[Effects of microinjection of L-arginine into the depressor area of ventral surface of medulla oblongata on cardiovascular responses].

AIM: To study the effects of L-arginine, a precursor for the synthesis of nitric oxide, when it was microinjected into the functionally identified depressor area in ventral surface of medulla oblongata (VSMd) on cardiovascular responses. METHODS: Artery pressure (AP), perfusion pressure of the kidney (PPK) and heart rate were recorded to study the effects of microinjection of NO related drugs into VSMd. RESULTS: (1) Unilateral microinjection of L-arginine (60 - 100 nmol) into VSMd produced prominent dose-related pressor effect and increased PPK but without significant changes in heart rate. (2) Microinjection of L-Arg (100 nmol) 3 min after microinjection of methylene blue (10 nmol) into VSMd did not significantly change AP and PPK. (3) Unilateral microinjection L-glutamate (350 nmol) into VSMd elicited depressor effect (-34.97% +/- 4.33%). The depressor effect was significantly dosed related attenuated by prior microinjection L-arginine (60 - 100 nmol) into the same area. CONCLUSION: These results suggest that the L-arginine - NO pathway in the VSMd participate in the central regulation of artery pressure and the pathway may have a key role in inhibiting glutamatergic neurotransmission in the anesthetized rats.

[Effect of microinjection of L-arginine into the caudal pressor area of medulla oblongata on cardiovascular responses in rats].

AIM: To study the effect of microinjection L-arginine, a precursor for the synthesis of nitric oxide into the functionally identified caudal pressor area (CPA) in ventral surface of medulla oblongata. METHODS: Artery pressure (AP), renal perfusion pressure (RPP) and heart rate were recorded to study the effects of microinjection of NO related drugs into CPA. RESULTS: (1) Unilateral microinjection of L-arginine (60 - 100 nmol) into CPA produced prominent dose-related depressor and bradycardic effects and reduced renal perfusion pressure. (2) Unilateral microinjection of L-arginine (100 nmol) 3 min after microinjection of methylene blue (10 nmol) into CPA did not significantly change AP and RPP. (3) Unilateral microinjection of L-glutamate (350 nmol) into CPA elicited pressor effect which was significantly dose-related attenuated by prior microinjection of L-arginine (60-100 nmol) into the same area. CONCLUSION: Theses results suggest that L-arginine-NO pathway in the CPA participates in the central regulation of arterial pressure and may have a key role in the inhibiting of glutamatergic neurotransmission in the anesthetized rats.

[Role of caudal pressor area of medulla oblongata in vasomotor tone of peripheral vessels].

To study the role of the caudal pressor area (CPA) on the ventral surface of medulla oblongata in vasotonia of the skeletal muscles and kidneys, perfusion pressures of vessels in skeletal muscles and kidneys were recorded to observe effects of microinjection of L-glutamate (L-glu) into CPA. The results are as follows. L-glu induced a significant increase of artery pressure (AP), perfusion pressure of muscles (PPm) and perfusion pressure of kidney (PPk), which was markedly attenuated by prior injection of phentolamine or propranolol to the bilateral pressor area. These results indicate that the vascular roles of CPA were mainly mediated via alpha- and/or beta-receptors.

Inhibitory effects of S-nitrosocaptopril on vasomotor tone.

AIM: To study effects of captopril (Cap) and S-nitrosocaptopril (CapNO) on vascular tension. METHODS: Tension of rabbit aortic rings and perfusion pressure of rat renal artery (PPr) were examined to evaluate the effects of CapNO. RESULTS: CapNO (3 nmol.L-1-10 mumol.L-1) produced concentration-dependent vasorelaxation response in the rings of rabbit thoracic aortas. Endothelium denudation did not alter the relaxations to CapNO. In contrast, Cap had no vasorelaxing effect on the rings precontracted with phenylephrine. CapNO (10 nmol.L-1) decreased rat PPr in vivo (P < 0.01), and the effect was concentration-dependent and reversible. Cap showed a reduction in rat PPr only at the concentration 1000 nmol.L-1 (P < 0.05). The relaxing potency of CapNO was 100 times higher than that of Cap in this respect. Pre-perfusion of rat renal arteries with NG-monomethyl-L-arginine monoacetate (L-NMMA, 0.03 nmol.L-1) or L-arginine (3 nmol.L-1) did not significantly blocked the relaxing effect induced by CapNO. CONCLUSION: CapNO had a direct vasodilatory effect.

[On the difference of cardiovascular effects between caudal ventrolateral medulla pressor area (cVMP) and rostrolateral medulla pressor area (rVMP)].

In 56 urethane anesthetized Wistar rats, bilateral microinjection of glutamate (L-glu) was used to observe the difference of cardiovascular effects between caudal ventrolateral medulla pressor area (cVMP) and rostral ventrolateral medulla pressor area (rVMP). The results showed that the pressor effect of cVMP was weaker than that of rVMP and was not accampanied by responses in heart rate. In the latter case, an increase of heart rate was involved. The baroreflex was inhibited when rVMP was activated by L-glu but facilitated when cVMP was activated. The above results suggest that the pathway and functions of the cardiovascular effects of rVMP are different from those of cVMP.

[Alpha 1-adrenoceptor involved in the process of VSMp control of renal sympathetic nerve activities in spinal cord in rats].

Experiment were performed on 40 urethane anesthetized Wistar rats. After preinjection of 6-hydroxydopamine (6-OHDA) into subarachnoid cavity at inferior thoracic part. Enhancement of renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) induced by electrical stimulation of pressor area of ventral surface of medulla (VSMp) were attenuated; but intrathecal phenylephrine had no effects. The results suggest that the alpha 1-adrenoceptors mediating descending excitatory effects of VSMp are located postsynaptically on the sympathetic preganglionic neurons.

[Effects of pressor area of ventral surface of medulla oblongata on the vasotonicity of renal vessels of rats].

Electrical stimulation of the pressor area of the ventral surface of medulla oblongata (VSMp) of rat elicited an enhancement of renal sympathetic nerve activities (RSNA) and an increase of MAP, pressure of kidney (PPK), which depended on the integrity of renal sympathetic nerve (RSN). The effect of VSMp on PPK could be blocked by alpha 2-adrenoceptor antagonist yohimbine, but not by alpha 1-adrenoceptor antagonist prazosine when VSMp was stimulated. alpha 2-adrenoceptor agonist clonidine perfused renal vessels induced PPK increase similar to that due to stimulation of VSMp. The results indicate that the effect of VSMp on PPK are mediated by RSN of alpha 2 type sympathetic transmitter in the tonic control renal vascularture.

[Characteristics of central acute resetting of high threshold baroreflex in rabbit's aortic nerves].

Experiments were performed on 37 urethane-anesthetized rabbits. The aortic nerves, carotid sinus nerves and vagus nerves were cut, MAP and renal sympathetic nerve activity (RSNA) were recorded. The conditional stimulation CSc (0.5 ms, 10 Hz, 4-6V, 5 min) was used to mimic the information of baroreflex non-medullated afferent fibers responding to acute increase of BP. Test stimulation TSa (0.02 ms, 0-80 Hz/30 s, 4-6V) and TSc (0.5 ms, 0-20 Hz/30s, 4-6V) was used to examine the responses of baroreflex A- and C-fibers. After CSc at 1 min the reflex MAP and RSNA of TSc was attenuated at 45.5% (P less than 0.01) and 10.6% (P less than 0.05), the MAP response of TSa was attenuated at 32.1% (P less than 0.05), but the RSNA response was not. From the further investigation it is concluded that the characteristics of central acute resetting are dependent on the components of baroreflex afferent fibers. The reflex responses are attenuated mainly by correspondent afferent components.

[Characteristics of central acute resetting of low threshold baroreflex in rabbit's aortic nerve].

Experiments were performed on 40 urethane-anesthetized rabbits. The aortic nerves, carotid sinus nerves and vagus nerves were cut, mean arterial pressure (MAP) and renal sympathetic nerve activity (RSNA) were recorded. The conditional stimulation (0.02 ms, 50 Hz, 4-6 V, 5 min) of central cut end of aortic nerve was used to evoke the afferent A-fibers and to mimic the response of low threshold baroreflex to holding pressure, so as to induce the central process of acute resetting. It was observed that after conditional stimulation ceased 1 min, the MAP and RSNA for response to stimulation of myelinated aortic afferent was attenuated at 41.8 +/- 7.6% (P less than 0.01, n = 11) and 19.31 +/- 2.6% (P less than 0.05, n = 11), but both MAP and RSNA were not significantly changed for non-myelinated fibers. The result suggests that the characteristics of central resetting were dependent on the component of baroreflex afferent fibers. The central resetting of low threshold myelinated afferent activities was attenuated only on the baroreflex produced by myelinated afferent fibers.