Combined Glucose-insulin Test Research Articles

Use of FreeStyle Libre for continuous glucose monitoring in adult horses.

To evaluate the feasibility of using the FreeStyle Libre (a continuous glucose monitoring system [CGMS]) for instantaneous continuous monitoring of interstitial glucose in adult horses and examine the applicability and accuracy of this system in horses submitted to combined glucose-insulin test (CGIT). Laboratory measurements and continuous glucose monitoring system (CGMS) readings were analyzed using a 2 × 2 factorial statistical model with repeated measures over time. This analysis assessed the effects of the test (factor 1), group (factor 2), and their interactions (test × group, test × time, and group × time). Pearson's correlation analysis was applied to blood glucose values. Mean comparisons were conducted using the t-test, and agreement between techniques was assessed via the Bland-Altman method, with a 95% confidence interval. Field study on private horse farms in association with a veterinary school. Ten healthy stallions were assigned to one of two groups based on their body condition scores (BCS). Group 1 (G1, n= 5) consisted of nonobese horses with a BCS of 5 or 6, while Group 2 (G2, n= 5) consisted of obese horses with a BCS of 7 or higher. A CGMS sensor was attached to the dorsolateral aspect of the proximal one third of each horse's neck. Laboratory blood glucose measurements and CGMS interstitial glucose readings were compared at different time points for up to 7days after sensor fixation. Obese horses were also submitted to CGIT on Day 4. A comparative analysis of glucose measurements obtained in G1 and G2 horses using the CGMS and enzymatic methods revealed significant group×time interactions (P<0.001) and time effects (P<0.001). No interactions were detected between group (P=0.45), test (P=0.62), group and test (P=0.28), or time and test (P=0.92). In G1 and G2, tests were significantly correlated (r=0.84 and P=0.00) at all time points (T0-T5). Agreement between the glucose values obtained using different methods was excellent despite a small time delay in CGMS detection of rapid changes in blood glucose. It was concluded that the CGMS can be used for indirect assessment of glycemic status (ie, based on interstitial glucose measurements) in nonobese and obese adult horses submitted to CGIT.

Plasma Amino Acid Concentration in Obese Horses with/without Insulin Dysregulation and Laminitis.

Laminitic horses commonly suffer from an endocrine disease such as equine metabolic syndrome. Hyperinsulinemia is considered a key factor in the pathogenesis of laminitis. Since insulin also affects protein turnover in the body, the resting plasma amino acid concentrations of obese horses that were presented for a combined glucose insulin test (CGIT) were determined. In total, 25 obese horses and two lean horses with recurrent laminitis underwent a CGIT. Of these, five were not insulin dysregulated (obese), 14 were insulin dysregulated (ID), and eight were insulin-dysregulated and laminitic (IDL). Significant differences in the resting concentrations between obese and insulin dysregulated and laminitic (citrulline p = 0.038, obese: 73.001 ± 12.661 nmol/mL, IDL: 49.194 ± 15.486 nmol/mL; GABA p = 0.02, obese: 28.234 ± 3.885 nmol/mL, IDL: 16.697 ± 1.679 nmol/mL; methionine p = 0.018, obese: 28.691 ± 5.913 nmol/mL, IDL: 20.143 ± 3.09 nmol/mL) as well as between insulin dysregulated individuals with and without laminitis (GABA p &lt; 0.001, ID: 28.169 ± 6.739 nmol/mL) regarding three amino acids were determined. This may be an interesting approach, especially for diagnostic testing and possibly also for the feed supplements of horses at risk of developing laminitis. However, further research, including a higher number of cases, is required.

Evaluation of the combined glucose-insulin and intravenous glucose tolerance tests for insulin dysregulation diagnosis in donkeys.

Insulin dysregulation (ID) and donkey metabolic syndrome (DMS) are common in this species. Contrary to horses, diagnostic guidelines compiling insulin cut-offs values and dynamic testing interpretations have not been reported for this species. To evaluate resting serum insulin concentrations, the combined glucose-insulin test (CGIT) and the glucose intravenous tolerance test (IVGTT) for the diagnosis of DMS with ID suspicion. Diagnostic test comparison. Six of 80 mix-breed adult donkeys fulfilled the inclusion criteria for DMS based on history or clinical evidence of recurrent laminitis, body condition >6 and neck score >2 or baseline insulin and leptin concentrations >20µIU/mL and >12ng/mL respectively. CGIT and IVGTT were performed in all donkeys within a week and interpreted following guidelines reported for equine metabolic syndrome (EMS). Insulin and glucose curves were analysed, proxies calculated and correlations and multivariate analysis assessed. Following EMS guidelines, CGIT classified 2 (using glucose-positive phase duration) or 3 (using insulin concentration) and IVGTT classified 5 donkeys as ID. ID donkeys showed a lower glucose/insulin ratio, QUICKI and RISQI, and a higher insulin/glucose ratio, MIRG and HOMA-B%. Comparison of these tests with additional dynamic testing including a larger number of ID donkeys is necessary. This is the first study evaluating dynamic tests to assess ID/DMS in DMS-suspected donkeys. IVGTT detected more ID donkeys than CGIT. EMS recommendations could also be used for DMS diagnosis, although a baseline insulin cut-off value is needed.

The influence of equine body weight gain on inflammatory cytokine expressions of adipose tissue in response to endotoxin challenge

BackgroundHuman obesity is linked with systemic inflammation. However, it is still controversial if equines produce more inflammatory cytokines with increasing body weight and if the production of those show breed type specific patterns. The main objective of this study was to determine if diet induced obesity is associated with increased inflammatory signatures in adipose tissue of equines and if a breed predisposition exists between ponies and horses. Additionally, we aimed to identify adipose tissue depot differences in inflammatory cytokine expression. Nineteen healthy, non-overweight and metabolically healthy equines received a hypercaloric diet for 2 years. Body weight, body condition score and cresty neck score were assessed weekly throughout the study. At three time points, insulin sensitivity was determined by a combined glucose-insulin test. Adipose tissue samples were collected from two intra-abdominal and two subcutaneous depots under general anesthesia at each time point after an endotoxin trigger. In the adipose tissue samples levels of CD68 mRNA (a marker of macrophage infiltration) and pro-inflammatory cytokine mRNA (IL-1β, IL-6 and TNFα) were analyzed with RT-qPCR. As markers of lipid metabolism mRNA levels of lipoprotein lipase (LPL) and fatty acid binding protein 4 (FABP4) were determined with RT-qPCR.ResultsCD68 mRNA levels increased with body weight gain in several adipose tissue (AT) depots (Wilcoxon signed rank test with Bonferroni correction; retroperitoneal AT horses: P = 0.023, mesocolonial AT horses: P = 0.023, subcutaneous tail head AT ponies: P = 0.015). In both abdominal depots CD68 mRNA levels were higher than in subcutaneous adipose tissue depots (Kruskal–Wallis-ANOVA with Bonferroni correction: P < 0.05). No breed related differences were found. Pro-inflammatory cytokine mRNA IL-1β, IL-6 and TNFα levels were higher in subcutaneous depots compared to abdominal depots after body weight gain. IL-1β, IL-6 and TNFα mRNA levels of mesocolon adipose tissue were higher in obese horses compared to obese ponies (Mann–Whitney-U test; IL-1β: P = 0.006; IL-6: P = 0.003; TNFα: P = 0.049). In general, horses had higher FABP4 and LPL mRNA levels compared to ponies in neck AT and tail AT at all time points.ConclusionOur findings suggest an increased invasion of macrophages in intra-abdominal adipose tissue with increasing body weight gain in equines in combination with a low dose endotoxin stimulus. This might predispose equines to obesity related comorbidities. In obese horses mesocolon adipose tissue showed higher inflammatory cytokine expression compared to obese ponies. Additionally, subcutaneous adipose tissue expressed more pro-inflammatory cytokines compared to intra-abdominal adipose tissue. Horses had higher FABP4 and LPL mRNA levels in selected AT depots which may indicate a higher fat storage capacity than in ponies. The differences in lipid storage might be associated with a higher susceptibility to obesity-related comorbidities in ponies in comparison to horses.

Comparison of fasted basal insulin with the combined glucose-insulin test in horses and ponies with suspected insulin dysregulation

Fasting horses for measurement of basal serum insulin concentration (fasting insulin; FI) has been recommended to standardise testing for insulin dysregulation (ID), yet limited data exist comparing it to dynamic tests. This study aimed to compare FI with the combined glucose-insulin test (CGIT) in horses suspect for ID. We hypothesised that FI would have poor sensitivity for detecting ID compared to CGIT using conventional cut-offs. Records were retrieved from CGITs performed in horses fasted for approximately 8h. Serum insulin and glucose concentrations were measured before and for 150min following an IV bolus of glucose followed by insulin. Correlations between FI and CGIT values were assessed. Youden’s index analysis was used to determine the optimal cut-off for FI. Logistic regression and Mann–Whitney U tests were used to determine factors affecting the results.CGITs (n=130) from 62 horses were evaluated. Compared to CGIT, sensitivity and specificity of FI for diagnosis of ID were 14.6% and 100% at a cut-off of 20μIU/mL and 63.4% and 87.2% at a cut-off of 5.2μIU/mL, respectively. FI was significantly correlated with insulin at 45min (rs=0.66) and 75min (rs=0.72); area under the curve for insulin (AUCinsulin; rs=0.67); glucose at 45min (rs=0.53); and AUCglucose (rs=0.50). Obesity was significantly associated with increased odds of a positive CGIT and horses with a positive CGIT were significantly older (P<0.05). In conclusion, FI correlated well with CGIT results and had adequate sensitivity and specificity at lower cut-offs, despite poor sensitivity at conventional cut-off values. Further research to derive cut-off values relevant to the fasting period is warranted.

Effects of body weight gain on insulin and lipid metabolism in equines

The objective of this study was to illuminate the changes in serum NEFA concentrations during a combined glucose-insulin test (CGIT) and basal serum triacylglycerides (TGs) with increasing BW in Shetland ponies and warmblood horses. Therefore, basal blood samples were taken during fasting and a CGIT was performed in 19 healthy equines (10 Shetland ponies, 9 warmblood horses) (t0). After one (t1) and two (t2) year(s) of receiving 200% of their maintenance metabolizable energy requirement, procedures were repeated in the same equines. Sixteen of 19 equines had no signs of insulin dysregulation confirmed by CGIT. Basal plasma glucose concentrations increased in ponies (P = 0.001) when comparing t0 and t2, and basal serum insulin concentrations increased in ponies (P = 0.009) and horses (P = 0.024) from t0 to t2. Basal serum NEFA concentrations increased in ponies comparing t0 and t2 (P = 0.01). During CGIT, NEFA levels dropped until reaching a nadir and subsequently recovered until reaching basal concentrations. The minimum serum NEFA value did not change over time in ponies or horses. However, a strong correlation between basal serum NEFA concentrations and the percentage drop to minimum NEFA levels was found in ponies. Two of three equines (one horse and one pony) graded as insulin-dysregulated suffered from laminitis at t2. The serum NEFA concentrations of these animals had a delay in recovery of the minimum NEFA levels. Basal serum TG levels did not change with BW gain, and no breed differences were observed. In conclusion, serum NEFA concentrations are useful parameters during CGIT to detect insulin dysregulation in equines. Thus, further investigation should be focused on lipid metabolism during insulin dysregulation.

Effect of intravenous glucose and combined glucose-insulin challenges on energy-regulating hormones concentrations in donkeys

Metabolic disorders are highly prevalent in donkeys. Differences in energy regulatory hormones and glucose dynamic testing, including the intravenous glucose tolerance test (IVGTT) and combined glucose-insulin test (CGIT), have been documented between donkeys and horses. The aims of this study were to characterise the insulin:glucagon (IGR) and glucagon:insulin (GIR) molar ratios, at baseline and in response to the IVGTT and CGIT in healthy donkeys, and to determine their correlation with endocrine (leptin, ghrelin and adiponectin) and morphometric variables. Median values and interquartile ranges (IQRs) for IGR and GIR in 49 healthy adult donkeys were 1.5 (IQR, 1.0–1.8) and 0.7 (IQR 0.5–0.9), respectively. IVGTT and CGIT were each performed on eight donkeys, while dynamic testing was performed on six donkeys due to loss of two donkeys from the study. IVGTT induced an increase in IGR (and a decrease in GIR) from 15 to 180min after the onset of the test, but had no effect on leptin, adiponectin or ghrelin concentrations. CGIT resulted in a significant elevation in IGR (and a decrease in GIR) from 15 to 120min after the onset of the test. Plasma leptin concentrations increased significantly at 240min. No correlations were found between ratios, hormones and morphometric measurements. The findings support differences between donkeys and horses, which are likely to be related to proportionally higher glucagon compared to insulin concentrations in donkeys, and may be relevant to disorders related to energy dysregulation in donkeys, including metabolic syndrome and dyslipidaemias.

Sustained, Low-Intensity Exercise Achieved by a Dynamic Feeding System Decreases Body Fat in Ponies.

BackgroundObesity in horses is increasing in prevalence and can be associated with insulin insensitivity and laminitis. Current treatment strategies for obesity include dietary restriction and exercise. However, whether exercise alone is effective for decreasing body fat is uncertain.HypothesisOur hypothesis was that twice daily use of a dynamic feeding system for 3 months would induce sustained, low‐intensity exercise thereby decreasing adiposity and improving insulin sensitivity (SI).AnimalsEight, university‐owned, mixed‐breed, adult ponies with body condition scores (BCS) ≥5/9 were used.MethodsTwo treatments (“feeder on” or “feeder off”) were administered for a 3‐month period by a randomized, crossover design (n = 4/treatment). An interim equilibration period of 6 weeks at pasture separated the 2 study phases. Measurements of body mass (body weight, BCS, cresty neck score [CrNS], and morphometry), body fat (determined before and after the “feeder on” treatment only), triglycerides, and insulin sensitivity (SI; combined glucose‐insulin test) were undertaken before and after treatments.ResultsThe dynamic feeding system induced a 3.7‐fold increase in the daily distance travelled (n = 6), compared to with a stationary feeder, which significantly decreased mean BCS (6.53 ± 0.94 to 5.38 ± 1.71), CrNS (2.56 ± 1.12 to 1.63 ± 1.06) and body fat (by 4.95%). An improvement in SI did not occur in all ponies.Conclusions and Clinical ImportanceA dynamic feeding system can be used to induce sustained (daily), low‐intensity exercise that promotes weight loss in ponies. However, this exercise may not be sufficient to substantially improve SI.

Characterization of the intravenous glucose tolerance test and the combined glucose–insulin test in donkeys

Glucose–insulin dynamic challenges such as the intravenous glucose tolerance test (IVGTT) and combined glucose–insulin test (CGIT) have not been described in donkeys. The objectives of this study were (1) to characterize the IVGTT and CGIT in healthy adult donkeys, and (2) to establish normal glucose–insulin proxies. Sixteen donkeys were used and body morphometric variables obtained each. For the IVGTT, glucose (300 mg/kg) was given IV. For the CGIT, glucose (150 mg/kg) followed by recombinant insulin (0.1 IU/kg) were administered IV. Blood samples for glucose and insulin determinations were collected over 300 min.In the IVGTT the positive phase lasted 160.9 ± 13.3 min, glucose concentration peaked at 323.1 ± 9.2 mg/dL and declined at a rate of 1.28 ± 0.15 mg/dL/min. The glucose area under the curve (AUC) was 21.4 ± 1.9 × 103 mg/dL/min and the insulin AUC was 7.2 ± 0.9 × 103 µIU/mL/min. The positive phase of the CGIT curve lasted 44 ± 3 min, with a glucose clearance rate of 2.01 ± 0.18 mg/dL/min. The negative phase lasted 255.9 ± 3 min, decreasing glucose concentration at rate of −0.63 ± 0.06 mg/dL/min, and reaching a nadir (33.1 ± 3.6 mg/dL) at 118.3 ± 6.3 min. The glucose and insulin AUC values were 15.2 ± 0.9 × 103 mg/dL/min and 13.2 ± 0.9 × 103 µIU/mL/min. This is the first study characterizing CGIT and IVGTT, and glucose–insulin proxies in healthy adult donkeys. Distinct glucose dynamics, when compared with horses, support the use of species-specific protocols to assess endocrine function.

Insulin dysregulation

Abnormalities of insulin metabolism include hyperinsulinaemia and insulin resistance, and these problems are collectively referred to as insulin dysregulation in this review. Insulin dysregulation is a key component of equine metabolic syndrome: a collection of endocrine and metabolic abnormalities associated with the development of laminitis in horses, ponies and donkeys. Insulin dysregulation can also accompany prematurity and systemic illness in foals. Causes of insulin resistance are discussed, including pathological conditions of obesity, systemic inflammation and pituitary pars intermedia dysfunction, as well as the physiological responses to stress and pregnancy. Most of the discussion of insulin dysregulation to date has focused on insulin resistance, but there is increasing interest in hyperinsulinaemia itself and insulin responses to feeding. An oral sugar test or in-feed oral glucose tolerance test can be performed to assess insulin responses to dietary carbohydrates, and these tests are now recommended for use in clinical practice. Incretin hormones are likely to play an important role in postprandial hyperinsulinaemia and are the subject of current research. Insulin resistance exacerbates hyperinsulinaemia, and insulin sensitivity can be measured by performing a combined glucose-insulin test or i.v. insulin tolerance test. In both of these tests, exogenous insulin is administered and the rate of glucose uptake into tissues measured. Diagnosis and management of hyperinsulinaemia is recommended to reduce the risk of laminitis. The term insulin dysregulation is introduced here to refer collectively to excessive insulin responses to sugars, fasting hyperinsulinaemia and insulin resistance, which are all components of equine metabolic syndrome.

Comparison of Insulin and Glucose Metabolism in Horses with Pituitary Pars Intermedia Dysfunction Treated Versus Not Treated with Pergolide

Equine pituitary pars intermedia dysfunction (PPID) is known to alter glucose/insulin metabolism. This study evaluated changes in parameters relating to glucose/insulin metabolism and determined whether there is a difference between pergolide-treated and untreated animals. We hypothesized that glucose/insulin dynamics in PPID horses receiving pergolide would be different than those in untreated horses. A total of 38 horses with diagnoses of PPID were included in the study (average age: 24 years). A total of 25 horses were untreated; 13 horses were treated with pergolide (>3 months). Parameters relating to glucose/insulin metabolism were determined in all horses, as follows: adrenocorticotropin-releasing hormone (ACTH), insulin, fructosamine, triglyceride, glucose, modified insulin-to-glucose ratio (MIRG), and reciprocal of the square root of insulin (RISQI). A combined glucose-insulin test (CGIT) was performed in 23 horses as not all owners agreed to the testing. Treated animals showed a tendency to have lower ACTH, but results were not significant. All animals had fructosamine levels exceeding reference values (mean value 314 ± 32 μmol/L; reference range: <280 μmol/L). There were no statistically significant differences between insulin, glucose, ACTH, triglycerides concentrations, RISQI/MIRG calculations, and CGIT results of pergolide-treated PPID and those of untreated horses. Five horses (13.2%) had combined hyperglycemia/hyperinsulinemia, whereas 7 horses (18.4%) displayed hyperglycemia, and 3 horses (7.9%) showed hyperinsulinemia alone. Forty percent of the horses with altered glucose/insulin metabolism were treated with pergolide. Based on RISQI and MIRG calculations, 19 animals displayed changes in glucose/insulin metabolism. Fourteen of twenty-three horses (61%) showed signs of insulin resistance in CGIT results. In conclusion, PPID horses frequently show alterations in glucose/insulin metabolism, but no significant differences were found between treated and untreated animals. Changes in insulin/glucose dynamics may not be a useful indicator of response to pergolide treatment.

Dietary restriction in combination with a nutraceutical supplement for the management of equine metabolic syndrome in horses

Few studies have examined the effect of dietary restriction in horses with equine metabolic syndrome (EMS). This study aimed to determine improvements in insulin sensitivity following dietary restriction for 6weeks, and to determine if the improvement would be greater in horses receiving short-chain fructo-oligosaccharides (sc-FOS). Dietary management involved feeding grass hay, restricted to 1.25% of body mass (BM) as daily dry matter intake and soaked in cold water prior to feeding, with the addition of a vitamin and mineral nutraceutical supplement with or without the addition of sc-FOS (10g/100kg).Soaking the hay resulted in a significant reduction in non-structural carbohydrates (38%, P=0.01), digestible energy (6.78%, P=0.01) and water soluble minerals. Following 6weeks of dietary restriction with soaked grass hay and nutraceutical supplement, horses lost an average of 6.8% BM and showed reductions in body condition score (BCS) and belly circumference. Sensitivity to insulin improved overall, as determined by the total insulin response during the combined glucose insulin test. The magnitude of improvement in insulin sensitivity was associated with the degree of insulin resistance recorded at outset, and the extent of overall losses in BM and BCS, but was independent of the addition of sc-FOS. The nutraceutical supplement was highly palatable and no adverse effects were noted. From the findings of this study a strict dietary program in combination with a specifically designed vitamin and mineral nutraceutical supplement can be recommended to obtain rapid improvements in BM, BCS and insulin sensitivity of animals presenting with EMS.

Clinical Assessment of Blood Glucose Homeostasis in Horses: Comparison of a Continuous Glucose Monitoring System with a Combined Intravenous Glucose and Insulin Test Protocol

The combined glucose-insulin test (CGIT) is helpful for evaluating insulin sensitivity. A continuous glucose monitoring system (CGMS) reports changes in interstitial glucose concentrations as they occur in the blood. Use of the CGMS minimizes animal contact and may be useful when performing a CGIT. Results obtained using a CGMS are useful for the evaluation of glucose responses during the evaluation of insulin sensitivity in equids. Seven mature, obese ponies. Ponies were equipped with CGMS for determination of interstitial glucose concentrations. Glucose (150 mg/kg, i.v.) and insulin (0.1 U/kg, i.v.) were administered and blood glucose concentrations determined at (minutes after time zero) 1, 5, 15, 25, 35, 45, 60, 75, 90, 105, and 120 with a hand-held glucometer. Blood chemistry results were compared with simultaneously obtained results using CGMS. Concordance coefficients determined for comparison of blood glucose concentrations determined by a hand-held glucometer and those determined by CGMS after the zero time point were 0.623, 0.764, 0.834, 0.854, and 0.818 (for delays of 0, 5, 10, 15, and 20 minutes, respectively). Interstitial glucose concentrations obtained by the CGMS compared favorably to blood glucose concentrations. CGMS may be useful for assessment of glucose dynamics in the CGIT.

Optimisation of the frequently sampled intravenous glucose tolerance test to reduce urinary glucose spilling in horses

The frequently sampled i.v. glucose tolerance test (FSIGTT) is used to evaluate glucose and insulin dynamics in horses, but it has not been determined whether urinary glucose spilling (UGS) affects results. UGS occurs in horses during the FSIGTT and this problem can be minimised by adjusting the dextrose and insulin dosages used. Six mature mares were included in this study. In the first phase, 6 FSIGTT procedures were performed in each horse to evaluate 6 different dextrose dosages. Six different insulin dosages were evaluated during the second phase of the study after administration of 300 mg/kg bwt dextrose. Area under the glucose (AUCg) and insulin (AUCi) curves were calculated and minimal model analyses performed. UGS was measured in the third and fourth phases of the study during the combined glucose insulin test and established FSIGTT. A new FSIGTT was developed and evaluated. Positive linear effects of dextrose dosage on AUCg, AUCi and acute insulin response to glucose were detected, with AUCg reaching a plateau at doses > or =200 mg/kg bwt. Insulin dosage had an inverse linear effect on AUCg, but other values remained unaffected. UGS occurred during all 3 tests and was the highest for the established FSIGTT and the lowest for the new FSIGTT. The type of FSIGTT performed did not affect minimal model results. Results indicate that the dextrose dosage of 300 mg/kg bwt used in the established FSIGTT is too high. UGS can be reduced by lowering the dextrose dosage to 100 mg/kg bwt. A new FSIGTT involving the administration of 100 mg/kg bwt dextrose followed by 20 mu/kg bwt insulin 20 min later is recommended for use in horses because this test provides adequate data for minimal model analysis while minimising UGS.

Physical characteristics, blood hormone concentrations, and plasma lipid concentrations in obese horses with insulin resistance

To compare obese horses with insulin resistance (IR) with nonobese horses and determine whether blood resting glucose, insulin, leptin, and lipid concentrations differed between groups and were correlated with combined glucose-insulin test (CGIT) results. 7 obese adult horses with IR (OB-IR group) and 5 nonobese mares. Physical measurements were taken, and blood samples were collected after horses had acclimated to the hospital for 3 days. Response to insulin was assessed by use of the CGIT, and maintenance of plasma glucose concentrations greater than the preinjection value for > or = 45 minutes was used to define IR. Area under the curve values for glucose (AUC(g)) and insulin (AUC(i)) concentrations were calculated. Morgan, Paso Fino, Quarter Horse, and Tennessee Walking Horse breeds were represented in the OB-IR group. Mean neck circumference and BCS differed significantly between groups and were positively correlated with AUC values. Resting insulin and leptin concentrations were 6 and 14 times as high, respectively, in the OB-IR group, compared with the nonobese group, and were significantly correlated with AUC(g) and AUC(i). Plasma nonesterified fatty acid, very low-density lipoprotein, and high-density lipoprotein-cholesterol (HDL-C) concentrations were significantly higher (86%, 104%, and 29%, respectively) in OB-IR horses, and HDL-C concentrations were positively correlated with AUC values. Measurements of neck circumference and resting insulin and leptin concentrations can be used to screen obese horses for IR. Dyslipidemia is associated with IR in obese horses.

Physiologic assessment of blood glucose homeostasis via combined intravenous glucose and insulin testing in horses

To characterize the physiologic response to i.v. bolus injection of glucose and insulin for development of a combined glucose-insulin test (CGIT) in horses. 6 healthy mares and 1 mare each with pituitary adenoma and urolithiasis. Horses were given a CGIT (glucose, 150 mg/kg; insulin, 0.1 U/kg); results were compared with a singular i.v. glucose tolerance test (GTT; 150 mg/kg) and a singular i.v. insulin sensitivity test (IST; 0.1 U/kg). Healthy horses were also given a CGIT after receiving xylazine and undergoing stress. Physiologically, the CGIT resulted in a 2-phase curve with positive (hyperglycemic) and negative (hypoglycemic) portions; the positive phase came first (250% of baseline at 1 minute). The descending segment declined linearly to baseline by approximately 30 minutes and to a nadir at 58% of baseline by 75 minutes. After a 35-minute valley, a linear ascent to baseline began. Addition of insulin in the CGIT increased glucose utilization by approximately 4.5 times during the positive phase but not during the negative phase. The diseases' effects and experimental inhibition of insulin secretion with xylazine and stress were detectable by use of the 2 phases of the CGIT. Only a single positive phase resulted from the GTT and a single negative phase from the IST CONCLUSIONS AND CLINICAL RELEVANCE: The CGIT resulted in a consistent, well-defined glycemia profile, which can be disrupted experimentally or by a disease process. The CGIT has clinical potential because it provides integrated information and more information than either the singular GTT or IST.

THE VALUE OF THE GLUCOSE TOLERANCE TEST, THE INSULIN TOLERANCE TEST, AND THE GLUCOSEINSULIN TOLERANCE TEST IN THE DIAGNOSIS OF ENDOCRINOLOGIC DISORDERS OF GLUCOSE METABOLISM1

CARBOHYDRATE METABOLISM is influenced by I many tissues, notably pancreatic islets, adrenal medulla, adrenal cortex, anterior pituitary, muscles and liver. As an aid in the diagnosis of various diseases, it has for a long time been useful to study the glucose content of the blood. Thus, the determination of this under fasting conditions may at once give the clue to the diagnosis. In many instances, however, because of compensatory adjustments the fasting level is normal in spite of a definite disturbance in the sugar metabolism (e.g., mild diabetes) and it is necessary to subject the sugar-regulatory mechanism to some selected strain in order to elicit an abnormality. What strain one chooses naturally should depend on what disorder one suspects. For example, if looking for hypo-insulinism one would test the ability of the body to adjust to an alimentary hyperglycemia, that is one would perform the ordinary sugar tolerance test. If it turned out that the patient had a decreased responsiveness to hyperglycemia, that is the curve was delayed in its fall—the findings would be consistent with hypoinsulinism although there would be other possibilities which could be tested by subjecting the mechanism to other strains (see below). It was the purpose of these investigations, which will be reported more fully elsewhere (1), to study the additional usefulness in endocrine diagnosis of two other types of sugar curves, the “combined glucose-insulin test” and the “insulin tolerance test.”