Multi-messenger observations of a binary neutron star merger

On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of ~1.7 s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg2 at a luminosity distance of 40+8-8 Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 Mo. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at ~40 Mpc) less than 11 hours after the merger by the One- Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ~10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position ~9 and ~16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta

Oral hypoglycemic agents: insulin secretagogues, alpha-glucosidase inhibitors and insulin sensitizers

In this review we present the agents that are in use in the treatment of type 2 diabetes. Sulfonylureas of the 1(st) and 2(nd) generation increase insulin secretion but can induce hyperinsulinemia and sometimes prolonged hypoglycemia. Glimepiride is a new 3(rd) generation sulfonylurea with some advantages over the other members of this group, such as a lower risk of hypoglycemia, no interaction with cardiovascular K-ATP-channels and a possibility that it may increase insulin sensitivity. There are also newer insulin secretagogues (such as neteglinide and repaglinide) with a rapid onset of action on the beta -cell, therefore inducing a more physiological profile of insulin secretion during meals. The category of insulin sensitizers includes metformin and thiazolidinediones. Metformin effectively reduces hyperglycemia, hyperlipidemia and macroangiopathy in patients with type 2 diabetes. This agent increases the sensitivity of the liver and peripheral tissues to insulin and, therefore, it could be considered as a drug of choice for the prevention of type 2 diabetes. Thiazolidinediones (rosiglitazone and pioglitazone) increase the sensitivity of the tissues to insulin. This mechanism of action makes them powerful therapeutic tools for the treatment of type 2 diabetes (and possibly other insulin resistant states) either alone or in combination with other oral agents. The category of agents that interfere with the absorption of glucose and lipids includes a-glucosidase inhibitors (acarbose and miglitol) and lipase inhibitors (or-listat). alpha -Glucocidase inhibitors improve the time relationship between plasma insulin and glucose increases after a meal. Therefore, these agents may be used in the treatment of patients with type 2 diabetes, either alone at a very early stage of this disease (when insulin secretion is still adequate), or in combination with insulin secretagogues. alpha -Glucosidase inhibition may also prove useful as a supplement to insulin therapy in patients with type 1 diabetes mellitus. The inhibitor of gastrointestinal lipase orlistat may prove a useful adjunct to hypocaloric diets in patients with type 2 diabetes and obesity

Thyroid hormone excess and glucose intolerance

The elevated plasma glucose levels in hyperthyroidism may be explained by increased rates of endogenous glucose production, due mainly to increased gluconeogenesis. The rates of insulin-stimulated glucose disposal in peripheral tissues in hyperthyroidism have been found, in general, either normal or increased. Skeletal muscle is the most important tissue for the disposal of glucose in response to insulin. In this tissue, insulin increases glucose disposal by stimulating glucose transport, glucose phosphorylation/glycolysis, glycogen synthesis and glucose oxidation. Studies examining insulin-stimulated glucose metabolism in skeletal muscle have suggested that, in the hyperthyroid state, it may be of primary importance to increase the rates of glycolysis and lactate formation relative to glucose oxidation in this tissue in order to provide substrate for gluconeogenesis (increase Cori cycle activity). This effect will be achieved primarily by a decrease in glycogen synthesis and an increase in glycogenolysis. When hyperthyroidism becomes more severe, an increased rate of glucose uptake into muscle may then be necessary since the increased conversion of glycogen to lactate could not be sustained for prolonged periods and might lead to a depletion in glycogen stores. This mechanism would ensure that the level of glucose in plasma is kept normal or slightly increased. Thus, an increased Cori cycle activity may be a necessary mechanism to provide optimal conditions in hyperthyroidism for the control of glucose utilization without increasing the risk of hypoglycemia. In addition to lactate, increased rates of gluconeogenesis in hyperthyroidism can also be sustained by increased plasma concentrations of amino acids (mostly glutamine and alanine) and glycerol, as well as by increased plasma concentrations of free fatty acids