A role for the adrenal renin-angiotensin system in the regulation of potassium-stimulated aldosterone production.

Potassium is a major regulator of aldosterone production. It also increases adrenal renin. The causal relationship between potassium and adrenal renin is not known. To evaluate the role of the intraadrenal renin-angiotensin (ANG) system in potassium-stimulated aldosterone synthesis and release, specific adrenal renin activity, PRA, and plasma aldosterone were measured during potassium loading or captopril treatment in the rat. Adrenal ANGs were determined using a HPLC system combined with RIA to obtain quantitative information on the components of the adrenal renin-ANG system. In addition, the effect of pretreatment with captopril on aldosterone production by isolated adrenal glomerulosa cells was examined. In intact animals potassium loading markedly increased adrenal renin and plasma aldosterone, whereas PRA was suppressed. The administration of captopril to rats in normal potassium balance did not suppress plasma aldosterone. Captopril treatment during potassium loading inhibited the potassium-induced increase in aldosterone. Furthermore, pretreatment with captopril suppressed adrenal ANG II and reduced the response of aldosterone production to extracellular potassium concentration by isolated adrenal glomerulosa cells in vitro. These results suggest that the adrenal renin-ANG system plays a significant role in the control of aldosterone production under potassium stimulation.

Local generation and release of angiotensin II in peripheral vascular tissue.

Isolated rat hindlegs were perfused with Krebs-Ringer solution, and immunoreactive angiotensin II (irAng II) released into the perfusate was directly determined using a Sep-Pak C18 cartridge connected to the perfusion system. High performance liquid chromatography clearly demonstrated the presence of angiotensin I (Ang I), angiotensin II (Ang II), and a small amount of angiotensin III. The spontaneous release of irAng II was as high as about 600 pg/30 min, which was stable up to 3 hours. Captopril added to the perfusion medium (10(-9) to 10(-6) M) suppressed irAng II release in a dose-dependent manner (p less than 0.001), and it (10(-6)M) caused a reciprocal increase of irAng I release (p less than 0.05). Oral pretreatment of captopril (50 mg/kg/day) for 1 week suppressed the irAng II release by 31% (p less than 0.02). The same treatment with SA 446, a highly lipophilic angiotensin converting enzyme inhibitor, inhibited the irAng II release by 63% (p less than 0.001). On the other hand, the two inhibitors suppressed the plasma irAng II to very similar extents. Pretreatment with SA 446 plus nephrectomy did not cause any further change in irAng II release as compared with that with SA 446 alone. These results provide direct proof for local generation and subsequent secretion of Ang II by peripheral vascular tissue.

Renin inhibitor and converting enzyme inhibitors suppress vascular angiotensin II.

The direct effects of a renin inhibitor, N-acetyl-pepstatin and five angiotensin converting enzyme inhibitors, captopril and the active diacid forms of enalapril, ramipril, cilazapril, and CS-622, on the vascular renin-angiotensin system were examined in isolated perfused rat mesenteric arteries. Vascular renin activity and angiotensin II (Ang II) released into the perfusate were determined. Infusion of N-acetyl-pepstatin (5 X 10(-8)-5 X 10(-6) M) suppressed vascular renin activity and Ang II release dose dependently. Isoproterenol (10(-6) M) induced a 135 +/- 30% increase in Ang II release from the basal value. N-Acetyl-pepstatin (5 X 10(-6) M) suppressed isoproterenol-induced Ang II release. Infusions of 5 X 10(-6) M captopril and the diacid forms of enalapril, ramipril, cilazapril, and CS-622 by themselves had little effect on Ang II release, but concomitant infusion of isoproterenol with these angiotensin converting enzyme inhibitors significantly decreased Ang II release (71 +/- 21%, 51 +/- 40%, 8 +/- 21%, 69 +/- 24%, and 44 +/- 29% increase, respectively, from the basal values). These results indicate that N-acetyl-pepstatin suppresses the vascular renin-angiotensin system. This effect may in part contribute to the hypotensive actions of renin inhibitors. Although angiotensin converting enzyme inhibitors also suppress locally generated Ang II, the mechanism and physiological significance still remain to be clarified.

Effects of endothelin on neuroeffector junction in mesenteric arteries of hypertensive rats.

The effect of endothelin, a novel vasoconstrictor peptide, on the adrenergic neuroeffector junction was investigated in isolated perfused mesenteric arteries of spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats. The vasoconstrictor responses to periarterial sympathetic nerve stimulation and exogenous norepinephrine were determined. Infusion of endothelin-1 increased the baseline perfusion pressure dose dependently to similar extents in the two strains. A subpressor dose of endothelin-1 (10(-10) M) enhanced the pressor response to norepinephrine; its effect was greater in WKY rats than in SHR. Endothelin-1 (10(-12) to 10(-10) M) attenuated the pressor response to sympathetic nerve stimulation, and the degree of inhibition tended to be less in SHR than in WKY rats. Higher doses (3 x 10(-10) and 10(-9) M) of endothelin-1 enhanced the pressor response to nerve stimulation in both WKY rats and SHR. Endothelin-1 inhibited norepinephrine release from rat mesenteric arteries; the inhibition was significantly less in SHR than in WKY rats. These results suggest that endothelin enhances the responsiveness of alpha-adrenergic receptors to catecholamines, whereas it inhibits presynaptic adrenergic neurotransmission. Thus, endothelin can interact with the neuroeffector junction in addition to having a vasoconstricting effect in peripheral vessels. The difference in the mode of modulation by endothelin at the vascular neuroeffector junction in SHR from that in WKY rats might explain the maintenance of hypertension.

Plasma inactive renin in patients with hyperthyroidism.

Active and inactive PRA were measured after 1 h at rest in 16 normal controls and 20 patients with hyperthyroidism. In some of the patients these measurements were repeated after they had become euthyroid or received 90 mg propranolol for 1 week. Inactive PRA was determined as the difference between total PRA after trypsin activation and active PRA. Active PRA was significantly higher (P less than 0.01) in untreated patients than in normal subjects; however, the inactive PRA of patients was not different compared with that of normal subjects. Active PRA was normalized, and inactive PRA did not change after achievement of euthyroidism. The proportion of active of total PRA was significantly correlated with the levels of serum thyroid hormones (T3 and T4) in hyperthyroid patients (r = 0.46; P less than 0.05 and r = 0.55; P less than 0.01, respectively). The administration of propranolol reduced active PRA (P less than 0.05) and increased inactive PRA slightly but not significantly. These results indicate that in hyperthyroidism, the in vivo conversion of inactive renin to active renin is probably facilitated by increased sympathetic activity.

Blood pressure response to an angiotensin II antagonist in patients with acromegaly.

The renin-angiotensin-aldosterone system in patients with acromegaly was evaluated by infusing [sarcosine1, isoleucine8]angiotensin II, a competitive angiotensin II antagonist, into five acromegalic patients with hypertension and three normotensive acromegalics. The drug was infused at a rate of 600 ng/kg . min for 30 min, 1 h after iv injection of 40 mg furosemide. In addition, before the infusion, plasma samples were obtained for determination of PRA and plasma aldosterone concentration. A significant pressor response to [sarcosine1, isoleucine8]angiotensin II was observed in all eight patients. Preinfusion PRA and plasma aldosterone concentration were significantly lower than in normal controls. It is concluded that in acromegaly, the renin-angiotensin-aldosterone system is suppressed and that this system is probably not involved in maintenance of the high blood pressure observed in some acromegalic patients.

Tissue angiotensinogen gene expression induced by lipopolysaccharide in hypertensive rats.

There is now convincing evidence that various tissues express their own tissue renin-angiotensin system, which may be regulated independently of the systemic renin-angiotensin system. However, little information is available on the regulation of the tissue renin-angiotensin system. We investigated the regulation of tissue angiotensinogen gene expression with respect to the development of hypertension. We measured basal and lipopolysaccharide-stimulated plasma angiotensinogen concentrations by radioimmunoassay and examined the expression of tissue angiotensinogen by Northern blot analysis in spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY) at 4 and 13 weeks of age. Basal plasma angiotensinogen concentration in SHR was comparable to that in WKY at 4 weeks of age and was significantly higher than that in WKY at 13 weeks of age. Lipopolysaccharide induced a significant increase in plasma angiotensinogen concentration in both WKY and SHR at 4 and 13 weeks of age. At 4 weeks of age, the basal levels of angiotensinogen mRNA in the liver, fat, adrenal, and aorta were higher in WKY than in SHR. At 13 weeks of age, the basal levels of angiotensinogen mRNA in the fat, adrenal, aorta, spleen, and kidney were higher in WKY than in SHR, while that in the liver did not differ significantly between the two strains. At 4 weeks of age, pretreatment with lipopolysaccharide increased the angiotensinogen mRNA levels in the liver, fat, adrenal, and aorta in both WKY and SHR. At 13 weeks of age, pretreatment with lipopolysaccharide increased the angiotensinogen mRNA levels in the liver, aorta, and adrenal; decreased those in the spleen; and had no effect in the kidney in both WKY and SHR. Interestingly, lipopolysaccharide increased the angiotensinogen mRNA level in fat only in SHR, with no effect in WKY, at 13 weeks of age. Lipopolysaccharide stimulated tumor necrosis factor-a mRNA expression in fat of WKY and SHR, and the increase in tumor necrosis factor-alpha mRNA level in SHR was significantly greater than that in WKY. Therefore, the increased tumor necrosis factor-alpha mRNA expression may be involved in the increased lipopolysaccharide-induced expression of angiotensinogen gene in fat of SHR at 13 weeks of age. These data suggest that the transcriptional and probably posttranscriptional regulation of angiotensinogen mRNA differs between SHR and WKY, that the regulation of angiotensinogen gene expression is tissue-specific, and that the altered expression of the angiotensinogen gene may be involved in the development of hypertension.

Responses of active and inactive plasma renin and changes in urinary kallikrein and plasma prekallikrein to various conditions in normal subjects.

Little is known about changes in inactive plasma renin in various conditions or the in vivo activation mechanism of inactive renin. The effects of various factors known to stimulate or suppress renin release on active and inactive PRA were examined in normal subjects. Inactive PRA was determined as the difference between the total PRA after trypsin activation and active PRA. Concurrent measurements of urinary kallikrein excretion and plasma prekallikrein activity were performed to assess the possible role of renal or plasma kallikrein in in vivo activation of inactive renin. Short term stimulation with iv furosemide and ambulation, infusion of isoproterenol, and administration of captopril increased active PRA, but had little or no effect on inactive PRA. Sodium restriction and sodium loading, each for 4 days, induced parallel changes in active and inactive PRA. The administration of propranolol for 4 days decreased active PRA but did not change inactive PRA. There were no significant correlations between the changes in urinary kallikrein excretion and those in active PRA or in the proportion of active to total PRA after any short term treatments, except furosemide administration. Plasma prekallikrein activity was correlated with the proportion of active renin only during the long term sodium balance study. The present data suggest that the mechanisms ofr the control of inactive and active renin are different. Neither renal nor plasma kallikrein seems to be consistently involved in the in vivo activation of inactive renin.

The effect of aging on urinary kallikrein excretion in normotensive subjects and in patients with essential hypertension.

The effect of aging on urinary kallikrein excretion (UkalV) was investigated in 54 normal subjects, 11-88 yr old, and 37 patients with essential hypertension, 17-82 yr old. Urinary sodium, potassium, and aldosterone excretion (U(Ald)V) were also measured in these subjects. Urinary sodium and potassium excretion in both normal subjects and hypertensive patients did not significantly change with aging. In normal subjects, U(kal)V (r = 0.45; P less than 0.001) and U(Ald)V (r = 0.58; P less than 0.01) significantly decreased with increasing age. U(kal)V was positively correlated with U(Ald)V (r = 0.44; P less than 0.001). In contrast, the hypertensive patients had a significant decrease with age in U(Ald)V (r = -0.36; P less than 0.05), but no significant age-related change in U(kal)V. No significant correlation between U(kal)V and U(Ald)V was observed in the hypertensive patients. In individuals less than 60 yr old, there was no significant difference in U(kal)V values between normal subjects and hypertensive patients. Hypertensive patients more than 60 yr old excreted more urinary kallikrein than normal subjects of the same age group (P less than 0.05). In conclusion, the age-related decrease of U(kal)V in normal subjects may be due to the reduced activity of the renin-angiotensin-aldosterone system. It remains to be elucidated whether the absence of the age-related decrease in U(kal)V in hypertensive patients is related to the pathogenesis or pathophysiology of essential hypertension.

Hormonal responses to long-term converting enzyme inhibition in hypertensive patients.

Captopril was given alone and in combination with diuretics to 49 patients with hypertension for 1 to 12 mol Within 2 mo blood pressure reduction correlated with pretreatment plasma renin activity and response to the infusion of angiotensin II antagonist, but these effects were not present at 4 mo. Plasma and urinary aldosterone were suppressed but serum converting enzyme activity, plasma bradykinin, kallikren, and prostaglandins (E and F) were in the normal range effect of captopril. Despite sustained reduction of blood pressure, plasma catecholamines were not elevated and urinary catecholamines were suppressed in patients on captopril alone. It is concluded that another mechanism, such as enhancement of renal or local kinin-prostaglandin system, as well as suppression of the renin-angiotensin-aldosterone system may be involved in the long-term efficacy of captopril. Sympathetic activity may also be depressed and contribute to the hypotensive effect.

Long-term effects of captopril in hypertension.

Captopril was given for treatment of hypertension alone or in combination with diuretics to 32 patients for 1- to 4-mo periods. The decrement of mean blood pressure after 1 and 2 mo correlated with pretreatment plasma renin activity (PRA) and the response of blood pressure to infusion of an angiotensin II antagonist. These correlations were no longer apparent after 4 mo of treatment. When subjects with a decrement of mean blood pressure that exceeded 13 mm Hg were compared with nonresponders, responders not only had higher control PRA and higher PRA at 1 mo of treatment, but also had decreased plasma aldosterone levels, decreased urinary aldosterone excretion, and increased serum postassium levels that persisted over the 4 mo of observation. The reduction of plasma aldosterone correlated with the fall of mean blood pressure. Urinary kallikrein, catecholamines, electrolytes, and endogenous creatinine clearance did not change in response to treatment. These findings indicate that the antihypertenisve activity of captopril on long-term administration probably depends in part on the blockade of angiotensin II, but other mechanisms cannot be excluded.

Hemodynamic, renal, and hormonal responses to alpha-human atrial natriuretic peptide in patients with congestive heart failure.

Hemodynamic, renal, and hormonal effects of intravenous bolus injection of 50 micrograms synthetic alpha-human atrial natriuretic peptide (alpha-hANP) were studied in eight patients with congestive heart failure. alpha-hANP caused significant reductions in mean blood pressure and systemic vascular resistance. These responses were sustained up to 90 minutes and not accompanied by reflex tachycardia. Cardiac index and stroke volume index increased significantly at 90 minutes and pulmonary capillary wedge pressure, pulmonary arterial pressure, and mean right atrial pressure remained unchanged. Urine volume, urinary sodium excretion, creatinine clearance, and fractional excretion of sodium increased significantly, but fractional excretion of potassium and phosphate did not change. Elevated plasma renin activity, plasma aldosterone, and norepinephrine were suppressed after the injection of alpha-hANP. The bolus injection of this peptide has moderately hypotensive, vasorelaxant, and natriuretic effects in patients with congestive heart failure.

Converting enzyme inhibitors regressed cardiac hypertrophy and reduced tissue angiotensin II in spontaneously hypertensive rats.

To examine the role of the tissue renin-angiotensin system in left ventricular hypertrophy, converting enzyme inhibitors were administered orally to 12-week-old male spontaneously hypertensive rats (SHR) for 4 weeks, and cardiac tissue angiotensin II was measured. Treatment with enalapril (10 mg/kg per day) and trandolapril (1 mg/kg per day) lowered systolic blood pressure, left ventricular weight and left ventricular angiotensin II content. Plasma angiotensin II concentration was increased by the treatment with enalapril whereas trandolapril did not cause any change. There was significantly positive correlation between left ventricular weight and angiotensin II content. Because angiotensin II promotes cell proliferation, these results suggest that cardiac tissue angiotensin II, rather than circulating angiotensin II, may account for the pathophysiology of left ventricular hypertrophy in SHR.

Urinary catecholamine response to glucagon in young and elderly patients with essential hypertension.

The role of the sympathetic nervous system (SNS) in essential hypertension was evaluated by examining the response of urinary catecholamines to the intramuscular injection of glucagon in both young and elderly normal subjects (total 16) and in both young and elderly patients with essential hypertension (total 16). Urine was collected for 2 hours before glucagon injection and for 2 and 4 hours after injection, for determination of adrenaline and noradrenaline. The increments of urinary adrenaline and noradrenaline after glucagon injection were significantly higher in young hypertensive than in young normotensive subjects or in normotensive and hypertensive elderly subjects. The observation that the reactivity of the SNS is increased in young patients with essential hypertension lends support to the hypothesis that the SNS is more important in the maintenance of hypertension in the young than in the elderly.

Effect of age on active and inactive plasma renin in normal subjects and in patients with essential hypertension.

The effect of age on the levels of active and trypsin-activatable inactive plasma renin was examined in 41 normal subjects and 54 patients with essential hypertension, during recumbency and after stimulation with furosemide and ambulation. Active renin levels in supine subjects and patients decreased with age. Inactive renin levels did not change with age in normal subjects, whereas in hypertensive patients they decreased with age. Following stimulation with furosemide and ambulation, the levels of active renin increased but the responsiveness to stimulus decreased with age in both groups. In contrast, inactive renin levels slightly increased after furosemide administration and ambulation, resulting in increased proportion of active to total renin. These data show that an acute stimulation with furosemide and ambulation affects mainly the active form of plasma renin, and the effect of age on inactive plasma renin in normal subjects may be different from that in patients with essential hypertension.

Active and inactive renin in the adrenal.

Specific renin has been identified in the outer layers of the adrenals of rat, mouse, and human and the inner cortical layers but not in the medulla of mouse adrenals. Nephrectomy causes a marked elevation of adrenal renin, presumably through hyperkalemia. The subcellular distribution of adrenal renin was investigated by Percoll density gradient. The renin activity in the dense granules from the capsules of nephrectomized rats was 15 times greater than that of intact rat. Most of the active form renin was found in dense renin granules. Immunohistochemical studies revealed that the dense granules increased in number after bilateral nephrectomy. Immunogold staining of these granules showed unequivocally the presence of renin therein. Adrenal capsules in organ culture were found to release renin at a steady rate. Renin release from bilaterally nephrectomized rat adrenals was 46 times greater than from the organs of intact animals. The mechanism of the control of renin secretion from the adrenal gland was different from the kidney in that the secretion was stimulated by potassium chloride (10 mol/L) or angiotensin II (10(-9) to 10(-7) mol/L) but not by ACTH (10(-9) to 10(-7) mol/L), suggesting stimulation by intracellular calcium. These results provide evidence that the adrenal synthesizes renin, stores it in specific secretory granules, and secretes it in a regulated manner. Prorenin in the adrenal tissue accounted for only 10% of the total renin whereas 90% of the secreted renin was inactive.

Angiotensin converting enzyme inhibitors suppress the vascular renin-angiotensin system of spontaneously hypertensive rats.

The effects of angiotensin converting enzyme (ACE) inhibitors on the release of angiotensin II (Ang II) from isolated mesenteric arteries of spontaneously hypertensive rats (SHRs) were examined. Delapril, enalapril, and captopril suppressed Ang II release in a dose-dependent manner. After oral treatment with delapril (10 mg/kg/day), enalapril (10 mg/kg/day), and captopril (50 mg/kg/day) for 1 week, the blood pressure of SHRs was significantly reduced in the three groups and 54%, 46%, and 36% decreases in basal Ang II release were observed, respectively, compared with control. However, low-dose captopril (10 mg/kg/day) had no effect on blood pressure or basal Ang II release. These results provide clear evidence that ACE inhibitors suppress vascular renin-angiotensin activity of SHRs, and the possible contribution of the tissue renin-angiotensin system to spontaneous hypertension is suggested.

Plasma angiotensinogen concentrations in obese patients.

A close relationship between obesity and hypertension has been recognized, and plasma angiotensinogen concentrations (p-AGT) have been reported to correlate with blood pressure (BP). However, little is known about AGT in obese patients with hypertension. To define the role of AGT in obese hypertension, we measured p-AGT in obese patients. The subjects were 42 obese patients diagnosed on the basis of a body mass index (BMI) of more than 25 kg/m2, and 21 sex- and age-matched nonobese patients, whose BMI was less than 25 kg/m2. The hypertensive patients had not previously received antihypertensive drugs. P-AGT (P < .05) and mean BP (P < .0001) was increased in the obese patients as compared with the nonobese patients. Positive correlations were observed between BMI and p-AGT, mean BP and p-AGT, and BMI and mean BP (all P < .05). However, after adjustment for blood pressure, p-AGT was not different between groups, and after adjustment a positive correlation remained only between BMI and mean BP. These results suggested the possible involvement of increased p-AGT in hypertension in obese patients, although this may be a secondary change to hypertension or obesity.

Effect of atrial natriuretic factor on central angiotensin II-induced responses in rats.

The effect of intracerebroventricular (ICV) injection of atrial natriuretic factor (ANF) on drinking and pressor responses induced by centrally administered angiotensin II (AII) was examined in the rat. The ICV injection of ANF attenuated water intake induced by AII or 48-hr water deprivation. In contrast, ANF did not affect AII-induced pressor responses. The ICV injection of ANF did not cause recognizable change in blood pressure in spontaneously hypertensive rats or Wistar-Kyoto rats. These results suggested that ANF in the brain is involved in the central control of water intake. Brain ANF may be considered as a selective antagonist of the dipsogenic effect of AII but not its pressor effect.

Evaluation of damaged small intestine of mouse following methotrexate administration.

PURPOSE: Methotrexate (MTX) treatment causes damage to the small intestine, resulting in malabsorption and diarrhea. The active and passive transport capacities of the small intestine are decreased by the treatment. The purpose of this study was to evaluate the damage to the small intestine of mice caused by MTX administration by examining the permeability of the paracellular pathway of the small intestinal epithelium. METHODS: MTX was administered orally to male ddY mice once daily for 1-6 days. The permeability of the small intestine to the nonabsorbable markers phenol red (PR) and fluorescein isothiocyanate (FITC) dextrans was examined using everted segments of the intestine. RESULTS: PR and FITC dextran permeation through the small intestine increased significantly in parallel with changes in body weight of the mice, wet weight of the small intestine and chemical composition of the small intestinal epithelium. CONCLUSIONS: In addition to changes in permeation through the transcellular pathway reported previously, this study revealed that MTX treatment disorders the paracellular barrier function of the small intestinal epithelium, resulting in increased permeation of nonabsorbable markers via the paracellular pathway of the small intestinal mucosa. The present approach to the examination of the barrier function of the intestinal epithelium could be of great use in evaluating the damage to the small intestine and malabsorption.