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Uterine and renal renin release after ligation of the uterine arteries in the pregnant rabbit
This section offers prompt first announcement of new observations or discoveries. Articles should be limited to 1,500 words and six references. Illustrations or additional references require a proportionate reduction in total words.
Uterine and renal renin release after ligation of the uterine arteries in the pregnant rabbit ?vfMI(:HAEI, U’ARREN
KATZ H. SHAPIRO
JEROME
G. PORUSH
SHYAX-YIH VI-I’.4 Nrooklw.
CHOL
ISRAEL ,YfW
k’od
Uteroplacantal ischemia is associated with uterine renin release in pregnant nephrectomized rabbits. In the present study, uterine and renal renin release after uteroplacental ischemia were investigated in 10 Australian white rabbits at 24 to 28 days’ gestation. Pentobarbital was administered, and both uterine arteries were ligated close to their origins. Blood samples were taken for plasma renin activity (PRA) determinations from the femoral artery, uterine vein, and right renal vein before ligation and at 30 and 80 minutes after ligation. Mean arterial blood pressure (MAP) was monitored throughout. In five additional pregnant rabbits renal btood flow (RBF) was measured with an electromagnetic flowmeter. The preliition uterine vein-artery PRA difference was not significant (1 .Q i 1.l ng/ml/hr). Postligation uterine vein-artery PRA was 11.4 r 3.2 at 30 minutes and 6.6 t 1 .Q ng/ml/hr at 90 minutes (p < 0.02). Preligation renal vein-artery PRA was 32.3 t 10.5 ngimllhr (p c 0.02) and did not change significantly after ligation. MAP remained stable and RBF was unchanged after uterine artery ligation. These observations confirm the finding that the kidney is the primary source of renin in the normal pregnant rabbit and demonstrate that following acute uteroplacental ischemia there is significant uterine renin release even when the kidneys are intact. (AM. J. OBSTET. GYNECOL. 138:876, 1980.)
fi ram !he Deparlment oj Obstetrzcs and Gynecology and the DtxGsion oJ Nephrology, Deportnwnt of Medic&, Brook&& Hospital Medical Centw. Repnuf requests; Jerome G. Porush, M.D., CL
676
UTEROPLACENTAL ischemia in the term rabbit has been shown to be associated with renaI morphology and function.* Ferris and were the first to demonstrate the release of amounts of uterine renin into the circulation tion of the uterine arteries in pregnant 000%9378/80/050676+03$00.30/0~
1980TheC.
pregnant changes in associates’ significant after, liganephrecV. Mosby Co.
Renin
Volume Number
196 5
Table
I. Arterial,
uterine,
and renal PRA (ng/ml/hr)
Before
ligation
FA
I/V
1 2 3 4 5 6 7 8 9 10 Mean SEM p value
15 18 35 :i
22 20 38 14 24 26 40 8 19 17 22.8 23.1 NS-F
19 39 8 24 13 20.9 23.1
FA
82 120 94 28 39 23 76 15 37 18 53.2 211.6
UV
28 92 51 53 40 60 166 45 28 38 60.1 k-13.1
85 2 12
MAP
57 117 50 63 51 65 174 66 31 41 71.5 f 13.5 CO.01
RV:
renal
vein;
MAP:
Methods Fifteen healthy Australian white rabbits, at 24 to 28 days’ gestation and weighing between 3.5 and 4.5 kg (4.1 ? 0.4), were studied. The animals were fed regular rabbit chow. All animals were anesthetized with pentobarbital intravenously, up to 30 mg/kg, with no additional doses during the experiment. In 10 animals a polyethylene Angiocath was inserted into the femoral artery through a groin incision and connected to a three-way stopcock. This line served for continuous blood pressure and pulse monitoring with a Statham pressure transducer (Statham Labs, Inc., Hato Rey, Puerto Rico) and a Sanborn recorder (Sanborn Corp., Waltham, Massachusetts) as well as for arterial blood sampling. Through a lower midline incision a laparotomy was performed and the uterine arteries, a uterine vein, and the right renal vein were exposed. The left renal vein was not utilized in this study since this vein drains blood of uterine origin through the left ovarian vein. All blood samples were obtained by direct with
a
25 gauge
needle
and
transferred
a 1 ml
syringe.
into ice-cooled
artery
ligation
677
arteries*
73 138 89 72 54 83 187 58 32 40 82.6 * 14.9 <0.05$
FA 25 187 39 54 44 53 158 68 45 40 71.3 k17.3 <0.02$
UV 43 192 43 57 46 57 176 72 51 42 77.9 k-17.9
RV 68 208 87 62 47 69 203 74 47 42 90.8 2 19.6 <0.05$
78 “_ 15
tomized rabbits. but they3 were unable to demonstrate any release in intact animals. In the present study, with the model of uteroplacental ischemia described by Ferris and associates,* we have examined uterine and renal renin release after ligation of the uterine arteries in term pregnant rabbits. The results indicate that acute uteroplacental ischemia in intact pregnant rabbits leads to significant uterine renin release.
puncture
of the uterine
RV
$
uterine
60 min after ligation
82 ” 15
NS: Not significant. *FA: Femoral artery; UV: uterine vein; tVenous versus arterial (before Iigation). SVersus value before ligation.
The blood was immediately
after
30 min after ligation RV
NO.
before and after ligation
release
mean
arterial
pressure
(mm
Hg).
tubes. The separated plasma was kept at -20” C until plasma renin activity (PRA) was assayed. Blood loss due to sampling was replaced with identical amounts of isotonic saline. After obtaining baseline arterial and venous blood samples, both uterine arteries were ligated close to their origin. This ligation permits only collateral circulation to persist, thus reducing the uterine blood flow by approximately 70’%.* Postligation blood samples were taken at 30 and 60 minutes. In five additional animals prepared in the same manner renal blood flow was continuously monitored with an electromagnetic flowmeter and a flow probe on the right renal artery (Carolina Medical Electronics, Inc., Winston-Salem, North Carolina). The flow probe was precalibrated with the rabbit’s blood in a bath filled with isotonic saline solution. In this group of rabbits the experimental procedure was identical to that for the other group except that blood samples for renin activity were not obtained since the presence of the flowmeter made it technically difficult to obtain these samples without significant manipulation of the renal artery which may have altered renal renin release. Only those animals with proper placement of the uterine artery ligatures as well as viability of most of the fetuses (confirmed at the end of the experiment) were included in the study. PRA was determined by radioimmunoassay with the angiotensin I Immunotope Kit (Squibb) with modification for generation at pH 5.5.4 The data were analyzed statistically by the paired t test. All results are expressed as mean + SE.
678
Katz et
al.
RSSUltS
Table I summarizes arterial, uterine, and renal venous PRA before and after uterine artery ligation in 10 pregnant rabbits. The preligation uterine vein-artery PRA difference was 1.9 t 1.1 nglmlihr (22.8 f 3.1 to 20.9 2 X.1), which is not significant. In contrast, renal 1 ein PRA was 53.2 It 11.6 ngimllhr, significantly higher than the arterial PRA (p < 0.02). Thirty minutes after ligation PRA increased significantly to 60.1 -+ 13.1 cp < 0.01) in arterial blood, to 71.5 2 13.5 (p < 0.01) in uterine ve~~ous blood, and to 82.6 z 14.9 ng/ml/hr (p < 0.05) in renal venous blood. At 60 minutes there was a fur-the]- (nonsignificant) increase in PRA to 71.3 1 17.3 in arterial blood, to 77.9 I 17.9 in uterine venous blood. and to 90.8 +- 19.6 ngimllhr in renal venous blood. After ligation of the uterine arteries, the rrterinr vein-artery PRA difference was 11.4 5 3.2 at 30 minlltes and 6.6 ? 1.9 ng/ml/hr at 60 minutes, both of which are statistically significant (p < 0.01). The renal vein-artery PRA differellce, which was 32.3 + 10.5 ngimlihr before ligation, tended to decrease after ligation (22.5 + 3.0 at 30 minutes and 19.5 t 6.0 ng/ml/hr at 60 minutes) but not significantly. Mean arterial pressure was 85 + 12 mm Hg before ligation and did not change significantly after ligation (Table I). In the five rabbits in which right renal blood fkJw was monitored, the baseline value was 75.6 ‘- 4.4 ml/min and remained stable at 76 +- 3.3 and 76.2 2 3.6 ml/min at 30 and 60 minutes after ligation. respectivel\,.
The results in the present study confirm the finding that under normal conditions the kidneys are the main source of the elevated PRA in pregnant rabbits,” as the preligation uterine vein-artery PRA difference was not significant, suggesting that there is Little or no contribution of rcnin of uteroplacental origin. Although uterine blood How was not measured in the present experiments, Ferris and co-workers’ demonstrated a decrease in uterine blood flow of approximately 70%
REFERENCES
I. Abitbol, M. M., Callo, G. R., Pirani, C. L., and Ober, W. B.: Production of experimental toxemia in the pregnant rabbit, AM. J. ORSTET. GYNECOI.. 124:460, 1976. 2. Ferris. ‘1‘. F., Stein, J. H., and Kaufman, J,: Uterine blood flow and uterine renin secretion. J, Clin. Invest. 51:2287. 1972.
3. Ferris, ‘I‘. F., Venuto, R. I,., and Bay, W. H.: Studies of the uterine circulation in the pregnant rabbit, in Lindheimer, M.D., Katz, A. I., and &span, F., editors: Hypertension in Pregnancy, New York, 1976. Wiley Medical Publications, pp. 351-361.
March 1, 1980 Am. J. Obstet. Cynecol.
(ranging from 13%) to 87%) following uterine artery ligation in nephrectomized pregnant rabbits. The present finding of a significantly higher PR,4 concentration in uterine venous blood compared to arterial blood after ligation when no difference existed prior to ligation strongly suggests that the pregnant rabbit uterus releases renin after uteroplacental ischemia even when the kidneys are intact. Since renal blood How and the mean renal vein-artery PRA difference did not change after uterine artery ligation (albeit measured in separate groups of rabbits), renal renin release would appear to have remained unchanged; however, examination of Table I reveals that renal vein-artery PRA did decrease in seven of the 10 rabbits at 30 minutes and in eight of the 10 rabbits at 60 minutes. In the present studies no significant changes were observed in systemic blood pressure during the period of uteroplacental ischemia. This finding differs from that of Ferris and co-workers,2 who noted a decrease in arterial blood pressure (and cardiac output) following uterine artery ligation in pregnant nephrectomized rabbits. The reason for this difference is not apparent but may be related to the presence of the kidneys in OUI model. In normal human pregnancy, uterine venous PRA is similar to peripheral venous PRA.” In contrast, in human hypertensive pregnancies in which uteroplacental ischemia is a dominant feature. higher PRA levels in the uterine vein compared to peripheral veins have been demonstrated.fi Although Ferris and coworkers” were the first to demonstrate uterine release of renin following uterine artery ligation in pregnant rabbits, they observed this phenomenon in nephrectomized rabbits only. The present experiments demonstrate that uteroplacental ischemia in pregnant rabbits leads to uterine renin release even when the kidneys are intact, making this model even more useful for further studies concerning the possible significance of uterine renin release during hypertensive pregnancies.
4. Cohen, E. L., Grim, C. E., Conn, J. W., Blough, W. M., Jr., Guyer, R. B., Kern, D. C., and Lucas, C. P.: Accurate and rapid measurement of plasma renin activity by radioimmunoassay. J. Lab. Clin. Med. 77:1025, 1971. 5. Kokot, F., and Cekanski, A.: Plasma renin activity in peripheral and uterine vein blood in pregnant and nonpregnant women, Br. J. Obstet. Gynaecol. 79:72, 1972. 6. Weir, R. J., Brown, J. J., Fraser, R., Kraszewski, A., Lever, A. F., McIlIwaine, G. M., Morton, J. J., Robertson, J. I. S., and Tree, M.: Plasma renin, renin substrate, angiotensin II and aldosterone in hypertensive disease of pregnancy, Lancet 1:291. 1973.
Uterine and renal renin release after ligation of the uterine arteries in the pregnant rabbit ?vfMI(:HAEI, U’ARREN
KATZ H. SHAPIRO
JEROME
G. PORUSH
SHYAX-YIH VI-I’.4 Nrooklw.
CHOL
ISRAEL ,YfW
k’od
Uteroplacantal ischemia is associated with uterine renin release in pregnant nephrectomized rabbits. In the present study, uterine and renal renin release after uteroplacental ischemia were investigated in 10 Australian white rabbits at 24 to 28 days’ gestation. Pentobarbital was administered, and both uterine arteries were ligated close to their origins. Blood samples were taken for plasma renin activity (PRA) determinations from the femoral artery, uterine vein, and right renal vein before ligation and at 30 and 80 minutes after ligation. Mean arterial blood pressure (MAP) was monitored throughout. In five additional pregnant rabbits renal btood flow (RBF) was measured with an electromagnetic flowmeter. The preliition uterine vein-artery PRA difference was not significant (1 .Q i 1.l ng/ml/hr). Postligation uterine vein-artery PRA was 11.4 r 3.2 at 30 minutes and 6.6 t 1 .Q ng/ml/hr at 90 minutes (p < 0.02). Preligation renal vein-artery PRA was 32.3 t 10.5 ngimllhr (p c 0.02) and did not change significantly after ligation. MAP remained stable and RBF was unchanged after uterine artery ligation. These observations confirm the finding that the kidney is the primary source of renin in the normal pregnant rabbit and demonstrate that following acute uteroplacental ischemia there is significant uterine renin release even when the kidneys are intact. (AM. J. OBSTET. GYNECOL. 138:876, 1980.)
fi ram !he Deparlment oj Obstetrzcs and Gynecology and the DtxGsion oJ Nephrology, Deportnwnt of Medic&, Brook&& Hospital Medical Centw. Repnuf requests; Jerome G. Porush, M.D., CL
676
UTEROPLACENTAL ischemia in the term rabbit has been shown to be associated with renaI morphology and function.* Ferris and were the first to demonstrate the release of amounts of uterine renin into the circulation tion of the uterine arteries in pregnant 000%9378/80/050676+03$00.30/0~
1980TheC.
pregnant changes in associates’ significant after, liganephrecV. Mosby Co.
Renin
Volume Number
196 5
Table
I. Arterial,
uterine,
and renal PRA (ng/ml/hr)
Before
ligation
FA
I/V
1 2 3 4 5 6 7 8 9 10 Mean SEM p value
15 18 35 :i
22 20 38 14 24 26 40 8 19 17 22.8 23.1 NS-F
19 39 8 24 13 20.9 23.1
FA
82 120 94 28 39 23 76 15 37 18 53.2 211.6
UV
28 92 51 53 40 60 166 45 28 38 60.1 k-13.1
85 2 12
MAP
57 117 50 63 51 65 174 66 31 41 71.5 f 13.5 CO.01
RV:
renal
vein;
MAP:
Methods Fifteen healthy Australian white rabbits, at 24 to 28 days’ gestation and weighing between 3.5 and 4.5 kg (4.1 ? 0.4), were studied. The animals were fed regular rabbit chow. All animals were anesthetized with pentobarbital intravenously, up to 30 mg/kg, with no additional doses during the experiment. In 10 animals a polyethylene Angiocath was inserted into the femoral artery through a groin incision and connected to a three-way stopcock. This line served for continuous blood pressure and pulse monitoring with a Statham pressure transducer (Statham Labs, Inc., Hato Rey, Puerto Rico) and a Sanborn recorder (Sanborn Corp., Waltham, Massachusetts) as well as for arterial blood sampling. Through a lower midline incision a laparotomy was performed and the uterine arteries, a uterine vein, and the right renal vein were exposed. The left renal vein was not utilized in this study since this vein drains blood of uterine origin through the left ovarian vein. All blood samples were obtained by direct with
a
25 gauge
needle
and
transferred
a 1 ml
syringe.
into ice-cooled
artery
ligation
677
arteries*
73 138 89 72 54 83 187 58 32 40 82.6 * 14.9 <0.05$
FA 25 187 39 54 44 53 158 68 45 40 71.3 k17.3 <0.02$
UV 43 192 43 57 46 57 176 72 51 42 77.9 k-17.9
RV 68 208 87 62 47 69 203 74 47 42 90.8 2 19.6 <0.05$
78 “_ 15
tomized rabbits. but they3 were unable to demonstrate any release in intact animals. In the present study, with the model of uteroplacental ischemia described by Ferris and associates,* we have examined uterine and renal renin release after ligation of the uterine arteries in term pregnant rabbits. The results indicate that acute uteroplacental ischemia in intact pregnant rabbits leads to significant uterine renin release.
puncture
of the uterine
RV
$
uterine
60 min after ligation
82 ” 15
NS: Not significant. *FA: Femoral artery; UV: uterine vein; tVenous versus arterial (before Iigation). SVersus value before ligation.
The blood was immediately
after
30 min after ligation RV
NO.
before and after ligation
release
mean
arterial
pressure
(mm
Hg).
tubes. The separated plasma was kept at -20” C until plasma renin activity (PRA) was assayed. Blood loss due to sampling was replaced with identical amounts of isotonic saline. After obtaining baseline arterial and venous blood samples, both uterine arteries were ligated close to their origin. This ligation permits only collateral circulation to persist, thus reducing the uterine blood flow by approximately 70’%.* Postligation blood samples were taken at 30 and 60 minutes. In five additional animals prepared in the same manner renal blood flow was continuously monitored with an electromagnetic flowmeter and a flow probe on the right renal artery (Carolina Medical Electronics, Inc., Winston-Salem, North Carolina). The flow probe was precalibrated with the rabbit’s blood in a bath filled with isotonic saline solution. In this group of rabbits the experimental procedure was identical to that for the other group except that blood samples for renin activity were not obtained since the presence of the flowmeter made it technically difficult to obtain these samples without significant manipulation of the renal artery which may have altered renal renin release. Only those animals with proper placement of the uterine artery ligatures as well as viability of most of the fetuses (confirmed at the end of the experiment) were included in the study. PRA was determined by radioimmunoassay with the angiotensin I Immunotope Kit (Squibb) with modification for generation at pH 5.5.4 The data were analyzed statistically by the paired t test. All results are expressed as mean + SE.
678
Katz et
al.
RSSUltS
Table I summarizes arterial, uterine, and renal venous PRA before and after uterine artery ligation in 10 pregnant rabbits. The preligation uterine vein-artery PRA difference was 1.9 t 1.1 nglmlihr (22.8 f 3.1 to 20.9 2 X.1), which is not significant. In contrast, renal 1 ein PRA was 53.2 It 11.6 ngimllhr, significantly higher than the arterial PRA (p < 0.02). Thirty minutes after ligation PRA increased significantly to 60.1 -+ 13.1 cp < 0.01) in arterial blood, to 71.5 2 13.5 (p < 0.01) in uterine ve~~ous blood, and to 82.6 z 14.9 ng/ml/hr (p < 0.05) in renal venous blood. At 60 minutes there was a fur-the]- (nonsignificant) increase in PRA to 71.3 1 17.3 in arterial blood, to 77.9 I 17.9 in uterine venous blood. and to 90.8 +- 19.6 ngimllhr in renal venous blood. After ligation of the uterine arteries, the rrterinr vein-artery PRA difference was 11.4 5 3.2 at 30 minlltes and 6.6 ? 1.9 ng/ml/hr at 60 minutes, both of which are statistically significant (p < 0.01). The renal vein-artery PRA differellce, which was 32.3 + 10.5 ngimlihr before ligation, tended to decrease after ligation (22.5 + 3.0 at 30 minutes and 19.5 t 6.0 ng/ml/hr at 60 minutes) but not significantly. Mean arterial pressure was 85 + 12 mm Hg before ligation and did not change significantly after ligation (Table I). In the five rabbits in which right renal blood fkJw was monitored, the baseline value was 75.6 ‘- 4.4 ml/min and remained stable at 76 +- 3.3 and 76.2 2 3.6 ml/min at 30 and 60 minutes after ligation. respectivel\,.
The results in the present study confirm the finding that under normal conditions the kidneys are the main source of the elevated PRA in pregnant rabbits,” as the preligation uterine vein-artery PRA difference was not significant, suggesting that there is Little or no contribution of rcnin of uteroplacental origin. Although uterine blood How was not measured in the present experiments, Ferris and co-workers’ demonstrated a decrease in uterine blood flow of approximately 70%
REFERENCES
I. Abitbol, M. M., Callo, G. R., Pirani, C. L., and Ober, W. B.: Production of experimental toxemia in the pregnant rabbit, AM. J. ORSTET. GYNECOI.. 124:460, 1976. 2. Ferris. ‘1‘. F., Stein, J. H., and Kaufman, J,: Uterine blood flow and uterine renin secretion. J, Clin. Invest. 51:2287. 1972.
3. Ferris, ‘I‘. F., Venuto, R. I,., and Bay, W. H.: Studies of the uterine circulation in the pregnant rabbit, in Lindheimer, M.D., Katz, A. I., and &span, F., editors: Hypertension in Pregnancy, New York, 1976. Wiley Medical Publications, pp. 351-361.
March 1, 1980 Am. J. Obstet. Cynecol.
(ranging from 13%) to 87%) following uterine artery ligation in nephrectomized pregnant rabbits. The present finding of a significantly higher PR,4 concentration in uterine venous blood compared to arterial blood after ligation when no difference existed prior to ligation strongly suggests that the pregnant rabbit uterus releases renin after uteroplacental ischemia even when the kidneys are intact. Since renal blood How and the mean renal vein-artery PRA difference did not change after uterine artery ligation (albeit measured in separate groups of rabbits), renal renin release would appear to have remained unchanged; however, examination of Table I reveals that renal vein-artery PRA did decrease in seven of the 10 rabbits at 30 minutes and in eight of the 10 rabbits at 60 minutes. In the present studies no significant changes were observed in systemic blood pressure during the period of uteroplacental ischemia. This finding differs from that of Ferris and co-workers,2 who noted a decrease in arterial blood pressure (and cardiac output) following uterine artery ligation in pregnant nephrectomized rabbits. The reason for this difference is not apparent but may be related to the presence of the kidneys in OUI model. In normal human pregnancy, uterine venous PRA is similar to peripheral venous PRA.” In contrast, in human hypertensive pregnancies in which uteroplacental ischemia is a dominant feature. higher PRA levels in the uterine vein compared to peripheral veins have been demonstrated.fi Although Ferris and coworkers” were the first to demonstrate uterine release of renin following uterine artery ligation in pregnant rabbits, they observed this phenomenon in nephrectomized rabbits only. The present experiments demonstrate that uteroplacental ischemia in pregnant rabbits leads to uterine renin release even when the kidneys are intact, making this model even more useful for further studies concerning the possible significance of uterine renin release during hypertensive pregnancies.
4. Cohen, E. L., Grim, C. E., Conn, J. W., Blough, W. M., Jr., Guyer, R. B., Kern, D. C., and Lucas, C. P.: Accurate and rapid measurement of plasma renin activity by radioimmunoassay. J. Lab. Clin. Med. 77:1025, 1971. 5. Kokot, F., and Cekanski, A.: Plasma renin activity in peripheral and uterine vein blood in pregnant and nonpregnant women, Br. J. Obstet. Gynaecol. 79:72, 1972. 6. Weir, R. J., Brown, J. J., Fraser, R., Kraszewski, A., Lever, A. F., McIlIwaine, G. M., Morton, J. J., Robertson, J. I. S., and Tree, M.: Plasma renin, renin substrate, angiotensin II and aldosterone in hypertensive disease of pregnancy, Lancet 1:291. 1973.