O. B. Holland

Further evaluation of saline infusion for the diagnosis of primary aldosteronism.

Normal subjects, normal-renin hypertensive patients, and low-renin hypertensive patients were evaluated by intravenous saline infusion and with a fludrocortisone acetate (Florinef) protocol to clarify diagnostic criteria for primary aldosteronism that are recommended for the saline infusion protocol. The patients consumed a 200 mEq sodium, 70 mEq potassium diet for 6 days, and on the last 3 days received Florinef 0.5 mg orally twice daily. On Days 3 and 6, urinary aldosterone and tetrahydroaldosterone excretions were determined, and on Days 4 and 7 plasma aldosterone (PA) was determined at 0600 after overnight recumbency and at 0800 after 2 hours of walking. Although the level of normal PA suppression by saline infusion has been commonly defined as 10 ng/dl, a value of 5 ng/dl was originally recommended. In 20 normal subjects and 45 normal-renin hypertensive patients, we found that the PA was almost always suppressed below 5 ng/dl. In 18 of 75 low-renin patients including five with aldosterone-producing adenoma (APA), the PA was never suppressed below 10 ng/dl; thus, these 18 patients had classical primary aldosteronism by generally accepted criteria. The Florinef protocol was performed in eight of these 18 patients and was abnormal in all. An abnormal Florinef protocol was also found in seven of 15 patients studied with PA suppression after saline infusion to between 5 and 10 ng/dl, but in only one of 24 patients studied with PA suppression below 5 ng/dl. Additional studies in the subgroup with abnormal results from the Florinef protocol indicated that none of these patients had evidence of APA, so they had nontumorous primary aldosteronism (NTPA).(ABSTRACT TRUNCATED AT 250 WORDS)

Dose-Dependent Systemic and Regional Hemodynamic Effects of Calcitonin Gene-Related Peptide

The dose-response effects of infused calcitonin gene-related peptide (CGRP), a potent vasodilator, on systemic and regional hemodynamics in the conscious rat remain incompletely defined. The radioactive microsphere technique provided these determinations before and after the intravenous administration of vehicle or 22, 65, 220, and 2200 pmol of CGRP. Neither vehicle nor 22 pmol of CGRP significantly changed any systemic or regional hemodynamic parameter. Starting at the 65-pmol dose, CGRP significantly decreased mean blood pressure and total peripheral resistance, while increasing heart rate without changing cardiac output. CGRP produced selective regional vasodilatory effects, with the coronary circulation being unusually sensitive. In contrast, CGRP caused significant increases in blood flow to the mesenteric and cutaneous circulations only at the two highest doses. CGRP increased plasma norepinephrine, epinephrine, and renin activity significantly at only the 2200-pmol dose. In conclusion, CGRP decreases blood pressure by peripheral vasodilation, with a threshold dose occurring between 22 and 65 pmol. In addition, the coronary circulation appears to be particularly sensitive to the vasodilatory properties of CGRP.

Urinary excretion of prostaglandin E2, prostaglandin F2 alpha, and thromboxane B2 in normotensive and hypertensive subjects on varying sodium intakes.

A deficiency in renal prostaglandins has been implicated in the pathogenesis of essential hypertension, particularly low renin hypertension. Previous studies of urinary prostaglandins as influenced by sodium balance and in essential hypertension have been handicapped by problems with assay methodology, inclusion of male subjects, and/or failure to standardize daily fluid consumption. We compared urinary excretion of prostaglandin E2 (PGE,), prostaglandin F ^ (PGF^), and thromboxane B2 (TxB2) in black and white normotensive and low-renin and normal-renin hypertensive women during two protocols producing sodium depletion (10 mEq sodium diet) and sodium loading (200 mEq sodium diet plus the fludrohydrocortisone Florinef, a synthetic mineralocorticoid). A constant fluid, potassium, and caloric intake was maintained throughout. Changes in plasma renin activity, urinary aldosterone excretion, and urinary kallikrein excretion were simultaneously assessed. As sodium intake decreased from 120 to 10 mEq sodium/day, increases in urinary PGF^ (502 ± 60 to 1222 ± 176 ng/24 hr, p < 0.01) and TxB; (99 ± 33 to 216 ± 77 ng/24 hr, p < 0.05) excretion were observed in normotensive subjects. These increases were not observed in the hypertensive patients, possibly because less renin stimulation was achieved during the low sodium diet. Alternatively, subnormal prostaglandin production may have contributed to the lesser renin stimulation. Furthermore, urinary PGF, excretion in hypertensive patients during sodium depletion indicated strong influences of race and renin status; namely, black and normal-renin hypertensives increased urinary PGF^ excretion during sodium depletion whereas white and low-renin hypertensives did not. When white hypertensives and normotensive subjects consumed either 120 or 200 mEq sodium diet, there were no consistent differences in urinary excretion of PGE2, PGF^, or TxB2. With sodium loading, urinary PGE,, PGF^, and TxB2 excretion did not change, whereas urinary kallikrein excretion increased. Urinary excretion of these prostanoids was therefore independent of mineralocorticoid and kallikrein effects upon the kidney. Thus, we found no evidence for a role of renal PGE2, PGF^, and TxB2 in natriuresis in humans. Urinary excretion of these prostanoids was decreased in hypertensive patients only during sodium depletion. (Hypertension 4: 735-741, 1982)

Synergistic effect of captopril with hydrochlorothiazide for the treatment of low-renin hypertensive black patients.

Diuretics have been particularly successful for treatment of low-renin hypertension (LRH), although they may cause metabolic complications such as hypokalemia and hyperglycemia. Since the efficacy of diuretics is largely limited by reactive angiotensin II production, a combination of a converting enzyme inhibitor with a diuretic should be synergistic, particularly in LRH, where heightened aldosterone production in response to angiotensin II has been noted. Eighteen patients with LRH were treated initially with either captopril alone (450 mg/day) or hydrochlorothiazide (HCTZ) (up to 100 mg/day). Captopril alone only reduced average placebo standing blood pressure from 151/100 to 146/96 mm Hg. Combination of HCTZ with captopril reduced average standing blood pressure to 111/76 mm Hg at 3 months and 116/81 mm Hg at 1 year while allowing reductions in average captopril dosage to 100 mg/day and HCTZ dosage to 40 mg/day and reductions in supplemental potassium administration and in HCTZ-induced hyperglycemia. Captopril monotherapy did not increase urinary excretion of kallikrein, prostaglandin E2, or 6-keto prostaglandin F1 alpha, a metabolite of prostacyclin, and did not reduce urinary aldosterone excretion chronically. Thus, a synergism of captopril with HCTZ may be advantageous in certain patients with LRH.

Effect of dietary calcium supplementation on blood pressure and calciotropic hormones in mineralocorticoid-salt hypertension

In order to determine the effect of dietary calcium supplementation on blood pressure and calciotropic hormones, we studied two groups (n = 12 each) of mineralocorticoid [deoxycorticosterone (DOC)]-salt hypertensive rats, one receiving a normal-calcium diet (0.6% calcium, as calcium carbonate) and the other a high-calcium diet (2.5% calcium), over an 8-week period. Dietary calcium supplementation significantly attenuated the rise in blood pressure. Serum ionized calcium concentrations were significantly decreased from baseline levels in both groups but tended to be higher among the calcium-supplemented rats. Serum concentrations of parathyroid hormone (PTH) and 1,25-dihydroxyvitamin D3 (1,25-D) were significantly higher in the DOC-salt rats than in normotensive rats fed normal rat chow [PTH: 49 +/- 4 versus 15 +/- 0.9 pg/ml (means +/- s.e.m.); 1,25-D: 108 +/- 7 versus 73 +/- 13 pg/ml, in DOC-salt and normotensive rats, respectively]. In the DOC-salt rats, dietary calcium supplementation did not significantly lower the elevated serum concentration of PTH (from 49 +/- 4 to 40 +/- 4 pg/ml; NS), but did significantly reduce that of 1,25-D (from 108 +/- 7 to 66 +/- 8 pg/ml; P less than 0.01). Since 1,25-D may increase vascular smooth muscle calcium uptake, dietary calcium supplementation may lower blood pressure in DOC-salt hypertension, in part, by suppressing 1,25-D.

Systemic and regional hemodynamic effects of dietary calcium supplementation in mineralocorticoid hypertension.

This study was undertaken to determine the systemic and regional hemodynamic effects of long-term dietary calcium supplementation in mineralocorticoid (DOC)-salt hypertension. Systemic and regional hemodynamic measurements were determined by the radioactive microsphere technique in conscious and unrestrained rats (kidneys intact) with DOC-salt-induced hypertension that were pair-fed either a normal calcium (0.6% by weight, n = 12) or a calcium-supplemented (high-calcium) diet (2.5% by weight, n = 12). After 7 to 8 weeks, there were no differences in weight, heart rate, or cardiac output between the two groups. In contrast, the high-calcium rats had a significantly lower mean blood pressure (125 +/- 4 mm Hg, mean +/- SEM) than the normal calcium rats (143 +/- 5 mm Hg); this finding appeared to result predominantly from a reduction in total peripheral resistance. The high-calcium rats had a higher renal blood flow (7.8 +/- 0.5% vs. 6.2 +/- 0.4% cardiac output; p less than 0.05) and lower renal (14.3 +/- 1 vs. 19.3 +/- 2 mm Hg/min/ml/g tissue; p less than 0.05) and jejunal vascular resistance than did the normal calcium rats. Two additional identical groups of normal calcium-and high-calcium-DOC-salt rats (n = 12 each) were also studied. In these rats, serum-ionized calcium decreased significantly (p less than 0.05) from baseline in both groups. Urinary sodium increased in both groups but did not differ significantly. In conclusion, dietary calcium supplementation attenuates the rise in peripheral vascular resistance that accompanies DOC-salt hypertension. This attenuated resistance appears to be relatively selective and is noted particularly in the renal vasculature.

Systemic and regional hemodynamic effects of 1,25-dihydroxyvitamin D3 administration.

OBJECTIVE To evaluate the cardiovascular effects of 1,25-dihydroxyvitamin D3 (1,25-D). DESIGN Recent studies suggest that Ca-regulating hormones may contribute to the genesis of hypertension. We determined systemic and regional hemodynamics 24 h after administration of 1,25-D or vehicle to normal conscious Sprague-Dawley rats. In addition, to dissociate the vascular effects of 1,25-D from changes in serum ionized Ca2+, 1,25-D and vehicle were administered to rats maintained for 3 days on a low-Ca diet. To evaluate the effect of the slight rise in serum ionized Ca2+ with 1,25-D administration, we infused CaCl or vehicle over 1 h into normal rats to raise the serum Ca2+ to near that of rats treated with 1,25-D. METHODS The radioactive microsphere technique was used. RESULTS Systemic hemodynamics (blood pressure, heart rate, cardiac output, total peripheral resistance and stroke volume) did not differ between the two groups receiving a normal-Ca diet. In these rats 1,25-D significantly decreased renal blood flow (RBF), increased renal vascular resistance (RVR) and slightly increased serum ionized Ca2+. Similarly, in rats receiving a low-Ca diet, 1,25-D administration decreased renal blood flow, increased renal vascular resistance and caused only a minimal increase in serum ionized Ca2+. A low-Ca diet also increased heart rate, cardiac blood flow and renal blood flow. Although CaCl infusion raised serum ionized Ca2+, blood pressure, renal blood flow and renal vascular resistance did not change significantly. CONCLUSION 1,25-D may constrict the renal vasculature directly or indirectly by enhancing the vascular sensitivity to circulating vasoconstrictors.

Plasma substance p levels in normotensive and hypertensive subjects

Since substance P is a potent natriuretic, diuretic, and vasodilatory peptide, a radioimmunoassay for substance P was developed, and its levels measured in the plasma of normal subjects and patients with essential hypertension. The plasma substance P levels were 186+/-14 pg/ml in normal subjects and 164+/-3 pg/ml in hypertensive patients. When the sodium content of their diet was reduced to 10 mEq/day, substance P levels failed to change, but plasma renin activity and urinary kallikrein increased. An acute saline infusion also failed to alter plasma substance P levels. Assuming an upright posture increased plasma renin activity, but not substance P, in both groups of subjects. Thus, it appears that substance P is not involved in the control of blood pressure, kallikrein excretion or renin release in man.

Haemodynamic response to magnesium administration in mineralocorticoid-salt and two-kidney, one clip renovascular hypertension

Recent interest has centred on the role of divalent cations in hypertension, particularly in relation to the renin-angiotensin system. This study was undertaken to determine the hypotensive effect of magnesium administration in relation to the state of activation of the renin-angiotensin system. The mean blood pressure (MBP) and heart rate (HR) response to either the acute intravenous administration of a pharmacological dose of MgSO4 or vehicle was determined in conscious mineralocorticoid-salt (DOCA-salt, low-renin) and two-kidney, one clip renovascular, high-renin hypertensive rats. Baseline MBP was higher in the renovascular than in the DOCA-salt rats, while there was no difference in HR or serum Mg concentration between the two. Following administration of MgSO4, serum Mg increased equally in both the DOCA-salt (1.4 +/- 0.8 to 4.9 +/- 0.16 mEq/l; P less than 0.001) and in the renovascular rats (1.8 +/- 0.14 to 4.4 +/- 0.27 mEq/l; P less than 0.001). Magnesium administration significantly lowered MBP over the 1-h infusion in the DOCA-salt (167 +/- 8 to 145 +/- 5 mmHg, P less than 0.001) but not the renovascular hypertensive rats (191 +/- 5 to 183 +/- 4, NS). We conclude that the blood pressure lowering effect of Mg is related, in part, to the state of activation of the renin-angiotensin system. The mechanism of this differential effect remains to be determined.

Rapid chromatographic purification of urinary steroid glucuronates for determination of aldosterone secretion rate

Aldosterone secretion rate (ASR) is utilized as a rapid screening procedure to detect subtle forms of hypertension. A rapid and robust chromatographic method has been developed, based on easily prepared, rigid matrices, which permit the flow of urine by suction through sequential purification columns. Both major metabolites, aldosterone glucuronate and tetrahydroaldosterone glucuronate, are isolated in ca. 75% yield. They are hydrolyzed and quantitated by high-performance liquid chromatography-radioimmunoassay (HPLC-RIA) or, for bulk preparation, further purified by preparative chromatofocusing. These two polar conjugates are isolated in nearly pure form by HPLC on a C2 column with a two-step gradient. An ASR determination can be completed in one to two working days; preparative-scale work takes somewhat longer.