The activation of protein kinase C prevents PGE2-induced inhibition of AVP-dependent cAMP accumulation in the rat outer medullary collecting tubule

Previous studies have demonstrated that prostaglandin E₂ (PGE₂) inhibits arginine vasopressin-(AVP)dependent adenosine 3,5-cyclic monophosphate (cAMP) accumulation in microdissected rat outer medullary collecting tubules (OMCD), by a mechanism unrelated to the inhibition of cAMP synthesis. The potential role of the activation of protein kinase C (PKC) to explain the negative regulation elicited by PGE₂ was investigated in this study. Single OMCD samples were pre-incubated (10 min, 30°C) in the presence or absence of either activators of PKC, phorbol 12-myristate 13-acetate (PMA), 1-oleoyl-2-acetyl-glycerol (OAG), dioctanoylglycerol (DOG) or an inhibitor of PKC, staurosporine (SSP). These compounds were present also with the agonists tested during the incubation period (4 min, 35°C). In contrast to PGE₂, activators of PKC did not decrease AVP-dependent cAMP accumulation (mean ±SEM): 1nM AVP=47.1±6.8 fmol · mm^–1· 4 min^–1; AVP + 0.3 M PGE₂=20.1±2.7, P<0.01 versus AVP; AVP + 10 nM PMA=42.0±4.7, NS versus AVP; AVP + 50 g/ml OAG=44.1±4.8. NS versus AVP, N= 5 experiments. However, 10 nM PMA prevented PGE₂-induced inhibition: AVP + PGE₂= 44.2±3.5% of the response to AVP and 90.3±3.2% without and with PMA respectively, N= 16. Similar results were obtained with either 50 g/ml OAG or 25 g/ ml DOG (AVP + PGE₂ + OAG=92.9±6.6% of the response to AVP, N= 8; AVP + PGE₂ + DOG=94.1 ±5.3%, N= 7). OAG, DOG, PMA or PMA + PGE₂ had no intrinsic agonist activity in the rat OMCD and the addition of an inactive phorbol ester did not prevent PGE₂-induced inhibition. SSP, 50 nM or 0.1 M, did not affect the inhibition due to PGE₂ but abolished the reversion by PMA of PGE₂-induced inhibition. A similar regulation was observed on forskolin-(FK)dependent cAMP accumulation: 5 M FK + 0.3 M PGE₂= 37.7±6.2% of the response to FK; FK + PGE₂ + 10 nM PMA=89.5±6.7%; FK + PGE₂ + PMA + 0.1 M SSP=43.1±7.9%, N= 4. The inhibition induced by an ₂-adrenergic agonist, clonidine 1 M, was not blocked by the activation of PKC. In fura-2-loaded OMCD samples, 10nM PMA decreased by 63.3±5.0% and by 57.2±7.1% the peak and plateau phases, respectively, of the increase in intracellular calcium concentration ([Ca²⁺]_i) obtained with PGE₂ when compared to control responses in the same tubules (n=12) and did not affect the increase in [Ca²⁺]_i induced by 0.1 mM carbachol. It is concluded that: (1) in the rat OMCD the activation of PKC by PMA or analogues of diacylglycerol did not reproduce PGE₂-induced inhibition of AVP- or FK-dependent cAMP accumulation, but prevented specifically this inhibitory action; and (2) this reversion might be the consequence of the effect of PKC activation which impaired the rises in [Ca²⁺]_i induced by PGE₂.     

Mobile Application for Promoting Gluten-Free Diet Self-Management in Adolescents with Celiac Disease: Proof-of-Concept Study

Celiac disease (CD) is a chronic disease treated by maintaining and managing a lifelong restrictive gluten-free diet. The purpose of this study was to develop a mobile application, Plan My C-Day, to promote self-management skills among youth with CD during adolescence—a time when decreased adherence often occurs—and examine its usability among adolescents with CD. Plan My C-Day contains three simulations of activities involving eating out and actions to take when preparing for these events. It was developed and pilot tested by 13 adolescents with CD. Application use and user perception data were collected and analyzed. Participants chose 160 actions within the simulations. For over 75% of participants, the time to complete the simulation decreased from the first to the third (last) simulation by an average of 50%. The average reported usability perception was 3.71 on a scale of 1 to 5, with system ease of use and ease of learning obtaining the highest scores. This study demonstrated that the Plan My C-Day mobile application’s self-management content, features, and functions operated well and that the simulations were easy to understand and complete. Further development will include the option to add self-created activities and adaptation to different languages and cultures.     

Soft Drink Consumption and Mental Health in Adolescents: A Longitudinal Examination

PurposePrevious studies showed associations between soft drink consumption and mental health problems in adolescents, but the direction of these effects is unknown. This study examines the hypotheses that soft drink consumption predicts aggression and depressive symptoms over time and that these mental health problems predict soft drink consumption.MethodsInterviews were conducted with 5,147 children and their caregivers from three sites at child ages 11, 13, and 16. At each time point, youth reported on their frequency of consuming soft drinks, aggressive behavior, and depressive symptoms. An autoregressive cross-lagged path model tested reciprocal relationships between soft drink consumption, aggressive behavior, and depressive symptoms over time.ResultsMore frequent consumption of soft drinks was associated with more aggressive behavior at each time point and depressive symptoms at ages 11 and 13 (r = .04 to .18, p ≤ .002). After adjusting for covariates and stability of each behavior over time, soft drink consumption at ages 11 and 13 predicted more aggressive behavior at the next time point (β = .08 and .06, p < .001). Aggressive behavior at age 13 also predicted more soft drink consumption at age 16 (β = .06, p = .002). Soft drink consumption at age 13 predicted fewer depressive symptoms (β = ?.04, p = .007), but depressive symptoms did not predict soft drink consumption.ConclusionsMore frequent consumption of soft drinks may contribute to aggressive behavior in adolescents over time; there is some support for reciprocal relationships. There is no evidence for soft drink consumption contributing to adolescents' depression. Future research should examine longitudinal effects over shorter intervals.     

Salbutamol disposition and dynamics in conscious rabbits: Influence of the route of administration and of the dose

This study assessed the influence of dose and route of administration on salbutamol kinetics and hypokaliemic effect. Salbutamol plasma kinetics were studied in a first group of 6 rabbits who received 60, 800, and 60 g/kg by the intravenous (iv), oral (po), and intratracheal (it) routes, respectively, at 1-week intervals. A second group of 6 rabbits received 120, 2400, and 120 g/kg of salbutamol by the same three routes. Multiple blood samples were withdrawn to assay salbutamol and potassium. Following iv salbutamol (60 g/kg), total plasma clearance was 82±5 ml/min per kg, apparent volume of distribution was 5.0±0.5 l/kg, and terminal half- life was 41±2 min. Similar values were estimated when 120 g/kg of salbutamol was administered iv or was given po or it. The bioavailability of po and it salbutamol was approximately 1 and 20%, respectively. For the first group, the maximal decrease in plasma potassium elicited by salbutamol was 0.80±0.19, 0.48±0.22, and 0.78±0.46 mmol/l, and for the second group, maximal decrement was 1.31±0.37, 0.70±0.24, and 0.84±0.17 mmol/l for the iv, po, and it routes, respectively. Compared to salbutamol peak plasma concentrations, maximal decrease in plasma potassium appeared between 60 and 108 min later for the iv route, 90 and 25 min later for po and it routes, and for this reason, the hypokaliemic effect was not associated to salbutamol plasma concentrations. The hypokaliemic effect was dependent upon the route, e.g., po>it>iv. It is concluded that (i) salbutamol plasma kinetics are first-order independently of the route of administration, and (ii) salbutamol hypokaliemic effect is modulated by the dose and the route of administration.List of abbreviations AUC Area under salbutamol plasma concentration-time curve - cl_INT Salbutamol intrinsic clearance - cl_T Salbutamol total plasma clearance - c_MAX Salbutamol maximal plasma concentration - F Fraction of the dose of salbutamol reaching the systemic circulation - iv Intravenous route of administration - it Intratracheal route of administration - po Oral route of administration - V_area Salbutamol apparent volume of distribution - T ₂ ¹ Salbutamol half-life of the terminal phase - t_MAX Time to observe the maximal decrease in plasma potassium - e_MAX Predicted maximal effect of salbutamol - EC₅₀ Concentration of salbutamol eliciting 50% of e_MAX Supported by the Medical Research Council of Canada (MT-10874). Sylvie Perreault is recipient of a Bourse Formation de troisième cycle des Fonds de la Recherche en Santé du Québec.     

Randomized, placebo-controlled trial of combined pentoxifylline and tocopherol for regression of superficial radiation-induced fibrosis.

PURPOSE: Radiation-induced fibrosis (RIF) is a rare morbid complication of radiotherapy, without an established method of management. RIF treatment with a combination of pentoxifylline (PTX) and alpha-tocopherol (vitamin E; Vit E) was recently prompted by the good results of a clinical trial and an animal study. The present double-blind, placebo-controlled, monocentric study was designed to assess the efficacy of this combination in treating RIF sequelae. PATIENTS AND METHODS: Twenty-four eligible women with 29 RIF areas involving the skin and underlying tissues were enrolled from December 1998 to April 2000. These patients, previously irradiated for breast cancer, were randomly assigned to four balanced treatment groups: (A) 800 mg/d of PTX and 1,000 U/d of Vit E; (B) PTX plus placebo; (C) placebo plus Vit E; and (D) placebo-placebo. The main end point measure was the relative regression of measurable RIF surface after 6 months of treatment. Assessment was completed by depth (with ultrasonography) and associated symptom measures. RESULTS: Twenty-two patients with 27 RIF areas were analyzed at 6 months. Mean RIF surface regression was significant with combined PTX/Vit E versus double placebo (60% +/- 10% v 43% +/- 17%; P =.038). The median slope for the speed of RIF surface area and volume regression was significantly higher for group A than groups B, C, and D. All treatments were well tolerated. CONCLUSION: Six months' treatment of combined PTX/Vit E can significantly reduce superficial RIF. Synergism between PTX and Vit E is likely, as treatment with each drug alone is ineffective, but these results require confirmation in larger series.