Corticosteroids decrease mRNA levels of SERCA pumps, whereas they increase sarcolipin mRNA in the rat diaphragm

In order to explore the potential role of the sarcoplasmic–endoplasmic reticulum Ca2+-ATPase (SERCA)-type pumps and of their modulators phospholamban (PLB) and sarcolipin (SLN) in the functional alterations of the diaphragm induced by corticosteroid treatment, expression of SERCA, PLB and SLN was assessed by RT-PCR in the diaphragm of rats treated daily for 5 days either with triamcinolone (80 mg kg−1, n = 8) or with saline (control; 0·6 ml, n = 8).Triamcinolone treatment reduced the normalised overall amount of all SERCA mRNA in diaphragm by 70 % compared to controls (P < 0·05). This reduction was accounted for by a relatively larger decrease in the SERCA1 mRNA (-69 %, P < 0·05) whilst the decrease in SERCA2 mRNA (-49 %, P = 0·09) did not reach statistical significance. As a result the relative proportion of SERCA2 mRNA was increased from 43 ± 7 % in control diaphragm to 52 ± 4 % after triamcinolone treatment (P < 0·05).Only the adult isoform of SERCA1 (i.e. SERCA1a) mRNA was found in the diaphragm of the 15-week-old control rats. Furthermore, triamcinolone treatment resulted in reduced levels of SERCA2a (-40 %, P < 0·05) and increased levels of SLN mRNA (+100 %, P < 0·05), while the decrease in PLB mRNA (-31 %, P = 0·277) did not reach statistical significance. SERCA1b, SERCA2b and SERCA3 mRNA levels fell below the detection limit in the diaphragm of both control and triamcinolone-treated rats.Compared to control diaphragm, control rat heart showed a relatively high PLB/(SERCA1 + SERCA2) mRNA ratio of 7·88 while this ratio amounted only to 0·16 in control extensor digitorum longus (EDL) muscle. Remarkably, the SLN/(SERCA1 + SERCA2) mRNA ratio in normal cardiac muscle (0·96) was nearly the same as in diaphragm, but in EDL it amounted to only 0·05 that in diaphragm. This indicates the very low expression of SLN in rat EDL.These data reveal that considerable alterations in SERCA mRNA levels accompany the functional changes seen in diaphragm after corticosteroid treatment. The relatively larger decrease in SERCA1 mRNA is in agreement with the selective type II fibre atrophy previously observed in the diaphragm of triamcinolone-treated rats, but the magnitude of SERCA alterations is more pronounced than expected on the basis of the structural changes in the diaphragm. The increase in SLN mRNA levels may represent a compensatory mechanism

Ventilação mecânica volume-controlada versus pressão controlada em modelo canino de lesão pulmonar aguda: efeitos cardiorrespiratórios e sobre o custo de oxigênio da respiração Volume controlled ventilation versus pressure controlled ventilation in a canine acute lung injury model: effects on cardiorespiratory parameters and oxygen cost of breathing

Introdução: Persiste a questão sobre se há vantagens mecânicas ou de trocas gasosas no uso da ventilação pressão-controlada (VPC) sobre a ciclada a volume (VCV). Objetivos: Comparar, de forma randômica, a VPC com a VCV com fluxo desacelerado nos modos assistido e controlado em modelo experimental de lesão pulmonar aguda. Métodos: Sete cães com lesão pulmonar aguda grave (PaO2/FIO2 < 100mmHg) induzida por ácido oléico intravenoso (0,05mg/kg) foram ventilados em VPC ou VCV, mantidos constantes o volume corrente e o tempo inspiratório. Nas duas modalidades os animais foram ventilados por 40 minutos no modo assistido seguido do modo controlado após curarização. Resultados: Não houve diferenças em relação às trocas gasosas (PaO2 e PaCO2), ao débito, ao transporte de oxigênio e à mecânica respiratória entre a VCV e a VPC. O consumo de oxigênio (VO2) após a curarização foi semelhante (124 &plusmn; 48 na VCV versus 143 &plusmn; 50ml/min na VPC, com p = 0,42). Entretanto, no modo assistido, houve tendência de maior VO2 na VPC (219 &plusmn; 72 versus 154 &plusmn; 67ml/min na VCV, p = 0,06). Isso associou-se a tendência de maior custo de oxigênio da respiração (COR) naquela modalidade, embora sem diferença estatística significante (31 &plusmn; 77 na VCV versus 75 &plusmn; 96ml/min na VPC, p = 0,23) e menor PvO2 (34 &plusmn; 7 versus 42 &plusmn; 6ml/min na VCV, p = 0,02). O pico de fluxo inspiratório nos ciclos assistidos foi maior na VPC (58 &plusmn; 9 versus 48 &plusmn; 4L/min na VCV, p = 0,01). A instituição da ventilação controlada por curarização reduziu em cerca de 20% o débito cardíaco e o DO2 em relação ao modo assistido, tanto na VCV quanto na VPC. Conclusões: Em um modelo de insuficiência respiratória grave, com elevado COR, a manutenção da ventilação controlada em relação à assistida melhorou a relação entre oferta e consumo de oxigênio. A VPC não trouxe benefícios às trocas gasosas ou à mecânica pulmonar em relação à VCV, podendo aumentar o COR no modo assistido no presente modelo.<br>Background: It is questionable whether pressure-controlled ventilation (PCV) has advantages over volume-cycled ventilation (VCV). Objectives: To compare PCV to VCV with decelerating flow profile during assisted and controlled modes in an acute lung injury experimental model. Methods: Severe acute lung injury (PaO2/FIO2 < 100 mmHg) was induced by oleic acid IV infusion (0.05 mg/kg) in seven dogs. The animals were submitted to PCV and VCV in a randomized sequence. After 40 minutes in the assisted mode, ventilation was changed to the controlled mode after neuromuscular blockade. The tidal volume and the inspiratory time were kept constant throughout the experiment. Results: There were no differences in gas exchange (PaO2 and PaCO2), cardiac output or oxygen delivery (DO2) between VCV and PCV. The same was observed regarding maximum airway and plateau pressures, and also to the static compliance. Oxygen consumption (VO2) after neuromuscular blockade was 124 &plusmn; 48 in VCV versus 143 &plusmn; 50 ml/min in PCV, p = 0.42. In the assisted mode, there was a statistical trend of a higher VO2 in PCV (219 &plusmn; 72 versus 154 &plusmn; 67 ml/min in VCV, p = 0.06), that was associated with a statistical trend of a higher oxygen cost of breathing (OCB) during assisted PCV, although without statistical significance (31 &plusmn; 77 in VCV versus 75 &plusmn; 96 ml/min in PCV, p = 0.23), and also in a lower PvO2 (34 &plusmn; 7 in PCV versus 42 &plusmn; 6 ml/min in VCV, p = 0.02). These occurred despite a higher maximum inspiratory flow in the assisted mode in PCV (58 &plusmn; 9 versus 48 &plusmn; 4 L/min in VCV, p = 0.01). In both VCV and PCV the institution of controlled ventilation reduced cardiac debit and DO2 in as much as 20% relative to the assisted mode. Conclusions: The implementation of controlled ventilation improved the oxygen delivery/consumption relationship in this severe and with high OCB acute lung injury model. The PCV offered no additional benefits to VCV and it was associated with a higher OCB during the assisted mode