated to protect the endothelium of diabetic patients undergoing phacofragmentation. These data do not clearly support an advantage of the small-incision cataract surgery made possible by the use of foldable IOLs.

Insulin's direct effects on the liver dominate the control of hepatic glucose production

Insulin inhibits glucose production through both direct and indirect effects on the liver; however, considerable controversy exists regarding the relative importance of these effects. The first aim of this study was to determine which of these processes dominates the acute control of hepatic glucose production (HGP). Somatostatin and portal vein infusions of insulin and glucagon were used to clamp the pancreatic hormones at basal levels in the nondiabetic dog. After a basal sampling period, insulin infusion was switched from the portal vein to a peripheral vein. As a result, the arterial insulin level doubled and the hepatic sinusoidal insulin level was reduced by half. While the arterial plasma FFA level and net hepatic FFA uptake fell by 40-50%, net hepatic glucose output increased more than 2-fold and remained elevated compared with that in the control group. The second aim of this study was to determine the effect of a 4-fold rise in head insulin on HGP during peripheral hyperinsulinemia and hepatic insulin deficiency. Sensitivity of the liver was not enhanced by increased insulin delivery to the head. Thus, this study demonstrates that the direct effects of insulin dominate the acute regulation of HGP in the normal dog.

Keratoconjunctival effects of diabetes mellitus in dogs

To compare Schirmer tear test (STT) values, corneal sensitivity, tear film break up times (TFBUTs), and tear glucose concentrations in relation to conjunctival microflora, and conjunctival cytologic and histologic findings among diabetic cataractous, nondiabetic cataractous, and nondiabetic noncataractous dogs. Procedures Fifteen dogs in each category underwent neuro-ophthalmic examination; aerobic, anaerobic and fungal conjunctival cultures; assessment of corneal touch threshold (CTT), STT, tear glucose, TFBUT; and conjunctival cytology and histology (in certain cases only). Degree of cataract and uveitis were critically graded. Glycemic control was estimated using serum fructosamine and glycosylated hemoglobin. STT values were significantly lower in diabetic cataractous than nondiabetic noncataractous dogs. CTT of diabetic cataractous dogs was significantly lower than that of nondiabetic noncataractous dogs. Mean TFBUTs were significantly less in diabetic cataractous dogs than nondiabetic cataractous and nondiabetic noncataractous dogs. Tear glucose concentrations were significantly higher in diabetic cataractous dogs than nondiabetic cataractous and nondiabetic noncataractous dogs. Conjunctival microbial isolates did not differ among groups. There were no significant differences in degree of cataract or uveitis between diabetic cataractous and nondiabetic cataractous groups. There was mild submucosal inflammatory infiltrate in conjunctival specimens from diabetic dogs. Conjunctival epithelial dysplasia and/or squamous metaplasia was/were detected in conjunctival biopsies of 5/7 diabetic dogs. Reductions in conjunctival goblet cell (GC) densities were noted in 4/7 diabetic dogs; there were no significant differences in mean GC densities among the three groups. Diabetic cataractous dogs have significantly altered keratoconjunctival characteristics compared to nondiabetic cataractous and nondiabetic noncataractous dogs.

Funduscopic findings following cataract extraction by means of phacoemulsification in diabetic dogs: 52 cases (1993-2003).

To determine prevalence of retinal hemorrhages and microaneurysms in dogs with diabetes mellitus following cataract extraction by means of phacoemulsification and identify potential risk factors. Retrospective study. Medical records of dogs undergoing phacoemulsification between 1993 and 2003 were reviewed, and information was recorded on signalment, history, physical examination findings, ophthalmic examination findings, results of laboratory testing, electroretinographic findings, and surgical findings. Glycemic control was classified as poor, intermediate, or good on the basis of baseline blood glucose concentration, perioperative body weight loss, daily insulin dosage, and presence of glucosuria and ketonuria. Data from diabetic and nondiabetic dogs were analyzed to determine prevalence and risk factors for development of retinal hemorrhages or microaneurysms following phacoemulsification. 11 of the 52 (21%) dogs with diabetes mellitus developed ophthalmoscopic signs of retinal hemorrhages or microaneurysms, compared with 1 of the 174 (0.6%) nondiabetic dogs. Median time from onset of diabetes mellitus to diagnosis of retinopathy was 1.4 years (range, 0.5 to 3.2 years). No risk factors for development of retinopathy were identified. Results suggest that retinal hemorrhages and microaneurysms may be more common and develop earlier in diabetic dogs than previously reported. This may affect treatment, as diabetic dogs survive longer with improved glycemic control.

Alpha-adrenoceptor-mediated coronary vasoconstriction is augmented during exercise in experimental diabetes mellitus.

This study tested whether alpha-adrenoceptor-mediated coronary vasoconstriction is augmented during exercise in diabetes mellitus. Experiments were conducted in dogs instrumented with catheters in the aorta and coronary sinus and with a flow transducer around the circumflex coronary artery. Diabetes was induced with alloxan monohydrate (n = 8, 40 mg/kg i.v.). Arterial plasma glucose concentration increased from 4.7 +/- 0.2 mM in nondiabetic, control dogs (n = 8) to 21.4 +/- 1.9 mM 1 wk after alloxan injection. Coronary blood flow, myocardial oxygen consumption (MVo(2)), aortic pressure, and heart rate were measured at rest and during graded treadmill exercise before and after infusion of the alpha-adrenoceptor antagonist phentolamine (1 mg/kg iv). In untreated diabetic dogs, exercise increased MVo(2) 2.7-fold, coronary blood flow 2.2-fold, and heart rate 2.3-fold. Coronary venous Po(2) fell as MVo(2) increased during exercise. After alpha-adrenoceptor blockade, exercise increased MVo(2) 3.1-fold, coronary blood flow 2.7-fold, and heart rate 2.1-fold. Relative to untreated diabetic dogs, alpha-adrenoceptor blockade significantly decreased the slope of the relationship between coronary venous Po(2) and MVo(2). The difference between the untreated and phentolamine-treated slopes was greater in the diabetic dogs than in the nondiabetic dogs. In addition, the decrease in coronary blood flow to intracoronary norepinephrine infusion was significantly augmented in anesthetized, open-chest, beta-adrenoceptor-blocked diabetic dogs compared with the nondiabetic dogs. These findings demonstrate that alpha-adrenoceptor-mediated coronary vasoconstriction is augmented in alloxan-induced diabetic dogs during physiological increases in MVo(2).

Evaluation of Plasma-Ionized Magnesium Concentration in 122 Dogs with Diabetes Mellitus: A Retrospective Study

The goal of this study was to evaluate plasma-ionized magnesium (iMg2+) concentration in a large group of dogs with naturally occurring diabetes mellitus and to determine whether dogs with diabetes mellitus have hypomagnesemia, as reported in diabetic humans and cats. Plasma iMg2+ concentrations were retrospectively evaluated at the time of initial examination of 122 diabetic dogs at the Matthew J. Ryan Veterinary Hospital of the University of Pennsylvania. Diabetic dogs were defined as having uncomplicated diabetes mellitus (DM, 78 dogs) diabetic ketoacidosis (DKA, 32 dogs), or ketotic nonacidotic diabetes mellitus (DK, 12 dogs) on the basis of presence or absence of metabolic acidosis or ketonuria. Twenty-two control dogs were used to determine reference values for plasma iMg2+ concentration in healthy dogs. Plasma iMg2+ concentration also was evaluated in 19 nondiabetic dogs with acute pancreatitis because many of the dogs with DKA had concurrent acute pancreatitis. Plasma iMg2+ concentration was significantly higher in dogs with DKA (median 0.41 mmol/L, reference range 0.14-0.72 mmol/L) than in dogs with DM (0.33 mmol/L, 0.17-0.65 mmol/L; P = .0002) or the control group (0.32 mmol/L, 0.26-0.41 mmol/L; P = .006). There were no significant differences between plasma iMg2+ concentrations in dogs with DM or DK compared with control dogs. We conclude that dogs with naturally occurring diabetes mellitus do not have marked hypomagnesemia on initial examination at a tertiary care center.

Corneal sensitivity in dogs with diabetes mellitus.

To compare aesthesiometer-determined corneal sensitivity between diabetic and nondiabetic dogs and to investigate the correlation between corneal sensitivity and duration of diabetes or status of glycemic control, as estimated by use of glycated blood protein concentrations. 23 diabetic and 29 nondiabetic normoglycemic dogs. A Cochet-Bonnet aesthesiometer was used to measure corneal touch threshold (CTT) in 5 corneal regions of each dog. At the time of ocular examination, duration of diabetes mellitus was estimated from the history, and blood was drawn for assessment of blood glycosylated hemoglobin and serum fructosamine concentrations. Median CTT for central, nasal, dorsal, temporal, and ventral corneal regions in nondiabetic dogs (1.6, 2.3, 2.8, 2.8, and 5.1 g/mm2, respectively) was significantly lower than in diabetic dogs (2.8, 4.0, 5.1, 5.1, and 6.6 g/mm2, respectively). Median regional CTT in diabetic dogs was not significantly correlated with estimated duration of diabetes mellitus or blood glycated protein concentrations. No significant difference was found in regional CTT between eyes of normoglycemic dogs with unilateral cataracts. Diabetic dogs have significantly reduced corneal sensitivity in all regions, compared with nondiabetic normoglycemic dogs. Regional variation in corneal sensitivity is similar in diabetic and normoglycemic dogs. Neither glycemic control nor duration of diabetes, as estimated, is significantly correlated with corneal hyposensitivity. Corneal nerve dysfunction may be associated with recurrent or nonhealing ulcers in diabetic dogs for which no other underlying cause can be found.

Insulin inhibits glucose production by a direct effect in diabetic depancreatized dogs during euglycemia.

In our previous studies in nondiabetic dogs and humans, insulin suppressed glucose production (GP) by both an indirect extrahepatic and a direct hepatic effect. However, insulin had no direct effect on GP in diabetic depancreatized dogs under conditions of moderate hyperglycemia. The present study was designed to investigate whether insulin can inhibit GP by a direct effect in this model under conditions of euglycemia. Depancreatized dogs were made euglycemic (approximately 6 mmol/l), rather than moderately hyperglycemic (approximately 10 mmol/l) as in our previous studies, by basal portal insulin infusion. After approximately 100 min of euglycemia, a hyperinsulinemic euglycemic clamp was performed by giving an additional infusion of insulin either portally (POR) or peripherally at about one-half the rate (1/2 PER) to match the peripheral venous insulin concentrations. The greater hepatic insulin load in POR resulted in greater suppression of GP (from 16.5 +/- 1.8 to 12.2 +/- 1.6 micromol. kg(-1). min(-1)) than 1/2 PER (from 17.8 +/- 1.9 to 15.6 +/- 2.0 micromol. kg(-1). min(-1), P < 0.001 vs. POR), consistent with insulin having a direct hepatic effect in suppressing GP. We conclude that the direct effect of insulin to inhibit GP is present in diabetic depancreatized dogs under conditions of acutely induced euglycemia. These results suggest that, in diabetes, the prevailing glycemic level is a determinant of the balance between insulin's direct and indirect effects on GP.

Coronary blood flow control is impaired at rest and during exercise in conscious diabetic dogs.

This study tested whether diabetes mellitus impairs coronary blood flow control sufficiently to alter the balance between myocardial oxygen delivery and metabolism. Dogs (n = 7) were instrumented with catheters in the aorta and coronary sinus, and with a flow transducer on the circumflex coronary artery. Coronary blood flow, myocardial oxygen consumption (MVO2), heart rate and aortic pressure were measured at rest and during treadmill exercise before and after induction of diabetes with alloxan monohydrate (40 - 60 mg/kg). Arterial plasma glucose concentration increased from 4.6+/-0.2 mM in non-diabetic, control dogs to 20.2+/-2.3 mM one week after alloxan injection. In non-diabetic control dogs, exercise increased MVO2 3.1-fold, coronary blood flow 2.7-fold, and heart rate 2.4-fold. Coronary venous PO2 decreased from 19.4+/-0.6 mmHg at rest to 14.7+/-0.7 mmHg during exercise. Diabetes significantly attenuated exercise coronary hyperemia and reduced coronary venous PO2 at rest (15.6+/-0.5 mmHg) and during exercise (12.6+/-0.8 mmHg). Diabetes also significantly reduced myocardial oxygen delivery at each level of exercise. Acute hyperglycemia alone did not alter exercise-induced coronary vasodilation or reduce coronary venous PO2. These findings demonstrate that experimental diabetes attenuates functional coronary hyperemia and impairs the balance between coronary blood flow and myocardial metabolism. However, this deleterious effect is not related to acute hyperglycemia but to the chronic disease process of diabetes mellitus.

ATP-dependent K(+) channels contribute to local metabolic coronary vasodilation in experimental diabetes.

This study tested whether ATP-dependent K(+) channels (K(ATP) channels) are an important mechanism of functional coronary hyperemia in conscious, instrument-implanted diabetic dogs. Data were collected at rest and during exercise before and after induction of diabetes with alloxan monohydrate (40-60 mg/kg intravenously). K(ATP) channels were inhibited with glibenclamide (1 mg/kg intravenously). In nondiabetic dogs, arterial plasma glucose concentration increased from 4.8 +/- 0.3 to 21.5 +/- 2.2 mmol/l 1 week after alloxan injection. In nondiabetic dogs, exercise increased myocardial oxygen consumption (MVO(2)) 3.4-fold, myocardial O(2) delivery 3.0-fold, and heart rate 2.4-fold. Coronary venous PO(2) decreased from 19.9 +/- 0.8 mmHg at rest to 14.8 +/- 0.8 mmHg during exercise. Diabetes significantly reduced myocardial O(2) delivery and lowered coronary venous PO(2) from 16.3 +/- 0.6 mmHg at rest to 13.1 +/- 0.9 mmHg during exercise. Glibenclamide did not alter the slope of the coronary venous PO(2) versus MVO(2) relationship in nondiabetic dogs. In diabetic dogs, however, glibenclamide further reduced myocardial O(2) delivery; coronary venous PO(2) fell to 9.0 +/- 1.0 mmHg during exercise, and the slope of the coronary venous PO(2) versus MVO(2) relationship steepened. These findings indicate that K(ATP) channels contribute to local metabolic coronary vasodilation in alloxan-induced diabetic dogs.

A subcutaneous glucose sensor with improved longevity, dynamic range, and stability of calibration.

To evaluate the lifetime, response time, linearity, glucose range, and calibration stability of two different types of continuous glucose sensor implants in a dog model. Glucose sensors based on the enzyme electrode principle that are coupled to a radio transmitter were evaluated on the bench top, sterilized, and then implanted subcutaneously in nondiabetic mongrel dogs. A multichannel radio receiver and PC data processor were used to record the sensor glucose data. Initial early reliable sensor responsivity was recognized by a vigorous hyperglycemic excursion after an intramuscular injection of glucagon. Periodically the dogs were made temporarily diabetic by blocking pancreatic insulin secretion by subcutaneous injection of a synthetic somatostatin (octreotide). By using exogenous insulin injection followed by intravenous glucose infusion, glucose levels were manipulated through the entire clinical range of interest: 2.2-38.9 mmol/l (40-700 mg/dl). Every 5-10 min, reference blood glucose samples were obtained and run in our hospital clinical laboratory. The glucose sensor data was evaluated by linear least squares optimization and by the error grid method. Beginning as early as postimplant day 7, the in vivo performances of sensors were evaluated by using glucose infusion studies performed every 1-4 weeks. Bench-top and in vivo 90% response-time sensors were in the range of 4-7 min during sensor lifetime. Best-performing sensors from both types are summarized as follows. The earlier-stage technology was less linear with a dynamic range of no more than 22 mmol/l glucose, had a best-case recalibration interval of 18 days, and had a maximum lifetime of 94 days. The improved later-stage technology sensors, which were constructed with the addition of bioprotective and angiogenic membranes, were linear over the full extended range of clinical interest (2.2-38.9 mmol/l [40-700 mg/dl glucose]), had a best-case recalibration interval of 20 days, and had a maximum lifetime of >160 days. Stable clinically useful sensor performance was demonstrated as early as 7 days after implantation and for a sensor lifetime of 3-5 months. This type of subcutaneous glucose sensor appears to be promising as a continuous and painless long-term method for monitoring blood glucose. Specifically sensors with top-layer materials that stimulate angiogenesis at the sensor/tissue interface may have better dynamic measurement range, longer lifetimes, and better calibration stability than our previously reported sensors.

Resistance to insulin's acute direct hepatic effect in suppressing steady-state glucose production in individuals with type 2 diabetes.

We and others have shown that insulin acutely suppresses glucose production in fasting nondiabetic humans and dogs, by both a direct hepatic effect and an indirect (extrahepatic) effect, and in diabetic dogs by an indirect effect alone. In type 2 diabetes, there is resistance to insulin's ability to suppress hepatic glucose production, but it has not previously been determined whether the resistance is primarily at the level of the hepatocyte or the peripheral tissues. To determine whether the diabetic state reduces the direct effect of insulin in humans, we studied nine patients with untreated type 2 diabetes who underwent three studies each, 4-6 weeks apart. 1) Portal study (POR): intravenous tolbutamide was infused for 3 h with calculation of pancreatic insulin secretion from peripheral plasma C-peptide. 2) Peripheral study (PER): equidose insulin was infused by peripheral vein. 3) Half-dose peripheral insulin study (1/2 PER): matched peripheral insulin levels with study 1. In all studies, glucose was clamped at euglycemia, glucose turnover was measured with the constant specific activity method, and 3-[3H]glucose was purified by high-performance liquid chromatography. Peripheral insulin was lower in POR versus PER but slightly higher in POR versus 1/2 PER, although most of the difference could be accounted for by higher proinsulin levels in POR (stimulated by tolbutamide). Calculated portal insulin was approximately 1.3-fold higher in POR versus PER and approximately 2.2-fold higher in POR versus 1/2 PER. In the final 30 min of the clamp, glucose production reached a lower steady-state level in PER than in POR (4.0 +/- 0.4 vs. 5.3 +/- 0.5 pmol(-1) x kg(-1) x min(-1), P < 0.05), despite the higher hepatic insulin level in POR. In contrast with our studies in nondiabetic individuals, glucose production was not more suppressed at steady state in POR versus 1/2 PER (5.3 +/- 0.4 micromol x kg(-1) x min(-1)), despite much higher hepatic insulin levels in POR. In conclusion, this is the first study in patients with type 2 diabetes to characterize insulin resistance to the acute direct suppressive effect of insulin on hepatic glucose production.

Increased dependence of glucose production on peripheral insulin in diabetic depancreatized dogs

We have recently found that in nondiabetic dogs and humans, suppression of glucose production (GP) is mediated by both peripheral and hepatic effects of insulin. We have also found that both nonesterified fatty acids (NEFA) and glucagon are important determinants of the peripheral effect of insulin on GP. However, in moderately hyperglycemic depancreatized dogs, suppression of GP appeared to be mediated by peripheral but not hepatic insulin. In this latter study, insulin concentrations were in the high postprandial range (approximately 300 pmol/L) and suppression of GP may have been close to maximum. The aim of the present study was to determine whether GP can be regulated by hepatic insulin in depancreatized dogs at low insulin concentrations in the postabsorptive range. Depancreatized dogs were maintained at moderately hyperglycemic levels (approximately 10 mmol/L) by subbasal insulin infusions. In paired experiments, additional low-dose equimolar insulin infusions (0.75 pmol/kg x min) were administered peripherally (PER, n = 6) or portally (POR, n = 6) during glucose clamps. This resulted in a minimal increase in peripheral insulin levels, which was greater in PER versus POR, 29.0 +/- 3.7 versus 11.7 +/- 2.2 pmol/L. Also, we infused insulin peripherally at half this rate (1/2 PER, n = 6) to match the increase in peripheral insulin levels in POR (1/2 PER, 14.6 +/- 2.2) and thus obtain a selective POR versus 1/2 PER difference in hepatic sinusoidal insulin levels. PER suppressed GP more than POR (45.4% +/- 4.0% v 35.3% +/- 6.8%, P < .001), whereas POR did not suppress GP more than 1/2 PER (35.6% +/- 6.3%). Therefore, suppression of GP was proportional to peripheral rather than hepatic sinusoidal insulin levels, as in our previous study at higher insulin concentrations. In conclusion, during glucose clamps in moderately hyperglycemic depancreatized dogs, (1) suppression of GP was dominated by insulin's peripheral effects not only at postprandial but also postabsorptive insulin levels, and (2) we found no evidence for a hepatic effect of insulin in suppressing GP. We hypothesize that this effect is reduced in the depancreatized dog model of diabetes due to hepatic insulin resistance and/or hyperglycemia.