Norby, Barbara

Background: Regadenoson is a selective A2A receptor agonist that is administered as a fixed dose bolus with rapid onset (∼30 sec), and short duration (∼2-4 min) of action. The aim of this study was to evaluate the feasibility of real-time myocardial contrast echocardiography (MCE) for quantification of coronary flow reserve (CFR) in healthy humans during regadenoson vasodilator stress. Methods: Fifteen subjects [3 males, age: 45.8±5.2 years, BMI 23.8±2.3 kg/m2] with normal LV wall motion and no CAD underwent real-time MCE. Three standard apical LV views were acquired during a continuous intravenous (IV) infusion of Definity (1.3 ml in 60 cc 0.9% saline at 200 ml/hr) at rest and during vasodilator stress (regadenoson 400 ug IV bolus). Following transient microbubble destruction, microbubble velocity (β, sec -1 ), myocardial blood volume (A, dB) and myocardial blood flow (MBF, dB/sec) were determined. Videodensitometric quantification using a 16-segment model at end-systole was performed off-line. Results: Quantification of reserve parameters was feasible in all (15/15) patients, 188/240 segments (78%)[82%, 80% and 70% of 4-, 2-, 3-chambers apical views] and 43/45 (95%) coronary territories [one each of Cx and RCA territories were not feasible]. Augmentation from baseline to vasodilator stress was observed for both ß (s -1 ) [0.65± 0.25 vs 0.79± 0.21, P=0.031] and MBF (dB/sec) [2.85± 1.43 vs 4.65± 2.06, P= 0.002], however A (dB) did not change [06.62± 2.57 vs 6.79±2.1, P=0.463]. CFR measurements from all views were similar (Fig 1). There was no significant difference between CFR measured in the 3 coronary territories, although some heterogeneity was noted in the posterior circulation CFR (Fig 2). Conclusion: Real-time MCE during Regadenoson vasodilator stress is feasible, and is a useful technique for the rapid noninvasive quantification of CFR in healthy humans.

OBJECTIVE—To determine mechanisms by which pioglitazone and metformin effect hepatic and extra-hepatic insulin action. RESEARCH DESIGN AND METHODS—Thirty-one subjects with type 2 diabetes were randomly assigned to pioglitazone (45 mg) or metformin (2,000 mg) for 4 months. RESULTS—Glucose was clamped before and after therapy at ∼5 mmol/l, insulin raised to ∼180 pmol/l, C-peptide suppressed with somatostatin, glucagon replaced at ∼75 pg/ml, and glycerol maintained at ∼200 mmol/l to ensure comparable and equal portal concentrations on all occasions. Insulin-induced stimulation of glucose disappearance did not differ before and after treatment with either pioglitazone (23 ± 3 vs. 24 ± 2 μmol · kg−1 · min−1) or metformin (22 ± 2 vs. 24 ± 3 μmol · kg−1 · min−1). In contrast, pioglitazone enhanced (P < 0.01) insulin-induced suppression of both glucose production (6.0 ± 1.0 vs. 0.2 ± 1.6 μmol · kg−1 · min−1) and gluconeogenesis (n = 11; 4.5 ± 0.9 vs. 0.8 ± 1.2 μmol · kg−1 · min−1). Metformin did not alter either suppression of glucose production (5.8 ± 1.0 vs. 5.0 ± 0.8 μmol · kg−1 · min−1) or gluconeogenesis (n = 9; 3.7 ± 0.8 vs. 2.6 ± 0.7 μmol · kg−1 · min−1). Insulin-induced suppression of free fatty acids was greater (P < 0.05) after treatment with pioglitazone (0.14 ± 0.03 vs. 0.06 ± 0.01 mmol/l) but unchanged with metformin (0.12 ± 0.03 vs. 0.15 ± 0.07 mmol/l). CONCLUSIONS—Thus, relative to metformin, pioglitazone improves hepatic insulin action in people with type 2 diabetes, partly by enhancing insulin-induced suppression of gluconeogenesis. On the other hand, both drugs have comparable effects on insulin-induced stimulation of glucose uptake.