Astrocyte Glycogen Is a Major Source of Hypothalamic Lactate in Rats With Recurrent Hypoglycemia.

Lactate is an important metabolic substrate for sustaining brain energy requirements when glucose supplies are limited. Recurring exposure to hypoglycemia (RH) raises lactate levels in the ventromedial hypothalamus (VMH), which contributes to counterregulatory failure. However, the source of this lactate remains unclear. The current study investigates whether astrocytic glycogen serves as the major source of lactate in the VMH of RH rats. By decreasing the expression of a key lactate transporter in VMH astrocytes of RH rats, we reduced extracellular lactate concentrations, suggesting excess lactate was locally produced from astrocytes. To determine whether astrocytic glycogen serves as the major source of lactate, we chronically delivered either artificial extracellular fluid or 1,4-dideoxy-1,4-imino-d-arabinitol to inhibit glycogen turnover in the VMH of RH animals. Inhibiting glycogen turnover in RH animals prevented the rise in VMH lactate and the development of counterregulatory failure. Lastly, we noted that RH led to an increase in glycogen shunt activity in response to hypoglycemia and elevated glycogen phosphorylase activity in the hours following a bout of hypoglycemia. Our data suggest that dysregulation of astrocytic glycogen metabolism following RH may be responsible, at least in part, for the rise in VMH lactate levels. ARTICLE HIGHLIGHTS: Astrocytic glycogen serves as the major source of elevated lactate levels in the ventromedial hypothalamus (VMH) of animals exposed to recurring episodes of hypoglycemia. Antecedent hypoglycemia alters VMH glycogen turnover. Antecedent exposure to hypoglycemia enhances glycogen shunt activity in the VMH during subsequent bouts of hypoglycemia. In the immediate hours following a bout of hypoglycemia, sustained elevations in glycogen phosphorylase activity in the VMH of recurrently hypoglycemic animals contribute to sustained elevations in local lactate levels.

ZT-01: A novel somatostatin receptor 2 antagonist for restoring the glucagon response to hypoglycaemia in type 1 diabetes.

AIM: To evaluate the pharmacokinetics and efficacy of a novel somatostatin receptor 2 antagonist, ZT-01, to stimulate glucagon release in rats with type 1 diabetes (T1D). METHODS: The pharmacokinetics of ZT-01 and PRL-2903 were assessed following intraperitoneal or subcutaneous dosing at 10 mg/kg. We compared the efficacy of ZT-01 with PRL-2903 to prevent hypoglycaemia during an insulin bolus challenge and under hypoglycaemic clamp conditions. RESULTS: Within 1 hour after intraperitoneal administration, ZT-01 achieved more than 10-fold higher plasma Cmax compared with PRL-2903. Twenty-four hour exposure was 4.7× and 11.3× higher with ZT-01 by the intraperitoneal and subcutaneous routes, respectively. The median time to reach hypoglycaemia of more than 3.0 mmol/L was 60, 70, and 125 minutes following vehicle, PRL-2903, or ZT-01 administration, respectively. Furthermore, rats receiving ZT-01 had significantly higher glucose nadirs following insulin administration compared with PRL-2903- and vehicle-treated rats. During the hypoglycaemic clamp, ZT-01 increased peak glucagon responses by ~4-fold over PRL-2903. CONCLUSIONS: We conclude that ZT-01 may be effective in restoring glucagon responses and preventing the onset of hypoglycaemia in patients with T1D.

Carvedilol prevents impairment of the counterregulatory response in recurrently hypoglycaemic diabetic rats.

Aim: It has been suggested that repeated activation of the adrenergic system during antecedent episodes of hypoglycaemia contributes to the development of counterregulatory failure. We previously reported that treatment with carvedilol, a non-specific ß-blocker, prevented the development of counterregulatory failure and improved hypoglycaemia awareness in recurrently hypoglycaemic non-diabetic rats. The current study investigated whether carvedilol has similar benefits in diabetic rats. Methods: Recurrently hypoglycaemic streptozotocin-diabetic rats (STZ+RH) were treated with carvedilol for one week prior to undergoing a hypoglycaemic clamp. Hypoglycaemia awareness was evaluated in streptozotocin-diabetic rats made hypoglycaemia unaware using repeated injections of 2-deoxyglucose. Results: Compared to hypoglycaemia-naïve STZ-diabetic controls, exogenous glucose requirements were more than doubled in the STZ+RH animals and this was associated with a 49% reduction in the epinephrine response to hypoglycaemia. Treating STZ+RH animals with carvedilol improved the epinephrine response to hypoglycaemia. Of note, neither recurrent hypoglycaemia nor carvedilol treatment affected the glucagon response in diabetic animals. Additionally, carvedilol treatment improved the feeding response to insulin-induced hypoglycaemia in diabetic animals made 'hypoglycaemia unaware' using repeated injections of 2-deoxyglucose, suggesting the treatment improved awareness of hypoglycaemia as well. Conclusion: Our data suggest that carvedilol may be useful in preventing impairments of the sympathoadrenal response and the development of hypoglycaemia unawareness during recurring episodes of hypoglycaemia in diabetic animals.

Repeated Activation of Noradrenergic Receptors in the Ventromedial Hypothalamus Suppresses the Response to Hypoglycemia.

Activation of the adrenergic system in response to hypoglycemia is important for proper recovery from low glucose levels. However, it has been suggested that repeated adrenergic stimulation may also contribute to counterregulatory failure, but the underlying mechanisms are not known. The aim of this study was to establish whether repeated activation of noradrenergic receptors in the ventromedial hypothalamus (VMH) contributes to blunting of the counterregulatory response by enhancing local lactate production. The VMH of nondiabetic rats were infused with either artificial extracellular fluid, norepinephrine (NE), or salbutamol for 3 hours/day for 3 consecutive days before they underwent a hypoglycemic clamp with microdialysis to monitor changes in VMH lactate levels. Repeated exposure to NE or salbutamol suppressed both the glucagon and epinephrine responses to hypoglycemia compared to controls. Furthermore, antecedent NE and salbutamol treatments raised extracellular lactate levels in the VMH. To determine whether the elevated lactate levels were responsible for impairing the hormone response, we pharmacologically inhibited neuronal lactate transport in a subgroup of NE-treated rats during the clamp. Blocking neuronal lactate utilization improved the counterregulatory hormone responses in NE-treated animals, suggesting that repeated activation of VMH ß2-adrenergic receptors increases local lactate levels which in turn, suppresses the counterregulatory hormone response to hypoglycemia.

Carvedilol prevents counterregulatory failure and impaired hypoglycaemia awareness in non-diabetic recurrently hypoglycaemic rats.

AIMS/HYPOTHESIS: This study evaluates whether the non-selective ß-blocker, carvedilol, can be used to prevent counterregulatory failure and the development of impaired awareness of hypoglycaemia (IAH) in recurrently hypoglycaemic rats. METHODS: Sprague Dawley rats were implanted with vascular catheters and intracranial guide cannulas targeting the ventromedial hypothalamus (VMH). These animals underwent either three bouts of insulin-induced hypoglycaemia or received three saline injections (control group) over 3 days. A subgroup of recurrently hypoglycaemic animals was treated with carvedilol. The next day, the animals underwent a hypoglycaemic clamp with microdialysis without carvedilol treatment to evaluate changes in central lactate and hormone levels. To assess whether carvedilol prevented IAH, we treated rats that had received repeated 2-deoxyglucose (2DG) injections to impair their awareness of hypoglycaemia with carvedilol and measured food intake in response to insulin-induced hypoglycaemia as a surrogate marker for hypoglycaemia awareness. RESULTS: Compared with the control group, recurrently hypoglycaemic rats had a ~1.7-fold increase in VMH lactate and this was associated with a 75% reduction in the sympathoadrenal response to hypoglycaemia. Treatment with carvedilol restored VMH lactate levels and improved the adrenaline (epinephrine) responses. In 2DG-treated rats compared with control animals receiving saline, food intake was reduced in response to hypoglycaemia and increased with carvedilol treatment. CONCLUSIONS/INTERPRETATION: We conclude that carvedilol may be a useful therapy to prevent counterregulatory failure and improve IAH.

Therapeutic hypothermia modulates complement factor C3a and C5a levels in a rat model of hypoxic ischemic encephalopathy.

BACKGROUND: Therapeutic hypothermia (HT) is the only intervention that improves outcomes in neonatal hypoxic-ischemic encephalopathy (HIE). However, the multifactorial mechanisms by which HT impacts HIE are incompletely understood. The complement system plays a major role in the pathogenesis of ischemia-reperfusion injuries such as HIE. We have previously demonstrated that HT modulates complement activity in vitro. METHODS: Term equivalent rat pups were subjected to unilateral carotid ligation followed by hypoxia (8% O2) for 45 min to simulate HIE. A subset of animals was subjected to HT (31-32°C for 6 h). Plasma and brain levels of C3a and C5a were measured. Receptors for C3a (C3aR) and C5a (C5aR) along with C1q, C3, and C9 were characterized in neurons, astrocytes, and microglia. RESULTS: We found that HT increased systemic expression of C3a and decreased expression of C5a after HIE. In the brain, C3aR and C5aR are predominantly expressed on microglia after HIE. HT increased local expression of C3aR and decreased expression on C5aR after HIE. Furthermore, HT decreased local expression of C1q, C3-products, and C9 in the brain. CONCLUSION: HT is associated with significant alteration of complement effectors and their cognate receptors. Complement modulation may improve outcomes in neonatal HIE.

Cyclophosphamide and topotecan as first-line salvage therapy in patients with relapsed ewing sarcoma at a single institution.

The combination of cyclophosphamide and topotecan (cyclo/topo) has shown objective responses in relapsed Ewing sarcoma, but the response duration is not well documented. We reviewed characteristics and outcome of 14 patients with Ewing sarcoma, treated uniformly at a single institution and offered cyclo/topo at first relapse. Six patients (43%) had relapse at distant sites. All patients received first-line salvage therapy with cyclophosphamide 250 mg/m and topotecan 0.75 mg/m, daily for 5 days repeated every 21 days. The median number of cycles was 4 (range 1 to 10). All toxicities were manageable, the most common being transient cytopenias. There were also 4 episodes of febrile neutropenia, and 3 episodes of gross hematuria. Response was assessable in 13 patients and showed progressive disease in 6 (46%), stable disease in 4 (31%), and partial response in 3 (23%). Nine patients had local control, consisting of radical surgery in 2, radiation in 3, and a combination in 4 patients. Response, when it occurred, was maintained for a median of 8 months (range, 4 to 28 mo). Four patients (29%) are alive at 3, 7, 9, and 110 months after relapse; 1 is receiving cyclo/topo, 1 is on third-line therapy, and 2 are in second and fourth remission. The low toxicity of this combination, and the lack of sustained responses, warrant its investigation in combination with targeted or novel therapeutic agents in relapsed disease.

Length of postnatal hospital stay in healthy newborns and re-hospitalization following early discharge.

BACKGROUND: The length of postnatal hospital stay for healthy newborns remains controversial. Proponents of early hospital discharge claim that it is safe, decreases the risk of iatrogenic infection, promotes family bonding and attachment, and reduces hospitalization care and patient costs. Disadvantages include delayed breastfeeding, manifestation of new conditions affecting newborns after early discharge, and improper discharge planning. AIM: The main aim of the study was to compare early discharge versus late discharge with the risk of readmission. PATIENTS AND METHODS: The length of hospital stay was recorded for all healthy newborns and infants and followed by investigation of any medical problem arising after discharge. Factors associated with readmission to the hospital were analyzed by Chi square and Mantel-Haenszel Common Odds Ratio Estimate (OR) with Confidence Limits (CL). RESULTS: A total of 478 babies were enrolled, of which 307 were discharged ≤ 48 hours. The overall length of stay was 39 hours (1.6 days). Thirty-eight (7.9%) newborns were re-hospitalized, with the most common cause being neonatal jaundice. Factors associated with readmission for jaundice were breastfeeding (OR: 10.3 CL3.10to32.20) and length of stay ≤ 48 hours (OR: 13.8, CL4.04 to 47.05). CONCLUSION: Hospital discharge at any time ≤ 48 hours significantly increases the risk for readmission as well as the risk for readmission due to hyperbilirubinemia. Planning and implementing a structured program for follow up of infants who are discharged ≤ 48 hours are vital in order to decrease the risk for readmission, morbidity and neonatal mortality.