Effect Of ANP Injection In PVN On Baroreflex In Conscious Rats

It has been proved by radioimmunoassay and immunohistochemistry that ANP exists in central nerve system, the nerve cells and the fibers overlap with other nerves cells and fibers which secrete angiotensinⅡor vasopressin (AVP), so it is considered that ANP may be involved in the central regulation of the water and salt metabolization and cardiovascular activity as a neurotransmitter or neuromodulator. Central nerve system modulates the cardiovascular activity mainly by baroreflex. In central nerve system, as a integration part of neuosecretion and autonomic nervous system, PVN plays key role in regulation of the water and salt metabolization and cardiovascular activity. It reported that PVN is one of nucleus groups which include much ANP in hypothalamic, however, there has been no any reports about the effect of ANP on the baroreflex in PVN. So our experiment investigated the effect by injecting ANP into PVN in conscious rats, and observed whether the regulation of ANP on baroreflex was related to central AVP by injectedOPC-21268, the blocker of AVP receptorⅠ, into lateral ventricle.The experiments were performed on mail Wistar rats weighting 280-400g. Rats were anesthetized by intraperitoneal of mixture of pentobarbial sodium, operated nucleus groups location intubatton and intubatton of remoral arterial and vein, then put them into the computer-controlled cylindrical metabolic cages. After two days, when the rats restituted to the normal condition so that could move freely, we did the four procedures of experiments as follows. The first was injecting different dose of ANP (0.6ng/0.2μl, 6ng/0.2μl, 60ng/0.2μl) into the PVN to observe the effects on sensitivity of baroreflex. Secondly observed the same effect by intravenous injecting AVP (60ng/0.04ml) the same dose as the maxmum quantity injected into nucleus groups. Thirdly, observed the same effect of injecting OPC-21268 (0.45μg/3μl) into lateral ventricle. Eventually, observed the effect of injecting ANP (60ng/0.2μl) into PVN on the regulation of baroreflex after preinjected OPC-21268 (0.45μg/3μl) into lateral ventricle. Control groups and experiment groups were used in every experiment. The sensitivity of baroreflex was indicated with the ratio between heart rate and average arterial pressure (△HR/△MAP, bpm/kpa) when the depressor reflex induced by phenylephrine.The results indicated: 1.ANP injection into PVN increased obviously the sensitivity of baroreflex (P<0.05), reached the peak value after 45 minutes, and it would restitute during 90-100 minutes showing certain dosedependence. 2. When ANP was intravenous injected, there was no significant change on △HR/△MAP (P>0.05). 3. When OPC-21268 (0.45μg/3μl) injected into lateral ventricle, the sensitivity of baroreflex almost did not decrease (P>0.05). 4. After preinjected OPC-21268 (0.45μg/3μl) into lateral ventricle, injected ANP (60ng/0.2μl) into PVN decreased the facilitation significantly of baroreflex vs control (P<0.05).The results suggested: 1. As a neurotransmitter or neuromodulater, ANP may be involved in the regulation of central cardiovascular activity caused by PVN, and facilitates baroreflex. 2. ANP and AVP probably make synergic reaction in the central regulation of the activity of baroreflex.