Characterization of neuro-humoral pathways involved in delayed gastric emptying of liquids due to mechanical right atrial stretch in awake rats

Right atrium mechanical stretch (AS) increases gastric motility in anesthetized rats. We aimed to study the effect of AS on gastric emptying (GE) in awake rats and the related neuro-humoral pathways ivolved. Male albino rats (N=361, 250-280g) had a silicone balloon inserted in the right atrium. After 24-h, the central venous pressure (CVP), heart rate (HR) and the mean arterial pressure (MAP) were monitored and after the initial 20-min, animals were randomly pre-treated with: saline (S, 0.1 ml/100g, i.v.), Atropine (A, 0.5mg/kg, i.v.), Guanethidine (GT, 10mg/kg, i.p.), hexamethonium (H, 10mg/kg, i.v.), L-NAME (3mg/kg, i.v.), L-Arginine (100mg/kg, i.v.)+L-NAME (3mg/kg, i.v.), Methylene Blue (MB, 3mg/kg, i.v.), Glibenclamide (GB, 1mg/kg, i.p) or Glibenclamide+Diazoxide (3mg/kg, i.v.) [GB+D], Dexamethazone (DEX, 1mg/kg, i.p.), Anantin (ANT, 5g, i.v.) or Atosiban (AT, 40g/kg/h, i.v.). Besides, in a separate group, we realized vagotomy (V), or splanchnotomy + celiac gangliectomy (SC) or afferent cardiac denervation with capsaicin (ACD) 72h before AS. In another set of animals, we realized right appendectomy (AX) one week before AS. Next, AS with saline zero (sham) or 50L was performed during 5min. In this group, rats were gavage fed with a test meal 20-min after AS and euthanized 10-min afterwards to study GE. Moreover we determined plasmatic levels of Ocytocin (OT), Atrial Natriuretic Peptide (ANP) and Corticosterone (CORT), and determined the neuronal activity in the paraventricular (PVN) or supraoptic (SON) hypothalamic regions by measuring expressed double-labeled c-fos-OT. Comparing to Sham, AS decreased GE (p<0.05). Besides, AS increased CVP and HR. AS decreased GE (p <0.05) in S, A, GT, L-Arginine+L-NAME, MB and GB+D groups. However pre-treatment with, H, L-NAME, GB, DEX, ANT or AT, as well as SV, SC, ACD or AX prevented the effect of AS on GE. AS increased OT and CORT plasmatic levels, but did not alter ANP. In spite of AS increasing the number of c-fos expressing neurons in the parvocellular region, we did not observe this finding in the magnocellular regions of PVN or SON. Besides, AS did not alter the number of fos-OT double-labeled neurons. Therefore the decrease of GE of fluids after AS in awake rats depends on an afferent pathway mediated by cardiac low pressure receptors, and both sympathetic and parasympathetic neurons participate in the cascade mediated by OT, ANP and NO through K +-ATP dependent channels.A distensão mecânica do átrio direito (DA) aumenta a motilidade gástrica em ratos anestesiados (Palheta et al., 2010). Resolvemos avaliar o efeito da DA sobre o esvaziamento gástrico (EG) de líquido em ratos acordados e as eventuais vias neuro-humorais relacionadas ao fenômeno. Utilizamos ratos albinos machos (n=361, 250-280g) que receberam um balão de silicone posicionado no átrio direito. Decorridos 24h, monitoramos a pressão venosa central (PVC), freqüência cardíaca (FC) e a pressão arterial média (PAM) e após os 20-min iniciais os animais foram aleatoriamente pré-tratados com: Salina (S, 0,1 ml/100g, i.v.), Atropina (A, 0,5 mg/kg, i.v.), Guanetidina (GT, 10 mg/kg, i.p.), Hexametônio (H, 10mg/kg, i.v.), L-NAME (3mg/kg, i.v.), L-Arg (100mg/kg, i.v.) + L-NAME (3 mg/kg, i.v.), Azul de metileno (MB, 3 mg/kg, i.v.), Glibenclamida (GB, 1 mg/kg, i.p.) ou Glibenclamida + Diazóxido (3mg/kg, i.v.) [GB + D], Dexametasona (DEX, 1mg/kg, i.p.), Anantin (ANT, 5 g, i.v.) ou Atosibana (AT, 40 g/kg/h, i.v.). Além disto, em grupos separados realizamos 72h antes da DA à vagotomia (V), ou esplancnotomia+ gangliectomia celíaca (SC) ou denervação cardíaca aferente com capsaicina (ACD). Em outro conjunto de animais realizamos aurilectomia direita uma semana antes da DA (AX). Em seguida ao tratamento farmacológico realizamos protocolo de falsa DA (controle) ou DA com 50L do balão intra-atrial durante 5min. Decorridos 20 min. da DA, os ratos foram alimentados por via oral com solução teste e, após 10-min sacrificados para estudo do EG. Além disto, determinamos os níveis plasmáticos de ocitocina (OT), Peptídeo Natriurético Atrial (ANP) e corticosterona (CORT). Para verificação da atividade neuronal avaliamos a expressão da proteína Fos e OT nas regiões hipotalâmicas do núcleo paraventricular (PVN) ou supra-óptico (SON). Comparado ao controle, a DA diminuiu o EG (p <0,05). Além disso, a DA aumentou a PVC e a FC. A DA diminuiu o EG (p