Effect of short-term ACE inhibitor treatment on peripheral insulin sensitivity in obese insulin-resistant subjects

AIMS/HYPOTHESIS

This study was designed to investigate the effect of short-term ACE inhibitor treatment on insulin sensitivity and to examine possible underlying metabolic and haemodynamic effects in obese insulin-resistant subjects.

METHODS

A randomised, double-blind placebo-controlled trial was performed in 18 obese insulin-resistant men (age, 53 +/- 2 years; BMI, 32.6 +/- 0.8 kg/m(2); homeostasis model assessment of insulin resistance, 5.6 +/- 0.5; systolic blood pressure [SBP], 140.8 +/- 3.2; diastolic blood pressure [DBP], 88.8 +/- 1.6 mmHg), who were free of any medication. The aim was to examine the effects of 2 weeks of ACE inhibitor treatment (ramipril, 5 mg/day) on insulin sensitivity, forearm blood flow, substrate fluxes across the forearm, whole-body substrate oxidation and intramuscular triacylglycerol (IMTG) content.

RESULTS

Ramipril treatment decreased ACE activity compared with placebo (-22.0 +/- 1.7 vs 0.2 +/- 1.1 U/l, respectively, p < 0.001), resulting in a significantly reduced blood pressure (SBP, -10.8 +/- 2.1 vs -2.7 +/- 2.0 mmHg, respectively, p = 0.01; DBP, -10.1 +/- 1.3 vs -4.2 +/- 2.1 mmHg, respectively, p = 0.03). Ramipril treatment had no effect on whole-body insulin-mediated glucose disposal (before: 17.9 +/- 2.0, after: 19.1 +/- 2.4 micromol kg body weight(-1) min(-1), p = 0.44), insulin-mediated glucose uptake across the forearm (before: 1.82 +/- 0.39, after: 1.92 +/- 0.29 micromol 100 ml forearm tissue(-1) min(-1), p = 0.81) and IMTG content (before: 45.4 +/- 18.8, after: 48.8 +/- 27.5 micromol/mg dry muscle, p = 0.92). Furthermore, the increase in carbohydrate oxidation (p < 0.001) and forearm blood flow (p < 0.01), and the decrease in fat oxidation (p < 0.001) during insulin stimulation were not significantly different between treatments.

CONCLUSIONS/INTERPRETATION

Short-term ramipril treatment adequately reduced ACE activity and blood pressure, but had no significant effects on insulin sensitivity, forearm blood flow, substrate fluxes across the forearm, whole-body substrate oxidation and IMTG content in obese insulin-resistant subjects.

Effect of angiotensin II on rat renal cortical 11beta-hydroxysteroid dehydrogenase

Renal 11beta-hydroxysteroid dehydrogenases (11beta-HSDs) are subject to modulation by various endogenous factors. 11beta-HSDs convert glucocorticoids into inactive 11-ketones and thereby determine tissue levels of active glucocorticoids and thus the extent of glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) activation. As such, modulation of the activity of renal 11beta-HSDs may contribute to the cascade of regulatory events involved in renal electrolyte water handling. We investigated whether renal 11beta-HSDs are modulated by elevated circulating angiotensin II. In rats infused for 2 wk with angiotensin II (250 ng/[kg x min] subcutaneously), plasma angiotensin II, aldosterone, and corticosterone were raised 5.1-, 10.7-, and 2.3-fold, respectively, compared with control rats. Angiotensin II infusion raised corticosterone 11beta-oxidation 1.46- and 1.35-fold in renal cortical proximal and distal tubules (enriched by Percoll centrifugation), respectively, but had no effect on 11beta-HSD1 and 11beta-HSD2 mRNA levels (semiquantitative reverse transcriptase polymerase chain reaction), except for distal tubular 11beta-HSD1 mRNA, which was decreased to 50%. In vitro treatment of freshly isolated tubules with angiotensin II for 45 min prior to assessment of 11beta-HSD activity showed no direct acute effects of angiotensin II on tubular corticosterone 11beta-oxidation. The enhanced renal tubular corticosterone 11beta-oxidation in vivo may partly protect renal GR and MR from elevated plasma corticosterone on angiotensin II infusion.

Renal haemodynamics and sodium excretory capacity during urapidil treatment in patients with essential hypertension

OBJECTIVE

Since renal sympathetic nerves are involved in the regulation of sodium excretion, we investigated whether treatment with urapidil, an alpha1-adrenoceptor blocking agent which also lowers sympathetic activity, alters sodium excretory capacity in patients with essential hypertension.

DESIGN

A double-blind, randomized, parallel-group study.

METHODS

Studies were carried out in 26 patients who were randomized to treatment with either placebo or urapidil for 8 weeks. Before and after treatment blood pressure, renal haemodynamics and various neurohormones were measured, as well as the response of these variables to a hypertonic saline infusion.

RESULTS

Urapidil had no effect on renal haemodynamics or neurohormones at rest However, as compared to placebo the saline-induced rises in renal plasma flow and glomerular filtration rate lasted longer during treatment with urapidil. Responses of renin, angiotensin II and catecholamines were not modified by urapidil. On the other hand, aldosterone was less suppressed while atrial natriuretic peptide was less stimulated following the saline load when patients had been treated with urapidil. Cumulative sodium excretion during a 3 h period from the moment of saline infusion was similar whether patients had been treated with placebo or with urapidil.

CONCLUSIONS

Our data show that urapidil interferes with renal haemodynamics after sodium loading but that any tendency to promote sodium output may be offset by changes in aldosterone and atrial natriuretic peptide. We conclude that urapidil, under the circumstances tested, does not affect the sodium excretory capacity of the kidney.

Altered flow-induced arterial remodeling in vimentin-deficient mice

The endothelial cytoskeleton plays a key role in arterial responses to acute changes in shear stress. We evaluated whether the intermediate filament protein vimentin is involved in the structural responses of arteries to chronic changes in blood flow (BF). In wild-type mice (V+/+) and in vimentin-deficient mice (V-/-), the left common carotid artery (LCA) was ligated near its bifurcation, and 4 weeks later, the structures of the occluded and of the contralateral arteries were evaluated and compared with the structures of arteries from sham-operated mice. Body weight and mean carotid artery BF did not differ between the strains, but LCA and right carotid artery (RCA) diameter (737+/-14 microm [LCA] and 723+/-14 microm [RCA] for V-/- versus 808+/-20 microm [LCA] and 796+/-20 microm [RCA] for V+/+) and medial cross-sectional area (CSAm) were significantly smaller in V-/- (21+/-1 and 22+/-2 x 10(3) microm(2) for LCA and RCA, respectively) than in V+/+ (28+/-2 and 28+/-3 x 10(3) microm(2) for LCA and RCA, respectively). In V+/+, LCA ligation eliminated BF in the occluded vessel (before ligation, 0. 35+/-0.02 mL/min) and increased BF from 0.34+/-0.02 to 0.68+/-0.04 mL/min in the RCA. In V-/-, the BF change in the occluded LCA was comparable (from 0.38+/-0.05 mL/min to zero-flow rates), but the BF increase in the RCA was less pronounced (from 0.33+/-0.02 to 0. 50+/-0.05 mL/min). In the occluded LCA of V+/+, arterial diameter was markedly reduced (-162 microm), and CSAm was significantly increased (5 x 10(3) microm(2)), whereas in the high-flow RCA of V+/+, carotid artery diameter and CSAm were not significantly modified. In the occluded LCA of V-/-, arterial diameter was reduced to a lesser extent (-77 microm) and CSAm was increased to a larger extent (10 x 10(3) microm(2)) than in V+/+. In contrast to V+/+, the high-flow RCA of V-/- displayed a significant increase in diameter (52 microm) and a significant increase in CSAm (5 x 10(3) microm(2)). These observations provide the first direct evidence for a role of the cytoskeleton in flow-induced arterial remodeling. Furthermore, they dissociate (1) between acute and chronic arterial responses to altered BF, (2) between alterations of lumen diameter and wall mass during arterial remodeling, and (3) between developmental and imposed flow-induced arterial remodeling.

High dietary potassium chloride intake augments rat renal mineralocorticoid receptor selectivity via 11beta-hydroxysteroid dehydrogenase

Glucocorticoid access to renal corticosteroid receptors is regulated by 11beta-hydroxysteroid dehydrogenases (11beta-HSDs), converting 11beta-hydroxyglucocorticoids into inactive 11-ketones. This mechanism plays a key role in maintaining normal salt-water homeostasis and blood pressure. To study whether renal cortical proximal and distal tubular 11beta-HSDs are modulated, upon shifting the electrolyte status (and may thereby contribute to adjusting the salt-water homeostasis), rats were treated for 14 days with diets with low (0.058 w/w%), normal (0.58%, which is the KCl content of standard European laboratory rat food) or high (5.8%) potassium chloride content. In proximal tubules, dietary KCl had no effect regarding corticosterone 11beta-oxidation in intact cells as well as 11beta-HSD1 and 11beta-HSD2 protein (Western blotting) and mRNA levels (semi-quantitative RT-PCR). In distal tubules, the low KCl diet also had no effect. However, distal tubules of rats fed the high KCl diet showed increased corticosterone 11beta-oxidation rates (1.6-fold, P<0.01) and 11beta-HSD2 protein (4-fold, P<0.01), whereas 11beta-HSD1 protein was decreased (no longer detected, P<0.05). Distal tubular 11beta-HSD mRNA levels were not changed upon dietary treatment. Our results suggest that upon dietary KCl loading distal tubular mineralocorticoid receptor selectivity for aldosterone is increased because of enhanced corticosterone 11beta-oxidation. This may contribute to the fine-tuning of salt-water homeostasis by the kidney.

Persistent abnormalities in plasma volume and renal hemodynamics in patients with a history of preeclampsia

OBJECTIVE

The objective was to test the hypothesis that women with a recent history of preeclampsia have abnormalities in renal hemodynamics and volume status.

STUDY DESIGN

We studied a group of 26 primiparous women with history of preeclampsia and a group of 12 parous women with a history of uneventful pregnancies (control group). At least 4 months post partum we compared the following variables between these groups: effective renal plasma flow, glomerular filtration rate, plasma volume, plasma concentration of active renin, plasma concentration of angiotensin II, plasma concentration of aldosterone, and plasma concentration of atrial natriuretic peptide.

RESULTS

Both plasma volume and plasma concentration of atrial natriuretic peptide were lower in the formerly preeclamptic group. Compared with the control subjects, the formerly preeclamptic group also had a lower effective renal plasma flow, a higher filtration fraction, and a higher renal vascular resistance. Intergroup differences in plasma concentration of active renin, plasma concentration of angiotensin II and plasma concentration of aldosterone were small and inconsistent.

CONCLUSIONS

Women with history of preeclampsia are relatively hypovolemic and tend to have lower effective renal plasma flow and higher renal vascular resistance and filtration fraction than do control subjects. These findings support the hypothesis that otherwise healthy women with a history of preeclampsia show abnormalities in their volume status and renal hemodynamics, irrespective of their blood pressure.

Time-related adaptations in plasma neurohormone levels and hemodynamics after myocardial infarction in the rat

BACKGROUND

Neurohormonal activation plays an important role in the progression of heart failure. In this study, we investigated the progression of neurohormonal activation in conjunction with the hemodynamic status of the rat after myocardial infarction (MI).

METHODS AND RESULTS

Male Wistar rats were subjected to sham or MI surgery. At 1, 3, 5, and 13 weeks after surgery, cardiac output (CO), mean arterial pressure (MAP), and total peripheral resistance (TPR), were measured. In separate groups of rats, blood was sampled at 1, 5, and 13 weeks after surgery and analyzed for various neurohormones. At 1 week after surgery, CO and TPR were not altered in MI rats, but plasma neurohormonal levels were elevated. At 3 and 5 weeks after surgery, reduced CO, increased TPR, and normal MAP were measured in MI rats compared to sham rats, but only endothelin levels were elevated. At 13 weeks after surgery, MAP was reduced in MI rats and CO and TPR were comparable between groups. Neurohormonal activation was again apparent in MI rats.

CONCLUSIONS

Myocardial infarction in the rat induces early neurohormonal activation, which normalizes hemodynamic parameters. A compensatory phase follows. At 13 weeks after MI, plasma concentrations of neurohormones are again elevated, perhaps as a sign of transition to decompensation.

A positive and reversible relationship between adrenergic nerves and alpha-1A adrenoceptors in rat arteries

We evaluated the relationship between the presence of adrenergic nerves and the presence of alpha-1 adrenoceptors (alpha-1 AR) in the arterial tree of the rat. The thoracic aorta and the carotid, mammary, renal and femoral arteries were isolated from 20-week-old male WKY rats, along with the superior mesenteric artery and small (first order) and resistance-sized (third order) side branches of this vessel. Norepinephrine content ([NE]) and specific binding of 300 pM [3H]prazosin were determined. To estimate the total density of alpha-1 AR ([alpha-1 AR]) as well as the density of alpha-1A AR ([alpha-1A AR]), binding experiments were performed with and without pretreatment of the preparations with the irreversible alpha-1B AR and alpha-1D AR antagonist chloroethylclonidine and in the absence and presence of the alpha-1A AR selective ligand (+)-niguldipine (30 nM). Also the presence of mRNA for alpha-1A AR was evaluated by use of reverse transcriptase-polymerase chain reaction (RT-PCR). In intact rats, arterial [NE] ranged between 0.1 and 15 ng/microgram DNA, arterial [alpha-1 AR] ranged between 12.4 and 46.8 fmol/mg protein and [alpha-1A AR] ranged between 0.05 and 27.9 fmol/mg protein. There was no significant correlation between [alpha-1 AR] and [NE]. However, with respect to the [alpha-1A AR] a significant correlation between [NE] and [alpha-1A AR] was observed. RT-PCR analysis confirmed the expression of alpha-1A AR in the densely innervated mesenteric resistance-sized arteries. Two weeks after chemical sympathectomy of the rats with 6-hydroxydopamine (i) arterial [NE] was markedly reduced, and (ii) a distinct reduction in the [alpha-1A AR] as percentage of the total [alpha-1 AR] density in mesenteric artery side branches was noted. These findings indicate that there is a positive and reversible relationship between the presence of adrenergic nerves and that of alpha-1A AR in rat arteries.

Effects of hypervolemia on interdialytic hemodynamics and blood pressure control in hemodialysis patients

The influence of hypervolemia on hemodynamics and interdialytic blood pressure, as well as in relation to vascular compliance, was investigated in 10 hemodialysis patients who were not receiving vasoactive medication. All subjects were studied during a relative normovolemic interdialytic period (from 1 kg below dry weight postdialytic until dry weight predialytic) and a hypervolemic interdialytic period (from 1 kg above dry weight postdialytic until 3 kg above dry weight predialytic). Interdialytic blood pressure was measured with an ambulatory blood pressure monitor. Cardiac output was echographically measured and total peripheral resistance calculated postdialytic, mid-interdialytic, and predialytic. At the same time, a blood sample was drawn for analyzing vasoactive hormones, sodium, and hematocrit. In all patients, ideal dry weight was estimated by echography of the caval vein. Arterial and venous compliance were measured with an ultrasound vessel wall movement detector system and a strain-gauge plethysmograph. After fluid load, an increase in intravascular volume, an increase in caval vein diameter and cardiac output, and a decrease in peripheral resistance was observed. No significant influence of a 3-L fluid load was found on interdialytic blood pressure course (153+/-24 mm Hg/90+/-19 mm Hg in the hypervolemic period and 146+/-27 mm Hg/89+/-22 mm Hg in the normovolemic period). Sodium and osmolality were similar in the hypervolemic and normovolemic interdialytic periods. After fluid load, a decrease in arginine vasopressin and angiotensin II was observed, which probably contributed to the decreased systemic vascular resistance. Catecholamines were not influenced by fluid load, but increased during the interdialytic period, suggesting accumulation after dialysis. Three of the 10 patients had higher systolic but not diastolic blood pressures after fluid load (159+/-13 mm Hg/81+/-22 mm Hg in the hypervolemic period and 135+/-16 mm Hg/81+/-22 mm Hg in the normovolemic period). No correlation could be found between arterial or venous compliance and blood pressure changes. We concluded that a 3-L interdialytic fluid load does not result in higher blood pressure in most hemodialysis patients.

Effects of angiotensin II on cardiac function and peripheral vascular structure during compensated heart failure in the rat

The present experiments were designed to test the hypothesis that the activation of the renin-angiotensin system during compensated heart failure may have adverse effects on cardiac function and change the peripheral vascular structure. ANG II (250 ng/kg/min) or saline (0.9% NaCl) were infused in myocardial-infarcted and sham-operated rats. After 2 weeks, cardiac function and peripheral vascular changes were investigated.

RESULTS

ANG II infusion reduced baseline cardiac index in sham rats but did not further reduce this index in ANG II-infused MI rats. Total peripheral resistance was similarly increased in ANG II-infused infarcted and sham rats, and also plasma ANG II concentrations were comparable. ANG II elevated systolic blood pressure by approximately 70 mm Hg in sham rats and increased the medial cross-sectional area of the superior mesenteric artery by 33%. However, ANG II infusions in MI rats resulted in only a minor increase in blood pressure, whereas the cross-sectional area of the superior mesenteric artery did not change. ANG II infusion had no effect on vessel dimensions of the resistance arteries of the pulmonary and mesenteric vascular bed of either group. Calculated ED50 and peak pressor response to acute ANG II injections were comparable in all groups, confirming the presence of functionally intact AT1 receptors. The increases in plasma atrial natriuretic peptide (ANP) and nitric oxide (NO) synthase activity (estimated by aortic cyclic GMP concentrations) were higher in ANG II-infused MI rats than in ANG II-infused sham rats.

CONCLUSION

ANG II infusion in rats with and without MI has comparable negative effects on cardiac function but has different effects on blood pressure and vascular structure. The concomitant increases in plasma ANP and NO synthase activity in ANG II-infused MI rats suggest that the growth stimulatory and hypertensive actions of ANG II in sham rats may be counter-regulated by activation of inhibitory neurohumoral systems such as ANP or NO in MI rats.

Reduced responsiveness of rat mesenteric resistance artery smooth muscle to phenylephrine and calcium following myocardial infarction

1. We evaluated responses of peripheral resistance arterial smooth muscle to alpha 1-adrenoceptor stimulation in a rat model of heart failure in relation to neurohumoral changes, wall structure, receptor density and cellular calcium handling. 2. Plasma samples and third order mesenteric artery side-branches were obtained from Wistar rats after induction of left ventricular infarction (M1) or sham surgery. Vessels were denuded of endothelium, sympathectomized, depleted of neuropeptides, and mounted in a myograph for recording of isometric force development in response to calcium, agonist and high potassium. Also, the morphology of these preparations was determined. Separate vessel segments were used in radioligand binding assays with [1H]-prazosin. 3. At 1 week after MI, circulating plasma levels of adrenaline, angiotensin II, atrial natriuretic factor (ANF) and vasopressin were significantly elevated. At 5 weeks only a significant elevation of ANF persisted. 4. At 5 weeks after MI, the structure of the vessels and responsiveness to high potassium or Bay K 8466 (10(6) mol l-1) were not modified. Yet, at this stage, sensitivity to phenylephrine was increased (pD2: 6.24 +/- 0.04 vs 5.98 +/- 0.04 for controls) while maximal contractile responses to phenylephrine in the presence of 2.5 mmol l-1 calcium (2.26 +/- 0.28 vs 3.53 +/- 0.34 N m-1) and the sensitivity to calcium in the presence of phenylephrine (pD2: 2.81 +/- 0.22 vs 3.74 +/- 0.16) were reduced. Responses to the agonist in calcium-free solution and the calcium sensitivity in the presence of 125 mmol l-1 potassium or of phorbol myristate acetate (PMA, 10(-6) mol l-1) were not altered. 5. At 5 weeks after MI, the density of prazosin binding sites was not reduced (4.04 +/- 1.40 vs 2.29 +/- 0.21 fmol microgram-1 DNA in controls). 6. In conclusion, myocardial infarction leads in the rat to a reduction of contractile responses of mesenteric resistance arterial smooth muscle to alpha 1-adrenoceptor stimulation. This seems to involve impaired agonist-stimulated calcium influx.

Renal extraction of atrial natriuretic peptide in hypertensive patients with or without renal artery stenosis

The renin-angiotensin-aldosterone system plays a major role in renovascular hypertension, but the relationship between renin release and the renal fractional extraction of atrial natriuretic peptide (ANP) in this condition is not well defined. We measured ANP levels in the renal veins and aortas of 49 untreated hypertensive patients studied under standardized conditions immediately before renal angiography. Twenty-one patients had renal artery stenosis, 13 of which were unilateral and 8 bilateral. Five of the 13 patients with unilateral renal artery stenosis had an elevated renin ratio (> or = 1.5). Patients with renal artery stenosis were older (P < .01) and had higher systolic pressures (P < .05) than patients with essential hypertension. Arterial levels of ANP were significantly higher in patients with unilateral or bilateral renal artery stenosis than in patients with essential hypertension (P < .05). Patients with hypertension and left ventricular hypertrophy had significantly higher arterial ANP levels than those with no hypertrophy (40 versus 26 pmol/L, P < .05), but in patients with renal artery stenosis, arterial ANP levels were similar in those with or without hypertrophy. Renal venous ANP levels were significantly higher in stenotic than in normal kidneys. Moreover, in unilateral renal artery stenosis, stenotic kidneys of patients with an elevated renin ratio (stenotic kidney/contralateral kidney > or = 1.5) had a significantly higher renal venous ANP level than stenotic kidneys of patients with normal renin ratio (30 versus 17 pmol/L, P < .05). However, the median fractional extraction of ANP was similar, around 0.50 (range, 0 to 0,83), in normal kidneys of hypertensive patients and in stenotic and contralateral kidneys of patients with renal artery stenosis. A significant inverse correlation between arterial ANP and renal venous active plasma renin concentration was found for normal kidneys (r= -.62, P < .01) of hypertensive patients without hypertrophy. However, for stenotic kidneys, no such relationship was apparent. A significant correlation between arterial ANP and the arteriovenous difference of ANP (r = +.92, P < .001) was found. This relationship was similar for normal and stenotic kidneys. In conclusion, an inverse relationship between arterial ANP and renal venous active plasma renin concentration exists in normal kidneys of essential hypertensive patients without left ventricular hypertrophy. Furthermore, data of ANP extraction through normal and stenotic kidneys suggest that saturation of ANP extraction does not occur. Increased levels of ANP in renal artery stenosis are likely caused by enhanced cardiac secretion of this peptide.

'Captopril test', with blood pressure and peripheral renin as response variables in hypertensive patients with suspected renal artery stenosis

In forty six hypertensive patients in whom a high level of clinical suspicion for renovascular hypertension was present on the basis of clinical clues, a captopril test was performed with either 25 mg of captopril or placebo on 2 separate days to determine prospectively the value of the captopril test. Blood pressure (BP) and peripheral renin were used as response variables. All patients had discontinued their anti-hypertensive medication and were not salt depleted. In all patients selective renal angiography was performed irrespective of the results of the captopril test. Twenty patients proved to have uni- or bilateral renal artery stenosis (RAS) giving a prevalence of 43%. After the placebo and after captopril there were no significant changes (absolute or proportional) in BP values between patients with essential hypertension or RAS, either for all measurements or if only the fall in BP was taken into account. The receiver operator characteristic curves of both baseline and post-captopril peripheral renin levels indicate that the captopril test does not discriminate appropriately between patients with essential hypertension and RAS. Therefore, we would not advise the use of the captopril test as a screening test for RAS in hypertensive patients in whom a high level of clinical suspicion for RAS is already present.

Renal arterial and venous endothelin in hypertensive patients with or without renal artery stenosis

Immunoreactive endothelin (ir-ET) levels were measured in the renal veins and aorta of 43 untreated hypertensive patients immediately before renal angiography. None of the patients used antihypertensive medication. Twenty-seven patients had renal artery stenosis, 17 of which were unilateral and 10 bilateral. Seven of the 17 patients with unilateral renal artery stenosis had an elevated renin ratio. Of the 16 patients with essential hypertension 6 had a unilateral small kidney with a normal blood supply. Although there was a trend towards higher levels of ir-ET in patients with renal artery stenosis, no significant differences in endothelin levels (venous or arterial) were found between different groups of patients or groups of kidneys. More than 75% of kidneys extracted endothelin, there being no significant differences between groups of kidneys. In conclusion, our data demonstrate that endothelin levels and renal endothelin extraction are comparable in essential hypertension and in hypertension associated with renal artery stenosis. Whereas renal uptake or endothelin is the rule, some kidneys, however, release this peptide irrespective of the presence or absence of renal artery stenosis.

Effects of candidate autocrine and paracrine mediators on growth responses in isolated rat arteries

We evaluated the effects of mediators that can be produced by smooth muscle and endothelial cells on growth responses in isolated arteries. Segments of carotid and renal arteries, denuded of endothelium, were isolated from adult rats and studied during tissue culture in the presence of indomethacin. Three days of culture in the presence of serum stimulated DNA synthesis in the media. During long-term culture new layers of cells developed at the borders of the arterial segments. Medial DNA synthesis depended less on serum than extramedial cell proliferation. During moderate stimulation, basic fibroblast growth factor and endothelin-1 enhanced and interleukin-1 and transforming growth factor-beta reduced medial DNA synthesis, whereas insulin-like growth factor-1, platelet-derived growth factor AA, platelet-derived growth factor BB, and angiotensin II were without effect. Of these factors, only endothelin-1 stimulated extramedial cell proliferation. In addition, serum-stimulated but not basic fibroblast growth factor-stimulated medial DNA synthesis was less marked in arteries that had not been denuded of endothelium than in ee-endothelialized arteries. Differences between preparations with and without endothelium persisted in the absence of L-arginine and in the presence of an inhibitor of nitric oxide synthase. These observations confirmed that DNA synthesis in the arterial media and extramedial cell proliferation are influenced by different factors. They further indicated that endothelial modulation of medial DNA synthesis does not seem to involved endothelium-derived prostaglandins, nitric oxide, or interleukin-1 and that it can be blunted by basic fibroblast growth factor.

DNA synthesis in isolated arteries of normotensive and hypertensive rats: effects of the endothelium

OBJECTIVES

To compare DNA synthesis in isolated arteries of normotensive and hypertensive rats and to evaluate whether removal of the endothelium affects this process.

DESIGN

Carotid and renal artery segments were isolated from normotensive Wistar, Wistar-Kyoto (WKY) and Sprague-Dawley rats, and from spontaneously hypertensive rats (SHR), transgenic Sprague-Dawley rats harbouring the mouse Ren-2 gene and from WKY rats rendered hypertensive by aortic coarctation.

METHODS

Artery segments were exposed in vitro to serum with or without previous gentle removal of the endothelium. Nuclear incorporation of the thymidine analogue 5-bromo-2'-deoxyuridine was visualized by immunocytochemistry and the percentage of labelled medial nuclei was determined.

RESULTS

In both types of artery, obtained from 6-week-old WKY rats and from 6-week-old SHR, removal of endothelium increased the percentage of 5-bromo-2'-deoxyuridine-labelled medial nuclei (L%). Also, in the arteries of 20-week-old Wistar rats, WKY rats and WKY rats rendered hypertensive by aortic coarctation and in vessels of 11-week-old Sprague-Dawley rats and Sprague-Dawley rats harbouring the mouse Ren-2 gene, removal of endothelium increased L%. Conversely, in the arteries of 20-week-old SHR removal of the endothelium did not alter L%. Furthermore, maximally stimulated DNA synthesis was considerably smaller in de-endothelialized arteries of adult SHR than in denuded vessels from the other strains and models.

CONCLUSION

These findings confirm that the endothelium can reduce DNA synthesis in the intact rat arterial smooth muscle. This effect is not modified by hypertension, but is selectively reduced in the arteries of adult SHR.

Mesenteric small artery changes after vasoconstrictor infusion in young rats

We evaluated whether chronic alpha 1-adrenergic stimulation, angiotensin II (AII), or increased blood pressure (BP) alters resistance arterial structure and function. Structural parameters and wall tension were recorded in mesenteric small arteries (MrA) isolated from 6-week-old normotensive Wistar Kyoto rats that had been infused for 4 days with saline (WKY), 2 mg/kg/day phenylephrine (WKY + PHE), or 0.3 mg/kg/day AII (WKY + AII) and from saline-infused spontaneously hypertensive rats (SHR). During the experimental period, systolic BP (SBP) did not change in WKY but increased in WKY + PHE, WKY + AII, and SHR. Relative cardiac mass did not differ between SHR and WKY, but was increased in WKY + PHE and WKY + AII. Stiffness and optimal lumen diameter of MrA did not differ between WKY and SHR and were not altered in WKY + PHE or WKY + AII. Maximal contractile responses and sensitivities for vasconstrictors and calcium in vessels of WKY + AII and SHR did not differ from those in WKY. In vessels of WKY + PHE, maximal responses to vasoconstrictors and sensitivities for norepinephrine (NE) and PHE were reduced. Relaxing responses to isoproterenol (ISO) and Na-nitroprusside did not differ between SHR and WKY and were not altered in WKY + PHE and WKY + AII. Those to acetylcholine (ACh) were reduced in WKY + PHE. Media cross-sectional area and media thickness were significantly larger in WKY + AII and SHR as compared with WKY but were not altered in WKY + PHE. These data indicate that in young rats AII leads to small artery hypertrophy and that neither increased BP or increased vasconstriction appear to be involved therein. Chronic alpha 1-adrenergic stimulation, on the other hand, did not modify small artery structure but resulted in nonselective reduction of arterial smooth muscle contractile reactivity.

Tonic tone in arteries exposed continuously to angiotensin II in vitro

We evaluated long-term actions of angiotensin II (ATII) on arterial smooth muscle. In isolated sympathectomized renal artery segments that had been denuded of endothelium, isometric force was recorded during 3 days of incubation in nutrient medium with and without 1 microM ATII. The peptide induced, after an acute transient contraction and a latency of at least 12 hr, a slowly developing tonic increase in wall tension. This chronic effect was not influenced by indomethacin but could be reversed by sodium-nitroprusside. In vessels that had been chronically exposed to ATII, acute contractile responses to high potassium, serotonin and ATII were not altered. Also effects on agonist-induced tone of removal and readministration of extracellular potassium were not modified. Relaxing responses after exposure to NH4Cl were attenuated. During continuous exposure of isolated arteries to ATII, release of a stable contractile factor could not be detected, nuclear incorporation of the thymidine analog 5-bromo-2'-deoxyuridine was not stimulated, but the media cross-sectional area was significantly increased. These observations indicate that ATII induces in arterial smooth muscle, besides its well known acute contractile effect and its trophic action, a long-term tonic increase in tone. The mechanism largely remains to be established, but may involve altered cellular handling of hydrogen ions.

Effects of the endothelium on growth responses in arteries

Observations in cell culture and during arterial organoid culture indicate that the endothelium may influence arterial wall mass. The endothelium can inhibit and promote stimulation of DNA synthesis in the underlying smooth muscle depending on the experimental conditions, the type of vessel, and the species. The process seems to be altered during neointima formation and in a genetic model of essential hypertension. In these respects, endothelial influences on arterial smooth growth resemble endothelial influences on arterial smooth muscle tone. The mediators that are involved, however, may differ.

Exercise and the pharmacokinetics of propranolol, verapamil and atenolol

The volumes of distribution of the beta-adrenoceptor blocking agents propranolol and atenolol, and the calcium antagonist verapamil, during exercise have been investigated. Changes in the plasma concentrations of atenolol and propranolol during exhaustive exercise at 70% of maximal aerobic power were compared after 1 week of oral treatment (propranolol 80 mg b.d. and atenolol 100 mg once daily) in 12 healthy volunteers. In a second study the effect of 10 min exercise at 50% of maximal aerobic power on steady state plasma concentrations of propranolol, atenolol and verapamil was compared in 7 healthy subjects. The drugs were administered by a continuous intravenous infusion. The plasma concentration of atenolol was not changed by exercise in either study, but the plasma concentrations of propranolol and verapamil were significantly increased in both studies. However, after correction for changes in plasma volume during exercise, the plasma propranolol concentration was not significantly elevated in the second study. From the results it is concluded that exercise led to a reduction in the volume of distribution of propranolol during prolonged exercise (25 min) at 70% Wmax, which was not clearly demonstrable during 10 min exercise at 50% Wmax. The volume of distribution of verapamil was reduced during 10 min exercise at 50% Wmax. No change in the volume of distribution of atenolol during exercise could be shown. The changes in the volumes of distribution of propranolol and verapamil during exercise may contribute to preventing an increase in the half-life of these drugs in patients performing prolonged physical exercise.

Endothelial modulation of DNA synthesis in isolated arteries of the rat

The endothelium can modulate the supply of growth factors to the underlying smooth muscle. In vitro experiments suggest that it may also influence the responsiveness of arterial smooth muscle to mitogens. In these experiments, we measured DNA synthesis in segments of carotid and renal arteries that were isolated from Wistar-Kyoto (WKY) rats and exposed to serum. Nuclear incorporation of the thymidine analogue, 5-bromo-2'-deoxyuridine (BrdUrd), was visualized by immunocytochemistry and the percentage of labeled nuclei (BrdUrd L%) was determined in the tunica media. In both types of artery isolated from 6- and 20-week-old WKY rats, mechanical removal of endothelium increased the BrdUrd L% in the tunica media. In carotid arteries of 20-week-old WKY rats, gentle denudation increased the incorporation of [3H]thymidine but not [14C]leucine. In denuded renal arteries of adult WKY rats, exogenous prostaglandin E2, iloprost, and transforming growth factor-beta (TGF-beta) reduced media labeling, which was not affected by Na nitroprusside. In renal arteries with endothelium, methylene blue and indomethacin did not affect medial DNA synthesis. These findings demonstrate that in arteries of young and adult rats, the endothelium reduces stimulated DNA synthesis. It is unlikely that basal production of nitric oxide or prostaglandins is involved herein. Endothelial inhibition of DNA synthesis but not protein synthesis in arteries indicates that the endothelium may influence the extent of arterial smooth muscle hypertrophy and hyperplasia.

In vivo DNA synthesis is not uniformly increased in arterial smooth muscle of young spontaneously hypertensive rats

We compared the distribution of DNA synthesis over the arterial tree of young normotensive Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR) with marginally elevated blood pressure. Six-week-old male SHR and WKY rats were therefore infused with 5-bromo-2'-deoxyuridine (BrdUrd) for 2 days and the nuclear incorporation of the thymidine analogue in the media of various arteries was determined by immunohistochemistry. In WKY rats, 2.5% of the arterial smooth muscle nuclei in elastic, muscular and resistance arteries incorporated BrdUrd. In SHR, DNA synthesis was more marked in large arteries than in resistance arteries. It was in addition significantly larger in the aorta, superior mesenteric, renal and femoral arteries of the SHR than in those of the WKY rats. However, nuclear incorporation of BrdUrd in vivo did not differ between SHR and WKY rats in aortic endothelium, carotid arterial smooth muscle, nor in mesenteric or renal resistance arteries. Between 6 and 20 weeks of age, the number of nuclear profiles per media cross-section did not increase in large arteries of WKY rats and SHR. During this period of time, however, carotid artery and thoracic aorta weight and DNA content increased. SHR large arteries gained more DNA than those of WKY rats. These data indicate that DNA synthesis is uniformly distributed over the arterial system in young WKY rats and that DNA synthesis is elevated in the smooth muscle of large arteries of 6-week-old SHR but not in their resistance arteries.

Growth responses in isolated elastic, muscular and resistance-sized arterial segments of the rat

To evaluate whether intravascular phenomena contribute to local differences in growth responses of the arterial wall, we evaluated responses to organoid culture in a broad variety of arterial preparations. Arterial segments were isolated from adult, normotensive rats, sympathectomized, denuded from endothelium, and suspended in medium supplemented with serum. As judged from the nuclear incorporation of the thymidine analogue 5-bromo-2'-deoxyuridine (BrdUrd), this induced a transient stimulation of DNA synthesis in only a fraction of the arterial smooth muscle cells in all types of arteries. This intramedial DNA synthesis was more marked in renal arteries than in carotid arteries or aortae and was least pronounced in main pulmonary, femoral, and superior mesenteric artery and in mesenteric resistance-sized arteries. Organoid culture of isolated arteries did not increase the cross-sectional area of the media or the number of medial cells. It rather resulted in proliferation of smooth-muscle-like cells outside the media. In addition, smooth-muscle-like cells migrated out of the isolated arterial segments during culture. The rate of proliferation of these isolated cells did not differ between large arteries of different anatomical origin. However, isolated cells derived from mesenteric resistance arteries proliferated at a rate that was 4 times slower than that of large artery cells. The presence of endothelium significantly reduced medial DNA synthesis in carotid and renal artery segments, but not in mesenteric resistance-sized preparations. These data indicate that growth responses of the arterial wall differ quantitatively with the anatomical location and branching order of the vascular segment. In addition to the regional heterogeneity of endothelial effects on mitogenic responses of arterial smooth muscle, this seems to be due to regional differences in the susceptibility of arterial smooth muscle to exogenous growth factors. In this respect, we speculate that subsets of growth-resistant and growth-prone arterial smooth muscle cells could be heterogeneously distributed over the arterial tree.

DNA synthesis in isolated arteries. Kinetics and structural consequences

We evaluated changes in DNA synthesis, structure, and mechanical activity in isolated arteries during exposure to growth factors. Renal arteries were isolated from rats, sympathectomized, denuded of endothelium, and maintained in tissue culture. Up to 4 days of culture did not affect maximal contractile responses to depolarization. From the results of nuclear incorporation of the thymidine analogue 5-bromo-2-deoxyuridine (BrdUrd), culture stimulated DNA synthesis. In the media, incorporation of BrdUrd was maximal after 3 days but fell precipitously thereafter. Culture of arterial segments did not, however, increase the cross-sectional area of the media, the ploidy of the arterial nuclei, or the number of medial cells. In contrast, new layers of cells, part of which displayed smooth musclelike properties, developed at the border of the segments. The outermost edge of this newly formed layer continued to incorporate BrdUrd for at least 2 wk. These data demonstrate that stimulation of DNA synthesis by continuous exposure of the arterial wall to exogenous growth factors is 1) transient in the media; 2) does not, at least initially, compromise contractile reactivity; 3) does not alter gross medial structure; but 4) leads to proliferation of smooth musclelike cells outside the media. These findings suggest that the number of smooth muscle cells in the arterial media is maintained constant in the presence of even strong mitogenic stimuli.

The influence of chronic treatment with verapamil on plasma atrial natriuretic peptide levels in young and elderly hypertensive patients

In a double-blind, placebo-controlled cross-over study, the plasma atrial natriuretic peptide (ANP) levels of nine young and ten elderly hypertensive patients were compared after placebo and after treatment with 120 mg verapamil given three times daily over 4 weeks. During placebo, plasma ANP levels proved to be higher in elderly patients than in young subjects. Chronic treatment with verapamil induced a rise in ANP levels in both young and elderly patients with hypertension.