n-type Ge/Si antennas for THz sensing

Ge-on-Si plasmonics holds the promise for compact and low-cost solutions in the manipulation of THz radiation. We discuss here the plasmonic properties of doped Ge bow-tie antennas made with a low-point cost CMOS mainstream technology. These antennas display resonances between 500 and 700 GHz, probed by THz time domain spectroscopy. We show surface functionalization of the antennas with a thin layer of α-lipoic acid that red-shifts the antenna resonances by about 20 GHz. Moreover, we show that antennas protected with a silicon nitride cap layer exhibit a comparable red-shift when covered with the biolayer. This suggests that the electromagnetic fields at the hotspot extend well beyond the cap layer, enabling the possibility to use the antennas with an improved protection of the plasmonic material in conjunction with microfluidics.

Evidence against a rate-limiting role of proinsulin processing for maximal insulin secretion in subjects with impaired glucose tolerance and beta-cell dysfunction

In subjects with impaired glucose tolerance (IGT) insulin secretion is impaired. Increased proinsulin/insulin (PI/I) ratios suggest that there is also reduced processing of proinsulin to insulin in this condition. The PI/I ratio in the insulin secretory granule is ideally assessed by plasma measurements in response to acute stimulation of insulin secretion. In the present study we tested the hypothesis that maximal stimulation of insulin secretion results in exhaustion of the proinsulin conversion pathway to insulin. We therefore determined the PI/I ratio in 11 normal glucose-tolerant subjects (NGT) and 11 subjects with IGT in response to glucose (squarewave hyperglycemic clamp, 10 mmol/L), glucagon-like peptide-1 (GLP-1; primed-continuous infusion), and arginine given during the continued GLP-1 infusion. In IGT, insulin levels were significantly lower during the first phase (144 +/- 20 vs. 397 +/- 119 pmol/L; P = 0.02), at the end of the GLP infusion (2142 +/- 350 vs. 5430 +/- 1091 pmol/L; P: = 0.002), and in response to arginine (3983 +/- 375 vs. 8663 +/- 1430 pmol/L; P = 0.005). In response to glucose, the minimum PI/I ratio was significantly higher in IGT (3.4 +/- 0.6%) than in NGT (1.4 +/- 0.5%; P = 0.02), suggesting defective proinsulin processing in this condition. In subjects with IGT, the PI/I ratio decreased significantly after GLP-1 priming (1.7 +/- 0.2%; P = 0.02) and after arginine given during GLP-1 (1.4 +/- 0.2%; P = 0.007) and was not significantly different from those values in NGT (1.3 +/- 0.2% and 1.3 +/- 0.2%, respectively; both P = NS). In conclusion, during maximal stimulation of insulin secretion in subjects with IGT, the PI/I ratio in plasma decreased significantly and was not different from that in normal controls. This strongly argues against the hypothesis that defective processing of proinsulin to insulin represents a major component of the beta-cell dysfunction in IGT.

Characterisation of beta-cell dysfunction of impaired glucose tolerance: evidence for impairment of incretin-induced insulin secretion

AIMS/HYPOTHESIS

Our studies were undertaken to characterise the defective insulin secretion of impaired glucose tolerance (IGT).

METHODS

We studied 13 normal glucose tolerant subjects (NGT) and 12 subjects with IGT carefully matched for age, sex, BMI and waist-to-hip ratio. A modified hyperglycaemic clamp (10 mmol/1) with a standard 2-h square-wave hyperglycaemia, an additional glucagon-like-peptide (GLP)-1 phase (1.5 pmol x kg(-1) x min(-1) over 80 min) and a final arginine bolus (5 g) was used to assess various phases of insulin secretion rate.

RESULTS

Insulin sensitivity during the second phase of the hyperglycaemic clamp was low in both groups but not significantly different (0.12 +/- 0.021 in NGT vs 0.11 +/- 0.013 micromol x kg(-1) x min(-1) x pmol(-1) in IGT, p = 0.61). First-phase insulin secretion was lower in IGT (1467 +/- 252 vs 3198 +/- 527 pmol x min(-1), p = 0.008) whereas the second phase was not (677 +/- 61 vs 878 +/- 117 pmol x min(-1), p = 0.15). The acute insulin secretory peak in response to GLP-1 was absent in IGT subjects who only produced a late phase of GLP-1-induced insulin secretion rate which was lower (2228 +/- 188 pmol x min(-l)) than in NGT subjects (3056 +/- 327 pmol x min(-1), p = 0.043). Insulin secretion in response to arginine was considerably although not significantly lower in IGT subjects. The relative impairment (per cent of the mean rate for NGT subjects) was greatest for the GLP-1 peak (19 +/- 9%).

CONCLUSION/INTERPRETATION

In this Caucasian cohort a defective insulin secretion rate is essential for the development of IGT. The variable degrees of impairment of different phases of the insulin secretion rate indicate that several defects contribute to its abnormality in IGT. Defects in the incretin signalling pathway of the beta cell could contribute to the pathogenesis of beta-cell dysfunction of IGT and thus Type II (non-insulin-dependent) diabetes mellitus.

A novel hyperglycaemic clamp for characterization of islet function in humans: assessment of three different secretagogues, maximal insulin response and reproducibility

BACKGROUND

Characterization of beta-cell function in humans is essential for identifying genetic defects involved in abnormal insulin secretion and the pathogenesis of type 2 diabetes.

MATERIALS AND METHODS

We designed a novel test assessing plasma insulin and C-peptide in response to 3 different secretagogues. Seven lean, healthy volunteers twice underwent a 200 min hyperglycaemic clamp (10 mmol L-1) with administration of GLP-1 (1.5 pmol. kg-1. min-1) starting at 120 min and an arginine bolus at 180 min. We determined glucose-induced first and second-phase insulin secretion, GLP-1-stimulated insulin secretion, arginine-stimulated insulin response (increase above prestimulus, DeltaIarg) and the maximal, i. e. highest absolute, insulin concentration (Imax). Insulin sensitivity was assessed during second-phase hyperglycaemia. On a third occasion 6 subjects additionally received an arginine bolus at > 25 mM blood glucose, a test hitherto claimed to provoke maximal insulin secretion.

RESULTS

Insulin levels increased from 46 +/- 11 pM to 566 +/- 202 pM at 120 min, to 5104 +/- 1179 pM at 180 min and to maximally 8361 +/- 1368 pM after arginine (all P < 0.001). The within subject coefficients of variation of the different secretion parameters ranged from 10 +/- 3% to 16 +/- 6%. Except for second-phase which failed to correlate significantly with DeltaIarg (r = 0.52, P = 0.23) and Imax (r = 0.75, P = 0.053) all phases of insulin secretion correlated with one another. The insulin concentration after the arginine bolus at > 25 mM glucose (n = 6) was 2773 +/- 855 pM vs. 7562 +/- 1168 pM for Imax (P = 0.003).

CONCLUSION

This novel insulin secretion test elicits a distinct pattern of plasma insulin concentrations in response to the secretagogues glucose, GLP-1 and arginine and is highly reproducible and can be used for differential characterization of islet function.

The core content of a generalist curriculum for general internal medicine, family practice, and pediatrics

The authors analyzed the educational content of the curricula developed for teaching in the generalist disciplines of pediatrics, family medicine, and general internal medicine. Fifteen educational components that constitute the core content shared by the three generalist disciplines are identified, described, and referenced. Tailoring the generalist curriculum for students and residents at the different stages of learning is reviewed, along with the refinement of the curriculum to meet the special needs of each generalist discipline. The success of a generalist curriculum will ultimately be measured by generalist career choices, quality of care, and both patient and professional satisfaction. The curricular determinants of success require institutional commitment to an educational philosophy that embraces the generalist disciplines, a core curriculum that provides education and training that are correlated with the demands of clinical practice, and generalist faculty who serve as role models, mentors, and teachers.