FETAL RENAL SYMPATHETIC NERVE ACTIVITY, BEHAVIOURAL STATE AND REGULATION OF THE FETAL CARDIOVASCULAR SYSTEM

Eugenie R. Lumbers, Ze-Yan Yu, Department of Physiology & Pharmacology, School of Medical Sciences, University of New South Wales, Sydney, NSW.

322 records of renal sympathetic nerve activity (RSNA), arterial pressure (MAP) and heart rate (HR) were obtained 1-3 days after surgery from 7 fetal sheep aged 127-136 days. Neither ewes nor fetuses were sedated or paralysed. Fetal behavioural state was determined from chart recordings of electrocortical activity (ECoG), eye movements (EOG), breathing movements (intra-tracheal pressure), and muscular activity (EMG, forearm muscles). Fetal state was classified as HV, i.e. high voltage ECoG, no breathing and minimal EOG; LV_B, i.e. low voltage ECoG, breathing and increased EOG; LV₀, i.e. low voltage ECoG, no breathing, increased EOG; there were two transitional states, HVtoLV and LVtoHV. Two second averages of integrated RSNA, and its amplitude and frequency were obtained as well as MAP and HR. RSNA was similar in HV, HvtoLV and LVtoHV but much lower in LV₀ (P<0.001). RSNA was greater in LV_B than in HV (P<0.05). These differences in RSNA were due to changes in amplitude but not in frequency of bursts. MAP was highest in HV compared to all other states (P<0.001) and lower in LV₀ and LV_B compared to levels obtained in the transitional state LVtoHV. HR was highest in HV compared to all other states (P<0.001) and lower in LV_B than during either of the 2 transitional states. (P<0.01). In HV, LV_B and LVtoHV there was a negative relationship between MAP and HR (P=0.01-0.003). In LV_B and LVtoHV there was a direct relationship between MAP and RSNA (P=0.001, P=0.08) and in LVtoHV there was also a negative relationship between HR and RSNA (P=0.02). Thus at normal arterial pressure, fetal RSNA and spontaneous baroreflex mediated regulation of fetal RSNA and HR are influenced by fetal behavioural state.