Comparative haemodynamic studies of resting and active skeletal muscle in anaesthetised rats: role of nitric oxide

Our previous studies have indicated that nitric oxide takes part in the basal regulation of vascular tone in skeletal muscle. The purpose of this study was to investigate whether nitric oxide has a role in the active hyperaemic response of a working muscle in a resting subject. Haemodynamic effects of nitric oxide synthase (NOS) inhibition (L-NAME, 10 mg/kg/30 min i.v. infusion) were determined simultaneously in the resting m. quadriceps femoris and in the working (breathing) m. rectus abdominis in anaesthetised rats (86Rb accumulation technique). L-NAME increased blood pressure and total peripheral resistance (TPR) while it decreased cardiac output. Blood flow (BF) decreased and vascular resistance (VR) increased both in resting (BF: 8.91+/-1.97-->5.92+/-2.59 ml/min/100 g, p<0.05: VR: 106+/-29.9-->212+/-113 R, p<0.01) and working (BF: 17.0+/-4.78-->6.93+/-2.15 ml/min/100 g, p<0.001; VR: 57.0+/-18.5-->160+/-56.7 R, p<0.01) muscle following NOS inhibition, but the percentile change of BF was higher in the working muscle (59%) than in the resting one (34%, p<0.001). There was a positive correlation between the cardiac output and the blood flow of the resting muscle with or without L-NAME administration, but blood flow of the working muscle failed to have any correlation with the cardiac output in control animals. However, L-NAME administration decreased both the cardiac output and the blood flow and similarly to the resting muscle a positive correlation was found. In conclusion, the haemodynamic effects of NOS inhibition are higher in working muscle than in the resting one: the nitric oxide may have important role in vasodilatation during muscle activity.

Nitric oxide synthase inhibitor L-NAME has no effect on 86Rb accumulation in rat renal cortical slices

The aim of present study was to investigate the effect of the nitric oxide synthase inhibitor L-NAME on the 86Rb uptake in rat renal cortical slices. Rats were divided into three groups: 1. CONTROL. 2. Acute: L-NAME (10 mg/kg i.v.) as a bolus 15 min before the excision of the kidneys. 3. Sub-chronic: L-NAME (10 mg/kg/day) per os for 4 days. Renal cortical slices were incubated for 10, 20, 30, 60, 90, 180 seconds in Krebs-Ringer solution containing 50 kBq 86Rb/100 ml (T = 37 degrees C, PO2 approximately 159 mm Hg). 56Rb accumulation (S/M) was calculated as the ratio of the radioactivity of the cortical slices (S) and the radioactivity of the incubating medium (M). The S/M ratio can be described as a function of time by the following equations.

CONTROL

y = 0.265 ln(x) - 0.220, r(xy) = 0.886; acute L-NAME: y = 0.224 ln(x) - 0.171, r(xy) = 0.921; sub-chronic L-NAME: y = 0.331 ln(x) - 0.496, r(xy) = 0.942. (y = S/M, x = t). p < 0.001 in all of the groups, but there is no difference between the groups. In conclusion, L-NAME administered in vivo failed to influence the in vitro 86Rb accumulation in rat renal cortical slices.

Intrarenal distribution of blood flow in sodium depleted and sodium loaded rats: role of nitric oxide

The renal hemodynamic effects of nitric oxide synthase (NOS) inhibition and dietary salt were studied in rats. L-NAME (0.1 mg/ml in the drinking fluid, about 12 mg/kg/day) was given for 4 days to rats receiving low (sodium depletion, SD), normal (N) or high (sodium load, SL) NaCl diet. Intrarenal hemodynamics was studied in anaesthesia. NOS inhibition decreased renal blood flow and increased renal vascular resistance in each group. Cortical and outer medullary but not inner medullary blood flow increased in direct ratio to the sodium intake. NOS inhibition decreased the blood flow and increased the vascular resistance in all layers of the kidney in SD, N, and SL rats as well. In SD and N, but not in SL rats L-NAME induced vasoconstriction was higher in the outer (OM) and inner medulla (IM) than in the cortex (C) [SD: DeltaCVR 43%, DeltaOMVR 54%, DeltaIMVR 84%; N: DeltaCVR 54%, DeltaOMVR 96%, DeltaIMVR 106%; SL: DeltaCVR 50%, DeltaOMVR 64%, DeltaIMVR 35%]; in normal rats blood flow shifts from the medulla toward the cortex. In conclusion, nitric oxide may have a role in the regulation of renal vascular tone not only in the case of regular sodium uptake but in the sodium depleted or loaded organism as well. However, nitric oxide has no role in the dietary salt evoked vascular adaptation in the kidney.

Role of nitric oxide in the regulation of blood flow in the rat submandibular gland during carotid artery occlusion

The possible involvement of nitric oxide in the preservation of blood flow to the rat submandibular gland after uni- or bilateral occlusion of the common carotid was studied. Glandular blood flow and mean blood pressure were monitored before, during and after carotid occlusion in the presence and absence of the nitric oxide synthase inhibitor N(omega)-nitro-L-arginine-methyl-ester (L-NAME). To calculate vascular resistance, the local perfusion pressure distal to the point of occlusion was also measured. In normal rats, uni- or bilateral carotid occlusion resulted in an immediate decrease in ipsilateral glandular blood flow. After the cessation of carotid occlusion, hyperaemia was observed in the submandibular gland. Both local perfusion pressure and vascular resistance decreased during carotid occlusion. In the group pretreated with L-NAME, trends in blood-flow responses to uni- or bilateral occlusion were identical to those registered in the control groups, though the magnitude of the alterations was significantly less. The well-maintained glandular blood flow was due to functioning vascular anastomoses and compensating dilatation of glandular blood vessels. Nitric oxide had only a restrained effect on this compensatory mechanism.

Effect of nitric oxide synthase inhibition on renal circulation and excretory function in anaesthetized rats

The effects of nitric oxide synthase (NOS) inhibition (effected using L-NAME, 14 mg (kg body mass (BM))(-1), administered intravenously) on systemic and renal circulation and renal excretory function has been investigated in anaesthetized Wistar rats subjected to one of two different degrees of isotonic extracellular (EC) volume expansion (40 and 60 ml x kg(-1) (240 min)(-1)). The administration of L-NAME resulted in an increase in mean arterial blood pressure and total peripheral vascular resistance (TPR), and a significant reduction in cardiac output (CO) and the kidney fraction of CO in both experimental groups. The total renal blood flow (RBF) dropped from 557 + 43.4 to 149 +/- 13.1 ml x min(-1) (100 g BM)(-1) and from 592 +/- 45.9 to 191 +/- 16.3 ml x min(-1) (100 g BM)(-1) in the 40 and 60 ml x kg(-1) (240 min)(-1) experimental volume expansion groups, respectively. A redistribution of the intrarenal circulation from the medulla of the kidney toward the cortex may have occurred. The NOS inhibition induced a significant decrease in the glomerular filtration rate (GFR; from 1.18 +/- 0.10 to 0.53 +/- 0.08 ml x min(-1) (100 g BM)(-1) and from 1.26 +/- 0.07 to 0.73 +/- 0.08 ml x min(-1) (100 g BM)(-1) in the 40 and 60 ml x kg(-1) (240 min)(-1) experimental volume expansion groups, respectively), and the filtration fraction increased. The urine excretion dropped in parallel with the GFR, while the reduction in sodium and potassium excretion was more marked than that of the GFR, raising the possibility of a direct effect on the kidney tubules. The difference in EC volume expansion (the calculated increases in the EC volume in the last 90 min were 1.30 and 5.44% in the two time control groups and 3.66 and 7.45% in the two L-NAME-treated groups) did not induce any significant modification of the L-NAME effect.

Blood flow of the right and left submandibular gland during unilateral carotid artery occlusion in rat: role of nitric oxide

The aim of the present study was to investigate the effect of unilateral carotid artery occlusion on the blood flow of submandibular gland in anesthetized rats and identify the role of nitric oxide (NO) in blood flow changes after the artery occlusion. L-NAME (N omega-nitro-L-arginine-methyl-ester; 10 mg/kg/day, per os) dissolved in tap water was used to block nitric oxide synthase. Glandular blood flow was measured using Sapirstein's indicator (86Rb) distribution technique. In the control animals the blood flow of left (ligated side) submandibular gland was lower than in the right (unligated side) one (right: 76.4+/-15.4 ml/min/100 g, 64.1+/-13.4 ml/min/100 g, p<0.01). The blood flow of submandibular glands decreased in NOS blocked group versus control. The vascular resistance after L-NAME treatment was elevated (control: 11+/-2.3 R/kg, L-NAME: 17.5+/-4.1 R/kg, p<0.001). In L-NAME group the difference between blood flow value of the left and right submandibular gland was significantly lower than in the control group (control: -16%, NAME: -8%, p<0.01).

CONCLUSION

The maintenance of the blood flow in the left submandibular gland during ligation of the left common carotid artery could be due to the good vascular anastomotic system at these regions and adaptation of the submandibular vessels to the decreased perfusion pressure. Nitric oxide may have a role in the regulation of blood flow tinder this condition.

Nitric oxide synthase inhibition increases vascular resistance in sodium and water loaded rats

The aim of this study was to investigate whether nitric oxide might be involved in the adaptation of the cardiovascular system in sodium and water loaded organisms. The effects of a semi-chronic (4 day) inhibition of nitric oxide production were studied in normovolemic and per os sodium and water loaded rats. Nitric oxide synthase was inhibited by L-NAME (10 mg/kg in normovolemic and 14 mg/kg in sodium loaded rats) dissolved in the drinking solution. Blood pressure, cardiac output (Stewart-Hamilton's principle) and its regional fractions (Sapirstein's technique using 86Rb isotope as indicator), total peripheral resistance and regional vascular resistances were determined on the 5th day in sodium pentobarbital anaesthesia. The increase in blood pressure following L-NAME pretreatment in both groups was similar, but the elevation of total peripheral resistance was 106% in normovolemic and only 30% in sodium loaded animals. The cardiac output decreased by 44% in normovolemic and 14% in sodium loaded groups after nitric oxide synthase inhibition. The organ vascular resistances increased and organ blood flows decreased after L-NAME administration. These changes were less pronounced in sodium and water load, especially those in the skeletal muscle and intestine. Nitric oxide-induced changes in vascular resistance are more pronounced in normovolemia than in sodium load; sodium load might influence the nitric oxide production. The share of nitric oxide in the setting of vascular tone is different in the various organs.

Blood flow of the submandibular gland in sodium-depleted and -loaded rats: effect of nitric oxide synthase inhibition

The present investigations were designed to study the hemodynamic effects of different sodium diets in the submandibular gland of rats with or without nitric oxide (NO) synthesis inhibition. Experimental animals were kept on: (1) standard chow and tap water ad libitum (normal group, N), or (2) wheat and distilled water ad libitum for 4 weeks (sodium-depleted animals, SD), or (3) standard chow and saline ad libitum for 4 weeks (sodium-loaded animals, SL). NO synthase was inhibited by N omega-nitro-L-arginine-methyl-ester (L-NAME, 10 mg/kg per day) in the last week. The rats were anesthetized, and blood pressure, cardiac output (Stewart-Hamilton's principle) and blood flow (BF) of the submandibular gland (Sapirstein's technique) were determined. High sodium intake resulted in a 47% increase of glandular BF as compared to BF measured in the control group. In all groups L-NAME decreased BF (ml/min per 100 g gland) as compared to those of rats with no L-NAME treatment (N: 76.4 +/- 15.4 vs. 56.0 +/- 11.6, P < 0.05; SD: 71.0 +/- 17.7 vs. 56.2 +/- 15.1, n.s.; SL: 112 +/- 29.4 vs. 66.9 +/- 18.4, P < 0.001), whereas the vascular resistance (VR, mm Hg x ml-1 x s x kg-1) increased (N: 11.0 +/- 2.3 vs. 17.5 +/- 4.1, P < 0.001; SD: 11.0 +/- 2.7 vs. 17.0 +/- 4.2, P < 0.01; SL: 8.5 +/- 2.4 vs. 14.9 +/- 4.6, P < 0.001). The increase in VR after L-NAME treatment was 64% in normal, 55% in sodium-depleted and 75% in sodium-loaded rats. Our results suggest that NO takes part in the regulation of vascular resistance and BF in the submandibular gland. Sodium load itself increases BF of the submandibular gland and this phenomenon may partly be mediated by NO.

Effect of neonatal sympathectomy by 6-hydroxydopamine on renal hemodynamic parameters in adult rats

Newborn rats were sympathectomized with 6-hydroxydopamine (6-OHDA) (10 mg/100 g b.w., once daily on the first 4 postnatal days). Hemodynamic parameters were determined at the 55th d of life. In comparison to non-sympathectomized control rats the blood pressure and total peripheral resistance of 6-OHDA treated animals were significantly diminished whereas the cardiac output was enhanced. In sympathectomized rats the resistance values of the whole kidney as well as of the cortex and outer medulla were lower than in control animals. No redistribution of renal blood flow was detectable. The results show a long lasting effect of neonatal denervation by 6-OHDA at least up to the 55th d of life.

Effects of indomethacin and naproxen on renal p-amino-hippurate (PAH) excretion in rats during postnatal development

Effects of the cyclooxygenase inhibitors indomethacin and naproxen on renal PAH excretion were studied in volume-expanded and sodium-loaded, conscious rats of different ages. Indomethacin and naproxen reduce renal PAH excretion in 5- and 10-day-old rats but not in rats of older ages. Findings can be explained by a decrease in glomerular filtration rate. In addition, a competitive inhibition of PAH transport by the organic acids indomethacin and naproxen must be mentioned. Until now it is not known whether or not there is a direct or indirect influence of prostaglandins on processes involved in tubular PAH transport.

Renal blood flow after stimulation of p-aminohippurate transport

Repeated administration of cyclopenthiazide enhances renal PAH excretion in rats. In the 1st hr after an acute PAH load the renal excretion of PAH is doubled compared with controls. Haemodynamic measurements show that this acute PAH load is related to an increase in renal blood flow, in particular to a distinct increase in blood flow in the renal cortex. This increase in renal blood flow and in intrarenal blood distribution is higher than in stimulated rats. The increase in renal excretion of PAH is stimulated rats is not connected with an increase in renal blood flow. After an acute PAH load an additional increase in renal blood flow in stimulated rats could not be observed as compared with non stimulated control rats.