Citations

Abstract Background: How endogenous testosterone (Te), 5α-dihydrotestosterone (DHT), and estradiol (E2) regulate pulsatile GH secretion is not understood. Hypothesis: Conversion of Te to androgenic (Te→DHT) or estrogenic (Te→E2) products directs GH secretion. Subjects and Location: Healthy older men (N = 42, ages 50–79 yr) participated at an academic medical center. Methods: We inhibited 5α-reduction with dutasteride and aromatization with anastrozole during a pharmacological Te clamp and infused somatostatin (SS), GHRH, GH-releasing peptide-2 (GHRP-2), and l-arginine/GHRH/GHRP-2 (triple stimulus) to modulate GH secretion. Endpoints: Deconvolution-estimated basal and pulsatile GH secretion was assessed. Results: Administration of Te/placebo elevated Te by 2.8-fold, DHT by 2.6-fold, and E2 concentrations by 1.9-fold above placebo/placebo. Te/dutasteride and Te/anastrozole reduced stimulated DHT and E2 by 89 and 86%, respectively. Stepwise forward-selection regression analysis revealed that 1) Te positively determines mean (P = 0.017) and peak (P < 0.001) GH concentrations, basal GH secretion (P = 0.015), and pulsatile GH secretion stimulated by GHRP-2 (P < 0.001); 2) Te and E2 jointly predict GH responses to the triple stimulus (positively for Te, P = 0.006, and negatively for E2, P = 0.031); and 3) DHT correlates positively with pulsatile GH secretion during SS infusion (P = 0.011). These effects persisted when abdominal visceral fat was included in the regression. Conclusion: The present outcomes suggest a tetrapartite model of GH regulation in men, in which systemic concentrations of Te, DHT, and E2 along with abdominal visceral fat determine the selective actions of GH secretagogues and SS.

Abstract Context: Hypoglycemia limits the efficacy of intensive insulin therapy. The extent to which continuous insulin infusion (CSII) overcomes this limitation is unclear. Objective: The aim was to summarize evidence on the effect of CSII and multiple daily injections (MDIs) on glycemic control and hypoglycemia. Data Sources: We searched electronic databases between 2002 and March 2008. Study Selection: We selected published randomized trials of CSII vs. MDI. Data Extraction: Reviewers working in duplicate and independently extracted study characteristics and quality and differences in glycosylated hemoglobin (HbA1c) and hypoglycemic events. Data Synthesis: We found 15 eligible randomized trials of moderate quality, with elevated baseline and end-of-study HbA1c levels. Patients with type 1 diabetes using CSII had slightly lower HbA1c [random-effects weighted mean difference, −0.2%; 95% confidence interval (CI), −0.3, −0.1, compared with MDI], with no significant difference in severe (pooled odds ratio, 0.48; 95% CI, 0.23, 1.00) or nocturnal hypoglycemia (pooled odds ratio 0.82, 95% CI 0.33, 2.03). Adolescents and adults with type 1 diabetes enrolled in crossover trials had nonsignificantly fewer minor hypoglycemia episodes per patient per week (−0.08; 95% CI, −0.21, 0.06) with CSII than MDI; children enrolled in parallel trials had significantly more episodes (0.68; 95% CI, 0.16, 1.20; Pinteraction = 0.03). Outcomes were not different in patients with type 2 diabetes. Conclusions: Contemporary evidence indicates that compared to MDI, CSII slightly reduced HbA1c in adults with type 1 diabetes, with unclear impact on hypoglycemia. In type 2 diabetes, CSII and MDI had similar outcomes. The effect in patients with hypoglycemia unawareness or recurrent severe hypoglycemia remains unclear because of lack of data.