The Functional Development Of Fetal Central RAS And PKC Mechanisms In The Regulation Of Cardiovascular And Cerebrovascular Responses

Aims:Brain rennin-angiotensin system(RAS)plays an important role in the cardiovascular regulation and maintenance of body fluid homeostasis. Increasing evidence suggests that an over activated RAS contributes importantly to hypertension development programmed during fetal life. In the present study,we focused on the functional development of regulation system of cardiac and cerebrovascular responses.Combine the in vivo study on conscious animals with the in vitro study,we investigated the functional development of angiotensin-converting enzyme(ACE),a key enzyme of the intrinsic brain RAS.Furthermore,we investigated the functional development of the protein kinase C(PKC), an important pathway of angiotensin(Ang)Ⅱbiological effects,in the regulation of cerebral arterial contractility.Methods:In in vivo study,nearterm ovine fetuses were chronically prepared with thyrohyoid,nuchal and thoracic esophagus,and diaphragm electromyogram electrodes,as well as lateral ventricle and vascular catheters.Electrodes were also implanted on the parietal dura for determination of fetal electrocorticogram(ECoG).After recovery,fetal cardiovascular responses,swallowing,ECoG were monitored during basal period and the experimental period following intracerebroventricular (i.c.v.)injection.Plasma arginine vasopressin(AVP)and oxytocin(OT) concentrations and c-fos expression in the brain were examined,too.In in vitro vessel study,vascular tension and[Ca2+]i responses were simultaneously measured in segments of main branch middle cerebral arteries(MCA)from near-term fetal and nonpregnant female adult sheep.Results:1.ACE mRNA was detected in specific central area;2.Ⅰ.c.v. AngⅠsignificantly increased fetal blood pressure,swallowing activity, and plasma AVP and OT concentration.Captopril,an inhibitor of ACE, significantly suppressed these responses induced by central AngⅠadministration;3.AngⅠevoked an increase of c-fos expression in putative regulation centers in cardiovascular and body fluid homeostasis; 4.In both fetal and adult MCA,PKC activation produced a significant increase of vessel tone with no significant increase in[Ca2+]i;5.In fetal,but not adult MCA,the selective BK channel blocker significantly increased PDBu-induced vascular contraction and[Ca2+]i,which was totally eliminated by the removal of extracellular Ca2+ or by the inhibition of the L-type Ca2+-channels.6.In both fetal and adult, specific ERK inhibitor U-0126 significantly inhibited PKC-induced vascular contraction without effect on[Ca2+]i;7.In only fetal MCA, Rho kinase inhibitor Y-27632 inhibited PgC-induced vascular contraction.Conclusion:The results indicate that the central endogenous ACE has developed and is functional at least at the last third of gestation.AngⅠcan be converted to AngⅡby endogenous ACE to exert its biological effects.In light of the important role of AngⅡon the vessel smooth muscle,we investigated functional development of PKC,one of the critical pathways of AngⅡ,on the cerebral arterial contractility.The results suggest that in fetal MCA,PDBu-induced PKC stimulation may activate BK channels to inhibit Ca2+ influx through L-type Ca2+ channels, thus preventing an increase in[Ca2+]i and producing a Ca2+-independent contraction.This relationship between PKC and BK channels is not apparent in adult MCA,however.MAPK/ERK pathway plays an important role in the PKC-induced arterial contraction in both fetal and adult MCA,while Rho A/Rho kinase pathway is only involved in fetal MCA.These results suggest that there are various developmental differences of PKC vasoregulation mechanisms between mature and immature cerebral arteries.