Glutamate receptors in RVLM modulate sympathetic baroreflex in conscious rabbits

In this study, we examined the effect of excitatory amino acid (EAA) receptor blockade in the rostral ventrolateral medulla (RVLM) on the renal sympathetic baroreflex in conscious rabbits. Rabbits were implanted with guide cannulas for bilateral microinjections into the RVLM (+2 to +3 mm from the obex, n = 8) or into the intermediate ventrolateral medulla (IVLM; 0 to +1 mm from the obex, n = 5) and with an electrode for measuring renal sympathetic nerve activity (RSNA). After 7 days of recovery, microinjection of the EAA receptor antagonist kynurenate (10 nmol) into the RVLM did not affect resting RSNA or arterial pressure. Kynurenate decreased the gain of the RSNA baroreflex by 53% but did not change the reflex range. By contrast, injection of kynurenate into the IVLM increased resting arterial pressure and RSNA by 27 mmHg and 88%, respectively, but did not alter the RSNA baroreflex gain or range. Pentobarbital sodium anesthesia attenuated the gain and range of the RSNA baroreflex by 78 and 40%, respectively. Under these conditions, microinjection of kynurenate into the RVLM did not cause any further change in the gain of this reflex. These results suggest that endogenous EAA neurotransmitters in the RVLM are important in modulating the sympathetic baroreflex in conscious rabbits. Anesthesia can mask the functional significance of EAAs in the RVLM in modulating the baroreflexes, which may explain why previous studies in anesthetized animals found no effect of blocking EAA receptors in the RVLM on sympathetic baroreflexes.

Neuropeptide Y and Y1-receptor agonists increase blood flow through arteriovenous anastomoses in rat tail

The purpose of this study was to characterize neuropeptide Y (NPY)-induced vasodilation in the rat tail. Sterile surgical technique was used (with pentobarbital sodium anesthesia) to equip rats with a jugular catheter and a blind-ended thermocouple reentrant tube next to the carotid artery. Tail skin and core temperature were measured with thermocouples during experiments. Tail skin blood flow was monitored with a laser Doppler flowmeter, and tail total blood flow and volume were measured with plethysmography. After baseline data were collected, saline, NPY (16, 32, 64, and 128 μg/kg), [Leu31Pro34]NPY (63.25 μg/kg), or NPY[13–36] (44.7 μg/kg) was administered intravenously. Tail total blood flow, volume, and tail skin temperature increased, whereas tail skin blood flow and core temperature decreased in response to both NPY- and the Y1-receptor agonist [Leu31Pro34]NPY but not in response to saline or NPY[13–36]. Studies conducted with the use of color microspheres demonstrated that arteriovenous anastomoses are involved in this NPY-induced vasodilation.

A new approach to normalize myocardial temperature in the open-chest pig model

To prevent unphysiological temperature fluctuations in the myocardium in the open-chest model, we constructed a thermocage. Five pigs under pentobarbital sodium anesthesia underwent repetitive left anterior descending (LAD) coronary artery occlusions. Myocardial temperature was measured without any thoracic temperature-controlling device and in the presence of either a heating lamp or the thermocage. Without any thoracic temperature-controlling device, the temperature at 5-mm myocardial depth was 1.28 ± 0.33°C below the intra-abdominal temperature ( P < 0.05). During a proximal 5-min LAD occlusion, myocardial temperature decreased by 1.86 ± 1.02°C in the ischemic area ( P < 0.05). Both the heating lamp and the thermocage abolished the difference between intra-abdominal and myocardial temperatures and prevented the decrease in myocardial temperature during ischemia. Only the thermocage minimized myocardial temperature fluctuations due to air currents and prevented epicardial exsiccation. We conclude that either a thermocage or a heating lamp may be used to normalize myocardial temperature in the open-chest pig model. However, the thermocage is superior to the lamp in minimizing temperature fluctuations and preventing epicardial exsiccation.

Urinary acidification and net acid excretion in adult rats treated neonatally with enalapril

Neonatal blockade of the renin-angiotensin system in rats induces irreversible renal histological abnormalities, including papillary atrophy and an impaired urinary concentrating ability. The aim was to investigate urinary acidification and net acid excretion in adult Wistar rats treated neonatally with enalapril (10 mg ⋅ kg−1 ⋅ day−1) or vehicle from 5 to 24 days of age. Analyses were performed in both metabolic balance studies and renal clearance experiments performed under pentobarbital sodium anesthesia. There were no differences between groups in urine pH or urinary excretion rates of bicarbonate, titratable acid, or ammonium, neither during control conditions nor after chronic NH4Cl loading (assessed before and after Na2SO4infusion). Glomerular filtration rate, maximal tubular bicarbonate reabsorption, and the urine-to-blood[Formula: see text] gradient in alkaline urine during NaHCO3 infusion did not differ between groups. Neonatally enalapril-treated rats showed a urine concentration defect and papillary damage. In conclusion, neonatal enalapril treatment produces a differentiated abnormality in tubular function in which urine concentration is impaired but urinary acidification and net acid excretion are intact.

Direct measurement of nitric oxide release in gastric mucosa during ischemia-reperfusion in rats

Nitric oxide (NO) generation in the rat gastric mucosa during ischemia-reperfusion was measured using an NO-sensitive electrode. Under pentobarbital sodium anesthesia, an electrode was inserted into the submucosa from the serous membrane side in the fundus. After steady-state baseline recording, the celiac artery was clamped for 30 min, and then ischemia-reperfusion was achieved by removing the clamp. The clamping of the celiac artery caused a decrease in blood flow and an increase in NO level in the gastric tissue. Just after the removal of the clamp, the NO level rapidly fell and returned to the baseline level. Administration of N G-nitro-l-arginine methyl ester (an NO synthase inhibitor, 30 mg/kg ip) before ischemia significantly attenuated both the increase in NO level during ischemia and the formation of acute gastric mucosal lesions observed after 60 min reperfusion. Administration of superoxide dismutase (a superoxide radical scavenger, 10,000 U/kg iv) at the end of ischemia inhibited both the rapid decrease in NO level during the reperfusion and the gastric mucosal erosions. Because NO and superoxide radical produce a highly reactive peroxynitrite, it can be argued that NO has an important pathological role in acute gastric mucosal injury induced by ischemia-reperfusion. Our conclusion was strongly supported by immunohistochemical staining of nitrotyrosine residues, an indication of peroxynitrite formation.

Glycyl-l-glutamine [β-endorphin-(30—31)] attenuates hemorrhagic hypotension in conscious rats

The profound hypotension caused by acute hemorrhage is thought to involve opioid peptide neurons. In this study, we tested whether glycyl-l-glutamine [Gly-Gln; β-endorphin-(30—31)], a nonopioid peptide derived from β-endorphin processing, prevents the cardiovascular depression induced by hemorrhage in conscious and anesthetized rats. Previously, we found that Gly-Gln inhibits the hypotension and respiratory depression produced by β-endorphin and morphine but does not affect opioid antinociception. Hemorrhage (2.5 ml/100 g body wt over 20 min) lowered arterial pressure in conscious rats (from 120.1 ± 2.9 to 56.2 ± 4.7 mmHg) but did not change heart rate significantly. Intracerebroventricular Gly-Gln (3, 10, or 30 nmol) pretreatment inhibited the fall in arterial pressure and increased heart rate significantly. The response was dose related and was sustained during the 35-min posthemorrhage interval. Pentobarbital sodium anesthesia potentiated the hemodynamic response to hemorrhage and attenuated the effect of Gly-Gln. Gly-Gln (10 or 100 nmol icv) did not influence arterial pressure or heart rate in normotensive rats. These data indicate that Gly-Gln is an effective antagonist of hemorrhagic hypotension.

Insulin is degraded extracellularly in wounds by insulin-degrading enzyme (EC 3.4.24.56)

The exact mechanism by which insulin reverses impaired wound healing is unknown. Previous investigators have shown that insulin is degraded in experimental wounds, suggesting that the action of insulin may be locally modified. The following study corroborates these findings and identifies the major proteinase responsible for insulin degradation in wound fluid (WF). Adult male Fisher rats were wounded by subcutaneous implantation of polyvinyl alcohol sponges while under pentobarbital sodium anesthesia. WF and serum were collected on 1, 5, 10, and 14 days postinjury. Decreased insulin concentration in late WF correlated with an increased insulin-degrading activity. Multiple proteinases appear to participate in the overall degradation of insulin in WF. However, the primary enzyme responsible for insulin degradation in WF was characterized by immunoprecipitation and immunoblotting and identified as the neutral thiol-dependent metalloproteinase, insulin-degrading enzyme (EC 3.4.24.56 ). Exogenous steroid administration caused a decrease in WF insulin-degrading activity. Glucagon and adrenocorticotrophin degradation was also observed, whereas minimal degradation of insulin-like growth factors I and II and epidermal growth factor was detected in WF. The ability to extracellularly degrade insulin may represent a unique mechanism for the regulation of this hormone’s role in healing wounds.

Potentiation to vasodilators by nitric oxide synthase blockade in superior mesenteric but not hepatic artery

Our objective was to determine the vasodilator effect of adenosine and isoproterenol on the hepatic artery (HA) and superior mesenteric artery (SMA) before and after blockade of nitric oxide (NO) production to evaluate the possibility of organ specificity. Vascular circuits supplied blood flow to the liver or intestine in cats under pentobarbital sodium anesthesia. The NO synthase (NOS) antagonist N(G)-nitro-L-arginine methyl ester (L-NAME; 2.5 mg/kg iv) increased arterial pressure from 106.4 +/- 7.6 to 141.4 +/- 8.1 mmHg and raised basal vascular tone in the SMA but not in the HA. The NOS substrate L-arginine (75 mg/kg) reversed these effects. The decrease in perfusion pressure in response to adenosine was 51.7 +/- 2.9, 135.2 +/- 6.1, and 16.7 +/- 2.4 mmHg, respectively, for control and after L-NAME and L-arginine. Isoproterenol was also potentiated in the SMA. Adenosine and isoproterenol were not potentiated in the HA by L-NAME. Potentiation did not occur when HA or SMA basal tone was elevated by norepinephrine. In conclusion, L-NAME increased basal tone for the SMA and potentiated the dilation induced by adenosine and isoproterenol in the SMA but not in the HA. This study provides evidence that there is a highly organ-specific compensatory mechanism in which the absence of NO promotes potentiation of other vasodilators.

The effect of GIP and glucagon-like peptides on intestinal basolateral membrane hexose transport

The effect of gastric inhibitory polypeptide (GIP) and the related glucagon-like peptides-1 and -2 (GLP-1 and GLP-2) on jejunal basolateral membrane glucose transport was investigated to determine if the upregulation produced by luminal hexoses could be explained by the release of one or more of these peptides. Luminal perfusion of the rat jejunum for 4 h, under pentobarbital sodium anesthesia, with 100 mM D-glucose produced a significant increase in plasma GIP levels. Vascular infusion of saline containing 100-800 pM GIP also increased the maximal transport rate for carrier-mediated glucose uptake in jejunal basolateral membrane vesicles. The effect of vascular 400 pM GIP was maximal after 1 h and maintained out to 4 h. The effect of luminal glucose could be blocked by preinjection with anti-GIP antibodies, whereas an antineurotensin antibody had no effect. Vascular infusion with 800 pM GLP-1-(7-36) amide had no effect, but GLP-2 (400 and 800 pM) increased the D-glucose maximal transport rate. An anti-GLP antibody was able to block the response to luminal glucose.