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

Microanatomic features of pancreatic islets and immunolocalization of glucose transporters in tissues of llamas and alpacas

OBJECTIVE

To describe the microanatomic features of pancreatic islets and the immunohistochemical distribution of glucose transporter (GLUT) molecules in the pancreas and other tissues of New World camelids.

ANIMALS

7 healthy adult New World camelids, 2 neonatal camelids with developmental skeletal abnormalities, and 2 BALB/c mice.

PROCEDURE

Samples of pancreas, liver, skeletal muscle, mammary gland, brain, and adipose tissue were collected postmortem from camelids and mice. Pancreatic tissue sections from camelids were assessed microscopically. Sections of all tissues from camelids and mice (positive control specimens) were examined after staining with antibodies against GLUT-1, -2, -3, and -4 molecules.

RESULTS

In camelids, pancreatic islets were prominent and lacked connective tissue capsules. Numerous individual endocrine-type cells were visible distant from the islets. Findings in neonatal and adult tissues were similar; however, the former appeared to have more non-islet-associated endocrine cells. Via immunostaining, GLUT-2 molecules were detected on pancreatic endocrine cells and hepatocytes in camelids, GLUT-1 molecules were detected on the capillary endothelium of the CNS, GLUT-3 molecules were detected throughout the gray matter, and GLUT-4 molecules were not detected in any camelid tissues. Staining characteristics of neonatal and adult tissues were similar.

CONCLUSIONS AND CLINICAL RELEVANCE

In New World camelids, microanatomic features of pancreatic islets are similar to those of other mammals. Data suggest that the poor glucose clearance and poor insulin response to hyperglycemia in adult camelids cannot be attributed to a lack of islet cells or lack of GLUT molecules on the outer membrane of those cells.

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.