Serum 25-hydroxyvitamin D status among Saudi children with and without a history of fracture.

BACKGROUND: The significance of vitamin D deficiency in the incidence of bone fractures in children has been under investigated. Here, we aimed to associate serum 25-hydroxyvitamin D levels and fractures in Saudi children. MATERIALS AND METHODS: This cross-sectional study was conducted in 1022 Saudi children without fracture history [476 boys (age 14.56 ± 1.81, BMI 22.38 ± 5.81) and 546 girls (age 13.57 ± 1.67, BMI 22.24 ± 4.94)] and 234 Saudi children with a history of fracture [148 boys (age 14.25 ± 1.39, BMI 22.66 ± 6.08) and 86 girls (age 13.76 ± 1.35, BMI 21.33 ± 1.35)]. Anthropometric and fasting serum biochemical data were collected. Serum 25-hydroxyvitamin D level was assessed using electrochemiluminescence. RESULTS: Mean circulating 25-hydroxyvitamin (25OH) D level in subjects with a history of fracture was significantly lower in both boys (p < 0.01) and girls (p < 0.01) than those without, however both groups had low mean 25(OH)D levels. Furthermore, age was positively associated with 25-hydroxyvitamin D in boys (p < 0.05) and negatively in girls (p < 0.05) with a history of fracture. CONCLUSION: In conclusion, vitamin D levels were significantly lower in children with a history of bone fractures in both boys and girls than those without such a history; even in the absence of fracture history, vitamin D status correction is warranted in the general Saudi pediatric population.

Comparisons in childhood obesity and cardiometabolic risk factors among urban Saudi Arab adolescents in 2008 and 2013.

BACKGROUND: We aimed to compare the prevalence of childhood obesity and other cardiometabolic risk factors from two independent cohorts (2008 and 2013) in Riyadh, Saudi Arabia. METHODS: A total of 4549 adolescents aged 12-18 years [2454 boys, 2095 girls], taken from two independent cohorts, 5 years apart (2008 and 2013), were included. Anthropometrics were measured, and fasting blood samples were taken to ascertain glucose and lipid profile. RESULTS: The overall prevalence of obesity was significantly higher in 2013 [15.3 (95% confidence interval 13.7-16.9)] than 2008 [12.6 (11.3-13.9)] (P = 0.012). Stratified by sex, the prevalence of obesity among boys was significantly higher in 2013 than 2008 [2008 = 12.0 (10.3-13.7) versus 2013 = 17.4 (15.1-19.7); P < 0.001]. The age groups 13 and 15 years had a significantly higher mean triglycerides in 2013 than 2008 (P-values 0.003 and <0.001, respectively) and lower mean HDL-cholesterol also in the 13 years old age group (P < 0.001). CONCLUSIONS: The prevalence of childhood obesity in Saudi Arabia has increased in particular age groups (13-15 years) during a 5-year span. Special attention is warranted in these vulnerable age groups, particularly in boys, as cardiometabolic risk factors appear to worsen.

Normal circulating PTH in Saudi healthy individuals with hypovitaminosis D.

Recent studies in the Middle East have shown an increased incidence of vitamin D deficiency across this region of year-round sunlight. There is scarcity of information, however, as to the levels of 1,25-dihydroxyvitamin D [1,25(OH)2D], the active form of vitamin D, and its associations with cardiometabolic parameters in an Arab cohort and this study aims to fill this gap. In a cross-sectional study, 33 male and 43 female (22 children and 54 adults, total 76) Saudis with previously established low levels of serum 25-hydroxyvitamin D [25(OH)D] (<50 ng/ml or 20 nmol/l) were recruited. Anthropometrics were obtained and fasting blood samples were taken for a routine measurement of glucose, lipid profile, calcium, and albumin, while serum 25(OH)D, 1,25-(OH)2D, and intact PTH were quantified using specific ELISAs. Serum calcium, intact PTH, and 1,25(OH)2D were all within the normal range in both children and adults in both genders. In all subjects, serum 1,25(OH)2D was not associated with intact PTH, while circulating 1,25(OH)D inversely correlated with systolic blood pressure (p=0.01) and waist circumference (p=0.04). Thus, vitamin D deficient Saudi children and adults with normal levels of 1,25-(OH)2D also had normal circulating calcium and PTH. This study suggests that local cutoffs should be set that will be of clinical significance in the identification of those at true risk for harder end-points, such as secondary hyperparathyroidism and bone-related diseases.

Hypovitaminosis D associations with adverse metabolic parameters are accentuated in patients with Type 2 diabetes mellitus: a body mass index-independent role of adiponectin?

BACKGROUND: Hypovitaminosis D has been associated with an increased prevalence of Type 2 diabetes mellitus (DMT2) and metabolic syndrome manifestations. The purpose of this study was to examine the association between 25-hydroxy-vitamin D (25-OH-VitD) levels and indices of insulin resistance (IR), including adipocytokines, in a Saudi population with or without DMT2. SUBJECTS AND METHODS: A total of 266 subjects (153 DMT2 and 113 healthy controls) aged 26-80 yr were randomly selected from the existing Biomarkers Screening in Riyadh Program (RIYADH Cohort). Subjects were assessed clinically, anthropometry was performed, morning blood chemistries, including fasting glucose (FG), triglycerides, total cholesterol, LDL cholesterol (LDL-C), and HDL cholesterol were obtained. Homeostasis model assessment of IR (HOMA-IR) was calculated, and serum 25-OH-VitD, leptin, adiponectin, resistin, insulin, high sensitivity CRP (hsCRP), and tumor necrosis factor α concentrations were measured using specific assays. RESULTS: In DMT2 subjects, negative correlations between 25-OH-vitD and body mass index (BMI), FG, insulin, HOMA-IR, cholesterol, LDL-C, and hsCRP were observed, while a positive correlation between 25-OH-VitD and adiponectin was detected. The later remained significant after controlling for BMI. Interestingly, only weak and nonsignificant associations between 25-OH-VitD and metabolic parameters were observed in the control group, whereas, when the entire population was examined, negative correlations were evident primarily between 25-OH-VitD and FG, HOMA-IR, total cholesterol, LDL-C. These associations remained significant after controlling for BMI. CONCLUSIONS: These results suggest that hypovitaminosis D associations with metabolic disturbances are accentuated in DMT2. The BMIindependent positive correlation between 25-OH-VitD and adiponectin suggests a potential role for this adipocytokine as a link between 25-OH-VitD and IR in patients with DMT2.

Urinary iodine is associated with insulin resistance in subjects with diabetes mellitus type 2.

BACKGROUND: Diabetes Mellitus (DM) is a major health problem worldwide and its prevalence in Saudi Arabia has reached 31.6%. Patients with diabetes mellitus are at an increased risk of thyroid disease. The purpose of this study was to examine the urinary excretion of iodine in type 2 DM (T2DM) patients, and to assess the clinical implication of iodine status on T2DM. METHODS: A total of 266 adult Saudis aged 18-55 years (109 T2DM patients and 157 healthy controls) were randomly selected from the Riyadh Cohort Study. Subjects were assessed for anthropometry, morning blood chemistries including fasting glucose, and lipid profile; serum concentrations of leptin, adiponectin, resistin, insulin, aPAI, hsCRP, Ang II, TNF-α, TSH, T3, T4, urine creatinine, urine iodine were measured using specific assays. RESULTS: The concentration of urine iodine was significantly lower in T2DM than in healthy control subjects (84.6±2.3 vs. 119.4±3.4, p<0.001), which remained significant after creatinine correction and controlling for age (p=0.01). Furthermore, urinary iodine is negatively correlated with waist, hips, SAD, glucose, insulin, HOMA-IR triglyceride, resistin, angiotensin II (Ang II), and CRP, while it was positively associated with TSH. CONCLUSIONS: The decreased levels of iodine concentration in T2DM patients and its likely deleterious effects on metabolic functions calls for a systematic approach to thyroid disease screening in diabetic patients. Routine annual urinary iodine determination is recommended and should target T2DM patients at risk of thyroid dysfunction.

Blood thiamine and its phosphate esters as measured by high-performance liquid chromatography: levels and associations in diabetes mellitus patients with varying degrees of microalbuminuria.

BACKGROUND: Thiamine deficiency has been linked to microvascular complications in patients with diabetes mellitus (DM). In this study, we aim to assess blood and urine thiamine status by high performance liquid chromatography (HPLC) in patients with DM Type 1 and Type 2 (DMT1, DMT2) and to identify associations with markers of incipient nephropathy and kidney dysfunction. SUBJECTS AND METHODS: A total of 205 subjects (43 DMT1 and 162 DMT2) with and without microalbuminuria and 26 non-diabetic controls were included. Fasting blood samples were collected and anthropometric parameters were measured. Fasting blood, lipid and renal profile were determined routinely. Blood thiamine concentration, its phosphate esters and urine thiamine were quantified using HPLC. RESULTS: Blood thiamine concentrations (ng 1-1) were decreased by 75.7% and 49.6% in patients with DMT1 and DMT2, respectively [controls (54.8+/-11.4); DMT1 (41.5+/-17.9); DMT2 (27.2+/-12.7), p<0.001]. Among those with normo-albuminuria, urinary excretion of thiamine was significantly increased to 390.1 microg/ml and 1212.4 microg/ml in DMT1 and DMT2 respectively, as compared to controls (326.4 microg/ml). DMT1 and DMT2 patients with micro- albuminuria on the other hand had 2.5- and 3.4-fold increase in urinary excretion of thiamine compared to controls. CONCLUSION: Low levels of blood thiamine are present in patients with DMT1 and DMT2, and are associated with increased thiamine clearance.

Gender-specific associations between insulin resistance, hypertension, and markers of inflammation among adult Saudis with and without diabetes mellitus type 2.

PURPOSE: In view of the important roles of the pro-inflammatory cytokines tumor necrosis factor alpha (TNF-α), interleukin-6 (IL-6) and the acute phase reactant C-reactive protein (CRP) in glucose metabolism and pathogenesis of diabetes mellitus type 2 (DMT2), we assessed gender-specific differences and relative associations of these inflammatory biomarkers to insulin resistance (IR) and risk markers for DMT2. MATERIALS AND METHODS: Serum levels of TNF-α, IL-6 and CRP were determined in 119 clinically diagnosed DMT2 cases, 114 non-DMT2 subjects with IR, and 97 age-matched controls. Fasting blood samples were collected and serum glucose levels, lipid profile, and inflammatory markers were analyzed. RESULTS: In women, a significant association between elevated levels of IL-6 and risk of developing IR [Odds ratio (OR), 4.389, 95 % Confidence Interval (CI) 1.6-11.52, p = 0.004] was found. Significant associations were also found between elevated levels of CRP and risk of hypertension only in female subjects [OR (95% CI) 2.153 (1.04-4.53), p = 0.046]. While, in male subjects, a significant association between elevated levels of TNF-α and risk of developing IR [OR (95% CI) 2.32 (1.09-4.93), p = 0.029] was found. CONCLUSION: The present study showed apparent gender differences in the association of IL-6, CRP, and TNF-a with risks of IR and hypertension, and this could be attributed to sexual dimorphism in fat distribution.

Telomere length in relation to insulin resistance, inflammation and obesity among Arab youth.

AIM: The aim of this study was to determine the associations of telomere length to markers of obesity, insulin resistance and inflammation in Saudi children. METHODS: A total of 69 boys and 79 girls, aged 5-12 years, participated in this cross-sectional study. Anthropometrics were measured. Serum glucose and lipid profile were measured using routine laboratory methods. Serum insulin, leptin, adiponectin, resistin, tumour necrosis factor-alpha and active plasminogen activator inhibitor 1 were quantified using customized multiplex assay kits. C-reactive protein and angiotensin II were quantified using ELISA. Leucocyte telomere length was examined by quantitative real time PCR utilizing IQ cycler. RESULTS: Mean telomere length was significantly shorter in obese boys compared with their lean counterparts (p = 0.049), not in girls. It was not associated to insulin resistance, adipocytokines and markers of inflammation. In girls, the significant predictor of telomere length was waist circumference, explaining 24% of variance (p = 0.041) while in boys, systolic blood pressure explained 84% of the variance (p = 0.01). CONCLUSION: Childhood obesity in boys corresponds to shorter leucocyte telomere length which is not evident in girls. The association of leucocyte telomere length to blood pressure and waist circumference in children suggests clinical implications as to the contribution of these parameters in premature ageing.

Bioequivalence of Jusline following subcutaneous administration in healthy subjects.

OBJECTIVE: The aim of the current work is to evaluate the pharmacokinetic and pharmacodynamic profile of a new human insulin preparation (jusline) following subcutaneous administration in healthy subjects, and to compare this profile with Humulin insulin. METHODS: 20 healthy male subjects received a single dose of 0.2 U/kg of test (Jusline) or reference insulin (Humulin) during an euglycemic clamp keeping blood sugar constant (90 +/- 5 mg/dl) by changing the glucose infusion rate. Pharmacokinetic and pharmacodynamic measurements were taken from blood measurements of glucose, insulin, and C-peptide levels for tested insulin formulations. RESULTS: The mean values of the individual AUC ratios were well within the 90% confidence interval (100.5% for Regular, 101.9% for NPH, and 100.0% for Premixed Regular/NPH (30/70)). Similarly, Cmax and tmax were within the bioequivalence limit (80 - 125%). The maximum GIR were 10.20 mg/kg/min and 9.72 mg/kg/min for Jusline Regular and Humulin Regular, respectively. The maximum GIR were 7.09 mg/kg/min and 7.91 mg/kg/min for Jusline NPH and Humulin NPH, respectively. The maximum GIR and tGIRmax were 6.39 mg/kg/min and 6.63 mg/kg/ min for Jusline Premixed Regular/NPH (30/70) and Humulin Premixed Regular/NPH (30/70), respectively. Both insulin products produced similar suppression of endogenous C-peptide level (-29.76% to -50.22%). CONCLUSION: The present study demonstrated that after subcutaneous administration, there are no significant differences between Jusline and Humulin to promote peripheral glucose uptake.

Hyperhomocysteinemia and retinal vascular occlusive disease.

PURPOSE: Elevated plasma homocysteine is an independent risk factor for thrombosis and vascular disease. This prospective study compared plasma total homocysteine levels in patients with retinal vascular occlusive disease and in matched healthy controls. METHODS: We measured plasma total homocysteine in 56 consecutive patients with recently diagnosed retinal vascular occlusive disease: 36 had central retinal vein occlusion, 12 branch retinal vein occlusion, and 8 retinal artery occlusion, and compared them with 59 age- and sex-matched healthy controls. Homocysteine levels were determined by high-performance liquid chromatography with electrochemical detection. Hyperhomocysteinemia was defined as a plasma homocysteine level above the 95th percentile in the control group (13.6 micromol/L). RESULTS: Mean plasma total homocysteine levels were significantly higher in patients than controls (16.1 +/- 8.3 vs. 8.96 +/- 5.6 micromol/L p < 0.001). Mean homocysteine levels were significantly higher in the retinal vein occlusion and retinal artery occlusion groups than the control group (15.3 +/- 8.2 and 20.95 +/- 6.9 vs 8.96 +/- 5.6 micromol/L, p < 0.001). Estimates of the relative risk indicated that the risk of hyperhomocysteinemia was significantly higher in patients with retinal vascular occlusive disease than controls. Hyperhomocysteinemia was present in 37 (66.1%) of the 56 patients with retinal vascular occlusive disease but only 2 (3.4%) controls (odds ratio [OR] 47.5, 95% confidence interval [CI] 9.8-149.9). Hyperhomocysteinemia was present in 29 (60.4%) of the patients with retinal vein occlusion (OR 43.5, 95% CI 8.77-141.93) and in 6 (75%) patients with retinal artery occlusion (OR 85.5, 95% CI 7.49-1,173.1). CONCLUSIONS: High plasma homocysteine is a risk factor for retinal vascular occlusive disease so it may be useful to measure homocysteine in the management of these patients. A randomized, controlled trial is required to study the effect of lowering with homocysteine folic acid and other B vitamins on the risk of recurrent vascular occlusion in the same eye or its development in the fellow eye.

Correlates of insulin autoantibodies with beta cell function at the time of diagnosis of diabetes mellitus.

In this article, the author discusses the prevalence of insulin autoantibodies (IAA) and endogenous insulin secretion in Saudi patients at the onset of diabetes. A positive result, defined as a value greater than 3 SD above the mean binding of normal, was found in 8 (7.6%) of 105 of the patients with diabetes and in 3 (5.7%) of 53 of the healthy control subjects. The relation between the presence of IAA and the pancreatic beta cell secretory activity was studied by determining the levels of insulin and C-peptide in the fasting state and 6 minutes after intravenous injection of 1 mg glucagon. All the IAA positive subjects had a response to glucagon stimulation test. A positive correlation was found between basal and after stimulation for both insulin and C-peptide (r = 0.79, P < 0.001; r = 0.85, P < 0.001 for insulin and r = 0.76, P < 0.001; r = 0.81, P < 0.001 for C-peptide, respectively). Therefore, the current finding indicates that there is no direct effect of IAA on the pancreatic beta cell potential activity in Saudi patients with diabetes at the time of diagnosis, suggesting further that these patients have no insulin deficiency or have mild insulin dependency.

Insulin receptor binding from mid-term and full-term placentas of patients with gestational diabetes mellitus and normal pregnant women.

Insulin receptor binding was examined in the microvillous membranes of mid-term (20-22 weeks of gestation, MT) and full-term (FT) placentas from patients with gestational diabetes mellitus (GDM) and in normal pregnant control (N). Mid-term placentas were obtained from patients who have had spontaneous abortion. The maximum per cent specific binding (%SB) in MT placenta for GDM was significantly lower (4.8%) compared with the FT placenta (22%, p < 0.001), while in the N group the maximum per cent specific binding for MT placenta was 14.1% compared with 26% for the FT placenta (p < 0.001). Binding data from FT placenta of well-controlled GDM patients were similar with the FT placenta from N group (22% SB for GDM VS 26% SB for N). Even as there were similarities in the binding characteristics of FT placentas from both groups the placental membrane protein content in the GDM group was lower by 50% compared with the N control (2.5 +/- 0.11 VS 4.8 +/- 0.15 mg protein/g placenta respectively, p < 0.001) suggesting that in the GDM group achieving a tight glycemic control could improve receptor affinities. Data from the competitive binding assay of GDM patients showed that the insulin necessary to achieve 50% inhibition (ID50) was significantly lower in MT compared with the FT placenta (0.9 x 10(-9) M VS 3.8 x 10(-9) M, p < 0.001) but in the N placenta there was no alteration in the ID50 of MT and FT placentas (3.1 x 10(-9) M VS 4 x 10(-9) M, p < 0.01, respectively). The present study demonstrated that in GDM the placental insulin receptor binding was significantly lower in spontaneously aborted placenta compared with placentas collected at full-term. Furthermore, these data suggest that the objective to achieve a tight glycemic control in GDM patients could optimize insulin receptor function similar to that of a normal pregnancy. Thus a full term placenta from GDM patients under a well managed glycemic control throughout the entire duration of pregnancy would result in an optimum insulin receptor function.

Vanadate enhances insulin-receptor binding in gestational diabetic human placenta.

Although vanadium is found abundantly in animal and plant kingdoms its biological effects are not clear. Vanadate compounds have been shown to normalize blood glucose levels in streptozotocin treated rats, enhance glucose oxidation and improve the sensitivity to insulin by enhanced receptor binding in rat adipocytes. The aim of the present study was to investigate the effect of vanadate, at high (0-8 mmol l-1) and low (0-1.0 mmol l-1) physiological concentrations, on [125I]-insulin binding in the placenta of three groups of patients, namely from normal (N) controls, gestational diabetics (GDM) and women with risk factors in their medical history for developing diabetes mellitus (RF). Vanadate at low concentrations (0.2-0.6 mmol l-1) enhanced the maximal binding 2-fold in GDM placenta but only increased (up to 1.2-fold) the binding slightly at high concentrations (5 mmol l-1). However with placenta from normal or women at risk, vanadate increased the [125I]-insulin binding up to 1.2-fold both at low and high concentrations. Thus it appears that vanadate augments insulin binding in the placenta from women with gestational diabetes mellitus.

Histological changes in placental syncytiotrophoblasts of poorly controlled gestational diabetic patients.

It seems reasonable to expect that biochemical changes occurring in the pregnant woman with diabetes should be reflected in the placenta structure. However, it has not been possible to correlate placental morphology with glycemic control in a comparison between those with long life diabetes and poorly controlled gestational diabetes. In the present study we have histologically studied the syncytiotrophoblast of human placentae from overt diabetic and poorly controlled gestational diabetic patients. Using specific staining techniques and direct light microscopy we qualitatively studied these placentae and compared them with the normal placentae. We found fibrin thrombi, villous oedema, hyperplasia and thickening of basement membrane in the placentae of poorly controlled gestational diabetic mothers. Direct microscopy revealed that these various changes in syncytiotrophoblast structure were marked in the poorly controlled gestational placenta compared with overt diabetics, and could have been due to the presence of histochemical compounds e.g. general carbohydrates and lipids. These studies may indicate that poor control of diabetes during the gestation as indicated by high level HbAlc may result in the accummulation of carbohydrate compounds and fat droplets in the placental basement membrane, leading to structural changes in the placental cells.

Features of insulin receptor interaction in placenta from normal, overt and poorly controlled gestational diabetic patients.

Features of insulin binding to trophoblast plasma membranes were studied in six normal pregnant women (NP), six overt diabetes (ODP) and six poorly controlled glycemic gestational patients (PCDP) i.e. women who did not strictly follow the management of diabetes mellitus during pregnancy. A decreased maximum specific insulin receptor binding per 0.1 mg membrane protein in placenta from PCDP (12%) was found comparing with that from ODP or NP (17.5% and 36.2%, respectively, P < 0.01), The insulin binding in PCDP declined at a faster rate until it reached minimum when studied at a higher temperature (25-37 degrees C). The binding equilibrium was likewise attained faster at this temperature than that at lower temperature of 4 degrees C for all studied groups. The insulin receptor binding in all studied groups was pH dependent. The maximum binding in ODP and PCDP groups was attained at pH 7.8 while for NP maximum binding was at pH 7.4. The competitive binding assay was carried out with 14 concentrations of unlabelled insulin and the half maximal displacement of 125I-insulin was at 8 x 10(-9) M, 6 x 10(-9) M and 4 x 10(-9) M for NP, ODP and PCDP, respectively (P < 0.05) suggesting the differences in the effect of glycemic control on the insulin binding. Furthermore the binding yielded curvilinear Scatchard plots with the apparent affinity of the receptors being affected in the ODP and PCDP groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Obesity and major metabolic indices in newly diagnosed Saudi diabetic patients.

Metabolic indices were assessed in 217 Saudi diabetic patients and 57 control subjects in relation to Body Mass Index (BMI). Patients with BMI values greater than or equal to 27 in male and greater than or equal to 25 in female were considered obese. Obesity was found more frequent in females (82.7%) than in males (40.9%) (p less than 0.01). Basal glucose and HbA1C levels were lower in obese males than in females. C-peptide levels were higher (p less than 0.01) in the obese subjects than in the non-obese. Within the obese group c-peptide levels were higher in males than in females. Triglycerides and total lipids were also higher in the obese group. Our result suggests that a varying degree of obesity influences the rate of both beta cell secretion, insulin resistance and impaired lipid metabolism.

Endogenous insulin secretion in newly diagnosed diabetic patients in Saudi Arabia.

Diabetes mellitus is a major health problem in Saudi Arabia. The evaluation of endogenous insulin secretion at diagnosis has not yet been studied in this population. We have therefore studied fasting and post-glucagon stimulation levels of glucose, insulin and C-peptide in 216 newly diagnosed untreated diabetic patients. The mean +/- SD fasting insulin and C-peptide levels were 14.0 +/- 1.8 microU/ml and 1.8 +/- 0.4 ng/ml, while post-glucagon stimulation levels were 21.1 +/- 3 microU/ml and 2.4 +/- 0.4 ng/ml. There were significant post-stimulatory increment levels for insulin, from 4.9 to 13.7 microU/ml, and C-peptide from 0.2 to 1.3 ng/ml (P less than 0.001). Such increments did not affect specified age distribution. We found a significant correlation between the fasting levels and post-stimulation levels of C-peptide and insulin. Obesity correlated with higher basal and post-stimulation levels of both hormones (r = 0.67, P less than 0.001). The mean +/- SD fasting insulin and C-peptide levels were 18.5 +/- 9.1 microU/ml and 2.4 +/- 0.8 ng/ml for obese patients and 11.5 +/- 5.1 microU/ml and 1.9 +/- 1.1 ng/ml for non-obese patients. The type of diabetes among the Saudi adult diabetic patients studied is characterized by high basal C-peptide and insulin levels which increase significantly with stimulation, suggesting diminished but present endogenous B-cell function.

Comparative studies on the major features of insulin receptors in mammalian and non-mammalian liver membranes.

1. The camel has insulin receptors that by multiple function criteria are very similar to those of the other mammals (rabbit and rat) and non-mammals (chicken and pigeon), with sharp pH dependence to insulin binding at pH 7.2-7.6. 2. Equilibrium binding was faster at higher temperatures (24-37 degrees C) than at lower (4 degrees C). 3. Binding data yielded curvilinear Scatchard plots with half maximal displacement of 125I-insulin at 9 x 10(-9) M, 2.5 x 10(-9) M, 6.3 x 10(-10) M for camel, rabbit, pigeon and chicken respectively, suggesting differences in mammalian and non-mammalian liver membranes. 4. Autoradiogram patterns showed the presence of an identical subunit structure with Mr 74,000 for all membranes studied. Pigeon membrane showed a band with Mr 110,000, the absence of which in other membranes could be due to the degradation factor or the concentration of disuccinimidyl suberate (DSS).