Do kappa opioid receptors regulate cardiovascular responses to severe haemorrhage in conscious newborn lambs? (859.3)

Abstract

Previously, we showed that activation of kappa opioid receptors (KORs) influences systemic haemodynamics and the baroreflex control of heart rate (HR) in conscious lambs. The endogenous ligand for KORs, Dynorphin, is increased in response to severe blood loss however, any role for KORs in the haemodynamic responses to haemorrhage in the newborn is not known. In the present study, mean, systolic and diastolic arterial pressures (MAP, SAP, DAP) as well as HR were measured for 30 min before (Control) and 60 min after 30% haemorrhage in conscious lambs (aged ~one week, N=7) after pretreatment with vehicle (experiment one) or the selective KOR antagonist, GNTI (experiment two). After vehicle, MAP fell from 75±5 (Control) to 48±9 mmHg by 10 min after haemorrhage and remained decreased. This response resulted from a decrease in both SAP and DAP and was not altered by pretreatment with GNTI. HR decreased from 189±29 (Control) to 139±30 beats/min 10 min after haemorrhage; this response was attenuated by GNTI. Therefore, KORs do not appear to influence the blood pressure response to severe blood loss early in life but do abrogate the HR response to haemorrhage.Grant Funding Source: Supported by the CIHR.