Regional differentiation of blood flow responses to microinjection of sodium nitroprusside into the nucleus tractus solitarius of anesthetized rats

Use of giant-sized flow-through venous flap for simultaneous reconstruction of dual or multiple major arteries in salvage therapy for complex upper limb traumatic injury

BACKGROUND/OBJECTIVES

Salvage repair after complex upper limb traumatic injury is surgically challenging due to underlying major arterial impairment with complicating a large-sized soft tissue defect. The purpose of this study was to evaluate the effectiveness and safety of using a giant-sized (≥100 cm(2)) flow-through venous flap for reconstruction of dual or multiple forearm, metacarpal, or digital arteries after complex upper limb traumatic injury.

METHODS

Seven patients were consecutively hospitalized for emergency salvage repair after complex upper limb traumatic injury between March 2012 and May 2014. The forearm and palmar artery defects were repaired using the calf great saphenous vein flap and the volar forearm venous flap, respectively.

RESULTS

The flow-through venous flap ranged from 9.5 cm × 12.0 cm to 12.0 cm × 20.0 cm (mean, 158.4 cm(2)) in size. The flaps and affected limbs survived uneventfully in five patients, with one patient experiencing distal flap marginal necrosis and a second patient requiring amputation of the affected limb. Computed tomography angiography showed patent vessels in all patients. The mean total active motion of the repaired fingers was 199.5° versus 258.8° for the contralateral counterpart (77.1%). The sensory return was determined to be S2 in 2 patients, S3 in 3 patients and S3+ in 1 patient. The disability scores for the arm, shoulder, and hand ranged from 4.6-18.2 (mean, 11.3), and the mean Michigan hand outcomes questionnaire score was 7.8 ± 0.9.

CONCLUSIONS

The flow-through venous flap is an effective and safe treatment alternative for salvage therapy of a ≥100-cm(2) complex upper limb traumatic injury with dual or multiple major arterial impairment. This technique allows simultaneous reconstruction of dual or multiple artery injuries and an extensive soft tissue defect. Serious surgical site infection remains a major safety concern and necessitates radical debridement in complicating cases.

Injection of l-glutamate into medial prefrontal cortex induces cardiovascular responses through NMDA receptor – nitric oxide in rat

We have reported that l-glutamate (l-glu) microinjections into ventral portion of medial prefrontal cortex (vMPFC) caused tachycardia and blood pressure increase in unanesthetized rats. In the present study, we report the subtype of vMPFC glutamatergic receptor mediating the response as well as the possible involvement of nitric oxide (NO) in these cardiovascular responses. Microinjection of 200nL of l-glu (81nmol) into the vMPFC of unanesthetized rats caused long-lasting pressor and tachycardic responses which were abolished by pretreatment with 4nmol of the specific NMDA receptor antagonist AP7. The response was not affected by 4nmol of the non-NMDA receptor antagonist NBQX. Local pretreatment with 80nmol of the unspecific nitric oxide synthase (NOS) inhibitor NG-nitro-l-arginine methyl ester (l-NAME) or 0.08nmol of the specific neuronal NOS (nNOS) inhibitor N(omega)-Propyl-l-arginine (N-Propyl) blocked l-glu effects. Microinjection of the NO donor sodium nitroprusside (SNP: 3, 9, 27 or 81nmol) in the vMPFC caused dose-related long-lasting pressor and tachycardic responses in unanesthetized rats, which were similar to those caused by l-glu. These results suggest that cardiovascular responses evoked by local injection of l-glu into the vMPFC of unanesthetized rats are caused by activation of a local NMDA receptor-NO pathway.

Differential role of nitric oxide in regional sympathetic responses to stimulation of NTS A2a adenosine receptors

Our previous studies showed that preganglionic adrenal (pre-ASNA), renal (RSNA), lumbar, and postganglionic adrenal sympathetic nerve activities (post-ASNA) are inhibited after stimulation of arterial baroreceptors, nucleus of the solitary tract (NTS), and glutamatergic and P2x receptors and are activated after stimulation of adenosine A1 receptors. However, stimulation of adenosine A2a receptors inhibited RSNA and post-ASNA, whereas it activated pre-ASNA. Because the effects evoked by NTS A2a receptors may be mediated via activation of nitric oxide (NO) mechanisms in NTS neurons, we tested the hypothesis that NO synthase (NOS) inhibitors would attenuate regional sympathetic responses to NTS A2a receptor stimulation, whereas NO donors would evoke contrasting responses from pre-ASNA versus RSNA and post-ASNA. Therefore, in chloralose/urethane-anesthetized rats, we compared hemodynamic and regional sympathetic responses to microinjections of selective A2a receptor agonist (CGS-21680, 20 pmol/50 nl) after pretreatment with NOS inhibitors Nomega-nitro-L-arginine methyl ester (10 nmol/100 nl) and 1-[2-(trifluoromethyl)phenyl]imidazole (100 pmol/100 nl) versus pretreatment with vehicle (100 nl). In addition, responses to microinjections into the NTS of different NO donors [40 and 400 pmol/50 nl sodium nitroprusside (SNP); 0.5 and 5 nmol/50 nl 3,3-bis(aminoethyl)-1-hydroxy-2-oxo-1-triazene (DETA NONOate, also known as NOC-18), and 2 nmol/50 nl 3-(2-hydroxy-2-nitroso-1-propylhydrazino)-1-propanamine (PAPA NONOate, also known as NOC-15)], the NO precursor L-arginine (10-50 nmol/50 nl), and sodium glutamate (500 pmol/50 nl) were evaluated. SNP, DETA NONOate, and PAPA NONOate activated pre-ASNA and inhibited RSNA and post-ASNA, whereas l-arginine and glutamate microinjected into the same site of the NTS inhibited all these sympathetic outputs. Decreases in heart rate and depressor or biphasic responses accompanied the neural responses. Pretreatment with NOS inhibitors reversed the normal depressor and sympathoinhibitory responses to stimulation of NTS A2a receptors into pressor and sympathoactivatory responses and attenuated the heart rate decreases; however, it did not change the increases in pre-ASNA. We conclude that NTS NO mechanisms differentially affect regional sympathetic outputs and differentially contribute to the pattern of regional sympathetic responses evoked by stimulation of NTS A2a receptors.

A study on the mechanism by which sodium nitroprusside, a nitric oxide donor, applied to the anteroventral third ventricular region provokes facilitation of vasopressin secretion in conscious rats

We reported previously that sodium nitroprusside (SNP) applied to the anteroventral third ventricular region (AV3V), a pivotal area for autonomic functions, facilitates vasopressin (AVP) secretion in conscious rats. The aim of this study was to pursue the problems of whether nitric oxide (NO) generated from the agent may be responsible for the phenomenon, and whether it may be mediated by cyclic guanosine monophosphate (cGMP), the biosynthesis of which could reportedly be activated by NO. The infusion of SNP into the AV3V of conscious rats produced dose-related increases in plasma AVP, the maximal responses of which appeared at 5 min. Blood pressure and heart rate tended to rise at 15 min. The plasma osmolality, sodium, potassium or chloride did not show marked alteration following the SNP administration. Although the SNP solution was hypertonic and hypernatremic, AV3V application of hypertonic saline with a relatively higher osmolality and an equal sodium level was significantly less effective in augmenting plasma AVP. When injected into the lateral ventricle, SNP did not change plasma AVP and reduced arterial pressure, different from the results provoked by the AV3V application. The rise in plasma AVP in response to the AV3V application of SNP was diminished by preadministration of hemoglobin, a scavenger of NO, that did not affect the responses of the other variables. In contrast, pretreatment with methylene blue, an agent capable of antagonizing the potency of NO to activate guanylate cyclase, did not attenuate but potentiated the responses of both plasma AVP and arterial pressure to the AV3V infusion of SNP. Hemoglobin or methylene blue given alone into the AV3V did not affect any of the variables monitored. On the other hand, the AV3V injection of 8-bromo cGMP, a stable analogue of cGMP, was not potent for causing a significant rise in plasma AVP, in contrast to the notable AVP-enhancing effect of 8-bromo cAMP. Arterial pressure and heart rate were elevated by both of these agents, whereas the remaining variables were not altered. Histological inspection indicated that the infusion sites of the drugs in the AV3V had included areas such as the organum vasculosum of the lamina terminalis, median preoptic nucleus, medial preoptic nucleus and periventricular nucleus. On the basis of these results, we concluded that the AVP secretion prompted by the AV3V application of SNP may be attributable to NO, whereas its well-known ability to stimulate guanylate cyclase activity may hardly contribute to this phenomenon.

Central control mechanisms of circulation in the medulla oblongata by nitric oxide

Nitric oxide (NO) is involved in numerous physiological functions. Besides its role as an endothelium-dependent relaxing factor (EDRF), NO inhibits platelet aggregation, contributes to cytotoxicity against bacteria, is active in synaptic transmission within the brain, etc. NO synthase (NOS) is distributed in brain regions related to the regulation of cardiovascular functions. NO has been inferred not only to act directly on vascular vessels, but also to regulate circulation within the brain. In this review paper, we mainly consider the functions of NO in the cardiovascular center of the medulla oblongata. That is, we describe the anatomical distribution of NOS in the brain, effects of intravenous and intracerebroventricular administration of NOS inhibitors on the circulation, effects of microinjection of NO donors and NOS inhibitors into the nucleus tractus solitarius (NTS) and ventrolateral medulla (VLM), the results of electrophysiological studies on these areas, and finally, the data obtained by new molecular biological techniques.

Injection of antisense oligos to nNOS into nucleus tractus solitarii increases blood pressure

We investigated the cardiovascular effects of bilateral microinjection of antisense oligodeoxynucleotides (oligos) into the nucleus tractus solitarii (NTS) to neuronal nitric oxide synthase (nNOS) to suppress the expression of nNOS molecular biologically. In urethane-anesthetized, paralyzed Wistar-Kyoto rats, bilateral microinjection of nNOS antisense oligos (20 pmol in a 50nl volume) into the NTS produced a significant increase in mean arterial blood pressure at 30-60min after injection, compared with rats injected with nNOS sense or scrambled oligos. Immunohistochemical study demonstrated that nNOS immunoreactivity in the rat NTS was suppressed by nNOS antisense oligos. These results indicate that suppression of the nNOS gene using antisense in the NTS increases blood pressure.

Neural mechanisms in nitric-oxide-deficient hypertension

Nitric oxide is hypothesized to be an inhibitory modulator of central sympathetic nervous outflow, and deficient neuronal nitric oxide production to cause sympathetic overactivity, which then contributes to nitric-oxide-deficient hypertension. The biochemical and neuroanatomical basis for this concept revolves around nitric oxide modulation of glutamatergic neurotransmission within brainstem vasomotor centers. The functional consequence of neuronal nitric oxide in blood pressure regulation is, however, marked by an apparent conflict in the literature. On one hand, conscious animal studies using sympathetic blockade suggest a significant role for neuronal nitric oxide deficiency in the development of nitric-oxide-deficient hypertension, and on the other hand, there is evidence against such a role derived from 'knock-out' mice lacking nitric-oxide synthase 1, the major source of neuronal nitric oxide.