Parasitol Res (1992) 78:553-556
Parasitnlngy Research
9 Springer-Verlag 1992
Changes in atrial natriuretic factor and plasma renin activity in dogs infected with Trypanosoma brucei* J.M. Ndung'u 1, N.G. Wright 2, F.W. Jennings 2 and Max Murray 2 1 Kenya Trypanosomiasis Research Institute - Muguga P.O. Box 362, Kikuyu, Kenya 2 University of Glasgow Veterinary School, Bearsden Road, Bearsden, Glasgow G61 IQH Scotland Accepted June 30, 1992
Abstract. When beagle dogs were infected with Trypanosoma brueei, a marked reduction in the plasma concentration o f atrial natriuretic factor ( A N F ) occurred in the terminal stage of the disease during weeks 3 and 4. At the same time there was an increase in plasma renin activity (PRA) after infection. Ultrastructural studies of the atria of these dogs demonstrated a reduction in A N F granules. The changes in A N F and P R A occurred in association with severe pancarditis and the development of heart failure. By impairing the ability of the heart and kidneys to regulate blood volume, the alterations in A N F and P R A could be involved in the pathogenesis of heart failure in T. brucei-infected dogs.
In addition to its role as a vascular pump, the heart is an important endocrine organ, producing an atrial natriuretic factor (ANF), a combined vasorelaxant, natriuretic and diuretic h o r m o n e (Mendez et al. 1987). A N F is secreted by atrial myocytes of mammalian hearts in response to stretch (Cantin et al. 1988) and induces a number of important effects. In the circulation, A N F exerts a direct vasorelaxant action by inhibiting the vasoconstrictor effect of angiotensin II (AII; Harris et al. 1987; Bache et al. 1988). In the kidneys, A N F increases the glomerular filtration rate and, via its inhibitory effect on renin secretion from juxtaglomerular cells, causes an indirect reduction in plasma A I I concentration. A N F also decreases reabsorption of the glomerular filtrate by the proximal tubules by inhibiting AII-stimulated sodium and water transport (Harris et al. 1987). The disease caused by infection o f dogs with Trypanosoma brucei is characterised by pantropic tissue damage, * These investigations received support from the UNDP/World Bank/WHO Special Programme for Research and Training in Tropical Diseases. The dags were kept at Glasgow University Veterinary School. The senior author (J.M.N.) was on a British Council scholarship Correspondence to: J.M. Ndung'u
including severe pancarditis, and if the dogs are untreated, death occurs a r o u n d week 4 after infection, with clinical and pathological findings being indicative of heart failure (Morrison et al. 1981). The changes in cardiac function that lead to this heart failure syndrome have not been elucidated. The present study was carried out in dogs to investigate the possible effects of infection with T. brucei on plasma and atrial concentrations of A N F and plasma renin activity (PRA).
Materials and methods A total of 12 female beagles aged 7 months were used, of which 8 were inoculated intravenously with approximately 5 • J 0~ Trypanosoma brueei GVR35/c.1. The source of the stabilate and the management of the dogs have been described elsewhere (Ndung'u et al. 1989). The other 4 dogs were kept as uninfected controls. Experimental design ANF studies. Before and during the infection, 5 ml blood was collected from the jugular vein at least twice a week in chilled tubes containing ethylenediaminetetraacetic acid (EDTA) as an anticoagulant and sufficient Trasylol (Bayer UK) to give a final concentration of 50 kallikrein inhibitor units per millilitre of blood. The samples were centrifuged at 3000 g for 10 min at 4~ C. The plasma obtained was then stored at --20~ C. Assay of plasma ANF was performed using the radioimmunoassay method described by Richards et al. (1987). PRA studies. Blood samples (1 ml) were collected into chilled tubes maintained at 3~ and centrifuged at 3000 g for 10 rain at room temperature. Plasma was stored at -20 ~ C and PRA was estimated using the method of Millar et al. (1980). Transmission electron microscopy. On days 10, 15, 21 and 22, two of the infected dogs were euthanised for transmission electron microscopic (TEM) investigations. The uninfected dogs were also euthanised at the end of the experimental period. Small pieces of cardiac muscle measuring less than 1 mm in thickness were obtained from the walls of both atria and ventricles immediately after the dogs had been euthanised and were placed in Karnovsky's fixative (2.5% paraformaldehyde + 2% gluteraldehyde; Karnovsky
554 1965). After immersion in fixative for at least 3 h, the tissues were washed in 0.1 M cacodylate buffer for 1 h, dehydrated in a graded series of acetone, embedded in an Emix resin and sectioned with glass knives using an LKB MKIII ultratome. Ultrathin sections were stained with uranyl acetate and lead citrate and examined with a JOEL CXI00II transmission electron microscope. Parallel histological methods were used to assess the overall myocardial damage as described by Ndung'u (1990). Results
Clinical findings Detailed clinical findings have been reported elsewhere ( N d u n g ' u et al. 1991). In brief, after a prepatent period of between 5 and 6 days, all eight infected dogs developed signs of disease characterised by a fever of up to 40.6 ~ C; severe parasitaemia; generalised lymph node, spleen and liver enlargement; pallor of mucous m e m branes; and, finally, panophthalmitis, wasting and weight loss. In Weeks 3 and 4, clinical, electrocardiographic and echocardiographic changes indicative of severe heart damage and development of congestive heart failure were observed. These included bradycardia, weak heart beats, increased capillary refill times, dyspnoea and coughing, p o o r left ventricular function, valvular incompetence, heart blocks, sinus arrest, S - T segment elevation and accumulation of pericardial effusion.
Fig. 2. An electron micrograph of atrial natriuretic granules (arrows) in a perinuclear region of the right atrium of an uninfected dog. Most of the granules are highly electron-dense. M, Mitochondria; F, myofibrils. TEM, 28650
Plasma A N F In control dogs, the mean concentration of A N F remained within the range of 18.75 _+7.11 pg/ml. The m e a n changes in plasma A N F observed in infected dogs are shown in Fig. 1. For the first 2 weeks after infection, the concentration o f A N F fluctuated within the above range. However, during week 3, a consistent drop in concentration occurred in all dogs, and this persisted into the terminal stages of the disease in week 4.
250
-1
T-
Fig. 3. An electron micrograph of atrial natriuretic granules in a perinuclear region of the right atrium of a dog infected with Trypanosoma brucei for 22 days. The granules are few, poorly electrondense and relatively small. The Golgi complex (G) is prominent. N, Nucleus; L, lipid. TEM, 26900
35
- 30
200
150 .E~
20
"13 ~"
INFECTION 100
15
13-
E]
10 50-
(31
r
-
-4
[]
*
-2
0
2
4
6
8
10
12
14
16
18
Plasma P R A The level of P R A remained low during the first 2 weeks of infection (Fig. 1). In weeks 3 and 4 there was a rapid rise in PRA, coinciding with the decrease in A N F . The mean level of P R A in control dogs remained within the range of 8.44 _+3.61 m U / m l throughout the study period.
0
20
22
Histology and T E M studies
Days After Infection
Fig. 1. Mean changes in plasma ANF and PRA in dogs infected with Trypanosoma brueei
Detailed histology studies have been described elsewhere ( N d u n g ' u /990). tn brief, there was severe myocardial
555 damage in the form of myocyte degeneration and necrosis, including increased lipid deposition, a feature observed in both atrial and ventricular myocardial cells. T E M examination o f the atrial myocardium of uninfected dogs demonstrated the presence of many uniform, electron-dense perinuclear granules in the myocytes (Fig. 2). A few granules were also scattered between myofibrils and were occasionally located in the subsarcolemmal region. In myocytes from hearts of dogs infected for 21 and 22 days, there was a marked reduction in the number, size and density of atrial granules (Fig. 3). The Golgi complexes were prominent and distended. In both infected and control dogs, similar granules were not found in the ventricular myocardial cells. Discussion
Trypanosoma brucei infection in dogs leads to widespread tissue damage, including severe pancarditis; if the animals are not treated, death results from congestive heart failure (Morrison et al. 1981). The pathogenic mechanisms that lead to heart failure are not understood. Although death most probably results from failure of the heart as a pump, the present studies indicate that the severity of the disease may well be influenced by impaired regulation of hormones that control blood volume and blood flow dynamics. Thus, in T. brucei-infected dogs it was found that marked changes in plasma A N F and PRA occurred. The fall in plasma A N F was associated with a reduction in the number, size and density of atrial granules. The latter are known to be the storage sites for A N F , releasing the hormone in response to atrial stretch. The cause of the atrial stretch is usually attributed to increased blood pressure, which leads to elevated intra-atrial pressure. Two factors acting either individually or in concert may have caused the reduction in A N F in the storage sites and in the circulation. Firstly, as a result of atrial stretch, it is possible that secretion of A N F was occurring faster than synthesis, leading to secretory exhaustion. Secondly, decreased synthesis secondary to myocyte damage might have triggered the reduction in A N F granules and plasma ANF. Indeed, it is likely that both factors were operating concurrently, since T. brucei infection in dogs leads to marked atrial damage (Morrison et al. 1981; Kaggwa et al. 1983) and, hence to stretch of cardiac myocytes. The presence of distended Golgi complexes in the damaged atrial myocytes suggests that synthesis of A N F was probably continuing but could not keep up with the rate of secretion. In the terminal stage of infection the fall in A N F was accompanied by a marked increase in PRA. The latter finding may have been the result of increased secretion of renin following the removal of the inhibitory effect of A N F 'on the juxtaglomerular cells. This inverse relationship between A N F and renin secretion has been demonstrated in in vivo studies in sodium-deprived humans in whom infusion of A N F decreased P R A and plasma aldosterone in a dose-dependent manner (Oelkers et al. 1988). In other studies, endogenous A N F
release by rapid atrial pacing in dogs caused a decrease in P R A followed by a marked rebound increase at 60 min post-pacing (Walsh et al. 1987). It is also possible that a reduction in renal arterial blood pressure secondary to poor left ventricular function might have caused an increase in PRA. Under normal physiological conditions, renin would stimulate the angiotensin-converting enzyme, leading to increased production of AII from AI. Due to its dual activities of vasoconstrictor action and enhancement of sodium retention, AII would cause increased blood pressure, thereby having a negative feedback action on the pressure-dependent release of renin (Kirchheim et al. 1988). In the present investigation, however, the failing heart was probably unable to sustain arterial blood pressure, leading to continued secretion of renin and retention of sodium and water. For this reason, human patients suffering from congestive heart failure are given angiotensin-converting enzyme inhibitors (ACEI). It is possible that the use of ACEI at the time of trypanocidal treatment in parasitised dogs might reduce the volume load to the heart and, hence, the risk of development of congestive heart failure. The changes in A N F and PRA observed in these studies suggest that both might play a significant role in the pathogenesis of the heart failure syndrome. It is likely that an increase in P R A and a decrease in A N F caused sodium retention and increased water intake, leading to plasma volume expansion and increased venous return to an already failing heart. In the absence of A N F , the dogs were unable to control the increased volume load, which exacerbated the degree of heart failure.
Acknowledgements. The authors wish to thank Dr. H.J. Dargie and Dr. D.B. Northridge of the Cardiology Clinic, Western Infirmary, for their advice and the technical staff of the Departments of Veterinary Medicine, Anatomy and Parasitology as well as Dr. J. Doyle and Ms. A. Spiers of the MRC Blood Pressure Unit, Western Infirmary, Glasgow (where hormone analysis was done), for their assistance during these investigations.
References Bache RJ, Dai X, Schwartz JS, Chen DG (1988) Effects of atrial natriuretic peptide in the canine coronary circulation. Circ Res 62:178-183 Cantin M, Thibault G, Ding J, Gutkowska J, Garcia R, Jasmin G, Hamet P, Genest J (1988) ANF in experimental congestive heart failure. Am J Pathol 130:552-568 Harris PJ, Thomas D, Morgan TO (1987) Atrial natriuretic peptide inhibits angiotensin-stimulated proximal tubular sodium and water reabsorption. Nature 326:697 698 Kaggwa E, Munyua WK, Mugera GM (1983) The pathology of Trypanosoma brucei in the dog. Bull Anita Health Prod Afr 33:69-75 Karnovsky MJ (1965) A formaldehyde-gluteraldehyde fixative of high osmolarity for use in electron microscopy. J Cell Biol 17: 127A-138A Kirchheim H, Ehmke H, Persson P (1988) Physiology of the renal baroreceptor mechanism of renin release and its role in congestive heart failure. Am J Cardiol 62:68E 71E Mendez RE, Pfeffer JM, Ortola FV, Block KD, Anderson S, Seidman JG, Brenner BM (1987) Atrial natriuretic peptide tran-
556 scription, storage and release in rats with myocardial infarction. Am J Physiol 253 :HI449-H1455 Millar JA, Leckie BJ, Morton JJ, Jordan J, Tree M (1980) A micro assay for active and total renin concentration in human plasma based on antibody trapping. Clin Chem 101:5-15 Morrison WI, Murray M, Sayer PD, Preston JM (1981) The pathogenesis of experimentally induced Trypanosoma brueei infection in the dog: 1. Tissue and organ damage. Am J Pathol 102:168181 Ndung'u JM (1990) Clinical and immunopathological aspects of heart damage in dogs infected with Trypanosoma brucei. PhD Thesis, University of Glasgow, pp 42-43 Ndung'u JM, Eckersall PD, Jennings FW, Wright NG, Murray M (1989) Changes in lipid metabolism in dogs experimentally infected with Trypanosoma brucei. Proceedings of the 20th Meeting of the International Scientific Council for Trypanoso-
miasis Research and Control (ISCTRC), Mombasa, Kenya, 1014 April 1989, pp 304-314 Ndung'u JM, McEwan NA, Jennings FW, Murray M (1991) Cardiac damage in dogs infected with Trypanosoma brueei." clinical and electrocardiographic features. J Small Anita Pract 32: 579584 Oelkers W, Kleine S, Bahr V (1988) Effects of incremental infusions of atrial natriuretic factor on aldosterone, renin, and blood pressure in humans. Hypertension 12: 462-467 Richards AM, Tonolo G, McIntyre GD, Leckie BJ, Robertson JIS (1987) Radio-immunoassay for plasma alpha human atrial natriuretic peptide: a comparison of direct and pre-extracted methods. Hypertension 5:227-236 Walsh KP, Williams TDM, Canepa-Anson R, Pitts E, Lightman SL, Sutton R (1987) Effects of endogenous atrial natriuretic peptide released by rapid atrial pacing in dogs. Am J Physiol 253 : R599-R604
Parasitnlngy Research
9 Springer-Verlag 1992
Changes in atrial natriuretic factor and plasma renin activity in dogs infected with Trypanosoma brucei* J.M. Ndung'u 1, N.G. Wright 2, F.W. Jennings 2 and Max Murray 2 1 Kenya Trypanosomiasis Research Institute - Muguga P.O. Box 362, Kikuyu, Kenya 2 University of Glasgow Veterinary School, Bearsden Road, Bearsden, Glasgow G61 IQH Scotland Accepted June 30, 1992
Abstract. When beagle dogs were infected with Trypanosoma brueei, a marked reduction in the plasma concentration o f atrial natriuretic factor ( A N F ) occurred in the terminal stage of the disease during weeks 3 and 4. At the same time there was an increase in plasma renin activity (PRA) after infection. Ultrastructural studies of the atria of these dogs demonstrated a reduction in A N F granules. The changes in A N F and P R A occurred in association with severe pancarditis and the development of heart failure. By impairing the ability of the heart and kidneys to regulate blood volume, the alterations in A N F and P R A could be involved in the pathogenesis of heart failure in T. brucei-infected dogs.
In addition to its role as a vascular pump, the heart is an important endocrine organ, producing an atrial natriuretic factor (ANF), a combined vasorelaxant, natriuretic and diuretic h o r m o n e (Mendez et al. 1987). A N F is secreted by atrial myocytes of mammalian hearts in response to stretch (Cantin et al. 1988) and induces a number of important effects. In the circulation, A N F exerts a direct vasorelaxant action by inhibiting the vasoconstrictor effect of angiotensin II (AII; Harris et al. 1987; Bache et al. 1988). In the kidneys, A N F increases the glomerular filtration rate and, via its inhibitory effect on renin secretion from juxtaglomerular cells, causes an indirect reduction in plasma A I I concentration. A N F also decreases reabsorption of the glomerular filtrate by the proximal tubules by inhibiting AII-stimulated sodium and water transport (Harris et al. 1987). The disease caused by infection o f dogs with Trypanosoma brucei is characterised by pantropic tissue damage, * These investigations received support from the UNDP/World Bank/WHO Special Programme for Research and Training in Tropical Diseases. The dags were kept at Glasgow University Veterinary School. The senior author (J.M.N.) was on a British Council scholarship Correspondence to: J.M. Ndung'u
including severe pancarditis, and if the dogs are untreated, death occurs a r o u n d week 4 after infection, with clinical and pathological findings being indicative of heart failure (Morrison et al. 1981). The changes in cardiac function that lead to this heart failure syndrome have not been elucidated. The present study was carried out in dogs to investigate the possible effects of infection with T. brucei on plasma and atrial concentrations of A N F and plasma renin activity (PRA).
Materials and methods A total of 12 female beagles aged 7 months were used, of which 8 were inoculated intravenously with approximately 5 • J 0~ Trypanosoma brueei GVR35/c.1. The source of the stabilate and the management of the dogs have been described elsewhere (Ndung'u et al. 1989). The other 4 dogs were kept as uninfected controls. Experimental design ANF studies. Before and during the infection, 5 ml blood was collected from the jugular vein at least twice a week in chilled tubes containing ethylenediaminetetraacetic acid (EDTA) as an anticoagulant and sufficient Trasylol (Bayer UK) to give a final concentration of 50 kallikrein inhibitor units per millilitre of blood. The samples were centrifuged at 3000 g for 10 min at 4~ C. The plasma obtained was then stored at --20~ C. Assay of plasma ANF was performed using the radioimmunoassay method described by Richards et al. (1987). PRA studies. Blood samples (1 ml) were collected into chilled tubes maintained at 3~ and centrifuged at 3000 g for 10 rain at room temperature. Plasma was stored at -20 ~ C and PRA was estimated using the method of Millar et al. (1980). Transmission electron microscopy. On days 10, 15, 21 and 22, two of the infected dogs were euthanised for transmission electron microscopic (TEM) investigations. The uninfected dogs were also euthanised at the end of the experimental period. Small pieces of cardiac muscle measuring less than 1 mm in thickness were obtained from the walls of both atria and ventricles immediately after the dogs had been euthanised and were placed in Karnovsky's fixative (2.5% paraformaldehyde + 2% gluteraldehyde; Karnovsky
554 1965). After immersion in fixative for at least 3 h, the tissues were washed in 0.1 M cacodylate buffer for 1 h, dehydrated in a graded series of acetone, embedded in an Emix resin and sectioned with glass knives using an LKB MKIII ultratome. Ultrathin sections were stained with uranyl acetate and lead citrate and examined with a JOEL CXI00II transmission electron microscope. Parallel histological methods were used to assess the overall myocardial damage as described by Ndung'u (1990). Results
Clinical findings Detailed clinical findings have been reported elsewhere ( N d u n g ' u et al. 1991). In brief, after a prepatent period of between 5 and 6 days, all eight infected dogs developed signs of disease characterised by a fever of up to 40.6 ~ C; severe parasitaemia; generalised lymph node, spleen and liver enlargement; pallor of mucous m e m branes; and, finally, panophthalmitis, wasting and weight loss. In Weeks 3 and 4, clinical, electrocardiographic and echocardiographic changes indicative of severe heart damage and development of congestive heart failure were observed. These included bradycardia, weak heart beats, increased capillary refill times, dyspnoea and coughing, p o o r left ventricular function, valvular incompetence, heart blocks, sinus arrest, S - T segment elevation and accumulation of pericardial effusion.
Fig. 2. An electron micrograph of atrial natriuretic granules (arrows) in a perinuclear region of the right atrium of an uninfected dog. Most of the granules are highly electron-dense. M, Mitochondria; F, myofibrils. TEM, 28650
Plasma A N F In control dogs, the mean concentration of A N F remained within the range of 18.75 _+7.11 pg/ml. The m e a n changes in plasma A N F observed in infected dogs are shown in Fig. 1. For the first 2 weeks after infection, the concentration o f A N F fluctuated within the above range. However, during week 3, a consistent drop in concentration occurred in all dogs, and this persisted into the terminal stages of the disease in week 4.
250
-1
T-
Fig. 3. An electron micrograph of atrial natriuretic granules in a perinuclear region of the right atrium of a dog infected with Trypanosoma brucei for 22 days. The granules are few, poorly electrondense and relatively small. The Golgi complex (G) is prominent. N, Nucleus; L, lipid. TEM, 26900
35
- 30
200
150 .E~
20
"13 ~"
INFECTION 100
15
13-
E]
10 50-
(31
r
-
-4
[]
*
-2
0
2
4
6
8
10
12
14
16
18
Plasma P R A The level of P R A remained low during the first 2 weeks of infection (Fig. 1). In weeks 3 and 4 there was a rapid rise in PRA, coinciding with the decrease in A N F . The mean level of P R A in control dogs remained within the range of 8.44 _+3.61 m U / m l throughout the study period.
0
20
22
Histology and T E M studies
Days After Infection
Fig. 1. Mean changes in plasma ANF and PRA in dogs infected with Trypanosoma brueei
Detailed histology studies have been described elsewhere ( N d u n g ' u /990). tn brief, there was severe myocardial
555 damage in the form of myocyte degeneration and necrosis, including increased lipid deposition, a feature observed in both atrial and ventricular myocardial cells. T E M examination o f the atrial myocardium of uninfected dogs demonstrated the presence of many uniform, electron-dense perinuclear granules in the myocytes (Fig. 2). A few granules were also scattered between myofibrils and were occasionally located in the subsarcolemmal region. In myocytes from hearts of dogs infected for 21 and 22 days, there was a marked reduction in the number, size and density of atrial granules (Fig. 3). The Golgi complexes were prominent and distended. In both infected and control dogs, similar granules were not found in the ventricular myocardial cells. Discussion
Trypanosoma brucei infection in dogs leads to widespread tissue damage, including severe pancarditis; if the animals are not treated, death results from congestive heart failure (Morrison et al. 1981). The pathogenic mechanisms that lead to heart failure are not understood. Although death most probably results from failure of the heart as a pump, the present studies indicate that the severity of the disease may well be influenced by impaired regulation of hormones that control blood volume and blood flow dynamics. Thus, in T. brucei-infected dogs it was found that marked changes in plasma A N F and PRA occurred. The fall in plasma A N F was associated with a reduction in the number, size and density of atrial granules. The latter are known to be the storage sites for A N F , releasing the hormone in response to atrial stretch. The cause of the atrial stretch is usually attributed to increased blood pressure, which leads to elevated intra-atrial pressure. Two factors acting either individually or in concert may have caused the reduction in A N F in the storage sites and in the circulation. Firstly, as a result of atrial stretch, it is possible that secretion of A N F was occurring faster than synthesis, leading to secretory exhaustion. Secondly, decreased synthesis secondary to myocyte damage might have triggered the reduction in A N F granules and plasma ANF. Indeed, it is likely that both factors were operating concurrently, since T. brucei infection in dogs leads to marked atrial damage (Morrison et al. 1981; Kaggwa et al. 1983) and, hence to stretch of cardiac myocytes. The presence of distended Golgi complexes in the damaged atrial myocytes suggests that synthesis of A N F was probably continuing but could not keep up with the rate of secretion. In the terminal stage of infection the fall in A N F was accompanied by a marked increase in PRA. The latter finding may have been the result of increased secretion of renin following the removal of the inhibitory effect of A N F 'on the juxtaglomerular cells. This inverse relationship between A N F and renin secretion has been demonstrated in in vivo studies in sodium-deprived humans in whom infusion of A N F decreased P R A and plasma aldosterone in a dose-dependent manner (Oelkers et al. 1988). In other studies, endogenous A N F
release by rapid atrial pacing in dogs caused a decrease in P R A followed by a marked rebound increase at 60 min post-pacing (Walsh et al. 1987). It is also possible that a reduction in renal arterial blood pressure secondary to poor left ventricular function might have caused an increase in PRA. Under normal physiological conditions, renin would stimulate the angiotensin-converting enzyme, leading to increased production of AII from AI. Due to its dual activities of vasoconstrictor action and enhancement of sodium retention, AII would cause increased blood pressure, thereby having a negative feedback action on the pressure-dependent release of renin (Kirchheim et al. 1988). In the present investigation, however, the failing heart was probably unable to sustain arterial blood pressure, leading to continued secretion of renin and retention of sodium and water. For this reason, human patients suffering from congestive heart failure are given angiotensin-converting enzyme inhibitors (ACEI). It is possible that the use of ACEI at the time of trypanocidal treatment in parasitised dogs might reduce the volume load to the heart and, hence, the risk of development of congestive heart failure. The changes in A N F and PRA observed in these studies suggest that both might play a significant role in the pathogenesis of the heart failure syndrome. It is likely that an increase in P R A and a decrease in A N F caused sodium retention and increased water intake, leading to plasma volume expansion and increased venous return to an already failing heart. In the absence of A N F , the dogs were unable to control the increased volume load, which exacerbated the degree of heart failure.
Acknowledgements. The authors wish to thank Dr. H.J. Dargie and Dr. D.B. Northridge of the Cardiology Clinic, Western Infirmary, for their advice and the technical staff of the Departments of Veterinary Medicine, Anatomy and Parasitology as well as Dr. J. Doyle and Ms. A. Spiers of the MRC Blood Pressure Unit, Western Infirmary, Glasgow (where hormone analysis was done), for their assistance during these investigations.
References Bache RJ, Dai X, Schwartz JS, Chen DG (1988) Effects of atrial natriuretic peptide in the canine coronary circulation. Circ Res 62:178-183 Cantin M, Thibault G, Ding J, Gutkowska J, Garcia R, Jasmin G, Hamet P, Genest J (1988) ANF in experimental congestive heart failure. Am J Pathol 130:552-568 Harris PJ, Thomas D, Morgan TO (1987) Atrial natriuretic peptide inhibits angiotensin-stimulated proximal tubular sodium and water reabsorption. Nature 326:697 698 Kaggwa E, Munyua WK, Mugera GM (1983) The pathology of Trypanosoma brucei in the dog. Bull Anita Health Prod Afr 33:69-75 Karnovsky MJ (1965) A formaldehyde-gluteraldehyde fixative of high osmolarity for use in electron microscopy. J Cell Biol 17: 127A-138A Kirchheim H, Ehmke H, Persson P (1988) Physiology of the renal baroreceptor mechanism of renin release and its role in congestive heart failure. Am J Cardiol 62:68E 71E Mendez RE, Pfeffer JM, Ortola FV, Block KD, Anderson S, Seidman JG, Brenner BM (1987) Atrial natriuretic peptide tran-
556 scription, storage and release in rats with myocardial infarction. Am J Physiol 253 :HI449-H1455 Millar JA, Leckie BJ, Morton JJ, Jordan J, Tree M (1980) A micro assay for active and total renin concentration in human plasma based on antibody trapping. Clin Chem 101:5-15 Morrison WI, Murray M, Sayer PD, Preston JM (1981) The pathogenesis of experimentally induced Trypanosoma brueei infection in the dog: 1. Tissue and organ damage. Am J Pathol 102:168181 Ndung'u JM (1990) Clinical and immunopathological aspects of heart damage in dogs infected with Trypanosoma brucei. PhD Thesis, University of Glasgow, pp 42-43 Ndung'u JM, Eckersall PD, Jennings FW, Wright NG, Murray M (1989) Changes in lipid metabolism in dogs experimentally infected with Trypanosoma brucei. Proceedings of the 20th Meeting of the International Scientific Council for Trypanoso-
miasis Research and Control (ISCTRC), Mombasa, Kenya, 1014 April 1989, pp 304-314 Ndung'u JM, McEwan NA, Jennings FW, Murray M (1991) Cardiac damage in dogs infected with Trypanosoma brueei." clinical and electrocardiographic features. J Small Anita Pract 32: 579584 Oelkers W, Kleine S, Bahr V (1988) Effects of incremental infusions of atrial natriuretic factor on aldosterone, renin, and blood pressure in humans. Hypertension 12: 462-467 Richards AM, Tonolo G, McIntyre GD, Leckie BJ, Robertson JIS (1987) Radio-immunoassay for plasma alpha human atrial natriuretic peptide: a comparison of direct and pre-extracted methods. Hypertension 5:227-236 Walsh KP, Williams TDM, Canepa-Anson R, Pitts E, Lightman SL, Sutton R (1987) Effects of endogenous atrial natriuretic peptide released by rapid atrial pacing in dogs. Am J Physiol 253 : R599-R604
