Clinical and Experimental Hypertension Part a Theory and Practice, Feb 1, 1990
It has been proposed that calcium supplementation in the diet is associated with a reduction in b... more It has been proposed that calcium supplementation in the diet is associated with a reduction in blood pressure. In the present study, we investigated vascular tissue sensitivity to a hypertensive factor (HF) in spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto rats (WKY) fed a high calcium diet, a low calcium diet and a food restricted diet. HF, which has been isolated from erythrocytes, increases blood pressure when injected into normotensive rats and stimulates calcium uptake by aortic rings in vitro. Five-week-old rats were divided into the following groups: SHR and WKY fed a regular diet (1% calcium), SHR and WKY fed a high calcium diet (4% calcium), SHR and WKY fed a low calcium diet (0.02% calcium) and SHR and WKY fed a regular diet (1% calcium) in which food intake was restricted to 65% of ad libitum intake. Food intake, body weight, urine phosphate excretion and blood pressure development were followed for 8 weeks. At sacrifice, plasma levels of calcium and phosphate were determined. Tissue responsiveness to HF was calculated by incubating aortic rings from the rats in the different groups with HF and measuring lanthanum-resistant calcium uptake. A 4-fold increase in dietary calcium reduced blood pressure and tissue responsiveness to HF in SHR. Neither parameter was affected by the high calcium diet in WKY. The low calcium diet had no effect on either blood pressure or tissue responsiveness to HF in SHR or WKY. Restriction of food intake induced a reduction in blood pressure and in tissue responsiveness to HF in SHR. It did not affect the same parameters in WKY. The results suggest that the increased tissue responsiveness to HF in the SHR may be associated with high blood pressure.
Levels and distribution of an angiotensin-forming enzyme, active at the physiological pH (isoreni... more Levels and distribution of an angiotensin-forming enzyme, active at the physiological pH (isorenin), were determined in the central nervous system of 24 rats treated with 25 mg/kg of deoxycorticosterone (DOC) subcutaneously, twice a week, plus saline to drink during 30 days and in 14 control animals. Different areas of the brain were excised and homogenized. Renin activity and concentration were determined by incubation of the supernatant of each homogenate at pH 7.2 alone and in the presence of an excess of renin substrate. The angiotensin generated was measured by radioimmunoassay. Concentration of the renin-like enzyme was significantly higher in the posterior hypophysis and in the brain stem of the experimental group; isorenin activity was higher in the hypothalamus, cerebral cortex, cerebellum, and brain stem of the DOC-salt-treated rats than in the control rats. Changes in the angiotensin-forming enzyme in the central nervous system of experimental animals, active at physiological pH, suggest that this isorenin system may play a role in the physiological response to DOC-salt in the rat. The significance of the brain isorenin system in the regulation of blood pressure requires further analysis.
Vascular alterations in DOC-salt hypertensive rats 10 and 30 days after the onset of the treatmen... more Vascular alterations in DOC-salt hypertensive rats 10 and 30 days after the onset of the treatment were studied and compared with those from rats receiving only DOC, rats drinking salt, and control rats. Wet weight and absolute amounts of deoxyribonucleic acid (DNA) and ribonucleic acid (RnA) of the artery wall were significantly increased in DOC-salt rats 10 and 30 days after the onset of the treatment. RNA/DNA and protein/DNA ratios were similar in all the experimental groups. The arteries of DOC-salt animals incorporated tritiated thymidine at a higher rate 10 days after beginning the treatment, while the uptake was similar in all the animals at the end of the experimental period. These results would indicate that, in this type of hypertension, the increase in artery mass is mainly the result of cellular hyperplasia, which is active during the early phase of the process; afterward the vascular wall reaches a new steady state characterized by a greater number of cells and no further cell proliferation.
The development of two-kidney, two clip Goldblatt hypertension (2K2C) in the rat seems to be unaf... more The development of two-kidney, two clip Goldblatt hypertension (2K2C) in the rat seems to be unaffected by chemical sympathectomy with 6-hydroxydopamine (6-HODA) and adrenal demedullation. Since this treatment only partially depletes vascular norepinephrine (NE) content, we evaluated the degree of sympathectomy achieved with the 6-HODA treatment and the structural vascular changes in treated and untreated animals. Litters of male Wistar rats were divided in two groups: 6-HODA-treated (6-HODA) animals (group 1) were injected with 6-HODA since the day of birth until the end of the experiment; control group (CG) animals (group 2) received the vehicle solution. When rats reached about 250 g, a silver clip (0.25 mm width) was placed on both renal arteries in half of them in each group; a sham operation was performed on the rest of the animals. Adrenal demedullation and denervation was performed in all 6-HODA animals. Blood pressure was followed weekly by the tail cuff method for 7 weeks. At the 8th week, Silastic cannulas were placed in the carotid artery and jugular vein in all the animals. Pressor responses to tyramine (0.05 and 0.1 mg), angiotensin (10, 40 and 160 ng), and norepinephrine (NE) (25, 100 and 400 ng) and the hypotensive effect of prazosin (1 mg/kg) were determined in the conscious rats. The pressor effect of carotid occlusion was registered 24 hours later. Animals were sacrificed, and the heart and artery weight as well as the nucleic acids and alkali soluble proteins content in the vascular wall were determined.(ABSTRACT TRUNCATED AT 250 WORDS)
Angiotensinogen is the most important component of the renin-angiotensin system present in the ce... more Angiotensinogen is the most important component of the renin-angiotensin system present in the cerebrospinal fluid (CSF) of the rat. Its physiological significance as well as its origin have not been clearly elucidated. In this experiment we have examined plasma renin activity (PRA) and plasma and CSF angiotensinogen concentration under the following experimental conditions in male rats of the Wistar strain: 1) adrenalectomy (Adx) 4 days prior to sample collection; controls were sham Adx animals; 2) nephrectomy (Nx) 48 hours before blood and CSF collection; controls were sham Nx rats; 3) DOC-salt treatment (Cortexon depot, 50 mg/kg.s.c. twice a week) plus saline to drink was given during 4 weeks; controls were intact rats; 4) DOC-salt plus captopril: captopril (100 mg/kg/day) in the drinking fluid was added to the treatment of experimental and control animals of Group 3; 5) two-kidney, two clip hypertension: silver clips placed in both renal arteries 8 weeks before samples collection; control: sham-operated rats; 6) water deprivation: rats deprived of water for 5 days; controls: intact rats; 7) peripheral sympathectomy: 6-hydroxydopamine (6-HODA) injected s.c. from birth until 16 weeks of age, adrenodemedullectomy and adrenal denervation performed at 8 weeks; controls were vehicle-injected animals. Determination of angiotensinogen concentration in plasma and CSF was accomplished by incubation of the samples with excess hog renin. The angiotensin I released as well as PRA were evaluated using an specific radioimmunoassay technique. PRA was significantly increased by Adx, captopril treatment, and water deprivation, and was almost suppressed by Nx, DOC-salt, and DOC-salt plus captopril treatment.(ABSTRACT TRUNCATED AT 250 WORDS)
The presence of isorenin active at the physiological pH was investigated in DOC-salt hypertensive... more The presence of isorenin active at the physiological pH was investigated in DOC-salt hypertensive rats. The effect of chronic captopril treatment was analyzed in similarly treated animals and in control rats. The levels of the plasma (PRA) and vascular enzyme (VRLA) were compared with those of untreated control animals. DOC-salt administration was maintained during 4 or 8 weeks. Captopril was given in the drinking fluid beginning 4 days before DOC-salt treatment. Renin-like activity was measured in the aorta and mesenteric arteries. DOC-salt treatment reduced PRA to almost undetectable levels while aorta renin-like enzyme only decreased to 50% at 4 weeks and was not changed at 8 weeks. Isorenin levels in the mesenteric artery did not show any significant variation. Captopril did not prevent the increase in blood pressure due to DOC-salt administration and it induced a significant increase in PRA and in VRLA in control rats whereas it did not increase either - enzyme in DOC-salt treated rats. In summary these results confirm the existence of a vascular isorenin and suggest that both binding and local synthesis of the enzyme could take place in the arterial wall.
Vascular structural changes were studied during the development of two-kidney one-clip renal hype... more Vascular structural changes were studied during the development of two-kidney one-clip renal hypertension. The weight of the arteries and the concentration and total amount of ribonucleic acid, deoxyribonucleic acid, alkali-soluble proteins, collagen and elastin of the vascular wall were measured. Tritiated thymidine uptake was also determined 15 and 30 days after clipping. Hypertension developed in 58% of the animals while the rest remained normotensive. A significant increase in artery weight and in the total amount of nucleic acids and proteins was found in hypertensive rats. The uptake of 3H thymidine by the arteries of hypertensive rats was significantly increased 15 days after clipping. This increment showed a significant correlation with blood pressure levels. Present data seem to indicate that the increase in vessel wall dimensions observed is partly due to an increase in the number of smooth muscle cells during the acute phase; this alteration appears to be mainly due to the rise in blood pressure.
Wet and dry weight, concentration and total amount of nucleic acids and proteins, and incorporati... more Wet and dry weight, concentration and total amount of nucleic acids and proteins, and incorporation of tritiated thymidine were measured in the arteries of rats after 7 and 15 days of unilateral nephrectomy, sham operation and in control animals. Arteries of uninephrectomized rats showed increased wet and dry weight, increased DNA and protein content after 7 and 15 days and a higher rate of tritiated thymidine uptake after the first week. These results suggest an early proliferative process in the arteries of unilateral nephrectomized rats.
We studied the morphological and contractile characteristics of rat thoracic aortic segments perf... more We studied the morphological and contractile characteristics of rat thoracic aortic segments perfused for 3 or 6 days under pulsatile conditions. Light microscopic examination of the segments revealed the presence of an unchanged tunica media. However, the intimal surface was mostly devoid of endothelial cells. The perfused aortic segments showed a dramatic increase in spontaneous tone when compared to fresh and sham-treated aortic segments. Maximum responses to potassium and norepinephrine were reduced after 3 days of perfusion (20-40% reduction), while maximum responses to 5-hydroxytryptamine and angiotensin II were not significantly different. After 6 days of perfusion, maximum responses to all agonist were reduced (50-60%). Sensitivity to norepinephrine was not affected by the treatment, while sensitivity to 5-hydroxytryptamine was reduced. The perfused aortic segments relaxed well in response to isoproterenol. Our system provides a useful experimental model for short-term studi...
Clinical and Experimental Hypertension Part a Theory and Practice, Feb 1, 1990
It has been proposed that calcium supplementation in the diet is associated with a reduction in b... more It has been proposed that calcium supplementation in the diet is associated with a reduction in blood pressure. In the present study, we investigated vascular tissue sensitivity to a hypertensive factor (HF) in spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto rats (WKY) fed a high calcium diet, a low calcium diet and a food restricted diet. HF, which has been isolated from erythrocytes, increases blood pressure when injected into normotensive rats and stimulates calcium uptake by aortic rings in vitro. Five-week-old rats were divided into the following groups: SHR and WKY fed a regular diet (1% calcium), SHR and WKY fed a high calcium diet (4% calcium), SHR and WKY fed a low calcium diet (0.02% calcium) and SHR and WKY fed a regular diet (1% calcium) in which food intake was restricted to 65% of ad libitum intake. Food intake, body weight, urine phosphate excretion and blood pressure development were followed for 8 weeks. At sacrifice, plasma levels of calcium and phosphate were determined. Tissue responsiveness to HF was calculated by incubating aortic rings from the rats in the different groups with HF and measuring lanthanum-resistant calcium uptake. A 4-fold increase in dietary calcium reduced blood pressure and tissue responsiveness to HF in SHR. Neither parameter was affected by the high calcium diet in WKY. The low calcium diet had no effect on either blood pressure or tissue responsiveness to HF in SHR or WKY. Restriction of food intake induced a reduction in blood pressure and in tissue responsiveness to HF in SHR. It did not affect the same parameters in WKY. The results suggest that the increased tissue responsiveness to HF in the SHR may be associated with high blood pressure.
Levels and distribution of an angiotensin-forming enzyme, active at the physiological pH (isoreni... more Levels and distribution of an angiotensin-forming enzyme, active at the physiological pH (isorenin), were determined in the central nervous system of 24 rats treated with 25 mg/kg of deoxycorticosterone (DOC) subcutaneously, twice a week, plus saline to drink during 30 days and in 14 control animals. Different areas of the brain were excised and homogenized. Renin activity and concentration were determined by incubation of the supernatant of each homogenate at pH 7.2 alone and in the presence of an excess of renin substrate. The angiotensin generated was measured by radioimmunoassay. Concentration of the renin-like enzyme was significantly higher in the posterior hypophysis and in the brain stem of the experimental group; isorenin activity was higher in the hypothalamus, cerebral cortex, cerebellum, and brain stem of the DOC-salt-treated rats than in the control rats. Changes in the angiotensin-forming enzyme in the central nervous system of experimental animals, active at physiological pH, suggest that this isorenin system may play a role in the physiological response to DOC-salt in the rat. The significance of the brain isorenin system in the regulation of blood pressure requires further analysis.
Vascular alterations in DOC-salt hypertensive rats 10 and 30 days after the onset of the treatmen... more Vascular alterations in DOC-salt hypertensive rats 10 and 30 days after the onset of the treatment were studied and compared with those from rats receiving only DOC, rats drinking salt, and control rats. Wet weight and absolute amounts of deoxyribonucleic acid (DNA) and ribonucleic acid (RnA) of the artery wall were significantly increased in DOC-salt rats 10 and 30 days after the onset of the treatment. RNA/DNA and protein/DNA ratios were similar in all the experimental groups. The arteries of DOC-salt animals incorporated tritiated thymidine at a higher rate 10 days after beginning the treatment, while the uptake was similar in all the animals at the end of the experimental period. These results would indicate that, in this type of hypertension, the increase in artery mass is mainly the result of cellular hyperplasia, which is active during the early phase of the process; afterward the vascular wall reaches a new steady state characterized by a greater number of cells and no further cell proliferation.
The development of two-kidney, two clip Goldblatt hypertension (2K2C) in the rat seems to be unaf... more The development of two-kidney, two clip Goldblatt hypertension (2K2C) in the rat seems to be unaffected by chemical sympathectomy with 6-hydroxydopamine (6-HODA) and adrenal demedullation. Since this treatment only partially depletes vascular norepinephrine (NE) content, we evaluated the degree of sympathectomy achieved with the 6-HODA treatment and the structural vascular changes in treated and untreated animals. Litters of male Wistar rats were divided in two groups: 6-HODA-treated (6-HODA) animals (group 1) were injected with 6-HODA since the day of birth until the end of the experiment; control group (CG) animals (group 2) received the vehicle solution. When rats reached about 250 g, a silver clip (0.25 mm width) was placed on both renal arteries in half of them in each group; a sham operation was performed on the rest of the animals. Adrenal demedullation and denervation was performed in all 6-HODA animals. Blood pressure was followed weekly by the tail cuff method for 7 weeks. At the 8th week, Silastic cannulas were placed in the carotid artery and jugular vein in all the animals. Pressor responses to tyramine (0.05 and 0.1 mg), angiotensin (10, 40 and 160 ng), and norepinephrine (NE) (25, 100 and 400 ng) and the hypotensive effect of prazosin (1 mg/kg) were determined in the conscious rats. The pressor effect of carotid occlusion was registered 24 hours later. Animals were sacrificed, and the heart and artery weight as well as the nucleic acids and alkali soluble proteins content in the vascular wall were determined.(ABSTRACT TRUNCATED AT 250 WORDS)
Angiotensinogen is the most important component of the renin-angiotensin system present in the ce... more Angiotensinogen is the most important component of the renin-angiotensin system present in the cerebrospinal fluid (CSF) of the rat. Its physiological significance as well as its origin have not been clearly elucidated. In this experiment we have examined plasma renin activity (PRA) and plasma and CSF angiotensinogen concentration under the following experimental conditions in male rats of the Wistar strain: 1) adrenalectomy (Adx) 4 days prior to sample collection; controls were sham Adx animals; 2) nephrectomy (Nx) 48 hours before blood and CSF collection; controls were sham Nx rats; 3) DOC-salt treatment (Cortexon depot, 50 mg/kg.s.c. twice a week) plus saline to drink was given during 4 weeks; controls were intact rats; 4) DOC-salt plus captopril: captopril (100 mg/kg/day) in the drinking fluid was added to the treatment of experimental and control animals of Group 3; 5) two-kidney, two clip hypertension: silver clips placed in both renal arteries 8 weeks before samples collection; control: sham-operated rats; 6) water deprivation: rats deprived of water for 5 days; controls: intact rats; 7) peripheral sympathectomy: 6-hydroxydopamine (6-HODA) injected s.c. from birth until 16 weeks of age, adrenodemedullectomy and adrenal denervation performed at 8 weeks; controls were vehicle-injected animals. Determination of angiotensinogen concentration in plasma and CSF was accomplished by incubation of the samples with excess hog renin. The angiotensin I released as well as PRA were evaluated using an specific radioimmunoassay technique. PRA was significantly increased by Adx, captopril treatment, and water deprivation, and was almost suppressed by Nx, DOC-salt, and DOC-salt plus captopril treatment.(ABSTRACT TRUNCATED AT 250 WORDS)
The presence of isorenin active at the physiological pH was investigated in DOC-salt hypertensive... more The presence of isorenin active at the physiological pH was investigated in DOC-salt hypertensive rats. The effect of chronic captopril treatment was analyzed in similarly treated animals and in control rats. The levels of the plasma (PRA) and vascular enzyme (VRLA) were compared with those of untreated control animals. DOC-salt administration was maintained during 4 or 8 weeks. Captopril was given in the drinking fluid beginning 4 days before DOC-salt treatment. Renin-like activity was measured in the aorta and mesenteric arteries. DOC-salt treatment reduced PRA to almost undetectable levels while aorta renin-like enzyme only decreased to 50% at 4 weeks and was not changed at 8 weeks. Isorenin levels in the mesenteric artery did not show any significant variation. Captopril did not prevent the increase in blood pressure due to DOC-salt administration and it induced a significant increase in PRA and in VRLA in control rats whereas it did not increase either - enzyme in DOC-salt treated rats. In summary these results confirm the existence of a vascular isorenin and suggest that both binding and local synthesis of the enzyme could take place in the arterial wall.
Vascular structural changes were studied during the development of two-kidney one-clip renal hype... more Vascular structural changes were studied during the development of two-kidney one-clip renal hypertension. The weight of the arteries and the concentration and total amount of ribonucleic acid, deoxyribonucleic acid, alkali-soluble proteins, collagen and elastin of the vascular wall were measured. Tritiated thymidine uptake was also determined 15 and 30 days after clipping. Hypertension developed in 58% of the animals while the rest remained normotensive. A significant increase in artery weight and in the total amount of nucleic acids and proteins was found in hypertensive rats. The uptake of 3H thymidine by the arteries of hypertensive rats was significantly increased 15 days after clipping. This increment showed a significant correlation with blood pressure levels. Present data seem to indicate that the increase in vessel wall dimensions observed is partly due to an increase in the number of smooth muscle cells during the acute phase; this alteration appears to be mainly due to the rise in blood pressure.
Wet and dry weight, concentration and total amount of nucleic acids and proteins, and incorporati... more Wet and dry weight, concentration and total amount of nucleic acids and proteins, and incorporation of tritiated thymidine were measured in the arteries of rats after 7 and 15 days of unilateral nephrectomy, sham operation and in control animals. Arteries of uninephrectomized rats showed increased wet and dry weight, increased DNA and protein content after 7 and 15 days and a higher rate of tritiated thymidine uptake after the first week. These results suggest an early proliferative process in the arteries of unilateral nephrectomized rats.
We studied the morphological and contractile characteristics of rat thoracic aortic segments perf... more We studied the morphological and contractile characteristics of rat thoracic aortic segments perfused for 3 or 6 days under pulsatile conditions. Light microscopic examination of the segments revealed the presence of an unchanged tunica media. However, the intimal surface was mostly devoid of endothelial cells. The perfused aortic segments showed a dramatic increase in spontaneous tone when compared to fresh and sham-treated aortic segments. Maximum responses to potassium and norepinephrine were reduced after 3 days of perfusion (20-40% reduction), while maximum responses to 5-hydroxytryptamine and angiotensin II were not significantly different. After 6 days of perfusion, maximum responses to all agonist were reduced (50-60%). Sensitivity to norepinephrine was not affected by the treatment, while sensitivity to 5-hydroxytryptamine was reduced. The perfused aortic segments relaxed well in response to isoproterenol. Our system provides a useful experimental model for short-term studi...
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