The fate of circulating biologically active peptides in the lungs

The factors which regulate the disappearance of endogenous active substances during pulmonary transit are discussed. The presence of hydrolytic enzymes in the cytosol is not the only factor regulating pulmonary metabolism. An uptake-transport process is required to permit access to intracellular enzymes. No endothelial cell transport mechanism has yet been described for peptides. However, bradykinin and angiotensin I are metabolized by the pulmonary circulation because the enzyme is localized on the luminal surface of the endothelial cells. The pulmonary and extrapulmonary conversion of angiotensin in rat is still a matter of debate. Evidence is presented which supports the idea that when low doses of angiotensin I (greater than 10 ng) are given intravenously, most of the conversion is pulmonary. With higher doses, extrapulmonary conversion also contributes to the final pressor effect of angiotensin I.

Transcriptional regulation of glucose-6-phosphatase catalytic subunit promoter by insulin and glucose in the carnivorous fish, Sparus aurata

Increase in glucose-6-phosphatase catalytic subunit (G6Pase, G6pc) transcription enhances hepatic glucose production in non-insulin-dependent diabetes mellitus (NIDDM). The fact that carnivorous fish is an alternative model to study NIDDM led us to clone and characterise the first G6pc promoter region reported for fish and non-mammalian animals. The 5'-flanking region of G6pc from gilthead sea bream (Sparus aurata) was isolated by chromosome walking. With SMART RACE-PCR, the transcription start site was located 106 base pairs (bp) upstream of the translational start. Transfection analysis in HepG2 cells located a functional promoter in the 850 bp 5'-flanking isolated fragment (positions -770 to +80 relative to the transcription start). Sequential 5'-deletion analysis of the promoter fragment revealed that a core functional promoter for basal transcription is comprised within the 190 bp upstream of the transcription start site. In vivo, glucose and insulin reduced G6Pase mRNA levels in the fish liver. Transfection experiments in HepG2 cells showed that insulin repressed S. aurata G6pc under high-glucose conditions. Synergistic activation of piscine G6pc promoter was induced by cotransfection with expression plasmids for hepatocyte nuclear factor-4alpha (HNF-4alpha) and peroxisome proliferator-activated receptor-gamma coactivator-1 (PGC-1alpha). No direct relationship was found between PGC-1alpha coactivation of HNF-4alpha transactivation and the repressive effect of insulin. Interestingly, insulin hardly affected G6pc promoter activity in the absence of glucose, suggesting that a reduced capacity of insulin-dependent repression of piscine G6pc may lead to insulin resistance in carnivorous fish.

Nonendothelial NO blunts sympathetic response of normotensive rats but not of SHR

The inhibitory role of NO on sympathetic-induced contraction of resistance vessels of spontaneously hypertensive rats (SHR) has not been defined. Accordingly, we investigated the effect of endothelial removal or NO synthase inhibition on vasoconstrictor responses to sympathetic stimulation or phenylephrine in perfused mesenteric beds isolated from normotensive rats (NR) and SHR. Electrical stimulation (10 to 64 Hz) of perivascular nerves elicited a frequency-dependent increase in perfusion pressure that was greater in preparations from SHR (maximal effect: 223.4+/-8.4 versus 117.6+/-10.3 mm Hg in NR, n=6, P<0.001), and endothelium removal did not affect these responses in arteries from NR but caused a significant shift to the left of the frequency-response curve in arteries from SHR. In arteries with endothelium, inhibition of NO synthase with N(G)-nitro-L-arginine (L-NNA, 50 micromol/L) augmented the vasoconstrictor responses to sympathetic stimulation in both NR and SHR preparations. In preparations that had the endothelium removed, however, L-NNA potentiated only the responses to sympathetic stimulation of NR arteries. Vasoconstrictor responses to phenylephrine was potentiated by endothelium removal and in the presence of L-NNA only when the endothelium was intact in both NR and SHR arteries. The number of NADPH-diaphorase-positive cells in the superior mesenteric sympathetic ganglion of SHR was significantly less compared with that of NR. In conclusion, these data suggest a prejunctional inhibitory action of non-endothelial-derived NO, most probably neuronal-derived NO, on sympathetic-mediated vasoconstriction in NR arteries. In contrast, enhancement of the sympathetic-mediated vasoconstriction in SHR arteries elicited by L-NNA can be attributed to inhibition of endothelial-derived NO.

Cardiac sympathetic overactivity and decreased baroreflex sensitivity in L-NAME hypertensive rats

The present study evaluated the possible changes in the autonomic control of heart rate in the hypertensive model induced by the inhibition of nitric oxide synthase. Rats were treated with N(G)-nitro-L-arginine methyl ester (L-NAME group) in the drinking water during 7 days, whereas control groups were treated with tap water (control group) or with the N(G)-nitro-D-arginine methyl ester (D-NAME group), an inactive isomer of the L-NAME molecule. The L-NAME group developed hypertension and tachycardia. The sequential blockade of the autonomic influences with propranolol and methylatropine indicated that the intrinsic heart rate did not differ among groups and revealed a sympathetic overactivity in the control of heart rate in the L-NAME group. The spectral density power of heart rate, calculated using fast-Fourier transformation, indicated a reduced variability in the low-frequency band (0.20-0.60 Hz) for the L-NAME group. The baroreflex sensitivity was also attenuated in these animals when compared with the normotensive control or D-NAME group. Overall, these data indicate cardiac sympathetic overactivity associated with a decreased baroreflex sensitivity in L-NAME hypertensive rats.

Enalapril prevents aortic hyperreactivity and remodelling in one-kidney, one-clip hypertensive rats without reducing arterial pressure

1. The present study was designed to evaluate the blood pressure-independent effects of angiotensin-converting enzyme (ACE) inhibition on cardiovascular structure and function in one-kidney, one-clip (1K1C) hypertensive rats. 2. The study was conducted in four groups of rats: (i) uninephrectomized normotensive rats (1K); (ii) 1K1C hypertensive rats; (iii) 1K rats treated with enalapril; and (iv) 1K1C rats treated with enalapril. Enalapril treatment (20 mg/kg per day, p.o.) was started after surgery to induce hypertension or nephrectomy and continued for 5 weeks. 3. The increase in blood pressure of 1K1C rats was associated with activation of cardiac and aortic, but not plasma, ACE activity and with hypertrophy of both heart and aorta. No difference in cardiac output and in vitro systolic function was observed among the groups. Hypertrophied aorta isolated from 1K1C rats displayed increased sensitivity to phenylephrine (PE) and unaltered responses to both acetylcholine (ACh) and sodium nitroprusside compared with the 1K group. 4. Enalapril treatment effectively inhibited plasma and tissue ACE activity in 1K1C and 1K rats. Enalapril did not prevent the development of hypertension and cardiac hypertrophy nor did it change haemodynamic parameters in 1K1C rats. However, enalapril prevented the increase in aortic media thickness and cross-sectional area and restored the hypersensitivity to PE in aortic rings of 1K1C rats. The endothelium-dependent response to ACh was enhanced by enalapril in the aorta of 1K but not 1K1C rats. 5. These results suggest a role for activated local angiotensin II generation in aortic but not cardiac hypertrophy secondary to 1K1C hypertension.

Effect of captopril on neurally induced contraction and relaxation of mesenteric arteries of renal hypertensive rats

The effect of captopril treatment on neurally induced vasoconstrictor and vasodilator responses was examined in the isolated mesenteric arterial bed from normotensive and one-kidney, one clip hypertensive (1K1C) rats. In isolated mesenteric beds, electrical field stimulation (EFS) of perivascular nerves at basal tone induced a frequency-dependent increase in perfusion pressure that was greater in preparations from hypertensive rats compared with those from normotensive rats. Captopril treatment was associated with a decrease in vasoconstrictor responses in the hypertensive group compared with its non-treated control. Responses to norepinephrine (320 ng) were greater in hypertensive than normotensive groups; captopril reduced this response only in the hypertensive group. In preconstricted mesenteric arteries perfused with solutions containing guanethidine (5 microM) and atropine (1 microM), EFS elicited a frequency-dependent decrease in perfusion pressure that was abolished by tetrodotoxin (1 microM). Vasodilator responses to EFS were not affected by captopril treatment, although they were smaller in the hypertensive group. Acetylcholine (10 ng) induced similar decreases in perfusion pressure of normotensive and 1K1C groups; captopril did not influence these responses. These results indicate that captopril treatment does not affect the reduced neurogenic vasodilation but normalizes the augmented sympathetic-mediated vasoconstrictor responses of mesenteric resistance vessels of chronic 1K1C hypertensive rats.

Cardiovascular effects of clonidine-like drugs in pithed rabbits

Administration (3 to 100 microg/kg IV) of clonidine, rilmenidine, and an imidazoline derivative, 2-(2-chlorophenylamino)imidazoline, in pithed nonstimulated rabbits caused a dose-dependent increase in mean arterial pressure without affecting heart rate. Prazosin (0.1 mg/kg IV) almost abolished the pressor responses to 2-(2-chlorophenylamino)imidazoline, partially inhibited those induced by clonidine, but failed to affect those elicited by rilmenidine. In contrast, yohimbine (1 mg/kg IV) blunted the pressor responses of the 3 drugs. In sympathetically stimulated pithed rabbits, 2-(2-chlorophenylamino)imidazoline induced only pressor effects, whereas clonidine and rilmenidine caused a transient pressure increase followed by a dose-dependent depressor effect. Yohimbine abolished the depressor effect of both drugs, which may have involved presynaptic alpha(2)-adrenoceptors. In conclusion, peripheral effects of 2-(2-chlorophenylamino)imidazoline and clonidine involved at least alpha(1)- and alpha(2)-adrenoceptor activation, whereas pressor and depressor effects of rilmenidine were mediated by alpha(2)-adrenoceptors.

Purification and substrate specificity of an angiotensin converting elastase-2 from the rat mesenteric arterial bed perfusate

A soluble angiotensin (Ang) II-generating enzyme has been purified to homogeneity from the rat mesenteric arterial bed (MAB) perfusate by a combination of gel filtration and affinity chromatographies. The enzyme is a glycoprotein of 28.5 kDa (SDS-PAGE), whose N-terminal sequence is identical with that of the rat pancreatic elastase-2; therefore the enzyme will henceforth be referred to as rat MAB elastase-2. When Ang I was used as the substrate, the enzyme specifically released Ang II and the dipeptide His-Leu (Km=36 microM; Kcat=1530 min-1). The catalytic efficiency (Kcat/Km=42.5 min-1 microM-1) of this reaction was comparable to those of other known Ang I-converting enzymes. The proteolytic specificity of the purified enzyme toward mellitin, oxidized insulin B chain, somatostatin-14 and renin substrate tetradecapeptide suggested that the enzyme-substrate interaction was defined by an extended substrate binding site, typical of elastases-2 of pancreatic origin. According to the sensitivity of the rat MAB elastase-2 to various inhibitors this enzyme could be described as a member of the chymostatin-sensitive group of Ang II-forming serine proteases. The localization and biochemical properties of this enzyme suggest that it might play a role in the regional control of vascular tonus.

Role of non-nitric oxide non-prostaglandin endothelium-derived relaxing factor(s) in bradykinin vasodilation

The most conspicuous effect of bradykinin following its administration into the systemic circulation is a transient hypotension due to vasodilation. In the present study most of the available evidence regarding the mechanisms involved in bradykinin-induced arterial vasodilation is reviewed. It has become firmly established that in most species vasodilation in response to bradykinin is mediated by the release of endothelial relaxing factors following the activation of B2-receptors. Although in some cases the action of bradykinin is entirely mediated by the endothelial release of nitric oxide (NO) and/or prostacyclin (PGI2), a large amount of evidence has been accumulated during the last 10 years indicating that a non-NO/PGI2 factor accounts for bradykinin-induced vasodilation in a wide variety of perfused vascular beds and isolated small arteries from several species including humans. Since the effect of the non-NO/PGI2 endothelium-derived relaxing factor is practically abolished by disrupting the K+ electrochemical gradient together with the fact that bradykinin causes endothelium-dependent hyperpolarization of vascular smooth muscle cells, the action of such factor has been attributed to the opening of K+ channels in these cells. The pharmacological characteristics of these channels are not uniform among the different blood vessels in which they have been examined. Although there is some evidence indicating a role for KCa or KV channels, our findings in the mesenteric bed together with other reports indicate that the K+ channels involved do not correspond exactly to any of those already described. In addition, the chemical identity of such hyperpolarizing factor is still a matter of controversy. The postulated main contenders are epoxyeicosatrienoic acids or endocannabinoid agonists for the CB1-receptors. Based on the available reports and on data from our laboratory in the rat mesenteric bed, we conclude that the NO/PGI2-independent endothelium-dependent vasodilation induced by BK is unlikely to involve a cytochrome P450 arachidonic acid metabolite or an endocannabinoid agonist.

Influence of sympathetic blockade on the acute hypertensive response to aortic constriction

The objective of the present study was to determine the contribution of the sympathetic nervous system to the hypertensive response to acute (45-min) aortic coarctation in conscious intact or sinoaortic-denervated (SAD) rats. Rats were treated chronically (5 wk) with guanethidine (50 mg.kg-1.day-1 i.p.) to induce sympathetic nerve degeneration or acutely with the alpha 1-adrenergic receptor antagonist prazosin. (1 mg/kg i.v.). Aortic constriction elicited a prompt and sustained rise in mean carotid pressure that was significantly greater in SAD than in intact rats. The increase in pressure was associated with reflex bradycardia only in the intact rats, whereas the heart rate of SAD rats did not change. Guanethidine treatment did not affect the arterial pressure or heart rate responses to aortic coarctation of intact rats but blunted the hypertensive response of SAD rats to the same values exhibited by intact rats. Prazosin administered 10 min after the beginning of aortic coarctation reduced the hypertensive response of SAD rats to the same level as that of intact rats. In conclusion, the data obtained by means of the association of sinoaortic deafferentation with chronic sympathectomy with guanethidine or acute alpha 1-adrenergic receptor blockade with prazosin indicate that the greater hypertensive response of SAD rats involves a lack of suppression of the sympathetic activity in the maintenance of the rise in pressure elicited by aortic coarctation.

Heart rate variability and baroreceptor function in chronic diabetic rats

In conscious chronic (12 to 18 weeks) streptozotocin diabetic rats, we examined the changes in basal heart rate, with particular attention to heart rate variability assessed by evaluating the standard deviation (bpm) of the lengths of adjacent pulse pressure. We also investigated in anesthetized rats the ability of the aortic baroreceptors to acutely (30 minutes) reset to hypertensive levels. For this purpose, pressure-nerve activity curves for the baroreceptors were obtained, and gain (slope of the curve) and mean arterial pressure at 50% of maximal baroreceptor activity were calculated. The shift of the pressure-nerve activity curve was used as an index of resetting. Conscious diabetic rats (n=6) exhibited lower mean arterial pressure (93+/-6 versus 109+/-4 mm Hg), heart rate (272+/-25 versus 359+/-11 bpm), and heart rate variability (18+/-7 versus 36+/-6 bpm) than control rats (n=7). Under anesthesia, diabetic rats (n=7) and control rats (n=8) exhibited similar mean arterial pressure (113+/-6 versus 109+/-7 mm Hg in control rats ), mean arterial pressure at 50% of maximal baroreceptor activity (117+/-5 versus 107+/-6 bpm), gain (1.66+/-0.08 versus 1.81+/-0.05%/mm Hg), and extent of resetting (44+/-12 versus 49+/-9%) to hypertensive levels. The present study demonstrated that conscious chronic diabetic rats presented lower heart rate variability than control rats. On the other hand, chronic diabetes was not associated with alterations in baroreceptor function or its ability to rapidly reset to hypertensive levels.

Nitric oxide blunts sympathetic response of pregnant normotensive and hypertensive rat arteries

Rat pregnancy is associated with a blunted response to vasocontrictors both in vivo and in vitro as well as a decrease in arterial pressure. We examined the influence of pregnancy on neurally induced vasoconstrictor and vasodilator responses of the isolated mesenteric arterial bed from normotensive Wistar and spontaneously hypertensive nonpregnant and 20-day pregnant rats and determined the possible role of nitric oxide (NO) in modulating these responses. MAP (mm Hg) in pregnant normotensive (98+/-1, n=13) and hypertensive (136+/-5, n=13) rats was lower (P<.05) than in nonpregnant controls (114+/-2, n=14, and 174+/-3, n=12, respectively). In isolated mesenteric arterial beds, electrical field stimulation (EFS; 34 V, 3 ms, 10-64 Hz) of perivascular nerves at basal tone induced a frequency-dependent increase in perfusion pressure that was significantly (P<.001) greater in preparations from hypertensive compared with normotensive rats. Pregnancy was associated with a significant decrease in the maximal vasoconstrictor response elicited by EFS in both normotensive and hypertensive groups compared with their nonpregnant controls. In phenylephrine-preconstricted mesenteric beds, EFS (60 V, 1 ms, 1-8 Hz) elicited a similar frequency-dependent decrease in perfusion pressure in normotensive and hypertensive groups, but pregnancy did not influence these responses. In the presence of the NO synthase inhibitor N(omega)-nitro-L-arginine (200 micromol/L), the maximal vasoconstrictor response induced by EFS was significantly (P<.001) augmented in both normotensive and hypertensive groups, and the differences observed between pregnant and nonpregnant groups were abolished. Responses to sodium nitroprusside were not affected by pregnancy, although they were greater in preparations from hypertensive rats. These results indicate that NO contributes to pregnancy-associated diminished vasoconstrictor response to sympathetic stimulation in the mesenteric arterial bed of both normotensive and hypertensive rats.

Role of endothelium in angiotensin II formation by the rat aorta and mesenteric arterial bed

We investigated the angiotensin II (Ang II)-generating system by analyzing the vasoconstrictor effect of Ang II, angiotensin J (Ang I), and tetradecapeptide (TDP) renin substrate in the absence and presence of inhibitors of the renin-angiotensin system in isolated rat aortic rings and mesenteric arterial beds with and without functional endothelium. Ang II, Ang I, and TDP elicited a dose-dependent vasoconstrictor effect in both vascular preparations that was completely blocked by the Ang II receptor antagonist saralasin (50 nM). The angiotensin converting enzyme (ACE) inhibitor captopril (36 microM) completely inhibited the vasoconstrictor effect elicited by Ang I and TDP in aortic rings without affecting that of Ang II. In contrast, captopril (36 microM) significantly reduced (80-90%) the response to bolus injection of Ang I, without affecting those to Ang II and TDP in mesenteric arteries. Mechanical removal of the endothelium greatly potentiated (70-95%) the vasoconstrictor response to Ang II, Ang I, and TDP in aortic rings while these responses were unaffected by the removal of the endothelium of mesenteric arteries with sodium deoxycholate infusion. In addition, endothelium disruption did not change the pattern of response elicited by these peptides in the presence of captopril. These findings indicate that the endothelium may not be essential for Ang II formation in rat mesenteric arteries and aorta, but it may modulate the response to Ang II. Although Ang II formation from Ang I is essentially dependent on ACE in both vessels, our results suggest the existence of an alternative pathway in the mesenteric arterial bed that may play an important role in Ang II generation from TDP in resistance but not in large vessels during ACE inhibition.

Vasopressor mechanisms in acute aortic coarctation hypertension

Angiotensin II (ANG II) and vasopressin (AVP) act together with the mechanical effect of aortic constriction in the onset of acute aortic coarctation hypertension. Blockade of ANG II and AVP V1 receptors demonstrated that ANG II acts on the prompt (5 min) rise in pressure whereas AVP is responsible for the maintenance (30-45 min) of the arterial pressure elevation during aortic coarctation. Hormone assays carried out on blood collected from conscious rats submitted to aortic constriction supported a role for ANG II in the early stage and a combined role for both ANG II and AVP in the maintenance of proximal hypertension. As expected, a role for catecholamines was ruled out in this model of hypertension, presumably due to the inhibitory effect of the sinoaortic baroreceptors. The lack of afferent feedback from the kidneys for AVP release from the central nervous system in rats with previous renal denervation allowed ANG II to play the major role in the onset of the hypertensive response. Median eminence-lesioned rats exhibited a prompt increase in proximal pressure followed by a progressive decline to lower hypertensive levels, revealing a significant role for the integrity of the neuroaxis in the maintenance of the aortic coarctation hypertension through the release of AVP. In conclusion, the important issue raised by this model of hypertension is the likelihood of a link between some vascular territory-probably renal-below the coarctation triggering the release of AVP, with this vasoconstrictor hormone participating with Ang II and the mechanical effect of aortic constriction in the acute aortic coarctation hypertension.

Effect of chronic estradiol administration on the acute pressor response to aortic coarctation in conscious rats

We investigated the effect of chronic estradiol administration on the pressor response elicited by acute (45 min) partial aortic constriction in conscious Wistar rats and on vascular reactivity to angiotensin II and vasopressin in vitro. Estradiol (10 micrograms kg-1 day-1, sc) or vehicle was administered for 7 days to young castrated male and female rats and to female rats that had stopped cycling (14-16 months of age). In the acute experiment of aortic coarctation in conscious rats, carotid pressure was monitored continuously before and for 45 min after partial abdominal aortic coarctation. In ovariectomized females the mean carotid pressure and heart rate before aortic coarctation were significantly lower in estradiol-treated animals (107 +/- 3 vs 119 +/- 3 mmHg and 360 +/- 31 vs 494 +/- 12 bpm). Estradiol did not affect the pressor response (145-150 mmHg) to aortic coarctation of castrated male rats or ovariectomized female rats but blunted the reflex bradycardia of ovariectomized rats. The onset of the pressor response to aortic coarctation was delayed in aged female rats as compared to the other groups. While estradiol treatment significantly accelerated the onset of hypertension in aged rats, it did not affect the pressor response of castrated animals. Full dose-response curves to angiotensin II and vasopressin were constructed in vitro in the isolated mesenteric arterial bed obtained from similarly treated groups. Estradiol did not affect the vasopressin sensitivity or responsiveness of any group, but caused a significant increase in angiotensin II sensitivity in ovariectomized rats only.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypertensive response to acute aortic coarctation in chronic vasopressin deficient states

We investigated the genesis of the hypertensive response to acute (45 min) aortic constriction in two models of chronic vasopressin (AVP) deficiency, i.e., Brattleboro strain and median eminence lesioned (MEL) Wistar rats. The same degree of partial aortic constriction, with a pneumatic cuff placed around the abdominal aorta, yielded a sudden and maintained increase in carotid pressure to the same extent in Brattleboro, MEL and sham-MEL rats. Blockage of AVP V1 receptors with d(CH2)5Tyr[Me]AVP did not affect the hypertensive response of Brattleboro or MEL rats, but gradually blunted the response of sham-MEL rats. Blockage of angiotensin II receptors with saralasin blunted the hypertensive response of the AVP-deficient subjects throughout the experiment, but only delayed (5-15 min) the onset of hypertension in sham-MEL rats. Simultaneous blockage of AVP and angiotensin II blunted the hypertensive response of sham-MEL and AVP-deficient rats throughout the experiment. These data demonstrate that when one vasoactive system is chronically absent, as is the case for AVP in Brattleboro and MEL rats, the renin-angiotensin system plays the major role in the pathophysiology of acute aortic coarctation hypertension.

[Erythropoietin and transfusions in patients with anemia of chronic renal failure origin : an update view]

Aiming to know the factors that influenced the use of erythropoietin (EPO) in chronic hemodialysis patients, we retrospectively studied 82 patients (41 male), of whom 15 received EPO. No differences, between patients receiving or not receiving EPO, were found in age (46.9 +/- 25 and 57 +/- 13 years respectively), male/female ratio (9/6 and 32/35 respectively), time on dialysis (36.4 +/- 25.6 and 36.8 +/- 31.8 months respectively), dialysis hours (3.19 +/- 0.6 and 3.33 +/- 0.39 h respectively) and proportion of diabetics (6.6 and 20.8% respectively). Prior to EPO use and compared to untreated patients, treated patients were transfused with a higher frequency (60 vs 22%) and with more units/patients/years (0.12 vs 0.08). Hemoglobin levels at the start of the treatment was similar in treated and untreated patients (8.4 +/- 1.46 vs 8.78 +/- 1.97 g/dl). EPO was indicated in 11 patients due to general symptomatology associated to anemia and in 4 due to cardiac failure or angina. We conclude that EPO treatment is indicated in approximately 18% of patients in dialysis. An adequate dialytic treatment may achieve optimal hemoglobin levels with minimal transfusion requirements and without need of EPO, thus reducing costs.

Effect of median eminence lesion on the hypertensive response due to acute aortic coarctation

The present study was designed to investigate the effect of a lack of vasopressin resulting from electrolytic lesion of the median eminence of the hypothalamus on the acute 45-min aortic coarctation hypertension elicited in conscious rats by means of a pneumatic cuff placed around the aorta above the renal arteries. Forty-eight hours after lesion, aortic constriction elicited a prompt (5-min) rise in mean carotid pressure from 115 +/- 2 to 149 +/- 2 mmHg, followed by a gradual decline to 129 +/- 2 mmHg. In contrast, sham-lesioned rats exhibited a prompt hypertensive response from 118 +/- 2 to 157 +/- 2 mmHg that leveled off throughout the experiment. Lesioned rats treated with saralasin presented a blunted hypertensive response (within 125 +/- 2 to 130 +/- 2 mmHg), whereas sham-lesioned rats showed only a delay in the onset of hypertension. The hypertensive response of lesioned rats was unaffected by the vasopressin antagonist [d(CH2)5Tyr(Me)]AVP, whereas sham-lesioned rats submitted to this treatment presented a prompt rise in pressure followed by a gradual decline at the end of the experiment. Lesioned and sham-lesioned rats treated with saralasin plus vasopressin antagonist showed a blunted hypertensive response throughout the experiment. These data demonstrate that the integrity of the median eminence plays a pivotal role in the maintenance (30-45 min) of acute aortic coarctation hypertension, presumably involving the release of vasopressin from the neurohypophysis, whereas angiotensin II mainly accounts for the prompt (5-15 min) rise in pressure.

Role of kinins in the acute antihypertensive effect of enalapril in hypertensive rats

1. We used the kinin antagonist HOE 140 to investigate the role of endogenous kinins in the acute antihypertensive effect of the angiotensin converting enzyme inhibitor enalapril in chronic and acute renal hypertensive rats. 2. In normotensive rats, treatment with HOE 140 (33 micrograms/kg, sc) caused a complete blockade of the depressor effect of bradykinin (100 ng, ia) without affecting the depressor effect of sodium nitroprusside (1 microgram, i.v.) or the basal blood pressure. 3. HOE 140 treatment (33 micrograms/kg, sc, plus 330 ng/min, i.v.) did not affect basal blood pressure of chronic (6-7 weeks) one-kidney, one clip and two-kidney, one clip hypertensive rats and in rats with acute hypertension, elicited by unclamping the renal pedicle that had been occluded for 5 h, but HOE 140 completely blocked the hypotensive response to bradykinin (100 ng, ia) during the 60-min period after enalapril administration (2 mg/kg, i.v.). 4. Acutely hypertensive rats treated or not with HOE 140 (33 micrograms/kg, sc, plus 330 ng/min, i.v.) presented a similar fall in blood pressure after enalapril (165 +/- 5 to 137 +/- 6 mmHg and 166 +/- 5 to 136 +/- 6 mmHg, respectively). 5. Untreated two-kidney, one clip hypertensive rats presented a rapid and sustained fall in blood pressure after enalapril (177 +/- 4 to 148 +/- 4 mmHg) that did not differ from the HOE 140-treated (33 micrograms/kg, sc, plus 330 ng/min, i.v.) group (177 +/- 6 to 154 +/- 4 mmHg). 6. One-kidney, one clip hypertensive rats treated with HOE 140 (33 micrograms/kg, sc, plus 330 ng/min, i.v.) showed a significantly smaller fall in blood pressure after enalapril (204 +/- 7 to 179 +/- 9 mmHg) compared to the untreated rats (197 +/- 7 to 149 +/- 2 mmHg). 7. These results indicate that kinin potentiation plays an important role in the antihypertensive effect of acutely administered angiotensin converting enzyme inhibitor in the one-kidney, one clip model of hypertension.

Blockers of the L-arginine-nitric oxide-cyclic GMP pathway facilitate baroreceptor resetting

We investigated the role of nitric oxide on rapid (25- and 40-minute) baroreceptor resetting during the onset of acute hypertension in rats treated with NG-nitro-L-arginine, an inhibitor of nitric oxide synthesis, and methylene blue, an inhibitor of guanylate cyclase. The effect of treatment with glibenclamide, an ATP-dependent K+ channel blocker, was also investigated. Arterial hypertension was provoked in a ramp progression by the drug NG-nitro-L-arginine alone or in association with aortic coarctation. Whole aortic nerve activity and carotid pressure were recorded in the anesthetized rats. The extent of rapid resetting was evaluated by means of the ratio (delta Systolic Threshold Pressure/delta Control Diastolic Pressure) x 100 as well as by the extent of displacement of the pressure-nerve activity curve defined by the ratio (delta Mean Arterial Pressure at 50% of maximum activity/delta Mean Arterial Pressure) x 100. All groups gave the same increase in mean arterial pressure at 25 and 40 minutes after the onset of hypertension. A greater extent of resetting to hypertensive levels was observed in the treated groups compared with coarctation alone. At 40 minutes after the onset of hypertension, the coarctation and nitro-L-arginine groups exhibited a further increase in the extent of resetting. The rats submitted to glibenclamide plus coarctation presented a slight but significant decrease in gain. These findings suggest that an active L-arginine-nitric oxide-cyclic GMP pathway blunts rapid resetting during the onset of hypertension. In addition, they also indicate that ATP-dependent K+ channels can also modulate rapid resetting of the baroreceptors to hypertensive levels.

Chronic converting enzyme inhibition facilitates baroreceptor resetting to hypertensive levels

We investigated the acute and chronic effects of converting enzyme inhibitors (captopril or enalapril) and of angiotensin II receptor blockade (DuP 753) on rapid (30-minute) baroreceptor resetting elicited by a prompt and sustained hypertensive response provoked by aortic constriction. Pressure-nerve activity curves, pressure at 50% of maximal baroreceptor activity, baroreceptor gain (slope of the curve), and systolic threshold pressure for baroreceptor activation were determined as indexes of baroreceptor function. A slight fall in mean arterial pressure after acute treatment with the converting enzyme inhibitor or DuP 753 was accompanied by a partial leftward curve shift, which is associated with a partial threshold shift and increase in gain. A maintained hypertensive stimulus caused a partial rightward curve shift and partial (49% to 56%) threshold shift to hypertensive levels in both acutely treated and control rats. The hypertensive stimulus provoked a partial rightward curve shift and complete (88% to 94%) threshold shift to hypertensive levels in chronically treated rats. The effect of enalapril on baroreceptor function was unaltered by the bradykinin antagonist Hoe 140. These data demonstrate that chronic inhibition of converting enzyme or blockade of angiotensin II receptors facilitates rapid resetting of the baroreceptors to hypertensive levels caused by partial aortic constriction without a change in baroreceptor sensitivity.

Physiopathogenesis of acute aortic coarctation hypertension in conscious rats

We investigated the role of vasopressin, angiotensin II, and catecholamines in the onset of acute (45-minute) aortic coarctation hypertension in conscious rats. Partial aortic constriction was performed by means of a pneumatic cuff placed around the abdominal aorta above the renal arteries for 15 or 45 minutes. A sham-operated group was used as control. Mean carotid pressure before aortic constriction did not differ between rat groups. Aortic constriction produced a similar increase of mean carotid pressure during 15 minutes (36 +/- 3 to 37 +/- 3 mm Hg above basal levels) and 45 minutes (37 +/- 2 to 39 +/- 3 mm Hg). Plasma vasopressin concentration after 15 minutes of coarctation (4.4 +/- 0.5 pg/mL) did not differ from that observed in control rats (3.0 +/- 0.8 pg/mL), whereas after 45 minutes, it was significantly higher (14.3 +/- 3.3 pg/mL). Plasma renin activity increased significantly after coarctation (21.7 +/- 4.1 and 29.9 +/- 2.9 ng angiotensin I/mL per hour, at 15 and 45 minutes, respectively) when compared with control rats (3.9 +/- 0.5 ng angiotensin I/mL per hour). After coarctation, plasma norepinephrine concentration was consistently reduced, whereas plasma epinephrine concentration did not differ from control rats. In conclusion, these data provide evidence for an effective vasopressor role for vasopressin in the genesis of acute (45-minute) aortic coarctation hypertension in conscious rats. In addition, although the results confirm that the renin-angiotensin system participates earlier in the onset of coarctation hypertension, they rule out a significant vasopressor role for catecholamines in the early development of hypertension.

Effect of bilateral nephrectomy on hypertension produced by acute aortic coarctation

1. The hemodynamic responses to acute (45 min) aortic coarctation were studied in conscious intact (N = 7) or bilaterally nephrectomized (N = 7) Wistar rats (250-320 g). The degree of constriction of the aorta was monitored by reducing aortic flow (measured with a pulsed Doppler flowmeter) to 40% of the basal level. 2. The nephrectomized rats presented a smaller (P < 0.05) increase in carotid pressure (14-17%) than the intact rats (25-36%). Although the aortic constriction reduced significantly the aortic flow to 40% of the basal level in both groups of rats, the calculated change in aortic resistance imposed by coarctation in the intact group was significantly (P < 0.05) higher (167-292%) than that observed (173-183%) in the nephrectomized group, except 5 min after coarctation. 3. The hemodynamic data obtained in the present study confirm our findings that nephrectomized rats display a blunted hypertensive response to acute aortic coarctation which is attributed mainly to the mechanical effect of constriction. In addition, the present data indicate that the release of vasopressor substances triggered by the kidneys in intact subjects are responsible for the gradual increase in aortic resistance during coarctation.

Increased vascular formation of angiotensin II in one-kidney, one clip hypertension

To assess the role of the vascular angiotensin II-generating system in one-kidney, one clip hypertension, we determined the angiotensin converting enzyme activity in plasma and vascular tissues and examined the pressor response to angiotensin II, angiotensin I, and tetradecapeptide renin substrate in isolated mesenteric arteries from one-kidney, one clip hypertensive rats 7 and 30 days after clipping the renal artery and in mesenteric arteries from age-matched normotensive rats. Angiotensin converting enzyme activity, determined in aortic and mesenteric tissues, was significantly augmented in the hypertensive (30 days after clipping) group, whereas plasma activity was normal. The vasoconstrictor responses elicited by angiotensin I and tetradecapeptide in arteries from hypertensive rats were found to be significantly potentiated 30 days after clipping, whereas the angiotensin II responses were basically unchanged. Saralasin completely blocked the vasoconstrictor responses, whereas captopril blocked only the responses to angiotensin I without affecting the responses elicited by angiotensin II and tetradecapeptide. Enalapril, an angiotensin converting enzyme inhibitor given intravenously to unanesthetized rats, significantly lowered the blood pressure of hypertensive rats. The pressor responses elicited by angiotensin II, angiotensin I, and tetradecapeptide were completely inhibited by saralasin, whereas enalapril blocked only the responses of angiotensin I but not those elicited by angiotensin II and tetradecapeptide. These results indicate that local formation of angiotensin II is increased in arteries of one-kidney, one clip hypertensive rats. The data obtained with tetradecapeptide renin substrate suggest an important role for nonrenin proteases in vascular angiotensin II formation.

Effect of bradykinin on isolated mesenteric arteries of the rat

Bradykinin is a potent vasodilator peptide; however, its half-life in vivo is very short because of various plasma and tissue peptidases that hydrolyze bradykinin to inactive fragments. We studied the role of kininase II (angiotensin converting enzyme) and neutral endopeptidase 24.11 (enkephalinase) in the catabolism of bradykinin in vascular tissue by determining the effect of inhibitors of kininase II (captopril) and of endopeptidase 24.11 (phosphoramidon) on the action of bradykinin on rat isolated mesenteric arteries. Because bradykinin may induce prostaglandin formation and release, we also studied the effect of a cyclooxygenase inhibitor, indomethacin, on the action of bradykinin. The mesenteric bed was isolated from rats (250-300 g) with rats under either anesthesia and was perfused with Krebs' solution (4 ml/min) containing phenylephrine (0.5-1.0 microgram/ml) to produce a mean perfusion pressure of 120-130 mm Hg. Bradykinin (2.5-40.0 ng), injected as a bolus, produced a dose-dependent decrease in perfusion pressure. In the presence of indomethacin (1.0 microgram/ml), the amplitude of the vasodilator responses to bradykinin was not significantly affected, although the duration of the responses was increased approximately two to four times. In the presence of captopril (1.0 microgram/ml), bradykinin elicited either a vasodilator or a biphasic effect. The vasodilator effect was greatly potentiated by captopril, whereas the duration of the response was unchanged when compared with control experiments. When present, the pressor responses were also dose related. In the presence of indomethacin plus captopril, bradykinin produced only a fall in perfusion pressure that lasted five to six times longer than without any treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Facilitation of noradrenergic transmission by angiotensin in hypertensive rats

We examined the angiotensin-induced potentiation of noradrenergic transmission in the isolated mesenteric arteries of one-kidney, one clip (1K1C) hypertensive rats. The angiotensin converting enzyme activity measured in plasma did not change during the development of hypertension, whereas the activity measured in the aortic tissue was significantly augmented 28 days after the renal artery was clipped. Although the pressor responses to nerve stimulation were basically unaltered, a significant increase in the sensitivity to norepinephrine developed during hypertension. The 1K1C preparations presented an increased sensitivity to the facilitatory effect of angiotensin II on the response to periarterial nerve stimulation. The facilitatory effect of angiotensin II on both nerve stimulation and exogenous norepinephrine was blocked by saralasin. Angiotensin I induced similar facilitatory action on noradrenergic transmission that was inhibited by saralasin. When a high concentration of angiotensin I was used, the facilitatory effect was significantly higher in mesenteric arteries from 1K1C rats than in controls. Captopril reduced the facilitatory effect of angiotensin I in 1K1C preparations, whereas the responses of the normotensive control rats were unaffected by captopril. These findings are consistent with angiotensin I acting directly on angiotensin II receptors or with angiotensin I being converted to angiotensin II by an alternative pathway not involving angiotensin converting enzyme.

Small cell carcinoma of the esophagus

The authors describe a case of small cell carcinoma of the esophagus, whose presenting complaint was abdominal pain, but no dysphagia. The patient had hepatic and gastric metastases and diarrhea, probably of endocrine origin.

[Chronic dialysis in advanced age patients: a reasonable therapeutic alternative?]

Thirty two elderly patients (mean age 68.8 +/- 6.95 years) were treated by maintenance hemodialysis or intermittent peritoneal dialysis. 28.1% were diabetics and no survivors in this group were observed after 24 months. Median survival for non diabetic patients was 72.4 months vs 9.03 months in diabetics (p < 0.01). The main cause of death was discontinuation of dialysis (33%) or cardiovascular disease. Thus, chronic dialysis is a reasonable treatment for elderly patients with end stage renal disease. However, diabetes is associated to a poor prognosis.

A survey of vasoactive peptide metabolizing enzymes in the rat mesenteric arterial bed perfusate

We have demonstrated that the isolated perfused rat mesenteric arterial bed (MAB) secretes peptidases capable of metabolizing bradykinin and angiotensin I. The major degradative pathway of bradykinin by enzymes found in the rat MAB perfusate was mediated by carboxypeptidase A-like activity, whereas angiotensin 1 degradation followed two main routes, one attributable to a carboxypeptidase A-like enzyme and the other to an endopeptidase. This latter enzyme seems to be a novel serine peptidase capable of releasing angiotensin II directly from both angiotensin I and renin substrate tetradecapeptide. The rat MAB perfusate was also shown to contain additional endo- and exopeptidases that might play a role in the metabolism of other vasoactive peptides. Our finding that isolated rat MAB secretes peptidases into the perfusion medium indicates that peptide processing within the microvasculature environment may be effected by enzymes besides those normally found in plasma or associated with cell membranes.

Autoimmune hemolytic anemia in ulcerative colitis. A case report with review of the literature

Autoimmune hemolytic anemia is a rare complication of ulcerative colitis. This report chronicles a patient successfully treated with steroids, and reviews treatment in previously reported cases. The fact that 21% of patients recovered with steroid therapy encourages a conservative approach before surgery is considered.

Reversal of hyperreactivity to bradykinin in renal hypertensive rats

Increased blood pressure responsiveness to bradykinin in comparison with other vasodilator agents was demonstrated in rats with long-term one-kidney and two-kidney, one clip hypertension. In the present study, we analyzed the reactivity to intra-aortically injected bradykinin in unanesthetized one-kidney, one clip hypertensive rats during the control period and 1, 5, and 8 hours after reversal of hypertension after removal of the renal artery constriction. One and 5 hours after unclipping the renal artery, the mean blood pressure decreased markedly (from 195 +/- 7 to 124 +/- 8 and 145 +/- 9 mm Hg, respectively), whereas the hyperreactivity to bradykinin reverted only slightly, and the responses to nitroprusside remained unchanged. In another group of hypertensive rats examined 8 hours after unclipping (pressure decreased from 192 +/- 4 to 143 +/- 8 mm Hg), the hyperreactivity to bradykinin had partially reverted. Significantly larger doses of bradykinin were necessary to produce the same decrease in blood pressure when compared with the control period (16.4 +/- 2.0 vs. 7.2 +/- 1.2 ng). The same degree of reversal of hyperreactivity to bradykinin was observed when the blood pressure of hypertensive rats was reduced (from 207 +/- 8 to 143 +/- 5 mm Hg) during 1 hour by hydralazine injection. Complete reversibility of bradykinin hyperreactivity was produced by nitroprusside infusion (from 201 +/- 13 to 142 +/- 10 mm Hg).(ABSTRACT TRUNCATED AT 250 WORDS)

Acute aortic coarctation hypertension: role of vasopressin and angiotensin II

The role of vasopressin (AVP) and angiotensin II (ANG II) in the onset of acute (45 min) aortic coarctation hypertension was studied in conscious rats. Changes in mean carotid pressure (MCP) and heart rate (HR) were measured in four groups of rats. Control rats presented a hypertensive response that attained a plateau 5 min after coarctation and remained near this level throughout the experiment. Rats treated with AVP V1-vascular receptor antagonist [1-(beta-mercapto-beta,beta-cyclopentamethylenepropionic acid), 2-(O-methyl)tyrosine]arginine vasopressin [d(CH2)5Tyr(Me)AVP] presented a prompt rise in MCP similar to the control rats, but in contrast to this group, the MCP started to decline progressively. Rats treated with saralasin presented a delay in the onset of hypertension right after coarctation but slowly attained values similar to those for control rats. In contrast, the rats treated with AVP antagonist plus saralasin showed a blunted MCP elevation throughout the experiment. Reflex bradycardia observed in the rats treated with saralasin or the AVP antagonist plus saralasin was similar to that observed in the control rats, whereas for the group treated only with AVP antagonist, the reflex bradycardia was more intense than for the other three groups, indicating an increased sensitivity of the baroreflex. These data demonstrate that in addition to the mechanical effect of aortic constriction, both ANG II and AVP participate in the onset of acute aortic coarctation hypertension. Moreover, the results indicate that ANG II acts on the prompt (5 min) rise in pressure, whereas AVP is responsible for the maintenance (30-45 min) of the arterial pressure elevation.

Acute changes in the renin-angiotensin system modify bradykinin and angiotensin reactivity and metabolism in conscious rats

We have shown that angiotensin I (AI) conversion as well as bradykinin (BK) inactivation and reactivity are altered in chronic renal hypertensive rats. In the present experiments we tested the possibility that acute renal hypertension or AI and AII infusion cause alterations in both systems. Pulmonary inactivation of BK was estimated by comparing intravenous and intraaortic equipressor doses (20 mm Hg), and the extent of AI conversion was assessed by determining the equipressor doses of AI and AII that produced a 20 mm Hg rise in mean arterial pressure (MAP). Acute renal hypertension was produced by unclamping the renal pedicle (URP) occluded for 5 hours in conscious rats. Before URP, the MAP was already increased (131 +/- 2 mm Hg) and captopril (10 mg/kg, i.v.) produced a fall of 27 +/- 8 mm Hg, suggesting that the renin-angiotensin system was overactive. After URP, MAP rose to 151 +/- 3 mm Hg, and captopril completely abolished the hypertension. Before URP, reactivity to BK was increased [doses 6 times smaller than control (C), 34 +/- 5 ng], and URP produced no further elevation. Pulmonary BK inactivation (97.5% +/- 4%) was the same before and after URP. Before URP, doses of AII 5 times greater than C (2 +/- 4 pmol) were necessary, and hyporeactivity to AII was markedly increased after URP (doses 300 times larger than C). After URP, the conversion was maximal (104% +/- 2% vs 49% +/- 3% in C), and it was already elevated before URP (82% +/- 10%) when six of the nine rats studied had maximal extent of conversion.(ABSTRACT TRUNCATED AT 250 WORDS)

Baroreceptor reflex in the rat after converting enzyme inhibition or angiotensin receptor blockade

1. One component of baroreflex responsiveness was quantitated in conscious rats using the heart rate response to a pressor injection of phenylephrine. 2. Endogenous angiotensin and its effectiveness were manipulated by sodium deprivation, converting enzyme inhibition and infusion of an angiotensin analogue. None of these manoeuvres changed the observed reflex responsiveness. 3. We conclude that endogenous angiotensin has no influence on the component of baroreceptor function that is described by the slope of the arterial pressure-heart rate relationship.