Ellen C. Laschansky

Elimination of the action of glucagon-like peptide 1 causes an impairment of glucose tolerance after nutrient ingestion by healthy baboons.

Glucagon-like peptide 1 (GLP-1) is an insulinotropic hormone released after nutrient ingestion which is known to augment insulin secretion, inhibit glucagon release, and promote insulin-independent glucose disposition. To determine the overall effect of GLP-1 on glucose disposition after a meal we studied a group of healthy, conscious baboons before and after intragastric glucose administration during infusions of saline, and two treatments to eliminate the action of GLP-1: (a) exendin-[9-39] (Ex-9), a peptide receptor antagonist of GLP-1; or (b) an anti-GLP-1 mAb. Fasting concentrations of glucose were higher during infusion of Ex-9 than during saline (4.44 +/- 0.05 vs. 4.16 +/- 0.05 mM, P < 0.01), coincident with an elevation in the levels of circulating glucagon (96 +/- 10 vs. 59 +/- 3 ng/liter, P < 0.02). The postprandial glycemic excursions during administration of Ex-9 and mAb were greater than during the control studies (Ex-9 13.7 +/- 2.0 vs. saline 10.0 +/- 0.8 mM, P = 0.07; and mAb 13.6 +/- 1.2 vs. saline 10.6 +/- 0.9 mM, P = 0.044). The increments in insulin levels throughout the absorption of the glucose meal were not different for the experimental and control conditions, but the insulin response in the first 30 min after the glucose meal was diminished significantly during treatment with Ex-9 (Ex-9 761 +/- 139 vs. saline 1,089 +/- 166 pM, P = 0.044) and was delayed in three of the four animals given the neutralizing antibody (mAb 946 +/- 262 vs. saline 1,146 +/- 340 pM). Thus, elimination of the action of GLP-1 impaired the disposition of an intragastric glucose meal and this was at least partly attributable to diminished early insulin release. In addition to these postprandial effects, the concurrent elevation in fasting glucose and glucagon during GLP-1 antagonism suggests that GLP-1 may have a tonic inhibitory effect on glucagon output. These findings demonstrate the important role of GLP-1 in the assimilation of glucose absorbed from the gut.

High-concentration supplemental perioperative oxygen to reduce the incidence of postcesarean surgical site infection: a randomized controlled trial.

OBJECTIVE: Most postcesarean infections are caused by anaerobic bacteria. Oxidative killing, an important defense against surgical infections, depends on the oxygen level in contaminated tissue. Among patients undergoing colorectal surgery, perioperative supplemental oxygen decreased infection rates by 50%. We tested the hypothesis that high-concentration inspired oxygen decreases the incidence of surgical site infection in women undergoing cesarean delivery. METHODS: Using a double blind technique, 143 women undergoing cesarean delivery under regional anesthesia after the onset of labor were randomly assigned to receive low- or high-concentration inspired oxygen via nonrebreathing mask during the operation and for 2 hours after. Surgical site infection was defined clinically as administration of antibiotics for postpartum endometritis or wound infection during the initial hospital stay or within 14 days of surgery. Interim statistical analysis was performed after 25% of the planned sample size (143 of 550) accrued using intention-to-treat principle. The stopping rule P value for futility was P>.11 with two planned interim analyses. RESULTS: Postcesarean infection occurred in 17 (25%, 95% confidence interval [CI] 15–35%) of 69 women assigned to high-concentration oxygen compared with 10 (14%, 95% CI 6–22%) of 74 women assigned to low-concentration inspired oxygen (relative risk 1.8, 95% CI 0.9–3.7, P=.13). The P value exceeded the P value for futility, suggesting these differences were unlikely to reach statistical significance with continued recruitment. CONCLUSION: High-concentration perioperative oxygen delivered through a nonrebreathing mask did not decrease the risk of postcesarean surgical site infection. CLINICAL TRIAL REGISTRATION: ClinicalTrials.gov, www.clinicaltrials.gov, NCT00670020 LEVEL OF EVIDENCE: I

Circulating prosomatostatin-derived peptides. Differential responses to food ingestion.

Prosomatostatin (pro-S) and its bioactive posttranslational products, somatostatin-14 (S-14), somatostatin-13 (S-13), and somatostatin-28 (S-28), were measured in human plasma by the use of immunoglobulins to the NH2-terminus of S-28 conjugated with agarose to separate them and, thereafter, by RIA with an antiserum recognizing the COOH-terminus of pro-S, and by specific RIA for the NH2-terminus of S-14 and pro-S. In healthy men, mean basal levels of pro-S were 4 pg equivalent S-14/ml; S-14/S-13 combined were 9 pg equivalent S-14/ml; and S-28 levels were 16 pg/ml. After a 700-kcal meal, pro-S, S-14, and S-14/S-13 did not change, whereas S-28 levels doubled by 120 min and remained elevated for 240 min. To evaluate the origins of these peptides, their levels were compared in peripheral, portal, gastric, and mesenteric veins of anesthetized patients and in patients with total resection of stomach and pancreas before and after nutrient intake. The stomach and small intestine were sources of both peptides; however, most S-28 originated in the small intestine. These findings suggest that, in contrast to S-14, S-28 is a hormone and may modulate postprandial nutrient absorption and use.

Somatostatin biosynthesis and release in the hypothalamus and pancreas of the rat

Abstract Somatostatin has been localized in several cells of neuroectodermal origin by immunocytochemistry and radioimmunoassay and is presumably synthesized and secreted locally, thereby fulfilling some of the characteristics of a neurotransmitter or neuromodulator.1,2 Recent studies in perfused dog pancreas and isolated rat islets indicate that somatostatinlike immunoreactivity (SLI) is secreted from D cells and its presence in the human cerebral spinal fluid implies release from peptidergic neurons.3–6 That peptide biosynthesis occurs by ribosomal mechanisms followed by posttranslational enzyme-mediated cleavage eventuating in peptides destined for secretion has been well established.7 Although nonribosomal synthesis of conventional neurotransmitters occurs and has been implicated in the synthesis of thyrotropin-releasing hormone and luteinizing hormone-releasing hormone,8 most evidence favors their biosynthesis through cleavage of large molecular weight precursors.9,10 The mechanisms of biosynthesis and release of somatostatin have not been elucidated. We present preliminary data in the rat consistent with the notion that hypothalamic neurons and the pancreatic D cell synthesize and release somatostatin through posttranslational scission of precursor polypeptides.

Effect of Somatostatin-28 on Dynamics of Insulin Secretion in Perfused Rat Pancreas

Somatostatin-28 (S-28), originating in gastrointestinal cells, is secreted into the circulatory system and rises in human plasma after ingestion of a mixed meal. Pancreatic β-cells contain specific, high-affinity receptors for S-28, and it is plausible that this peptide is a physiological modulator of insulin secretion. To evaluate the effects of physiological concentrations of S-28 on glucose-mediated insulin secretion, we used the perfused in situ rat pancreas under two conditions: 1) “square-wave” glucose infusion from 2.8 to 11.1 mM and 2) ramping of glucose at 0.28 mM/min throughout 45 min. S-28 concentrations of 16, 32, and 80 pM were separately coinfused for 40 min in the first condition and at 16 pM in the second condition. During square-wave glucose infusion, biphasic insulin secretion was elicited with marked attenuation of both phases during coinfusion with the two higher concentrations of S-28. At 16 pM S-28, which approximates postprandial At 16 pM S-28, which approximates postprandial concentrations, only first-phase secretion was suppressed. During ramping of glucose, insulin was released gradually and, in the presence of 16 pM S-28, was shifted to the right, indicating an increase in threshold glucose levels for insulin secretion. We concluded that S-28, at levels achieved postprandially, modulates the release of insulin by altering the threshold of sensitivity to glucose.

Thrittene, Homologous with Somatostatin-28(1–13), Is a Novel Peptide in Mammalian Gut and Circulation

Preprosomatostatin is a gene expressed ubiquitously among vertebrates, and at least two duplications of this gene have occurred during evolution. Somatostatin-28 (S-28) and somatostatin-14 (S-14), C-terminal products of prosomatostatin (ProS), are differentially expressed in mammalian neurons, D cells, and enterocytes. One pathway for the generation of S-14 entails the excision of Arg 13 -Lys 14 in S-28, leading to equivalent amounts of S-28(1–12). Using an antiserum (F-4), directed to the N-terminal region of S-28 that does not react with S-28(1–12), we detected a peptide, in addition to S-28 and ProS, that was present in human plasma and in the intestinal tract of rats and monkeys. This F-4 reacting peptide was purified from monkey ileum; and its amino acid sequence, molecular mass, and chromatographic characteristics conformed to those of S-28(1–13), a peptide not described heretofore. When extracts of the small intestine were measured by RIA, there was a discordance in the ratio of peptides reacting with F-4 and those containing the C terminus of ProS, suggesting sites of synthesis for S-28(1–13) distinct from those for S-14 and S-28. This was supported by immunocytochemistry, wherein F-4 reactivity was localized in gastrointestinal (GI) endocrine cells and a widespread plexus of neurons within the wall of the distal gut while immunoreactivity to C-terminal domains of S-14 and S-28 in these neurons was absent. Further, F-4 immunoreactivity persisted in similar GI endocrine cells and myenteric neurons in mice with a targeted deletion of the preprosomatostatin gene. We believe that these data suggest a novel peptide produced in the mammalian gut, homologous with the 13 residues of the proximal region of S-28 but not derived from the ProS gene. Pending characterization of the gene from which this peptide is derived, its distribution, and function, we have designated this peptide as thrittene. Its localization in both GI endocrine cells and gut neurons suggests that thrittene may function as both a hormone and neurotransmitter. (Endocrinology 143: 2599 –2609, 2002)

Endogenous Somatostatin-28 Modulates Postprandial Insulin Secretion Immunoneutralization Studies in Baboons

Somatostatin-28 (S-28), secreted into the circulation from enterocytes after food, and S-14, released mainly from gastric and pancreatic D cells and enteric neurons, inhibit peripheral cellular functions. We hypothesized that S-28 is a humoral regulator of pancreatic B cell function during nutrient absorption. Consistent with this postulate, we observed in baboons a two to threefold increase in portal and peripheral levels of S-28 after meals, with minimal changes in S-14. We attempted to demonstrate a hormonal effect of these peptides by measuring their concentrations before and after infusing a somatostatin-specific monoclonal antibody (mAb) into baboons and comparing glucose, insulin, and glucagon-like peptide-1 levels before and for 4 h after intragastric nutrients during a control study and on 2 d after mAb administration (days 1 and 2). Basal growth hormone (GH) and glucagon levels and parameters of insulin and glucose kinetics were also measured. During immunoneutralization, we found that (a) postprandial insulin levels were elevated on days 1 and 2; (b) GH levels rose immediately and were sustained for 28 h, while glucagon fell; (c) basal insulin levels were unchanged on day 1 but were increased two to threefold on day 2, coincident with decreased insulin sensitivity; and (d) plasma glucose concentrations were similar to control values. We attribute the eventual rise in fasting levels of insulin to its enhanced secretion in compensation for the heightened insulin resistance from increased GH action. Based on the elevated postmeal insulin levels after mAb administration, we conclude that S-28 participates in the enteroinsular axis as a decretin to regulate postprandial insulin secretion.

Invasive Obstetric Procedures and Cesarean Sections in Women with Known Herpes Simplex Virus Status During Pregnancy

Abstract Background Neonatal herpes is a potentially devastating infection that results from acquisition of herpes simplex virus (HSV) type 1 or 2 from the maternal genital tract at the time of vaginal delivery. Current guidelines recommend (1) cesarean delivery if maternal genital HSV lesions are present at the time of labor and (2) antiviral suppressive therapy for women with known genital herpes to decrease HSV shedding from the genital tract at the time of vaginal delivery. However, most neonatal infections occur in infants born to women without a history of genital HSV, making current prevention efforts ineffective for this group. Although routine serologic HSV testing of women during pregnancy could identify women at higher risk of intrapartum viral shedding, it is uncertain how this knowledge might impact intrapartum management, and a potential concern is a higher rate of cesarean sections among women known to be HSV-2 seropositive. Methods To assess the effects of prenatal HSV-2 antibody testing, history of genital herpes, and use of suppressive antiviral medication on the intrapartum management of women, we investigated the frequency of invasive obstetric procedures and cesarean deliveries. We conducted a retrospective cohort study of pregnant women delivering at the University of Washington Medical center in Seattle, Washington. We defined the exposure of interest as HSV-2 antibody positivity or known history of genital herpes noted in prenatal records. The primary outcome was intrapartum procedures including fetal scalp electrode, artificial rupture of membranes, intrauterine pressure catheter, or operative vaginal delivery (vacuum or forceps). The secondary outcome was incidence of cesarean birth. Univariate and multivariable logistic regressions were performed. Results From a total of 449 women included in the analysis, 97 (21.6%) were HSV-2 seropositive or had a history of genital herpes (HSV-2/GH). Herpes simplex virus-2/GH women not using suppressive antiviral therapy were less likely to undergo intrapartum procedures than women without HSV-2/GH (odds ratio [OR], 0.49; 95% confidence interval [CI], 0.25–0.95; P = .036), but this relationship was attenuated after adjustment for potential confounders (adjusted OR, 0.69; 95% CI, 0.34–1.41; P = .31). There was no difference in intrapartum procedures for women on suppressive therapy versus women without HSV-2/GH (OR, 1.17; 95% CI, 0.66–2.07; P = .60). Similar proportions of cesarean sections were performed within each group of women: 25% without history of HSV-2/GH, 30% on suppressive treatment, and 28.1% without suppressive treatment (global, P = .73). Conclusions In this single-site study, provider awareness of genital herpes infection either by HSV serotesting or history was associated with fewer invasive obstetric procedures shown to be associated with neonatal herpes, but it was not associated with an increased rate of cesarean birth.