POLY’XRTERITIS
13 MICE DUE HYPERTENSIOX
G.
T.
TO
SPONTANEOUS
HANEVELD
INTRODUCTION
In view of the importance of cardiovascular and hypertensive disease in man. attention has been paid to comparable lesions in animals. One can stud\normotensive animals in which the homeostatic mechanism has been artiliciallv disturbed; one can also focus on genetically hypertensive animals in the hop” of detecting some common factors in primary or essential hypertension. In this connection the spontaneously hypertensive rat (Okamoto, 1972) is a useful model for the study of hypertension. According to Upton (1971) the mouse citrr also provide model systems for studying several of the vascular lesions associated with ageing. Nterotizing polyarteritis is a severe lesion in ageing mice (,Upton, Conklin, Closgrove, Gude and Darden, 1967) and similar lesions have been observed iit the inbred and random-bred mouse colonies of our institute. In the present paper the histopathology of necrotizing polpartcritis will IX. described in relation to abnormally elevated blood pressure. MATERIALS
AND
METHODS
A detailed description of the equipment and the method for indirect measurements of blood pressure in mice were published previously (Van Nimwegen, 1’an Eijnsbergen. Van Boter and Mullink, 1973). The mice used were the conventional males and females belonging to the following inbred strains : C57Bl/LiARijCpb; NZB/BlLacCpb; lYZW/LeiCpb; CPB-FT; C:PB-Q; CPB-T and CPB-V. The mice were housed in plastic cages after weaning. The diet was Mus 6 1 (Looyen B.V. ; Wageningen) and drinking water was supplied ad libitum. Room temperature was maintained at approximately 23 “C. SPF mice horn the random-bred Cpb:SE colony were also studied. Their diet was steanlsterilized SRM (Hope Farms, Woerden) and their drinking water was chlorinated. Tissues and organs were histologically examined after fixation in 4 per cent aqueous formaldehyde, embedding in paraffin wax and staining with haemalum-eosin. Whcu appropriate the Periodic Acid Schiff (PAS) technique was applied and for demonstration of fibrin Verhoeff and Mallory stains were used. Presence of elastic connective tissue and collagen was demonstrated with Weigert-Van Gieson stain. 0 1979 Academic Press Inc. (London) Limited 0021-9975/79/01099-I-08 $02.00/O
POLYARTERITIS
Fig.
3. Hyalinc I’crivascular
deposit, a few infiltrating cellular reaction. HE.
Fig. 4. Necrosis marl deposits in the aortic wall. the rentre and at the right intramural
Fig.
5. The same Weigert-\‘an
aorta
as in Fig. 4. Increased Gicson. x 60.
AND
HYPERTENSION
cells and x 150.
pycnosis
Note the radial haemorrhage
distance
between
101
IN MICE
in
the
media
position of enlarged can bc seen vaguely.
and
occasional
of
mesenteric
artcriolcs.
muscle cell HE. :I, 60.
nuclei.
rupture
of elastic
ln~ers.
In
102
J.
W,
M.
A.
MULLINK
AND
G. T.
HANEVELD
layer (Fig. 2). Hyalinization of the media was prominent (Fig. 3) ; this material was PAS-positive, fibrin stains were negative. Vacuolation of the hyalin was regularly observed. In combination with hyalinosis and cellular infiltration the smooth muscle cells of the media became swollen and gradually lost their ability to stain. In the larger arteries the nuclei of these smooth muscle cells showed a radial position instead of the normal circular arrangement (Fig. 4).
Fig.
6. Superior mesenteric artery. Lumen is at the top. Gradual loss of staining power of the elastic layers. Note the normal stained remnants of the elastic layers at the adventitial site. At the right complete loss of structure and hyalinization. Weigert-van Gieson. :< 60.
Pycnosis and nuclear fragments in the media were frequently observed, both in combination with hyaline deposits and/or cellular infiltration, Haemorrhage into the media (Fig. 4) was mainly observed in the larger arteries. Scattered groups of swollen nuclei suggested the possibility of an early proliferative reaction.
Fig.
7. Local differences in proliferation, infiltration, irregular alteration of the mesenteric arterial
hyalinization and wall. HE. x 60.
necrosis
resulted
in highly
POLYARTERITIS
AND
HYPERTENSION
103
IN MICE
A gradual disappearance of elastic membranes was noted. This phenomenon was most prominent in the larger arteries. In combination with hyalin deposits. necrosis and haemorrhage, the distance between the elastic layers was increased /Fig. 5). Individual elastic layers ruptured, sometimes only in isolated foci. The staining capacity of the elastic fibres gradually decreased and finally disappearcti Fig. 6). In combination with the other features this resulted in irregular loss of th(‘ structure of the arterial wall (Fig. 7). In such areas ruptures of the aort:~ or rncsenteric arteries occasionally occurred, resulting in exsanguination.
l:ig. 8. Proliferative lesions of the intima, media and in the perivascular region. Mixed celiular inliltration extending from perivascular region to the proliferation of the arterial wall. At the left the normal structure is partially preserved. HE. ‘.: 60.
The proliferation of the perivascular connective tissue of the affected vessels extended into the media. In combination with proliferated elements of the arterial wall a complicated histological picture was observed together with hyaline remnants, nuclear fragments and cellular infiltration (Fig. 8).
Fig. 9. Sclerosis
and elastic
proliferation
of arteriole.
Weigert-van
G&on.
7 150.
lO$
J. W.
M. A. MULLINK
AND
G. T. HANEVELD
In some instances, only the subendothelial layer was preserved, while the other elements of the vascular wall were replaced by connective tissue in which a few scattered smooth muscle cells were still present. Combined with elastic proliferation this resulted in sclerosis of arterioles (Fig. 9) but the perivascular proliferation prevented haemorrhage even though degeneration and necrosis had caused disruption of the original arterial wall (Fig. 10).
Fig.
10. Rupture of locally altered arterial haemorrhage. Weigert-van Gieson.
x
wall. 60.
Perivascular
and
mural
proliferation
prevented
Various lesions were also observed in the intima. Hyaline deposits occurred in the intima with or without hyalinosis of the media. In rare instances, groups of “foam cells” were found in the subendothelial (Fig. 11) area. Remnants of such cells were seen in intimal proliferations, which otherwise consisted of collagen and elastic fibres. Splitting and duplication of the internal elastic membrane occurred in combination with the intimal proliferation.
Fig.
11. Perivascular endothelial
infiltration of renal artery branch. foam cells at the right. HE. x 60.
Intimal
proliferation
at the left. Note
the sub-
POLYARTERITIS
AND
HYPERTENSION
IN MICE
10.5
Endothelial nuclei were swollen or, rarely pycnotic. Mural thrombosis was sometimes observed in the larger arteries. Occasionally the arteriolar lumen was obliterated, probably due to thrombosis. The arteriolar lesions consisted predominantly of hyalinization, necrosis and I)erivascular infiltration.
Blood pressure determinations were performed on all mice in this stud! which showed clinical signs of disease. Many animals died during the pcntoI,arbitone-sodium anaesthesia; in a few no reliable data could be obtained. 111 8 mice showing necrotizing polyarteritis reliable blood pressure‘ va1uc.h were rccordcd. It appeared that all these 8 mice showed a blood prcssurc recording which was found to be elevated more than 20 mmHg, compared with their controls. The controls were 18 healthy mice of the same strain as tIlta discascd mice. They were maintained under identical conditions in the samt c’qrs. DISCUSSION
Despite the limited number of animals in which blood pressure could 1~. reliably recorded, it is evident that severe arterial lesions correlated cvith c*lcvated blood pressures. In man severe vascular alterations are considered to ix the result of malignant essential hypertension (Sanerkin, 197 1). Also hyptrrtension is reported to result in considerable changes in the pulmonary vasculat system (Wagenvoort, Heath and Edwards, 1964). In mice, the lesions ot’ uecrotizing polyarteritis were more of a degenerative nature than primaril) inflammatory. Together with the finding of an elevated blood pressure in all mice in which a reliable recording was obtained, this indicates that in lhc mouse, as in man, the arterial lesions may have resulted from a primaril> c%lcvatedblood pressure. The vascular lesions of malignant essential hypertension in man however art not identical to those observed in mice. The main differences noted kvere the absence of fibrinoid changes and the disappearance of the elastic membranes it1 the mouse. Severtheless, the occurrence of severe arterial lesions as a result (~f’abnormal high blood pressure in mice may be regarded as comparable to the situation in man. The difference of over 20 mmHg in blood pressures bet\\.ecn diseased mice and controls was found in previous work (hIullink, 197.3. In that study this limit appeared to be correlated with differences in the occurr(‘nc( of‘ pathological lesions in mice so that blood pressures of at least 20 mmHx l~igher than those in control mice may be regarded as hypertension. ;b it is true that necrotizing polyarteritis is the result of an abnormally lliqh I)lood pressure, the mice suffered from primary hypertension. The distribution and nature of the lesions found in our material is in xcordance \vith those described by Upton et nl. (1967). These authors. ho\\-ever, observed this abnormality in ageing RF mice only. In our situation 8 inbred strains and 1 random-bred group appeared to be affected. Vict2.s on the aetiology of this finding differ. Upton et al. (1967) suggested that the lesions may be autoimmune in nature. We no\v present the relationship
106
J.
W.
M.
A.
MULLINK
AND
G. T.
IIANEVELD
to spontaneous hypertension. Byrom ( 1954) and Wagenvoort (1959) stated that prolonged contraction of smooth muscle fihres as occurs in hypertension may lead to their disintegration with subsequent inflammatory reactions and our work indicates a relationship between spontaneous hypertension and vascular lesions. Necrotizing polyarteritis has a low incidence in several mouse strains and groups. If this abnormality should become a model for the study of arterial changes in malignant essential hypertension in man, a strain of mouse which shows a high incidence of this lesion is required. SUMMARY
Perivascular infiltration, medial hyalinization and necrosis, and proliferative lesions were observed in the arterial system of inbred and random-bred mice. Hypertension occurred in those mice in which blood pressure could be recorded. It is suggested that these vascular changes are due to primary hypertension. ACKNOWLEDGMENTS
Thanks
are due to Professor
G. Bras for his help
and
to Mr
H. Otter
for the
microphotographs. REFERENCES
Byrom, F. B. (1954). The pathogenesis of hypertensive encephalopathy and its relation to the malignant phase of hypertension. Experimental evidence from the hypertensive rat. Lancet, ii, 201. Mullink, J. W. M. A. (1975). Bloodp ressure and hypertension in the mouse. Thesis, Utrecht, The Netherlands. Okamoto, K. (1972). Spontaneous Hypertension. Its Pathogenesis and Complications. Igaku Shoin Ltd, Tokio; Springer-Verlag, Berlin. Sanerkin, N. G. (197 1). Vascular lesions of essential hypertension. Journal of Pathology, 103, 177-l 84. Upton, A. C., Conklin, J. W., Cosgrove, G. E., Gude, W. D., and Darden, E. B. (1967). Necrotizing polyarteritis in ageing mice. Laboratory Investigations, 16, 483-487. Upton, C. (1971). Vascular lesions associated with ageing in the mouse. In Animal Models for Biomedical Research, IV, pp. 68-73. National Academy of Science, Washington. Nimmegen, Chr. Van, Eijnsbergen, B. Van, Boter, J. Van, and Mullink, J. W. M. A. (1973). A simple device for indirect measurement of blood pressure in mice. Laboratory Animals, 7, 73-84. Wagenvoort, C. A. (1959). The morphology of certain vascular lesions in pulmonary hypertension. Journal of Pathology and Bacteriology, 78, 503-5 1 I. Wagenvoort, C. A., Heath, D., and Edwards, J. E. (1964). The Pathology qf the Pulmonary Vasculature. Charles C. Thomas, Springfield, Illinois. [Received for publication,
May 22nd, 19781
13 MICE DUE HYPERTENSIOX
G.
T.
TO
SPONTANEOUS
HANEVELD
INTRODUCTION
In view of the importance of cardiovascular and hypertensive disease in man. attention has been paid to comparable lesions in animals. One can stud\normotensive animals in which the homeostatic mechanism has been artiliciallv disturbed; one can also focus on genetically hypertensive animals in the hop” of detecting some common factors in primary or essential hypertension. In this connection the spontaneously hypertensive rat (Okamoto, 1972) is a useful model for the study of hypertension. According to Upton (1971) the mouse citrr also provide model systems for studying several of the vascular lesions associated with ageing. Nterotizing polyarteritis is a severe lesion in ageing mice (,Upton, Conklin, Closgrove, Gude and Darden, 1967) and similar lesions have been observed iit the inbred and random-bred mouse colonies of our institute. In the present paper the histopathology of necrotizing polpartcritis will IX. described in relation to abnormally elevated blood pressure. MATERIALS
AND
METHODS
A detailed description of the equipment and the method for indirect measurements of blood pressure in mice were published previously (Van Nimwegen, 1’an Eijnsbergen. Van Boter and Mullink, 1973). The mice used were the conventional males and females belonging to the following inbred strains : C57Bl/LiARijCpb; NZB/BlLacCpb; lYZW/LeiCpb; CPB-FT; C:PB-Q; CPB-T and CPB-V. The mice were housed in plastic cages after weaning. The diet was Mus 6 1 (Looyen B.V. ; Wageningen) and drinking water was supplied ad libitum. Room temperature was maintained at approximately 23 “C. SPF mice horn the random-bred Cpb:SE colony were also studied. Their diet was steanlsterilized SRM (Hope Farms, Woerden) and their drinking water was chlorinated. Tissues and organs were histologically examined after fixation in 4 per cent aqueous formaldehyde, embedding in paraffin wax and staining with haemalum-eosin. Whcu appropriate the Periodic Acid Schiff (PAS) technique was applied and for demonstration of fibrin Verhoeff and Mallory stains were used. Presence of elastic connective tissue and collagen was demonstrated with Weigert-Van Gieson stain. 0 1979 Academic Press Inc. (London) Limited 0021-9975/79/01099-I-08 $02.00/O
POLYARTERITIS
Fig.
3. Hyalinc I’crivascular
deposit, a few infiltrating cellular reaction. HE.
Fig. 4. Necrosis marl deposits in the aortic wall. the rentre and at the right intramural
Fig.
5. The same Weigert-\‘an
aorta
as in Fig. 4. Increased Gicson. x 60.
AND
HYPERTENSION
cells and x 150.
pycnosis
Note the radial haemorrhage
distance
between
101
IN MICE
in
the
media
position of enlarged can bc seen vaguely.
and
occasional
of
mesenteric
artcriolcs.
muscle cell HE. :I, 60.
nuclei.
rupture
of elastic
ln~ers.
In
102
J.
W,
M.
A.
MULLINK
AND
G. T.
HANEVELD
layer (Fig. 2). Hyalinization of the media was prominent (Fig. 3) ; this material was PAS-positive, fibrin stains were negative. Vacuolation of the hyalin was regularly observed. In combination with hyalinosis and cellular infiltration the smooth muscle cells of the media became swollen and gradually lost their ability to stain. In the larger arteries the nuclei of these smooth muscle cells showed a radial position instead of the normal circular arrangement (Fig. 4).
Fig.
6. Superior mesenteric artery. Lumen is at the top. Gradual loss of staining power of the elastic layers. Note the normal stained remnants of the elastic layers at the adventitial site. At the right complete loss of structure and hyalinization. Weigert-van Gieson. :< 60.
Pycnosis and nuclear fragments in the media were frequently observed, both in combination with hyaline deposits and/or cellular infiltration, Haemorrhage into the media (Fig. 4) was mainly observed in the larger arteries. Scattered groups of swollen nuclei suggested the possibility of an early proliferative reaction.
Fig.
7. Local differences in proliferation, infiltration, irregular alteration of the mesenteric arterial
hyalinization and wall. HE. x 60.
necrosis
resulted
in highly
POLYARTERITIS
AND
HYPERTENSION
103
IN MICE
A gradual disappearance of elastic membranes was noted. This phenomenon was most prominent in the larger arteries. In combination with hyalin deposits. necrosis and haemorrhage, the distance between the elastic layers was increased /Fig. 5). Individual elastic layers ruptured, sometimes only in isolated foci. The staining capacity of the elastic fibres gradually decreased and finally disappearcti Fig. 6). In combination with the other features this resulted in irregular loss of th(‘ structure of the arterial wall (Fig. 7). In such areas ruptures of the aort:~ or rncsenteric arteries occasionally occurred, resulting in exsanguination.
l:ig. 8. Proliferative lesions of the intima, media and in the perivascular region. Mixed celiular inliltration extending from perivascular region to the proliferation of the arterial wall. At the left the normal structure is partially preserved. HE. ‘.: 60.
The proliferation of the perivascular connective tissue of the affected vessels extended into the media. In combination with proliferated elements of the arterial wall a complicated histological picture was observed together with hyaline remnants, nuclear fragments and cellular infiltration (Fig. 8).
Fig. 9. Sclerosis
and elastic
proliferation
of arteriole.
Weigert-van
G&on.
7 150.
lO$
J. W.
M. A. MULLINK
AND
G. T. HANEVELD
In some instances, only the subendothelial layer was preserved, while the other elements of the vascular wall were replaced by connective tissue in which a few scattered smooth muscle cells were still present. Combined with elastic proliferation this resulted in sclerosis of arterioles (Fig. 9) but the perivascular proliferation prevented haemorrhage even though degeneration and necrosis had caused disruption of the original arterial wall (Fig. 10).
Fig.
10. Rupture of locally altered arterial haemorrhage. Weigert-van Gieson.
x
wall. 60.
Perivascular
and
mural
proliferation
prevented
Various lesions were also observed in the intima. Hyaline deposits occurred in the intima with or without hyalinosis of the media. In rare instances, groups of “foam cells” were found in the subendothelial (Fig. 11) area. Remnants of such cells were seen in intimal proliferations, which otherwise consisted of collagen and elastic fibres. Splitting and duplication of the internal elastic membrane occurred in combination with the intimal proliferation.
Fig.
11. Perivascular endothelial
infiltration of renal artery branch. foam cells at the right. HE. x 60.
Intimal
proliferation
at the left. Note
the sub-
POLYARTERITIS
AND
HYPERTENSION
IN MICE
10.5
Endothelial nuclei were swollen or, rarely pycnotic. Mural thrombosis was sometimes observed in the larger arteries. Occasionally the arteriolar lumen was obliterated, probably due to thrombosis. The arteriolar lesions consisted predominantly of hyalinization, necrosis and I)erivascular infiltration.
Blood pressure determinations were performed on all mice in this stud! which showed clinical signs of disease. Many animals died during the pcntoI,arbitone-sodium anaesthesia; in a few no reliable data could be obtained. 111 8 mice showing necrotizing polyarteritis reliable blood pressure‘ va1uc.h were rccordcd. It appeared that all these 8 mice showed a blood prcssurc recording which was found to be elevated more than 20 mmHg, compared with their controls. The controls were 18 healthy mice of the same strain as tIlta discascd mice. They were maintained under identical conditions in the samt c’qrs. DISCUSSION
Despite the limited number of animals in which blood pressure could 1~. reliably recorded, it is evident that severe arterial lesions correlated cvith c*lcvated blood pressures. In man severe vascular alterations are considered to ix the result of malignant essential hypertension (Sanerkin, 197 1). Also hyptrrtension is reported to result in considerable changes in the pulmonary vasculat system (Wagenvoort, Heath and Edwards, 1964). In mice, the lesions ot’ uecrotizing polyarteritis were more of a degenerative nature than primaril) inflammatory. Together with the finding of an elevated blood pressure in all mice in which a reliable recording was obtained, this indicates that in lhc mouse, as in man, the arterial lesions may have resulted from a primaril> c%lcvatedblood pressure. The vascular lesions of malignant essential hypertension in man however art not identical to those observed in mice. The main differences noted kvere the absence of fibrinoid changes and the disappearance of the elastic membranes it1 the mouse. Severtheless, the occurrence of severe arterial lesions as a result (~f’abnormal high blood pressure in mice may be regarded as comparable to the situation in man. The difference of over 20 mmHg in blood pressures bet\\.ecn diseased mice and controls was found in previous work (hIullink, 197.3. In that study this limit appeared to be correlated with differences in the occurr(‘nc( of‘ pathological lesions in mice so that blood pressures of at least 20 mmHx l~igher than those in control mice may be regarded as hypertension. ;b it is true that necrotizing polyarteritis is the result of an abnormally lliqh I)lood pressure, the mice suffered from primary hypertension. The distribution and nature of the lesions found in our material is in xcordance \vith those described by Upton et nl. (1967). These authors. ho\\-ever, observed this abnormality in ageing RF mice only. In our situation 8 inbred strains and 1 random-bred group appeared to be affected. Vict2.s on the aetiology of this finding differ. Upton et al. (1967) suggested that the lesions may be autoimmune in nature. We no\v present the relationship
106
J.
W.
M.
A.
MULLINK
AND
G. T.
IIANEVELD
to spontaneous hypertension. Byrom ( 1954) and Wagenvoort (1959) stated that prolonged contraction of smooth muscle fihres as occurs in hypertension may lead to their disintegration with subsequent inflammatory reactions and our work indicates a relationship between spontaneous hypertension and vascular lesions. Necrotizing polyarteritis has a low incidence in several mouse strains and groups. If this abnormality should become a model for the study of arterial changes in malignant essential hypertension in man, a strain of mouse which shows a high incidence of this lesion is required. SUMMARY
Perivascular infiltration, medial hyalinization and necrosis, and proliferative lesions were observed in the arterial system of inbred and random-bred mice. Hypertension occurred in those mice in which blood pressure could be recorded. It is suggested that these vascular changes are due to primary hypertension. ACKNOWLEDGMENTS
Thanks
are due to Professor
G. Bras for his help
and
to Mr
H. Otter
for the
microphotographs. REFERENCES
Byrom, F. B. (1954). The pathogenesis of hypertensive encephalopathy and its relation to the malignant phase of hypertension. Experimental evidence from the hypertensive rat. Lancet, ii, 201. Mullink, J. W. M. A. (1975). Bloodp ressure and hypertension in the mouse. Thesis, Utrecht, The Netherlands. Okamoto, K. (1972). Spontaneous Hypertension. Its Pathogenesis and Complications. Igaku Shoin Ltd, Tokio; Springer-Verlag, Berlin. Sanerkin, N. G. (197 1). Vascular lesions of essential hypertension. Journal of Pathology, 103, 177-l 84. Upton, A. C., Conklin, J. W., Cosgrove, G. E., Gude, W. D., and Darden, E. B. (1967). Necrotizing polyarteritis in ageing mice. Laboratory Investigations, 16, 483-487. Upton, C. (1971). Vascular lesions associated with ageing in the mouse. In Animal Models for Biomedical Research, IV, pp. 68-73. National Academy of Science, Washington. Nimmegen, Chr. Van, Eijnsbergen, B. Van, Boter, J. Van, and Mullink, J. W. M. A. (1973). A simple device for indirect measurement of blood pressure in mice. Laboratory Animals, 7, 73-84. Wagenvoort, C. A. (1959). The morphology of certain vascular lesions in pulmonary hypertension. Journal of Pathology and Bacteriology, 78, 503-5 1 I. Wagenvoort, C. A., Heath, D., and Edwards, J. E. (1964). The Pathology qf the Pulmonary Vasculature. Charles C. Thomas, Springfield, Illinois. [Received for publication,
May 22nd, 19781
