Metabolism ClinicaL and Experimental DECEMBER

VOL 41, NO 12

1992

PRELIMINARY REPORT

Pulmonary Arterial Brain Natriuretic Peptide Concentration Cardiopulmonary Hemodynamics During Exercise in Patients With Essential Hypertension Masakazu

Kohno, Takeshi Horio, Koji Yokokawa,

Kaname Akioka,

Miwako

and

Ikeda, and Tadanao

Takeda

Brain natriuretic peptide (BNP) is secreted through the coronary sinus of the human heart. The purpose of this study was to determine whether BNP secretion from the heart is stimulated by exercise and to examine the relationship between pulmonary arterial BNP concentrations and hemodynamic measurements, especially cardiopulmonary hemodynamics, during exercise in patients with essential hypertension. The exercise protocol consisted of three fixed workloads (25, 50, 75 W) on a bicycle ergometer in the supine position. The mean pulmonary arterial BNP level at rest was 14.8 ? 4.1 pg/mL, and BNP values gradually increased with higher stages of exercise. At the maximum exercise stage, the BNP value increased to 40.9 f 6.5 pg/mL. Close correlations of pulmonary arterial pressure (PAP) and pulmonary arterial wedge pressure (PAWP) with pulmonary arterial BNP level were observed at four points at rest and during each stage of exercise. In contrast, heart rate, mean blood pressure, cardiac index (Cl), and stroke index (SI) were not correlated with BNP values. Results suggest that cardiac secretion of BNP was increased during exercise in essential hypertensive subjects, and the observed increase of BNP may be related to elevated PAP and PAWP. The enhancement of BNP secretion during exercise in these patients may reflect increased redistribution of blood to the cardiopulmonary compartment Copyright c 1992 by W.B. Saunders Company

B

RAIN NATRIURETIC PEPTIDE (BNP) was first identified in porcine brain] and later isolated from porcine heart.? Porcine BNP consists of 26 amino acid residues with much homology to the sequence of atria1 natriuretic peptide (ANP).’ BNP has diuretic, natriuretic, and hypotensive effects, and it also relaxes the chick rectum, as ANP does.’ BNP interacts with the same receptors as ANP in vascular smooth muscle cells.3 A low-molecular-weight form of human BNP, human BNP32, that corresponds to the C-terminal sequence (77-108) of the human BNP precursor deduced from the cDNA sequence was found in the human atrium.4 Recently, Mukoyama et al and web have shown that this peptide is secreted through the coronary sinus of the human heart and that its concentration is high in patients with congestive heart failure and in hypertensive patients with left ventricular hypertrophy. Results obtained during diagnostic cardiac catheterization6 also suggest that concentrations in the pulmonary artery closely reflect the cardiac secretion of BNP, which contained true mixed venous blood, including the admixture of coronary sinus flow, that had not yet crossed the vascular bed of any organ. Therefore, we examined the relationship between pulmonary arterial BNP concentrations and hemodynamic measurements, esMetabolism, Vol41, No 12 (December), 1992: pp 1273-1275

pecially cardiopulmonary in patients with essential

hemodynamics, hypertension.

during

exercise

SUBJECTS AND METHODS Subjects We studied six patients (five men and one woman; mean age, 48 years; range, 25 to 58 years) with mild to moderate essential hypertension. Clinical evaluation indicated that all had stage I to II essential hypertension by World Health Organization criteria. Secondary hypertension was excluded by clinical history, physical examination, and routine laboratory tests including measurements of plasma renin activity, aldosterone, and catecholamines. None of the subjects was in the accelerated or malignant stage of hypertension. In addition, none had clinical evidence of pulmonary disease,

From the First Department of Internal Medicine, Osaka City University Medical School, Osaka, Japan. Supported by a Grant-in-Aid for Scientific Research (No. 6148210) ,from the Ministry of Education, Science, and Culture, Japan. Address reprint requests to Masakazu Kohno, MD, First Depanment of Internal Medicine, Osaka City University Medical School. l-5-7 Asahi-machi, Abeno-ku, Osaka 5?5, Japan. Copyright 0 1992 by W.B. Saunders Company 0026049519214112-0001$03.00i0

1273

1274

KOHNO ET AL

Table 1. Hemodynamic Parameters at Rest and During Ergometric Exercise in Patients With Essential Hypertension Parameters

At Rest

25W

84 r 16

103 t 18t

119 t 21t

135 i 26t

148~

16*

155 + 15t

157 f 15t

Heart rate (beatsimin) MAP (mm Hg)

135 ?I 17

PAP (mm Hg)

5ow

75W

14.8 + 2.0

25.1 ? 3.4t

29.0 t 4.4t

30.1 + 3.5t

PAWP (mm Hg)

9.7 + 2.1

15.5 + 4.0t

17.3 + 4.1t

19.2 2 3.0t

Cl (Llminlm2)

3.8 + 1.2

5.8 ? 1.8t

6.6 + 1.7t

7.5 + 1.9t

46.8 f 11.3

57.0 + 15.8*

57.0 + 14.5*

56.7 + 13.7”

St (mL/beat/m*)

lP < .05 and tP < .Ol compared with values at rest.

angina, myocardial infarction, or marked renal damage. Only subjects who had not been treated earlier with antihypertensive drugs or whose antihypertensive drug therapy had been discontinued for at least the preceding 2 weeks were included in the study. Procedures After informed consent was obtained, right-sided cardiac catheterization was performed using a triple-lumen Swan-Ganz catheter inserted percutaneously via an antecubital vein. The exercise protocol consisted of three tied workloads. After the patients had achieved hemodynamic stability, graded exercise was performed on a supine bicycle ergometer. The initial workload was 25 W for 4 minutes, the second was 50 W for 4 minutes, and the third was 75 W for 4 minutes. Heart rate, mean arterial pressure (MAP), pulmonary arterial pressure (PAP), pulmonary arterial wedge pressure (PAWP), cardiac index (CI), and stroke index (SI) were measured at rest and during each stage of exercise. Heart rate and rhythm were determined by an electrocardiogram; blood pressure was measured by the standard cuff technique; PAP and PAWP were determined from the Swan-Ganz catheter; cardiac output (CO) was determined by the thermodilution method; and CI and SI were calculated as CO/BSA and CIIHR, respectively, where BSA is body surface area and HR is heart rate. During the hemodynamic study, blood samples were taken from the pulmonary artery via the Swan-Ganz catheter. BNP radioimmunoassay. A blood sample (6 mL) was drawn directly into a siliconized disposable glass tube containing Trasylol (Bayer, Leverkusen, Germany) (500 kallikrein inactivator UlmL) and EDTA (1 mg/mL) chilled on ice. Plasma was separated by centrifugation at 1,700 x g for 10 minutes at 4°C and immediately frozen and stored at -80°C until the radioimmunoassay was performed. Immunoreactive BNP (ir-BNP) was extracted using a Sep-Pak Cls cartridge (Water Associates, Milford, MA) as previously reported.GThe concentration of plasma ir-BNP was measured with human BNP-32 antiserum and ‘251-1abeledhuman BNP-32 (Peninsula Laboratories, Belmont, CA) as previously described.’ This antibody reacted 100% with human BNP-32 and cross-reacted 0.05% with rat BNP-32; it showed no cross-reactivity with a-human ANP (l-28) or (5-28), a-rat ANP (l-28). porcine BNP-26, rat BNP-45,l3-endorphin, angiotensin II, vasopressin, or endothelin-1. The interassay variation was 11.7%, and the intraassay variation was 7.0%.

RESULTS Table 1 shows hemodynamic parameters measured at rest and during each stage of exercise. With higher stages of exercise, the hemodynamic measurements gradually increased, except for SI. At the stage of maximum exercise, heart rate, MAP, PAP, PAWP, CI, and SI were all higher than the corresponding values obtained at rest. Figure 1 shows changes in pulmonary arterial BNP concentrations at rest and during each stage of exercise. The mean pulmonary arterial BNP concentration at rest was 14.8 t 4.1 pg/mL. With higher stages of exercise, the BNP value gradually increased; at the maximum exercise stage, the BNP value increased to 40.9 k 6.5 pg/mL. Close correlations of PAP and PAWP with pulmonary arterial BNP concentration were observed at four points before and during each stage of exercise (Figs 2A and B). In contrast, heart rate, MAP, CI, and SI were not correlated with BNP values (heart rate: n = 24, r = .44; MAP: n = 24, r = .39; CI: n = 24, r = .26; SI: n = 24, r = .12). DISCUSSION

These results suggest that cardiac secretion of BNP was increased during exercise in essential hypertensive subjects

60 P < 0.01 I

I

50

P < 0.01

40 30 20 10

Statistics Comparisons between values obtained at rest and during exercise were analyzed by one-way ANOVA and reexamined by the method of Greenhouse and Geisser.’ Linear regression analysis was used to examine the relationships of plasma ir-BNP concentration to various parameters. All values are expressed as the mean f SD.

0 Rest Fig 1.

25watts

5Owatts

75watts

Changes in pulmonary arterial concentrations of BNP at rest

and during ergometric sion.

exercise in patients with essential hyperten-

BRAIN NATRIURETIC

1275

PEPTIDE AND HYPERTENSION

.

PLlmonary

arterial

p,es*ur*

hmHg)

Pu~monarv

wma

wedge

~c.sure

~mmml

Fig 2. Correlations of PAP (A) and PAWP (6) with pulmonary arterial concentration of BNP at four points obtained at rest and during each stage of exercise.

anci the observed increase of BNP may be related to elevated PAP and PAWP. This finding is essentially the same as that reported for ANP.s,” However, rat heart perfusion experiments using Langendorf s method before and after atria1 removalln,ll indicate that a considerable amount of BNP is secreted from the ventricles, and there-

fore the major origin of circulating BNP may be the ventricles. These observations may lead to the hypothesis that the wall stress caused by exercise stimulates secretion of BNP from the ventricles in hypertensive subjects. Two kinds of human receptors for natriuretic peptides. ANP-A and ANP-B receptors, that have the guanylate cyclase domain have been identified by molecular cloning.” The ANP-B receptor is activated more by BNP than by ANP, but the ANP-A receptor responds similarly to both natriuretic peptides.’ In addition, a longer half-life for plasma BNP than for human ANP( l-28) is demonstrated in humans.“J3 ANP and BNP also inhibit the secretion of newly isolated vasoconstrictive peptide, endothelin-1, in cultured human endothelial cells in a cyclic guanosine monophosphate-dependent process.*4 These observations may lead to the hypothesis that the increased secretion of BNP in hypertensive patients during exercise may play a role in the regulation of blood pressure, working together with ANP. However, as the increase in BNP level seems to be much lower than that of ANP,‘-’ it is necessary to clarify the physiological significance of increased plasma BNP concentrations during exercise in these patients and the relationship between the ANP-BNP system and blood pressure control.

REFERENCES 1. Sudoh T. Kangawa K, Minamino N, et al: A new natriuretic peptide in porcine brain. Nature 332:78-81.1988 2. Minamino N. Aburaya M, Ueda S, et al: The presence of brain natriuretic peptide of 12,000 daltons in porcine heart. Biochem Biophys Res Commun 155:740-746.1988 3. Chang MS. Lowe DG. Lewis M, et al: Differential activation by atrial and brain natriuretic peptides of two different receptor guanylate cyclases. Nature 341:68-72, 1989 4. Kambayashi Y, Nakao K, Mukoyama M, et al: Isolation and sequence determination of human brain natriuretic peptide in human atrium. FEBS Lett 259:341-345. 1990 5. Mukoyama M. Nakao K. Saito Y, et al: Human brain natriuretic peptide, a novel cardiac hormone. Lancet 335:801-802. 1990 C. Kohno M, Horio T. Yokokawa K. et al: Brain peptide as a cardiac hormone in essential hypertension. 92:29-34, 1992 7. Greenhouse SW. Geisser S: On methods profile data. Psychometrika 24:95-112, 1954

natriuretic Am J Med

in the analysis

of

+#. Nishikimi T, Kohno M, Matsuura T, et al: Circulating atrial natriuretic polypeptide during exercise in patients with essential hypertension. J Hypertens 4:546-549,1986 (suppl6) 9. Kohno M. Yokokawa

K. Yasunari

K, et al: Acute effects of cy-

and f3-adrenoceptor blockade on plasma atrial natriuretic peptides during exercise in elderly patients with mild hypertension. Chest 99:847-854, 1991 10. Ogawa Y. Nakao K, Mukoyama M, et al: Rat brain natriuretic peptide tissue distribution and molecular form. Endocrinology 1262225-2228, 1990 11. Kohno M, Horio T, Yoshiyama M. et al: Accelerated secretion of brain natriuretic peptide from the hypertrophied ventricles in experimental malignant hypertension. Hypertension 19:206-211, 1992 12. Nakao K, Sugawara A, Morii N, et al: The pharmacokinetics of a-human atrial natriuretic polypeptide in healthy subjects. Eur J Clin Pharmacol31:101-103. 1986 13. Mukoyama M, Nakao K. Hosoda K. et al: Brain natriuretic peptide as a novel cardiac hormone in humans. Evidence for an exquisite dual natriuretic system. atrial natriuretic peptide and brain natriuretic peptide. J Clin Invest 87:1402-1412. 1991 14. Kohno M, Yasunari K, Yokokawa K, et al: Inhibition by atrial and brain natriuretic peptides of endothelin-1 secretion after stimulation with angiotensin II and thrombin of cultured human endothelial cells. J Clin Invest 87:1999-2004, 1991 15. Saito Y, Nakao K, Itoh H, et al: Brain natriuretic peptide is a novel cardiac hormone. Biochem Biophys Res Commun 158:360368.1989