Laboratory Investigation Am J Nephrol 1992;12:259-264
a Medical Clinic IV, University of Erlangen-Niimberg, Erlangen, FRG: b Clinicoflnternal Medicine, Faculty of Medicine. University of Würzburg, FRG; c University of Southern California, Los Angeles, Calif., USA
Keywords Parathyroid hormone Atrial natriuretic peptide Release Acute volume expansion Calcium
Parathyroid Hormone Modulates the Release of Atrial Natriuretic Peptide during Acute Volume Expansion
Abstract In this study we investigated the effect of volume expansion on plasma and atrial concentrations of atrial natriuretic peptide (ANP) in the presence and absence of the parathyroid gland and under normocalcemic and hypocalcemic conditions. After volume expansion ANP concentration in plasma was signifi cantly (p < 0.001) higher in intact (702 ± 86 pg/ml) than in hypocalcemic parathyroidectomized (PTX) (271 ± 38 pg/ml) rats. Plasma ANP of PTX rats rendered normocalcemic with oral calcium supplementation increased to 402 ± 85 pg/ml after volume expansion. Results from this study suggest that para thyroid hormone (PTH) is required for augmented ANP secretion in response to acute volume loading and alterations of extracellular calcium may modu late volume-induced ANP release in PTX rats. We would discuss that a para thyroid gland-cardiac atria interaction exists and that changes in serum level of PTH may play a role in the regulation of fluid homeostasis via ANP secre tion.
Introduction Atrial natriuretic peptide (ANP) is a hormone that may regulate fluid and electrolyte homeostasis and blood pressure [ 1]. It is secreted primarily by the cardiac atria, but cells in the cardiac ventricles as well as the brain and in other sites also are capable for producing ANP [2-4], The main physiological stimulus of ANP secretion is a direct stretch and/or distension of the atrial wall resulting from volume expansion [5, 6]. Although atrial distension alone undoubtedly can cause secretion of ANP into the circulation there is some evidence indicating that other factors can modulate the release of this hormone. The fact
Supported by grants from the Deutsche Forschungsgemeinschaft Gc 568/1- 1.
Received: February 9 , 1992 Accepted: June 1,1992
that atrial stretch alone produces ANP release does not necessarily exclude the regulatory action of humoral stim ulation on ANP release. There is some evidence that ANP release may be influenced by humoral agents, pressor hor mones like vasopressin and adrenalin [7-9], hormones of anterior pituitary origin [10], glucocorticoids [11], endothelin [12, 13], calcitonin gene-related peptide [14], and dynorphin [ 15, 16]. Data obtained from experiments with isolated hearts or atria indicate that intracellular free cal cium may play an important part in mediating ANP release. ANP release can be activated by a calcium ionophore using the Langendorff preparation [ 17] or by incu bation of atria in vitro [ 18]. Earlier investigations pointed
Dr. Helmut Geiger Medizinische Klinik IV Universität Erlangen-Nürnberg Krankcnhausstrassc 12 D-W-8520 Erlangen (FRG)
© 1992 S. Karger AG, Basel 0250-8095/92/0124-0259 $2.75/0
Downloaded by: Nagoya University 133.6.82.173 - 1/11/2019 4:33:17 PM
Helmut Geiger3 Udo Bahner'0 Marianne Meissnera Christian Hugoa Michael Kirsteinb Roland M. Schaeferb August Heidlandb Shaul G. Massryc
Methods Male Sprague-Dawlcy rats weighing 250-330 g were housed in individual cages. On the day of the study, all rats were anesthetized with an intraperitoneal injection of 40-60 mg sodium pentobarbital/kg body weight (Fa. Ceva. Bad Segeberg. FRG). Surgical Preparation Animals were randomly selected for bilateral parathyroidectomy, while others were subjected to sham operation only. The success of parathyroidectomy was ascertained by a drop in serum calcium of at least 0.5 mmol/1. After a time interval of 7 days after parathyroidec tomy. the rats were introduced into the study protocol. Through an incision on the ventral surface of the neck, the left carotid artery was cannulated with polyethylene tubing. Additionally, polyethylene catheters were inserted into the left femoral artery and the left femo ral vein. The femoral arterial catheter was connected to Statham pressure transducer and pressure was recorded on an oscillographic recorder. Blood samples were obtained from the carotid artery for determination of plasma ANP. Saline was infused for volume expan sion into the femoral vein. At the end of the experiment the rats were killed by decapitation and blood samples were collected for determi nation of serum parameters. Pilot Studies In order to find the dosage for infusion of parathyroid hormone (PTH) we evaluated the blood pressure lowering effect of various amounts of 1-34 PTH (2.46, 4.93, 7.39 and 14.79 nmol). The maxi mum decrease of arterial blood pressure was observed with a dosage between 7.30 and 14.79 nmol PTH. Complementary to these doseresponse durves (blood pressure-time), we measured plasma ANP both during volume expansion and infusion with 1-34 PTH at differ ent time intervals (plasma ANP time). Design o f the Study Protocol A total of 10 groups made up of 8 rats each were studied. Group I: Infusion of 0.9% NaCl for 2 h (0.2 ml/h) in control rats (control plasma levels of ANP). Group II: Infusion of 0.9% NaCI (15 ml/kg Bw; 2 ml/min) for 2 min in sham-operated rats (volume expansion). Group III: Infusion of 0.9% NaCl (15 ml/kg Bw; 2 ml/min) for 2 min in hypocalcemic-parathyroidectomized rats (volume expan sion). Group IV: Infusion of 0.9% NaCl (15 ml/kg Bw; 2 ml/min) for 2 min (volume expansion) in normocalcemic-parathyroidectomized rats which had received 50 g calcium gluconatc/1 as drinking water for 4 days after parathyroidectomy.
260
Group V: Infusion ofCaCb(75 mgCaCL/kg) for 2 h (0.2 ml/h) in sham-operated rats. Group VI: Infusion of CaCb (75 mg CaCL/kg) for 2 h (0.2 ml/h) in hypocalcemic-parathyroidectomized rats. Group VII: Infusion of parathyroid hormone (1-84 PTH) (0.2 ml/h) for 2 h in intact rats (in total 6.31 nmol PTH). Group VIII: Infusion of 1-34 PTH (0.2 ml/h) for 2 h in intact rats (in total 7.39 nmol PTH). Group IX: Infusion of 1-34 PTH (0.2 ml/h) for 2 h (in total 7.39 nmol PTH), subsequently followed by infusion of 0.9% NaCl (15 ml/kg: 2 ml/min) for 2 min (volume expansion) in intact rats. Group X: Simultaneous infusion both of 0.9% NaCl (15 ml/kg: 2 ml/min) (volume expansion) and 1-34 PTH (in total 7.39 nmol) for 2 min in intact rats. Measurements Blood was collected for determination of serum osmolality (by freezing-point depression, Osmomat, Gonotec, Berlin, FRG), serum sodium, potassium, calcium and phosphate (by flame photometry. Eppendorf Co., Hamburg. FRG) magnesium (by atomic absorption spectrophotometry, Perkin Elmer 3030, Offenbach. FRG) and chlo ride (by Chlorimeter, Eppendorf). Serum was analyzed for total pro tein and albumin by an automatic analyzer (SMAC, Technicon). Radioimmunoassay 2.5 ml blood for determination of plasma ANP was collected in polypropylene tubes containing 500 klU/ml aprotinin (Bayer, Lever kusen. FRG). and immediately centrifuged at 4 °C. The plasma was removed and stored at - 70 °C until assayed. One milliliter of acidif ied plasma (2 A' HC1, pH 3-4) was applied to a SEP-PAK C18 reverse-phase octadodecylsilane cartridge column (Water Associates, Milford. Mass., USA) prewetted twice with 10 ml of 100% methanol and 10 ml 4% acetic acid. The column was then washed three times with 5 ml of 0.1 % trifluoracetic acid (TFA) followed by extraction with a mixture of 2 ml of 60% acetonitrile and 0.1 % TFA, freezedried. and redissolved in I ml of assay buffer with diluted Triton X-100 (2%). The mean recovery of two concentrations of standard ANP (101-126) was 72 ± 6% (mean ± SD). One milliliter of each sample in duplicate was used for the radioimmunoassay. A detailed description of the radioimmunoassay is given elsewhere [26], The rats were killed by decapitation and the hearts were removed quickly and dissected. After preparation of both atria they were boiled in 2 ml of 1.0 M acetic acid and 20 mM HCI for 5 min. Then the tissue was homogenized and diluted with 8 ml of a buffer of the following composition: 0.1 M sodium phosphate, 1 mM EDTA, 0.1 g/l sodium azide at pH 7.0. The samples were centrifuged for 30 min at 10.000 g. The supernatants were frozen at - 700C until radiommunoassay. We measured aliquots of 4 and 1 pi. Protein determination was per formed according to the method of Lowry et al. [27], Human alpha-ANP (1-28) (corresponding to human ANP (99126) was purchased from Peninsula Laboratories Europe Ltd.. Mer seyside. UK. The standard was dissolved in assay buffer and pre pared at final concentrations in the range of 1-128 pg/lOOpl per tube. The percentage cross-reactivity of ANP fragments with the antiserum used is as follows: human ANP (99-126) 100%, rat ANP (101-126) 90%, rat ANP (103-126) 100%. rat ANP (102-126) 88%. The sensitivity of the assay was 1.5 pg/tubc. The intra-assay and interassay variances were 8 and 12%, respectively, for blood samples to which rat ANP (103-126) was added. The plasma sample was assayed in duplicate and corrected by recovery rate.
Geiger/Bahner/Meissner/Hugo/Kirstein/ Schaefer/Heidland/Massry
PTH Modulates the Release of ANP
Downloaded by: Nagoya University 133.6.82.173 - 1/11/2019 4:33:17 PM
to a role for plasma ANP in regulating blood pressure and fluid balance under the condition of altered calcium intake and PTH status [19. 20]. Parathyroid hormone (PTH) which enhances entry of calcium into many cells [21-25] may, therefore, influence secretion of ANP. Our present study provides data demonstrating in intact ani mals that the presence of PTH is required for the aug mented ANP release during acute volume expansion.
Table 1. Scrum parameters, arterial blood pressure changes and results of plasma and atrial ATP (mean values ± SEM) Experimental groups 1
2
3
4
5
6
7
8
9
10
144± 1 106 ± 1
148 ±5 108 ±3
142 ±2 104 ± 1
141 ± 1 106 ± 1
136 ± 2 102 ± I
141 ± 1 101 ±1
140 ± 1 102 ±2
142 ± 1 104 ± 1
139 ± 1 105 ± 1
141 ± 1 106 ± 1
a Serum Sodium, mmol/1 Chloride, mmol/1 Potassium mmol/1 Calcium, mmol/1 Phosphate mmol/1 Magnesium mmol/1 Osmolality mosm/kg Total protein g/dl Albumin, g/dl
4.78 + 0.04 4.58 ±0.13 4.94 ±0.17 4.53 ±0.09 4.89±0.25 4.83 ±0.04 4.69±0.10 4.87 ±0.13 4.41 ±0.13 4.64 ±0.06 2.37 + 0.06 2.32 ±0.10 1.77 ±0.07 2.44 ±0.05 2.58±0.08 2.15 ±0.09 2.51 ±0.01 2.49 ±0.04 2.23 ± 0.01 2.25 ±0.02 2.55 + 0.15 2.41 ±0.12 3.20 ±0.10 2.44 ±0.26 2.43 ±0.13 3.33 ±0.07 2.40 ±0.10 2.21 ±0.05 2.03 ±0.06 2.47 ±0.06 0.91 ±0.04 0.77 ± 0.01 0.72 ±0.02 0.78 ±0.06 0.84 ±0.05 0.83 ±0.05 1.04 ±0.03 0.99 ±0.02 0.78 ±0.02 0.73 ±0.01 323 ± 3
310 ± 4
314 ± 2
305 ±2
322 ±2
325 ± 5
317 ± 1
329 ± 2
300 ±1
306 ±1
4.64 ±0.13 4.44 ±0.19 3.98 ±0.12 3.79 ±0.16 4.16± 0.10 4.68 ±0.07 4.38 ±0.06 4.17±0.05 4.13 ± 0.09 4.04 ±0.06 2.84 ±0.07 2.68 ±0.12 2.44 ±0.06 2.25 ± 0.11 2.61 ±0.06 2.79 ±0.04 2.69 ±0.04 2.81 ±0.04 2.43 ±0.05 2.49 ±0.04
b Mean arterial blood pressure Resting conditions mm Hg !06±3 End of experiment mm Hg 106 ±3
I13±2
109 ±3
! 13 ± 9
101+2
104 + 2
109 ±3
115±4
110 + 5
106 ±2
120 ± 3
109 ±4
115 ± 11
108 ± 1
110 ± 2
98 ±2
97 ±6
79 ±3
78±2
c ANP Plasma, pg/ml 114 ± 23 702 ±86 271 ±38 402 ±85 135 ± 9 69 ±14 57 ± 9 164 ± 16 64 ±13 237 ±35 Left atrium pg/mg protein 2.10 ± 0.18 2.90 ±0.42 1.51 ±0.29 1.64 ±0.24 2.08 ±0.15 1.85 ± 0.15 2.32 ±0.33 2.44±0.13 1.81 ±0.20 1.97 ±0.21 Right atrium pg/mg protein 2.95 ±0.41 3.57±0.40 2.81 ±0.31 2.88 ±0.54 3.37±0.26 2.83±0.43 3.76±0.29 3.15 ± 0.29 3.43±0.59 3.14 ±0.64
Results A detailed list of all serum parameters is given in table la, changes of arterial blood pressure are put to gether in table lb, and results of plasma and atrial ANP are listed in table lc. Significances were omitted from the tables for a better survey, but they are stated in the text.
Effect o f Volume Expansion Acute volume expansion in sham rats caused not only a pronounced increase of plasma ANP (702 ± 86 vs. 114 ± 23 pg/ml; p < 0.001). ANP in left atrial tissue (2.90 ± 0.42 vs. 2.10 ± 0.18 pg/mg protein, n.s.) and ANP in right atrium (3.57 ± 0.40 vs. 2.95 ± 0.41 pg/mg protein, n.s.) did not change significantly (n = 5). Effect o f Calcium Infusion Serum calcium was elevated by calcium infusion from 2.37 ± 0.06 to 2.58 ± 0.08 mmol/1 in sham-operated rats (group V)(p < 0.01) and from 1.36 ± 0.05 to 2.15 ± 0.09 mmol/1 (p < 0.001) in PTX rats (group VI). CaCN infu sion induced a significantly (p < 0.001) higher plasma concentration of ANP in intact rats compared to PTX rats (135 ± 9 vs. 69 ± 14 pg/ml), but both ANP levels are not significantly different from control animals without
261
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Data Analysis Statistical analysis of the data was performed according to the recommendations of Wallenstein et al. [28], The results are expressed as mean ± SEM. For the comparison of statistical significance between the groups student’s t test and Wilcoxon U test were used. For the multiple comparison, ANOVA fol lowed by the Bonferroni t test were used. Differences at the 95 % level were considered significant. Significance is given as p < 0.05, p < 0.01. p
a Medical Clinic IV, University of Erlangen-Niimberg, Erlangen, FRG: b Clinicoflnternal Medicine, Faculty of Medicine. University of Würzburg, FRG; c University of Southern California, Los Angeles, Calif., USA
Keywords Parathyroid hormone Atrial natriuretic peptide Release Acute volume expansion Calcium
Parathyroid Hormone Modulates the Release of Atrial Natriuretic Peptide during Acute Volume Expansion
Abstract In this study we investigated the effect of volume expansion on plasma and atrial concentrations of atrial natriuretic peptide (ANP) in the presence and absence of the parathyroid gland and under normocalcemic and hypocalcemic conditions. After volume expansion ANP concentration in plasma was signifi cantly (p < 0.001) higher in intact (702 ± 86 pg/ml) than in hypocalcemic parathyroidectomized (PTX) (271 ± 38 pg/ml) rats. Plasma ANP of PTX rats rendered normocalcemic with oral calcium supplementation increased to 402 ± 85 pg/ml after volume expansion. Results from this study suggest that para thyroid hormone (PTH) is required for augmented ANP secretion in response to acute volume loading and alterations of extracellular calcium may modu late volume-induced ANP release in PTX rats. We would discuss that a para thyroid gland-cardiac atria interaction exists and that changes in serum level of PTH may play a role in the regulation of fluid homeostasis via ANP secre tion.
Introduction Atrial natriuretic peptide (ANP) is a hormone that may regulate fluid and electrolyte homeostasis and blood pressure [ 1]. It is secreted primarily by the cardiac atria, but cells in the cardiac ventricles as well as the brain and in other sites also are capable for producing ANP [2-4], The main physiological stimulus of ANP secretion is a direct stretch and/or distension of the atrial wall resulting from volume expansion [5, 6]. Although atrial distension alone undoubtedly can cause secretion of ANP into the circulation there is some evidence indicating that other factors can modulate the release of this hormone. The fact
Supported by grants from the Deutsche Forschungsgemeinschaft Gc 568/1- 1.
Received: February 9 , 1992 Accepted: June 1,1992
that atrial stretch alone produces ANP release does not necessarily exclude the regulatory action of humoral stim ulation on ANP release. There is some evidence that ANP release may be influenced by humoral agents, pressor hor mones like vasopressin and adrenalin [7-9], hormones of anterior pituitary origin [10], glucocorticoids [11], endothelin [12, 13], calcitonin gene-related peptide [14], and dynorphin [ 15, 16]. Data obtained from experiments with isolated hearts or atria indicate that intracellular free cal cium may play an important part in mediating ANP release. ANP release can be activated by a calcium ionophore using the Langendorff preparation [ 17] or by incu bation of atria in vitro [ 18]. Earlier investigations pointed
Dr. Helmut Geiger Medizinische Klinik IV Universität Erlangen-Nürnberg Krankcnhausstrassc 12 D-W-8520 Erlangen (FRG)
© 1992 S. Karger AG, Basel 0250-8095/92/0124-0259 $2.75/0
Downloaded by: Nagoya University 133.6.82.173 - 1/11/2019 4:33:17 PM
Helmut Geiger3 Udo Bahner'0 Marianne Meissnera Christian Hugoa Michael Kirsteinb Roland M. Schaeferb August Heidlandb Shaul G. Massryc
Methods Male Sprague-Dawlcy rats weighing 250-330 g were housed in individual cages. On the day of the study, all rats were anesthetized with an intraperitoneal injection of 40-60 mg sodium pentobarbital/kg body weight (Fa. Ceva. Bad Segeberg. FRG). Surgical Preparation Animals were randomly selected for bilateral parathyroidectomy, while others were subjected to sham operation only. The success of parathyroidectomy was ascertained by a drop in serum calcium of at least 0.5 mmol/1. After a time interval of 7 days after parathyroidec tomy. the rats were introduced into the study protocol. Through an incision on the ventral surface of the neck, the left carotid artery was cannulated with polyethylene tubing. Additionally, polyethylene catheters were inserted into the left femoral artery and the left femo ral vein. The femoral arterial catheter was connected to Statham pressure transducer and pressure was recorded on an oscillographic recorder. Blood samples were obtained from the carotid artery for determination of plasma ANP. Saline was infused for volume expan sion into the femoral vein. At the end of the experiment the rats were killed by decapitation and blood samples were collected for determi nation of serum parameters. Pilot Studies In order to find the dosage for infusion of parathyroid hormone (PTH) we evaluated the blood pressure lowering effect of various amounts of 1-34 PTH (2.46, 4.93, 7.39 and 14.79 nmol). The maxi mum decrease of arterial blood pressure was observed with a dosage between 7.30 and 14.79 nmol PTH. Complementary to these doseresponse durves (blood pressure-time), we measured plasma ANP both during volume expansion and infusion with 1-34 PTH at differ ent time intervals (plasma ANP time). Design o f the Study Protocol A total of 10 groups made up of 8 rats each were studied. Group I: Infusion of 0.9% NaCl for 2 h (0.2 ml/h) in control rats (control plasma levels of ANP). Group II: Infusion of 0.9% NaCI (15 ml/kg Bw; 2 ml/min) for 2 min in sham-operated rats (volume expansion). Group III: Infusion of 0.9% NaCl (15 ml/kg Bw; 2 ml/min) for 2 min in hypocalcemic-parathyroidectomized rats (volume expan sion). Group IV: Infusion of 0.9% NaCl (15 ml/kg Bw; 2 ml/min) for 2 min (volume expansion) in normocalcemic-parathyroidectomized rats which had received 50 g calcium gluconatc/1 as drinking water for 4 days after parathyroidectomy.
260
Group V: Infusion ofCaCb(75 mgCaCL/kg) for 2 h (0.2 ml/h) in sham-operated rats. Group VI: Infusion of CaCb (75 mg CaCL/kg) for 2 h (0.2 ml/h) in hypocalcemic-parathyroidectomized rats. Group VII: Infusion of parathyroid hormone (1-84 PTH) (0.2 ml/h) for 2 h in intact rats (in total 6.31 nmol PTH). Group VIII: Infusion of 1-34 PTH (0.2 ml/h) for 2 h in intact rats (in total 7.39 nmol PTH). Group IX: Infusion of 1-34 PTH (0.2 ml/h) for 2 h (in total 7.39 nmol PTH), subsequently followed by infusion of 0.9% NaCl (15 ml/kg: 2 ml/min) for 2 min (volume expansion) in intact rats. Group X: Simultaneous infusion both of 0.9% NaCl (15 ml/kg: 2 ml/min) (volume expansion) and 1-34 PTH (in total 7.39 nmol) for 2 min in intact rats. Measurements Blood was collected for determination of serum osmolality (by freezing-point depression, Osmomat, Gonotec, Berlin, FRG), serum sodium, potassium, calcium and phosphate (by flame photometry. Eppendorf Co., Hamburg. FRG) magnesium (by atomic absorption spectrophotometry, Perkin Elmer 3030, Offenbach. FRG) and chlo ride (by Chlorimeter, Eppendorf). Serum was analyzed for total pro tein and albumin by an automatic analyzer (SMAC, Technicon). Radioimmunoassay 2.5 ml blood for determination of plasma ANP was collected in polypropylene tubes containing 500 klU/ml aprotinin (Bayer, Lever kusen. FRG). and immediately centrifuged at 4 °C. The plasma was removed and stored at - 70 °C until assayed. One milliliter of acidif ied plasma (2 A' HC1, pH 3-4) was applied to a SEP-PAK C18 reverse-phase octadodecylsilane cartridge column (Water Associates, Milford. Mass., USA) prewetted twice with 10 ml of 100% methanol and 10 ml 4% acetic acid. The column was then washed three times with 5 ml of 0.1 % trifluoracetic acid (TFA) followed by extraction with a mixture of 2 ml of 60% acetonitrile and 0.1 % TFA, freezedried. and redissolved in I ml of assay buffer with diluted Triton X-100 (2%). The mean recovery of two concentrations of standard ANP (101-126) was 72 ± 6% (mean ± SD). One milliliter of each sample in duplicate was used for the radioimmunoassay. A detailed description of the radioimmunoassay is given elsewhere [26], The rats were killed by decapitation and the hearts were removed quickly and dissected. After preparation of both atria they were boiled in 2 ml of 1.0 M acetic acid and 20 mM HCI for 5 min. Then the tissue was homogenized and diluted with 8 ml of a buffer of the following composition: 0.1 M sodium phosphate, 1 mM EDTA, 0.1 g/l sodium azide at pH 7.0. The samples were centrifuged for 30 min at 10.000 g. The supernatants were frozen at - 700C until radiommunoassay. We measured aliquots of 4 and 1 pi. Protein determination was per formed according to the method of Lowry et al. [27], Human alpha-ANP (1-28) (corresponding to human ANP (99126) was purchased from Peninsula Laboratories Europe Ltd.. Mer seyside. UK. The standard was dissolved in assay buffer and pre pared at final concentrations in the range of 1-128 pg/lOOpl per tube. The percentage cross-reactivity of ANP fragments with the antiserum used is as follows: human ANP (99-126) 100%, rat ANP (101-126) 90%, rat ANP (103-126) 100%. rat ANP (102-126) 88%. The sensitivity of the assay was 1.5 pg/tubc. The intra-assay and interassay variances were 8 and 12%, respectively, for blood samples to which rat ANP (103-126) was added. The plasma sample was assayed in duplicate and corrected by recovery rate.
Geiger/Bahner/Meissner/Hugo/Kirstein/ Schaefer/Heidland/Massry
PTH Modulates the Release of ANP
Downloaded by: Nagoya University 133.6.82.173 - 1/11/2019 4:33:17 PM
to a role for plasma ANP in regulating blood pressure and fluid balance under the condition of altered calcium intake and PTH status [19. 20]. Parathyroid hormone (PTH) which enhances entry of calcium into many cells [21-25] may, therefore, influence secretion of ANP. Our present study provides data demonstrating in intact ani mals that the presence of PTH is required for the aug mented ANP release during acute volume expansion.
Table 1. Scrum parameters, arterial blood pressure changes and results of plasma and atrial ATP (mean values ± SEM) Experimental groups 1
2
3
4
5
6
7
8
9
10
144± 1 106 ± 1
148 ±5 108 ±3
142 ±2 104 ± 1
141 ± 1 106 ± 1
136 ± 2 102 ± I
141 ± 1 101 ±1
140 ± 1 102 ±2
142 ± 1 104 ± 1
139 ± 1 105 ± 1
141 ± 1 106 ± 1
a Serum Sodium, mmol/1 Chloride, mmol/1 Potassium mmol/1 Calcium, mmol/1 Phosphate mmol/1 Magnesium mmol/1 Osmolality mosm/kg Total protein g/dl Albumin, g/dl
4.78 + 0.04 4.58 ±0.13 4.94 ±0.17 4.53 ±0.09 4.89±0.25 4.83 ±0.04 4.69±0.10 4.87 ±0.13 4.41 ±0.13 4.64 ±0.06 2.37 + 0.06 2.32 ±0.10 1.77 ±0.07 2.44 ±0.05 2.58±0.08 2.15 ±0.09 2.51 ±0.01 2.49 ±0.04 2.23 ± 0.01 2.25 ±0.02 2.55 + 0.15 2.41 ±0.12 3.20 ±0.10 2.44 ±0.26 2.43 ±0.13 3.33 ±0.07 2.40 ±0.10 2.21 ±0.05 2.03 ±0.06 2.47 ±0.06 0.91 ±0.04 0.77 ± 0.01 0.72 ±0.02 0.78 ±0.06 0.84 ±0.05 0.83 ±0.05 1.04 ±0.03 0.99 ±0.02 0.78 ±0.02 0.73 ±0.01 323 ± 3
310 ± 4
314 ± 2
305 ±2
322 ±2
325 ± 5
317 ± 1
329 ± 2
300 ±1
306 ±1
4.64 ±0.13 4.44 ±0.19 3.98 ±0.12 3.79 ±0.16 4.16± 0.10 4.68 ±0.07 4.38 ±0.06 4.17±0.05 4.13 ± 0.09 4.04 ±0.06 2.84 ±0.07 2.68 ±0.12 2.44 ±0.06 2.25 ± 0.11 2.61 ±0.06 2.79 ±0.04 2.69 ±0.04 2.81 ±0.04 2.43 ±0.05 2.49 ±0.04
b Mean arterial blood pressure Resting conditions mm Hg !06±3 End of experiment mm Hg 106 ±3
I13±2
109 ±3
! 13 ± 9
101+2
104 + 2
109 ±3
115±4
110 + 5
106 ±2
120 ± 3
109 ±4
115 ± 11
108 ± 1
110 ± 2
98 ±2
97 ±6
79 ±3
78±2
c ANP Plasma, pg/ml 114 ± 23 702 ±86 271 ±38 402 ±85 135 ± 9 69 ±14 57 ± 9 164 ± 16 64 ±13 237 ±35 Left atrium pg/mg protein 2.10 ± 0.18 2.90 ±0.42 1.51 ±0.29 1.64 ±0.24 2.08 ±0.15 1.85 ± 0.15 2.32 ±0.33 2.44±0.13 1.81 ±0.20 1.97 ±0.21 Right atrium pg/mg protein 2.95 ±0.41 3.57±0.40 2.81 ±0.31 2.88 ±0.54 3.37±0.26 2.83±0.43 3.76±0.29 3.15 ± 0.29 3.43±0.59 3.14 ±0.64
Results A detailed list of all serum parameters is given in table la, changes of arterial blood pressure are put to gether in table lb, and results of plasma and atrial ANP are listed in table lc. Significances were omitted from the tables for a better survey, but they are stated in the text.
Effect o f Volume Expansion Acute volume expansion in sham rats caused not only a pronounced increase of plasma ANP (702 ± 86 vs. 114 ± 23 pg/ml; p < 0.001). ANP in left atrial tissue (2.90 ± 0.42 vs. 2.10 ± 0.18 pg/mg protein, n.s.) and ANP in right atrium (3.57 ± 0.40 vs. 2.95 ± 0.41 pg/mg protein, n.s.) did not change significantly (n = 5). Effect o f Calcium Infusion Serum calcium was elevated by calcium infusion from 2.37 ± 0.06 to 2.58 ± 0.08 mmol/1 in sham-operated rats (group V)(p < 0.01) and from 1.36 ± 0.05 to 2.15 ± 0.09 mmol/1 (p < 0.001) in PTX rats (group VI). CaCN infu sion induced a significantly (p < 0.001) higher plasma concentration of ANP in intact rats compared to PTX rats (135 ± 9 vs. 69 ± 14 pg/ml), but both ANP levels are not significantly different from control animals without
261
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Data Analysis Statistical analysis of the data was performed according to the recommendations of Wallenstein et al. [28], The results are expressed as mean ± SEM. For the comparison of statistical significance between the groups student’s t test and Wilcoxon U test were used. For the multiple comparison, ANOVA fol lowed by the Bonferroni t test were used. Differences at the 95 % level were considered significant. Significance is given as p < 0.05, p < 0.01. p
