General Cardiology Cardiology 1992;80:12-17
Norman L.M. Wong Eric F.C. Wong David C.K. Hu
Atrial Natriuretic Factor Release in Cardiomyopathic Hamsters
Department of Medicine, University of British Columbia, Vancouver, Canada
Abstract
Studies were done in male cardiomyopathic and normal ham sters to examine the effect of heart failure on atrial natriuretic factor (ANF) secretion. Five groups of animals were studied. The hamsters were 70, 150, 200, 250 and 300 days old. The degree of heart failure became more severe with age. This was associated with a marked increase in left and right atrial weight. Plasma ANF rose in the cardiomyopathic hamsters with age, and no significant change was seen in the normal animals. ANF levels in the atrial tissue declined as the animals developed heart failure, suggesting that ANF release increased in heart failure. To examine these directly, the right and left atria of these animals were isolated and superfused in a modi fied Langendorff apparatus. The effluents from these experi ments were collected and analyzed for ANF levels. Analysis showed that ANF secretion (expressed as pg/min/mg of tissue) declined in heart failure. Since there were significant atrial hypertrophy, the results were also expressed as picogram per minute per atrium. When the data were shown as picogram per minute per atrium, there was a marked increase in ANF secretion. The present data show that one of the factors caus ing an increase in circulating ANF in heart failure is aug mented secretion.
Received: June 24.1991 Accepted: July 2,1991
Dr. N.L.M. Wong Department of Medicine. University Hospital U.B.C. Site. 2211 Wcsbrook Mall Vancouver, B.C. V6T 2B5 (Canada)
© 1992 S. Karger AG. Basel 0008-6312/92/ 0801 -0012$2.75/0
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Keyw ords Atrial natriuretic factor, release Experimental heart failure
Congestive heart failure is associated with salt and water retention. Early studies by Chimoskey et al. [ 1] suggested that this syndrome is due to a lack of ANF. This conclusion was derived from studies with cardiomyopathic hamsters, in which they found a reduction in the ANF content in the atria of these animals [2-5]. Later studies have shown that circulat ing ANF levels are elevated in man and ani mals with congestive heart failure. Studies by Edwards et al. [6] suggested that a deficiency of ANF in the atria is due to increased synthe sis and release. Studies in which the release of ANF from the atria is directly measured dur ing the development of heart failure have not been performed. The aim of the present study was to examine the spontaneous release of ANF from the atria of cardiomyopathic ham sters and appropriate controls.
Methods Male cardiomyopathic golden Syrian hamsters were bought from Canadian Hybrid Farms (Nova Sco tia. Canada). They were divided into five groups. The ages were 70. 150. 200. 250 and 300 days. On the day of the experiment, the hamsters were anesthetized with sodium pentobarbital (25 mg/kg i.p.). Blood samples were taken from the abdominal aorta for the measure ment of ANF. The liver and heart weights were noted. The right and left atria were isolated and perfused in a modified Langendorff apparatus as described before [7], Briefly, the atria were place in a perfusion chamber and perfused with Tyrode’s solution (0.5 ml/min at 37 °C). The perfusion solution was gassed with 5% Oj and 95% CO;, and the pH was 7.4. The atria were per fused for 60 min to allow hormone secretion to stabi lize before experiments began. The perfusion experi ments were conducted for 100 min. The effluents were collected with a fraction collector (LK.B, Bromma, Sweden) and stored at -2 0 °C until assayed. Tissue ANF contents and plasma levels were mea sured as described before [8], Blood samples were col lected into EDTA tubes and extracted with Sep-Pak
C-18 cartridges (Water Associates, Milford, Mass.. USA). ANF from the right and left atria and ventricles were homogenized separately and extracted with 0 .1 A' acetic acid. Radioimmunoassay was performed using antibodies bought from Peninsula Laboratory (Bel mont. Calif., USA): this antibody binds to the COOHterminal end. It cross-reacts 100% with human aANF, rat a-ANF and atriopeptin III. Synthetic rat aANF(2-1,000 pg/tubc) from Peninsula Laboratory was used to construct the standard curve. The sensitivity of the assay was at least 2 pg of ANF/tube with more than 95 % recovery. The results are expressed as means ± SEM. Statis tical analysis was done using analysis of variance and unpaired Student’s test.
Results
Heart, liver, right and left atria and body weights are summarized in table 1. 300-dayold cardiomyopathic hamsters had signifi cantly larger hearts. The heart weights were higher in the cardiomyopathic hamsters, com pared to normals. A difference in left atrial weight was also seen (250- and 300-day-old hamsters. The liver weight was significantly less in the cardiomyopathic hamsters, similar to that reported by Edwards et al. [6]. ANF measurements are summarized in ta ble 2. Plasma ANF levels increased with heart failure. The higher circulating ANF levels be came statistically signficant at 150 days. The differences between the two groups became greater as heart failure progressed. Atrial ANF concentrations in animals with severe heart failure (300 days old) were significantly lower than in the normal hamsters. In contrast to atrial ANF, ventricular ANF concentrations were greater in cardiomyopathic hamsters compared to normal hamsters. Although there was a significant increase in ventricular ANF, yet the amount of ANF present in the ventricle was relatively small compared to that present in the atria. The amount of ANF present in the ventricle of a 300-day-old car-
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Introduction
Table 1. Summary of body, heart, right and left atria and liver weights in normal and cardiomvopathic hamsters (n = 6. respectively) Age Body weight days g
Heart weight mg
Heart weight mg/gb.w.
RA weight mg
LA weight mg
Liver weight g
N
N
CHF
N
N
N
CHF
N
CHF
CHF
CHF
CHF
70
135 ±3
120** ±2
419 ±7
354** ±10
2.9 3.0 ± 0.1 ± 0.1
18 ±2
18 ±1
9 ±1
8 ±1
4.5 ± 0.2
3.9* ± 0.2
150
130 ±3
116** ±2
427 ±8
405 ±12
4.2* 3.8 ± 0.1 ± 0.2
16 ±2
19 ±2
9 ±1
11* ±1
4.6 ± 0.2
4.1** ± 0.2
200
133 ±2
116** ±1
493 ±17
462 ±17
3.2 3.5* ± 1.1 ± 0.1
17 ±4
25 ±5
8 ±1
10 ±2
4.6 ± 0.1
3.7* ± 0.1
250
128 ±2
117** ±2
482 ±18
498 ±28
3.7 4.3* ± 0.1 ± 0.2
16 ±2
24* ±2
9 ±1
19** ±3
4.3 ± 0.1
3.8** ± 0.1
300
129 ±2
120* ±2
432 ±8
519* ±17
3.3 4.3** ± 0.1 ± 0.1
12 ±1
25* ±3
8 60.6** 4.3 ± 1 ±13 ± 0.1
3.8** ± 0.1
Data are expressed as means ± SEM. CHF = Congestive heart failure: N = normal: RA = right atrium; LA = left atrium. * p < 0.05, ** p < 0.01, compared to the corresponding normal hamsters.
Table 2. ANF level in plasma, atria and ventricles of cardiomvopathic and normal hamsters Age days
Plasma ANF pg/ml
RAANF content, ng
LA ANF content, ng
Ventricular ANF content, ng
N
CHF
N
CHF
N
CHF
82 ±10
1,035 ±84
956 ±57
441 ±53
484 ±37
2.2 ±0.3
2.1* ±0.5
CHF
N
70
96 ±14
150
95 ±6
158** ±26
994 ±121
1.061 ±134
528 ±67
503 ±90
3.6 ±0.4
3.9 ±1.5
200
109 ±31
199** ±26
986 ±195
911 ±63
432 ±60
568 ±53
1.4 ± 0.2
8.7 ±2.7
250
94 ±6
227** ±32
960 ±57
1.052 ±70
467 ±32
561* ±51
2.7 ±0.4
9.9* ±2.3
300
84 ±7
522* ± 104
1.235 ±191
533** ±49
638 321** ±37 ±101
2.0 ± 0.2
52** ±13.1
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ANF Release in Cardiomvopathic Hamsters
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Data are expressed as means ± SEM. CHF = Congestive heart failure: N = normal; RA = right atrium; LA = left atrium. * p < 0.05. ** p < 0.01, compared to the corresponding normal hamsters.
diomyopathic hamster was 52 ± 1.3 ng as opposed to 533 ± 49 ng found in the right atrium. Perfusion experiments were done to de termine whether ANF secretion by the atrium is changed in heart failure. The left and right atria were isolated and perfused with a modified Langendorff preparation. The ANF release (pg/min/mg or pg/min/ atrium) is summarized in table 3. When the results are given in picogram per minute per milligram the cardiomyopathic hamsters re lease less ANF. Since the atria were larger in the cardiomyopathic hamsters, the results are also shown as the amount released by the whole atrium. When ANF secretion was ex pressed as picogram per minute per atrium. ANF release was higher in the cardiomyo pathic hamster. These differences are detect able in 150-, 250- and 300-day-old cardio myopathic hamsters.
Discussion
Our present study shows that the increase in plasma ANF levels is related with age in the cardiomyopathic hamsters. Previous studies have shown that these hamsters develop heart failure after 200 days of age [1], becoming more severe with increasing age. In the present study, as the hamsters got older, heart failure also became more severe. This is mani fested by the increase in heart weight, in par ticular the left atrial size. The liver weights did not increase, showing that these animals were suffering moderate failure. The plasma ANF level measured in 300-day-old cardio myopathic hamsters was 522 ± 104 pg/ml. These values are consistent with a previous report of Franch et al. [9] for hamsters with moderate failure. The increase in circulating ANF levels was accompanied by a reduction in the ANF con-
Table 3. Rate of ANF released by the atria of normal and cardiomyopathic hamsters Age days
ANF released, pg/min/mg RA N
ANF released, pg/min/atrium LA
CHF
N
RA CHF
LA
N
CHF
N
CHF
70
1.67 ±0.22
1.82 ±0.24
1.89 ±0.09
2.23 ±0.20
31.9 ±3.4
31.3 ±4.9
19.3 ±2.0
17.9 ±2.1
150
2.26 ±0.39
2.41 ±0.46
1.73 ±0.14
1.84 ±0.23
30 ±2.2
41.7** ±2.6
15.0 ±1.1
19.8* ±1.1
200
1.96 ±0.48
1.87 ±0.21
2.06 ±0.31
1.68 ±0.15
26.6 ±3.1
37.9 ±7.1
16.4 ± 1.6
±2.0
250
2.09 ±0.21
1.79 ±0.29
2.27 ±0.15
1.40 ±0.24
28.3 ±1.90
39.9* ±3.8
17.0 ±1.2
24.8* ±1.6
300
2.34 ±0.17
1.72* ±0.20
2.65 ±0.33
1.14** ±1.23
29.4 ±2.4
41.2** ±1.9
19.6 ±1.4
54.2** ±9.0
20.2
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CHF = Congestive heart failure: N = normal: RA = right atrium. LA = left atrium. * p < 0.05, ** p < 0.01, compared to the corresponding normal hamsters.
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Wong/Wong/Hu
humoral substances found in the circulation increased in proportion to the severity of heart failure [21]. Thus, with progression of heart failure, the increased release of ANF may partly be due to the stimulation of neurohumoral substances. Ventricular ANF contents were markedly increased in the cardiomyopathic hamsters [9, 22]. The ventricles of hamsters with severe heart failure have been shown to have secre tory granules containing immunoreactive ANF. This is in agreement with this report. The amount of ANF present in the ventricles rose significantly in the 250- and 300-dav-old hamsters. This coincided with the marked increase in circulating ANF levels. Thus, ven tricular ANF plays a part in the elevation in plasma ANF concentration. In summary, this study shows that ANF release by the atria is increased in congestive heart failure. This increase is related to the severity of heart failure. The ventricles also serve as a source of ANF in disease state. Thus high circulating ANF levels in heart fail ure are due to hypersecretion of this hormone by the atria and ventricles. Other mechanisms such as the reduction in ANF degradation or. alternatively, ANF from noncardiac sites have to be considered.
Acknowledgments This study was supported by a British Columbia Heart Foundation grant to D.C.K.H. and N.L.M.W. We acknow'ledge the technical assistance of Alice Fok and the secretarial assistance of Hilary Hall.
ANF Release in Cardiomyopathic Hamsters
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tent in the heart. These results are similar to those reported before [4. 9. 10]. It was as sumed that the reduction in the ANF content in the atria was due to enhanced release. In the present report, experiments were done to assess ANF release by the atria. The results showed that ANF secretion by the whole atria was increased. This augmentation was related with heart failure, since this was noted only in the older hamsters. This study also showed that the increase in ANF release was more prominent in the left atrium. This was associ ated with a greater hypertrophy of the left atrium. The increase in ANF release by the right atrium was more modest. The differ ential release of ANF by the left and right atria of cardiomyopathic hamsters had not been shown before. The mechanism of ANF release in conges tive heart failure is not known. Studies in ani mals have shown that the main factors affect ing ANF release arc atrial stretch and disten sion [11-15]. A significant correlation was found between pulmonary wedge pressure and pulmonary artery pressure and plasma ANF levels in patients with acute myocardial infarction and in patients with dilated cardio myopathy [16], suggesting that increased atrial pressure in heart failure is a stimulus for ANF release. In patients with heart failure, vasopressin, catecholamines and the rcnin-angiotensin-aldosterone system are activated [17-19], The effect of these substance on ANF release in normal animals has been examined. Sonnenberg and Veress [20] showed that vasopressin stimulates ANF release from an isolated rat atria. The effect of epinephrine and acetylcho line on the ANF release from an isolated rat atria was also studied. Both of these sub stances stimulate ANF release. It is possible that in the present study activation of neurohumoral substances promote the release of ANF from the atria. In addition, these neuro
References 7 Wong NLM, Wong EFC. Au GH, Hu DCK: Effect ofu- and ß-adrenergic stimulation in atrial natriuretic peptide release in vitro. Am J Phys iol 1988;255:E260-E264. 8 Wong NLM. Huang D, Geo NS. Wong EFC. Hu DCK: EfTectsof thy roid status on atrial natriuretic pep tide release from isolated ra: atria. Am J Physiol 1989:256:E64-E67. 9 Franch HA. Dixon RAF. Blaine F.H.I. Siegl PSK: Ventricular atrial natriuretic factor in the cardiomyopathic hamster model of congestive heart failure. Circ Res 1988:52:3136. 10 Ding J. Thibault G. Gutkowska J. Garcia R. Karabalsos T, Jaskun G. Genest J. Cantin M: Cardiac and plasma atrial natriuretic factor in experimental congestive heart fail ure. Endocrinology 1987:121:248257. 11 Ledsome RN. Wilson N. Courneya CA. Rankin AJ: Release of atrial na triuretic peptide by atrial distension. Can J Physiol Pharmacol 1985:63: 739-742. ' 12 Bites ER. Shenker Y. Grckin RJ: The relationship between plasma levels of immunorcactivc atrial na triuretic hormone and hemody namic function in man. Circulation 1986:73:1155-1161. 13 Bilder GE. Schofield TL. Blaine EH: Release of atrial natriuretic factor: Effects of repetitive stretch and tem perature. Am J Physiol 1986:251: F817-F82I. 14 Metzler CH. Lee ME, Trasher TN. Ramsay DJ: Increased right or left atrial pressure stimulates release of atrial natriuretic peptides in con scious dogs. Endocrinology 1986: 119:2396-2398.
15 Edwards BS, Zimmerman RS. Schwab TR, Heubleim DM. Burnett JC: Atrial stretch, not pressure is the principal determinant controlling the acute release of atrial natriuretic factor. Circ Res 1988:62:19 1- 195. 16 Hara H. Ogihara T. Nakamaru M. Rakugi H, Tateyama H: Changes in the levels of plasma atrial natriuretic peptide, hemodynamic measure ments, and the levels of vasoactive hormones during the clinical course of congestive heart failure. Clin Car diol 1988;11:743-747. 17 Francis GS. Goldsmith SR. Levine BT. Olivari MT, Cohn JN: The neu rohumoral axis in congestive heart failure. Ann Intern Med 1984; 1101: 370-377. 18 Catterjee K. Viquerat CE. Daly P: Neurohumoral abnormalities in heart failure. Heart Fail 1985:1:6983. 19 Parmley WW: Pathophysiology of congestive heart failure. Am J Car diol I985:55:9A-I4A. 20 Sonnenberg H. Veress AT: Cellular mechanism of release of atrial natri uretic factor. Biochem Biophys Res Commun 1984;124:443-449. 21 Mcttaur B. Ronleau JL, Bichet D. Juneau C. Kortas C. Barjon JN. de Champlain J: Sodium and water ex cretion abnormalities in congestive heart failure. Ann Intern Med 1985: 105:161-167. 22 Currie MG. Oehlenschlager WF. Kurtz DT: Profound elevation of ventricular and pulmonary atriopeptin in a model of heart failure. Biochem Biophys Res Commun 1987;148:1158-1164.
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1 Chimoskcy JE, Spielman WS. Brandi MA. Hcidemann SR: Car diac alria of BIO 14-6 hamslcrs are deficient in natriuretic factor. Science 1984;223:820-822. 2 Burnett JC Jr. Kao PC. Hu DCK. Heser DW. Heublein D. Granger JP, Opgeworth JJ, Reeder GS: Atrial natriuretic peptide elevation in con gestive heart failure in the human. Science 1986:231:1145-1147. 3 Cody RJ. Atlas SA. Leragh JH. Kuto SH. Com I IB. Ryman KS. Shaknovich A. Pandolfino K. Clark M. Carargo MJF. Scarborough RM. Lewiki JA: Atrial natriuretic factor in normal subjects and heart failure pa tients: Plasma levels and renal hor monal and hemodynamic responses to peptide infection. J Clin Invest 1986:78:1362-1374. 4 Tsuonda K. Haosman GP, Smithran E, Johnston Cl: Atrial natri uretic peptide in chronic heart fail ure in the rat: A correlation with ventricular dysfunction. Circ Res 1986:59:256-261. 5 Riegger GA. Eisner D. Kromer EP. Daffner C. Frossmann WG. Muders F. Paschcr EW. Kochsick K: Atrial natriuretic peptide in congestive heart failure in the dog: Plasma lev els. cyclic guanosine monophos phate. ultrastructure of atrial myoendocrine cells, and hemody namic. hormonal and renal effects. Circulation 1988;77:398-406. 6 Edwards BS. Ackermann DM, Schwab TR. Heublein DM. Ed wards WD. Wold LE. Burnett JC: The relationship between atrial granularity and circulating atrial na triuretic peptide in hamsters with congestive heart failure. Mayo Clin Proc 1986:61:517-521.
Norman L.M. Wong Eric F.C. Wong David C.K. Hu
Atrial Natriuretic Factor Release in Cardiomyopathic Hamsters
Department of Medicine, University of British Columbia, Vancouver, Canada
Abstract
Studies were done in male cardiomyopathic and normal ham sters to examine the effect of heart failure on atrial natriuretic factor (ANF) secretion. Five groups of animals were studied. The hamsters were 70, 150, 200, 250 and 300 days old. The degree of heart failure became more severe with age. This was associated with a marked increase in left and right atrial weight. Plasma ANF rose in the cardiomyopathic hamsters with age, and no significant change was seen in the normal animals. ANF levels in the atrial tissue declined as the animals developed heart failure, suggesting that ANF release increased in heart failure. To examine these directly, the right and left atria of these animals were isolated and superfused in a modi fied Langendorff apparatus. The effluents from these experi ments were collected and analyzed for ANF levels. Analysis showed that ANF secretion (expressed as pg/min/mg of tissue) declined in heart failure. Since there were significant atrial hypertrophy, the results were also expressed as picogram per minute per atrium. When the data were shown as picogram per minute per atrium, there was a marked increase in ANF secretion. The present data show that one of the factors caus ing an increase in circulating ANF in heart failure is aug mented secretion.
Received: June 24.1991 Accepted: July 2,1991
Dr. N.L.M. Wong Department of Medicine. University Hospital U.B.C. Site. 2211 Wcsbrook Mall Vancouver, B.C. V6T 2B5 (Canada)
© 1992 S. Karger AG. Basel 0008-6312/92/ 0801 -0012$2.75/0
Downloaded by: Stockholm University Library 130.237.165.40 - 1/19/2019 2:50:00 AM
Keyw ords Atrial natriuretic factor, release Experimental heart failure
Congestive heart failure is associated with salt and water retention. Early studies by Chimoskey et al. [ 1] suggested that this syndrome is due to a lack of ANF. This conclusion was derived from studies with cardiomyopathic hamsters, in which they found a reduction in the ANF content in the atria of these animals [2-5]. Later studies have shown that circulat ing ANF levels are elevated in man and ani mals with congestive heart failure. Studies by Edwards et al. [6] suggested that a deficiency of ANF in the atria is due to increased synthe sis and release. Studies in which the release of ANF from the atria is directly measured dur ing the development of heart failure have not been performed. The aim of the present study was to examine the spontaneous release of ANF from the atria of cardiomyopathic ham sters and appropriate controls.
Methods Male cardiomyopathic golden Syrian hamsters were bought from Canadian Hybrid Farms (Nova Sco tia. Canada). They were divided into five groups. The ages were 70. 150. 200. 250 and 300 days. On the day of the experiment, the hamsters were anesthetized with sodium pentobarbital (25 mg/kg i.p.). Blood samples were taken from the abdominal aorta for the measure ment of ANF. The liver and heart weights were noted. The right and left atria were isolated and perfused in a modified Langendorff apparatus as described before [7], Briefly, the atria were place in a perfusion chamber and perfused with Tyrode’s solution (0.5 ml/min at 37 °C). The perfusion solution was gassed with 5% Oj and 95% CO;, and the pH was 7.4. The atria were per fused for 60 min to allow hormone secretion to stabi lize before experiments began. The perfusion experi ments were conducted for 100 min. The effluents were collected with a fraction collector (LK.B, Bromma, Sweden) and stored at -2 0 °C until assayed. Tissue ANF contents and plasma levels were mea sured as described before [8], Blood samples were col lected into EDTA tubes and extracted with Sep-Pak
C-18 cartridges (Water Associates, Milford, Mass.. USA). ANF from the right and left atria and ventricles were homogenized separately and extracted with 0 .1 A' acetic acid. Radioimmunoassay was performed using antibodies bought from Peninsula Laboratory (Bel mont. Calif., USA): this antibody binds to the COOHterminal end. It cross-reacts 100% with human aANF, rat a-ANF and atriopeptin III. Synthetic rat aANF(2-1,000 pg/tubc) from Peninsula Laboratory was used to construct the standard curve. The sensitivity of the assay was at least 2 pg of ANF/tube with more than 95 % recovery. The results are expressed as means ± SEM. Statis tical analysis was done using analysis of variance and unpaired Student’s test.
Results
Heart, liver, right and left atria and body weights are summarized in table 1. 300-dayold cardiomyopathic hamsters had signifi cantly larger hearts. The heart weights were higher in the cardiomyopathic hamsters, com pared to normals. A difference in left atrial weight was also seen (250- and 300-day-old hamsters. The liver weight was significantly less in the cardiomyopathic hamsters, similar to that reported by Edwards et al. [6]. ANF measurements are summarized in ta ble 2. Plasma ANF levels increased with heart failure. The higher circulating ANF levels be came statistically signficant at 150 days. The differences between the two groups became greater as heart failure progressed. Atrial ANF concentrations in animals with severe heart failure (300 days old) were significantly lower than in the normal hamsters. In contrast to atrial ANF, ventricular ANF concentrations were greater in cardiomyopathic hamsters compared to normal hamsters. Although there was a significant increase in ventricular ANF, yet the amount of ANF present in the ventricle was relatively small compared to that present in the atria. The amount of ANF present in the ventricle of a 300-day-old car-
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Introduction
Table 1. Summary of body, heart, right and left atria and liver weights in normal and cardiomvopathic hamsters (n = 6. respectively) Age Body weight days g
Heart weight mg
Heart weight mg/gb.w.
RA weight mg
LA weight mg
Liver weight g
N
N
CHF
N
N
N
CHF
N
CHF
CHF
CHF
CHF
70
135 ±3
120** ±2
419 ±7
354** ±10
2.9 3.0 ± 0.1 ± 0.1
18 ±2
18 ±1
9 ±1
8 ±1
4.5 ± 0.2
3.9* ± 0.2
150
130 ±3
116** ±2
427 ±8
405 ±12
4.2* 3.8 ± 0.1 ± 0.2
16 ±2
19 ±2
9 ±1
11* ±1
4.6 ± 0.2
4.1** ± 0.2
200
133 ±2
116** ±1
493 ±17
462 ±17
3.2 3.5* ± 1.1 ± 0.1
17 ±4
25 ±5
8 ±1
10 ±2
4.6 ± 0.1
3.7* ± 0.1
250
128 ±2
117** ±2
482 ±18
498 ±28
3.7 4.3* ± 0.1 ± 0.2
16 ±2
24* ±2
9 ±1
19** ±3
4.3 ± 0.1
3.8** ± 0.1
300
129 ±2
120* ±2
432 ±8
519* ±17
3.3 4.3** ± 0.1 ± 0.1
12 ±1
25* ±3
8 60.6** 4.3 ± 1 ±13 ± 0.1
3.8** ± 0.1
Data are expressed as means ± SEM. CHF = Congestive heart failure: N = normal: RA = right atrium; LA = left atrium. * p < 0.05, ** p < 0.01, compared to the corresponding normal hamsters.
Table 2. ANF level in plasma, atria and ventricles of cardiomvopathic and normal hamsters Age days
Plasma ANF pg/ml
RAANF content, ng
LA ANF content, ng
Ventricular ANF content, ng
N
CHF
N
CHF
N
CHF
82 ±10
1,035 ±84
956 ±57
441 ±53
484 ±37
2.2 ±0.3
2.1* ±0.5
CHF
N
70
96 ±14
150
95 ±6
158** ±26
994 ±121
1.061 ±134
528 ±67
503 ±90
3.6 ±0.4
3.9 ±1.5
200
109 ±31
199** ±26
986 ±195
911 ±63
432 ±60
568 ±53
1.4 ± 0.2
8.7 ±2.7
250
94 ±6
227** ±32
960 ±57
1.052 ±70
467 ±32
561* ±51
2.7 ±0.4
9.9* ±2.3
300
84 ±7
522* ± 104
1.235 ±191
533** ±49
638 321** ±37 ±101
2.0 ± 0.2
52** ±13.1
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ANF Release in Cardiomvopathic Hamsters
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Data are expressed as means ± SEM. CHF = Congestive heart failure: N = normal; RA = right atrium; LA = left atrium. * p < 0.05. ** p < 0.01, compared to the corresponding normal hamsters.
diomyopathic hamster was 52 ± 1.3 ng as opposed to 533 ± 49 ng found in the right atrium. Perfusion experiments were done to de termine whether ANF secretion by the atrium is changed in heart failure. The left and right atria were isolated and perfused with a modified Langendorff preparation. The ANF release (pg/min/mg or pg/min/ atrium) is summarized in table 3. When the results are given in picogram per minute per milligram the cardiomyopathic hamsters re lease less ANF. Since the atria were larger in the cardiomyopathic hamsters, the results are also shown as the amount released by the whole atrium. When ANF secretion was ex pressed as picogram per minute per atrium. ANF release was higher in the cardiomyo pathic hamster. These differences are detect able in 150-, 250- and 300-day-old cardio myopathic hamsters.
Discussion
Our present study shows that the increase in plasma ANF levels is related with age in the cardiomyopathic hamsters. Previous studies have shown that these hamsters develop heart failure after 200 days of age [1], becoming more severe with increasing age. In the present study, as the hamsters got older, heart failure also became more severe. This is mani fested by the increase in heart weight, in par ticular the left atrial size. The liver weights did not increase, showing that these animals were suffering moderate failure. The plasma ANF level measured in 300-day-old cardio myopathic hamsters was 522 ± 104 pg/ml. These values are consistent with a previous report of Franch et al. [9] for hamsters with moderate failure. The increase in circulating ANF levels was accompanied by a reduction in the ANF con-
Table 3. Rate of ANF released by the atria of normal and cardiomyopathic hamsters Age days
ANF released, pg/min/mg RA N
ANF released, pg/min/atrium LA
CHF
N
RA CHF
LA
N
CHF
N
CHF
70
1.67 ±0.22
1.82 ±0.24
1.89 ±0.09
2.23 ±0.20
31.9 ±3.4
31.3 ±4.9
19.3 ±2.0
17.9 ±2.1
150
2.26 ±0.39
2.41 ±0.46
1.73 ±0.14
1.84 ±0.23
30 ±2.2
41.7** ±2.6
15.0 ±1.1
19.8* ±1.1
200
1.96 ±0.48
1.87 ±0.21
2.06 ±0.31
1.68 ±0.15
26.6 ±3.1
37.9 ±7.1
16.4 ± 1.6
±2.0
250
2.09 ±0.21
1.79 ±0.29
2.27 ±0.15
1.40 ±0.24
28.3 ±1.90
39.9* ±3.8
17.0 ±1.2
24.8* ±1.6
300
2.34 ±0.17
1.72* ±0.20
2.65 ±0.33
1.14** ±1.23
29.4 ±2.4
41.2** ±1.9
19.6 ±1.4
54.2** ±9.0
20.2
15
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CHF = Congestive heart failure: N = normal: RA = right atrium. LA = left atrium. * p < 0.05, ** p < 0.01, compared to the corresponding normal hamsters.
16
Wong/Wong/Hu
humoral substances found in the circulation increased in proportion to the severity of heart failure [21]. Thus, with progression of heart failure, the increased release of ANF may partly be due to the stimulation of neurohumoral substances. Ventricular ANF contents were markedly increased in the cardiomyopathic hamsters [9, 22]. The ventricles of hamsters with severe heart failure have been shown to have secre tory granules containing immunoreactive ANF. This is in agreement with this report. The amount of ANF present in the ventricles rose significantly in the 250- and 300-dav-old hamsters. This coincided with the marked increase in circulating ANF levels. Thus, ven tricular ANF plays a part in the elevation in plasma ANF concentration. In summary, this study shows that ANF release by the atria is increased in congestive heart failure. This increase is related to the severity of heart failure. The ventricles also serve as a source of ANF in disease state. Thus high circulating ANF levels in heart fail ure are due to hypersecretion of this hormone by the atria and ventricles. Other mechanisms such as the reduction in ANF degradation or. alternatively, ANF from noncardiac sites have to be considered.
Acknowledgments This study was supported by a British Columbia Heart Foundation grant to D.C.K.H. and N.L.M.W. We acknow'ledge the technical assistance of Alice Fok and the secretarial assistance of Hilary Hall.
ANF Release in Cardiomyopathic Hamsters
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tent in the heart. These results are similar to those reported before [4. 9. 10]. It was as sumed that the reduction in the ANF content in the atria was due to enhanced release. In the present report, experiments were done to assess ANF release by the atria. The results showed that ANF secretion by the whole atria was increased. This augmentation was related with heart failure, since this was noted only in the older hamsters. This study also showed that the increase in ANF release was more prominent in the left atrium. This was associ ated with a greater hypertrophy of the left atrium. The increase in ANF release by the right atrium was more modest. The differ ential release of ANF by the left and right atria of cardiomyopathic hamsters had not been shown before. The mechanism of ANF release in conges tive heart failure is not known. Studies in ani mals have shown that the main factors affect ing ANF release arc atrial stretch and disten sion [11-15]. A significant correlation was found between pulmonary wedge pressure and pulmonary artery pressure and plasma ANF levels in patients with acute myocardial infarction and in patients with dilated cardio myopathy [16], suggesting that increased atrial pressure in heart failure is a stimulus for ANF release. In patients with heart failure, vasopressin, catecholamines and the rcnin-angiotensin-aldosterone system are activated [17-19], The effect of these substance on ANF release in normal animals has been examined. Sonnenberg and Veress [20] showed that vasopressin stimulates ANF release from an isolated rat atria. The effect of epinephrine and acetylcho line on the ANF release from an isolated rat atria was also studied. Both of these sub stances stimulate ANF release. It is possible that in the present study activation of neurohumoral substances promote the release of ANF from the atria. In addition, these neuro
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