Horst Zier

The function of a hydrogen peroxide-detecting electroenzymatic glucose electrode is markedly impaired in human sub-cutaneous tissue and plasma

Electroenzymatic glucose sensors implanted into sub-cutaneous (s.c.) tissue of human subjects and experimental animals exhibit lower sensitivities to glucose than in buffer solutions before implantation. The mechanism of the decrease of sensitivity is not known. Sensors used in this study were fabricated from platinum wires (diameter 0.125 mm) with covalently bound glucose oxidase at the tip of the wire. After coating the tip with polyurethane, wires were placed into 27 gauge steel needles. Sensors were operated potentiostatically at 700 mV against Ag/AgCl pseudo-reference electrodes. These sensors were implanted s.c. in 6 diabetic patients for 7 h. In 4 patients, sensors were responsive to successive increases of plasma glucose levels. Mean sensitivity to glucose in s.c. tissue was 29% of in vitro sensitivity. In 2 patients there was a sudden decrease of sensor currents, unrelated to glucose, shortly after implantation. Sensors were inhibited in human plasma to a similar extent. When sensors were exposed to native plasma and to plasma ultrafiltrate (mol. wt. < 10 kDa) for 10 h, identical decreases of signals were found. Exposure to dialysed plasma (mol. wt. > 12 kDa) caused much less decrease of sensor signals. Losses of sensor sensitivities to glucose in s.c. tissue and in plasma were totally reversible upon re-exposure of sensors to buffer solutions. We conclude that sensor inactivation in plasma and possibly in s.c. tissue is caused by low molecular weight substances not retained by the polyurethane membrane.

Incidence of Hypoglycemic Episodes in Diabetic Patients Under Continuous Subcutaneous Insulin Infusion and Intensified Conventional Insulin Treatment: Assessment by Means of Semiambulatory 24-hour Continuous Blood Glucose Monitoring

The incidence and magnitude of hypoglycemia (i.e., blood glucose values < 50 mg/dl) were assessed by continuous blood glucose monitoring over 24 h in 10 insulin-dependent diabetic (IDD) patients treated with continuous subcutaneous insulin infusion (CSII) and 9 IDD patients under intensified conventional treatment (ICT). A newly developed, battery-powered blood glucose monitor was employed. Patients were thus enabled to move freely in the hospital premises. Despite similar quality of previous blood glucose control (HbA1: 8.0 ± 0.05% CSII versus 8.0 ± 0.3% ICT, x¯ ± SEM), the obtained profiles showed better regulation under CSII treatment (mean blood glucose [MBG], 99.6 ± 10.0 versus 133.1 ± 7.4 mg/dl; M-value, 12.3 ± 3.5 versus 26.2 ± 4.1; mean amplitude of glycemic excursion [MAGE], 71.9 ± 8.7 versus 132.9 ± 14.2 mg/dl; CSII versus ICT, x¯ ± SEM). The incidence of blood glucose values < 50 mg/dl was 9/10 patients (CSII) and 5/9 patients (ICT). In both groups, hypoglycemia was most frequent at noon and was related to elevated pre- and postprandial free insulin levels. Patients became aware of hypoglycemia only in 6/23 episodes (CSII) and 6/8 episodes (ICT). Our data indicate that CSII as well as ICT may result in postprandial hyperinsulinemia leading to frequent hypoglycemic episodes of variable length, reassessing the traditional experience of close correlation between aggressive insulin therapy and enhanced hypoglycemic risk.

Similar effects of pulsatile and constant intravenous insulin delivery.

Effects of constant and pulsatile i.v. insulin delivery were examined in seven healthy subjects by means of euglycemic clamp technique. Each subject received constant insulin infusion (0.175 mU/kg.min) or insulin pulses at 12-min intervals (2.1 mU/kg) in randomized order for 8-h periods (08.00-16.00 h). Endogenous secretion of insulin was inhibited by concomitant administration of somatostatin (300 micrograms/h). Serum insulin concentrations during constant infusion (12 +/- 1 microU/ml) did not differ from basal values (11 +/- 1 microU/ml). Pulsatile insulin delivery resulted in oscillations of mean concentrations between values of about 10 and 20 microU/ml. Mean blood glucose concentrations during experiments were kept at 80 +/- 1 mg/dl, irrespective of the mode of insulin administration. Moreover, dextrose requirements for maintenance of these glucose concentrations did not differ over the hole periods of examination. We conclude that effects of constant and pulsatile delivery of basal amounts of insulin are not different. This at least applies to peripheral, short-term insulin administration in somatostatin-treated normal man, during an euglycemic clamp.