Estradiol effects on plasma renin activity and aldosterone in chronically catheterized castrated sheep

The administration of 17-beta estradiol to human, and all the animals species tested, results in blood volume expansion. This effect has been postulated to be mediated through an increase in the circulating levels of aldosterone. We infused 17-beta estradiol (30 micrograms/kg/day) into 5 chronically-castrated ewes over a 3-week period, and determined the plasma concentrations of 17-beta estradiol, PRA, and aldosterone at weekly intervals. By the end of the third week, 17-beta estradiol plasma concentration had increased 150-fold, while PRA increased 2-fold; aldosterone decreased 40% from baseline values. Thus, during a period in which we have previously observed blood volume expansion, there was a dissociation between the levels of 17-beta estradiol and aldosterone. These findings question the theory that the estradiol-mediated blood volume increase observed during pregnancy is secondary to an increase in the circulating aldosterone levels.

Relationship of circadian rhythms of uterine activity with term and preterm delivery

OBJECTIVE

Our aim was to document the presence or significance of circadian uterine activity rhythms in pregnant women who delivered at term and preterm.

STUDY DESIGN

We measured uterine activity in 19 women divided into a control group (low risk for preterm labor, term delivery, n = 7), a group at high risk for preterm labor, term delivery (n = 6), and a group at high risk for preterm labor, preterm delivery (n = 6). Patients were hospitalized for 24 hours every 2 weeks from 26 weeks' gestation until delivery. Uterine activity was measured continuously by external tocodynamometer.

RESULTS

Patients delivering at term demonstrated a nocturnal surge (4 to 7 AM) in uterine activity the last 80 days before delivery (p < 0.05, analysis of variance). Patients delivered preterm showed an initial nocturnal surge of uterine activity similar to those delivered at term, but this disappeared 24 days before delivery (p > 0.05, analysis of variance).

CONCLUSION

Uterine activity nocturnal surges normally precede term delivery. These surges are lost in women who deliver prematurely.

Increased lymphatic pumping ability in pregnant ewes

OBJECTIVE

Daily the lymphatic system returns several liters of fluid to the systemic circulation. Unlike blood, lymph is pumped against a pressure gradient. Because vessels in the systemic circulation are hyporesponsive to vasoconstrictor hormones during pregnancy, we decided to assess whether lymphatic pumping ability was decreased during pregnancy.

STUDY DESIGN

Ten pregnant ewes were chronically catheterized in the left thoracic duct and jugular vein. Four days after surgery thoracic duct pumping ability was determined by measuring the lymph flow rate as a function of outflow pressure by varying the height at which lymph flow drains in an open-flow system.

RESULTS

Lymph flow was plotted against outflow pressure, and the value at which lymph flow decreases is defined as the "breaking point." The outflow pressure at which lymph flow equals zero is the "stopflow" pressure; this value defines the pumping ability. The pregnant ewes had a breaking point of -1 +/- 2.7 versus 14.4 +/- 3.0 mm Hg (mean +/- SD) for the nonpregnant sheep. Stopflow pressures were 62 +/- 7.3 versus 23.9 +/- 4.7 mm Hg (mean +/- SD) for the nonpregnant ewes (p < 0.05).

CONCLUSIONS

The ability of the lymphatic system to generate pressure is increased during pregnancy, but the breaking point is diminished. Alterations of lymphatic pumping ability could explain fluid retention under pathophysiologic conditions.

Acute intrauterine hypoxia increases amniotic fluid prostaglandin F metabolites in the pregnant sheep

OBJECTIVE

Amniotic fluid infection promotes cytokine release, prostaglandin production, and premature labor. In several tissues local hypoxia also activates the secretion of cytokines. Many patients initially seen in premature labor carry small-for-gestational-age fetuses, a condition associated with intrauterine hypoxia. The purpose of our study was to determine whether a reduction in placental blood flow and subsequent acute hypoxia affects prostaglandin secretion by the placenta.

STUDY DESIGN

We chronically catheterized six pregnant sheep at 120 days of gestation. We placed catheters in the maternal and fetal femoral arteries and in the amniotic fluid cavity. A flow probe and snare were placed around the common uterine artery.

RESULTS

A 30-minute uterine circulation occlusion of 30% of its control value produced an increase in prostaglandin F metabolite from 790 +/- 157 to 944 +/- 184 pg/ml within 10 minutes (p < 0.01). Additional uterine blood flow reduction to 60% of control increased the amniotic fluid prostaglandin F metabolites concentration to 894 +/- 202 (p < 0.05, analysis of variance). No increase in mean intrauterine pressure was detected (p > 0.1).

CONCLUSIONS

We speculate that the prostaglandin increase in amniotic fluid in response to intrauterine hypoxia could eventually lead to premature labor. Whether the increase in prostaglandins is mediated by changes in cytokines is unknown at the present time.

Long-term vascular volume expansion maintains elevated thoracic duct lymph flow

OBJECTIVE

To investigate the mechanisms responsible for edema seen during pregnancy, we tested whether lymph vessels are able to pump high volumes over long periods of time.

STUDY DESIGN

In six chronically catheterized nonpregnant ewes, we examined left thoracic duct lymph flow rate and fluid balance responses to the administration of a balanced isotonic solution at a rate of 1 L/hr for 20 hours. Because estrogen administration decreases lymphatic contractility against outflow pressure, we also administered conjugated estrogens (Premarin) during the last 3 hours of the fluid infusion (experimental time 17 to 20 hours).

RESULTS

After volume loading for 16 hours, the mean +/- SEM lymph flow rate, blood volume, and arterial pressure rose 100% +/- 26%, 20% +/- 2.3%, and 16% +/- 8.1%, respectively. Vascular compliance decreased significantly and, as evidenced by a lack of body weight changes, interstitial fluid volume failed to change (p < 0.05, analysis of variance). The transcapillary oncotic pressure difference increased by 2 mm Hg; venous pressure increased by 5.2 mm Hg. These data suggest that transcapillary forces favored fluid movement into the interstitium. Lymph flow rate remains elevated after blood volume expansion to a level similar to that described during pregnancy in sheep. A transient decrease in urinary output (approximately 20%) occurred with no changes in lymph flow rate, arterial pressure, or blood volume.

CONCLUSION

Lymph flow rate is able to compensate for the increased capillary filtration observed during prolonged blood volume expansion.

Circadian myometrial and endocrine rhythms in the pregnant rhesus macaque: effects of constant light and timed melatonin infusion

Six chronically catheterized rhesus macaques maintained on a 12-hour-light/dark cycle (lights on from 7 AM to 7 PM) showed a nocturnal uterine activity rhythm with peak contractile events between 9 and 11 PM (p less than 0.05). In blood samples collected at 3-hour intervals over a 24-hour period, we determined that plasma melatonin and progesterone concentrations were elevated at night whereas estradiol, estrone, and cortisol reached peak concentrations in the early morning (p less than 0.05). Lights were then left on for the remainder of the study. After 12 days in constant light, daily rhythms in uterine activity and plasma steroid levels were relatively unchanged, whereas melatonin concentrations were suppressed. Animals then received a timed infusion of melatonin (0.2 mg/kg/hr each day from 7 PM to 6 AM daily until delivery). The nocturnal uterine activity rhythm and the rhythms in plasma steroid concentrations were maintained. We conclude that the 24-hour patterns in maternal uterine activity and plasma steroid hormone levels are circadian rhythms generated by an endogenous biologic clock and do not appear to be driven by the pattern of melatonin in circulation.

Real-time microcomputer-based analysis of spontaneous and augmented labor

In an attempt to develop a reproducible, objective measure of adequate uterine activity in labor, real-time measurements of intrauterine pressure amplitude and contraction frequency, interval, duration, and integral were made in 54 patients, 11 of whom received oxytocin augmentation. We determined the active pressure integral required per centimeter of cervical dilatation, expressed in kPa seconds, and the mean active pressure, expressed in kPa. The augmented group had a significantly higher mean active pressure integral per centimeter than those in normal labor (P less than .01). There was a trend, which did not reach statistical significance, for subjects who required oxytocin augmentation of labor to develop a higher mean active pressure than those in normal labor. However, the correlation of any uterine contractility index (Montevideo units, Alexandria units, mean active pressure) with progress in labor was poor. We conclude that women with dysfunctional labor require more uterine activity for progress in labor than women with normally progressing labor, and that the computer-derived "area under the curve" is not a better predictor of labor progress than Montevideo units.

Cardiovascular changes after closure of uterine circulation during pregnancy

To assess the effects of the presence of the uteroplacental circulation on the systemic arterial pressure, blood volume, and cardiac output during pregnancy, we measured those variables and plasma renin activity (PRA) during a 30-min period before and after occlusion of the uterine circulation. After uterine vascular occlusion, pregnant rabbits (n = 7) experienced a drop in mean arterial pressure of 8.7%, heart rate of 9.5%, cardiac output of 30.2%, and hematocrit of 18.2% (each with P less than 0.05). Stroke volume decreased an average of 29.7%; however, it did not reach significance. PRA and venous pressure did not change significantly from the control period (P greater than 0.1). Nonpregnant rabbits did not experience changes in arterial or venous pressures, hematocrit, heart rate, cardiac output, or PRA after closure of the uterine circulation. To exclude the possibility that the findings were secondary to the release of toxic products to the peritoneal cavity by the ischemic pregnant uterus, we also studied the effect of closure of the uterine circulation in five anesthetized pregnant guinea pigs. These animals' uteri were exteriorized and maintained in a sealed plastic container during the experiment. In these animals, arterial pressure decreased 15.6% by 10 min (P less than 0.05). The finding of a significant decrease in arterial pressure and heart rate is compatible with the idea that the uterine circulation produces a substance with a short half-life that has a significant direct effect on the heart and/or systemic vascular tone.

Use of magnesium sulfate to treat hyperstimulation in term labor

Magnesium sulfate has been shown in vivo and in vitro to decrease the frequency of uterine contractions while maintaining the amplitude; we therefore decided to assess the use of magnesium sulfate infusion in cases of uterine hyperstimulation. The medical records were reviewed retrospectively for 37 term pregnant patients diagnosed as having uterine hyperstimulation during labor. None of them had medical or obstetric complications. Twenty-two of them received oxytocin augmentation for abnormal labor. Although the vast majority of these patients had a decrease of the hyperstimulation while being given the magnesium, 31.8% in the group receiving oxytocin alone (P less than .05). Fifteen additional patients received magnesium sulfate for uterine hyperstimulation although they were not receiving oxytocin; of these, 16.7% required cesarean delivery. This rate was no different from that of the patients who required labor augmentation, but was double the overall primary cesarean rate at our hospital. There appears to be a group of patients with abnormal uterine activity (either spontaneous or associated with oxytocin augmentation) that responds to treatment with magnesium sulfate.

Estrogen effects on lymph flow as a function of outflow pressure in ewes

The purpose of the present study was to assess whether acute estrogen administration decreased the lymphatic vessel's "pumping" ability. An additional goal was to assess whether estrogen affected the capillary filtration (used here as the total transfer of fluid and protein across the capillaries evidenced by the thoracic duct lymph flow rate). We reasoned that if estrogen administration decreases the lymph pumping ability against outflow pressure, then this phenomenon could help to explain the interstitial fluid retention seen during chronic estrogen. In six nonpregnant ewes we studied the thoracic lymph flow rate measured at different outflow pressures, before and after the acute administration of 50 mg of Premarin (conjugated estrogenic hormones). We also continuously determined arterial and venous pressures and heart rate. The arterial pressure declined from a mean of 99 +/- 0.33 (SE) mmHg to 95.4 +/- 0.2 mmHg (P less than 0.05) after the administration of estrogen. Heart rate increased from 88.5 +/- 0.8 to 111.3 +/- 1.2 beats/min (P less than 0.01). Venous pressure, plasma and lymph protein concentrations, and hematocrit did not change significantly (P greater than 0.1). Lymph flow rate declined progressively when measured against positive outflow pressure, whereas it remained stable when measured against negative pressure. Lymph flow rate during negative outflow pressure was higher after the administration of estrogen 0.044 +/- 0.002 vs. 0.032 +/- 0.002 ml.min-1.kg-1 for the control period (P less than 0.05). The calculated outflow pressure at which lymph flow rate became zero was similar for the period before or after the estrogen administration (P greater than 0.1).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of outflow pressure and vascular volume loading on thoracic duct lymph flow in adult sheep

Studies have shown that lymph flow rate from several tissues depends on the pressure at the outflow end of the lymphatics. The left thoracic lymph duct is the largest lymphatic vessel and it transports a majority of the body's lymph. We varied outflow pressure for the left thoracic lymph duct independent of venous pressure in six unanesthetized, nonpregnant adult ewes with chronic lymphatic and venous catheters. When outflow pressure was negative, the thoracic duct lymph flow rate was independent of outflow pressure and averaged 0.040 +/- 0.004 (SE) ml.min-1.kg body wt-1. Lymph flow began to decrease with increasing outflow pressure only when outflow pressure was significantly greater than venous pressure. Above this breakpoint, lymph flow decreased linearly with outflow pressure and ceased at an outflow pressure of 25.6 +/- 4.2 mmHg. After vascular volume loading with lactated Ringer solution, steady-state thoracic duct lymph flow increased to 351 +/- 54% of control and was independent of outflow pressure when outflow pressure was negative. As outflow pressure was elevated, lymph flow began to decrease at the same breakpoint as before volume loading, and lymph flow ceased at the same outflow pressure as before volume loading. Thus this study shows that there is a plateau where thoracic duct lymph flow rate is independent of outflow pressure. In addition venous pressure under normal or volume-loaded conditions is not an impediment to thoracic duct lymph flow in unanesthetized sheep. Large increases in venous pressure are required to totally block thoracic duct lymph flow.

Lymph flow rate response to angiotensin II is decreased in pregnant sheep

Pregnancy in humans is associated with a number of physiologic changes including interstitial fluid retention (edema) and a decrease in the systemic vascular response to infused angiotensin II. In nonpregnant sheep angiotensin II increases the lymph flow rate by what appears to be a direct effect on the lymphatic vessels. The purpose of this study was to test the hypothesis that during pregnancy the lymph flow rate response to angiotensin II infusion is decreased in relation to that of the nonpregnant state. We speculate that a decrease in lymph flow may explain the interstitial fluid retention observed during human pregnancy. In nine nonpregnant and five pregnant chronically catheterized ewes, we infused angiotensin II at rates of 0.1, 10, and 1000 ng/kg/min during a 5-minute period, with intervals of at least 15 minutes between doses. At the highest angiotensin II dose, peak lymph flow rate increased 286% in pregnant ewes compared with an increase of 344% in the nonpregnant sheep (p less than 0.05). No changes occurred in the intravascular volume, plasma or lymph protein concentration, or venous pressure. The arterial pressure responses to angiotensin II were decreased in pregnant sheep (p less than 0.05). These results are compatible with a model for fluid retention in pregnancy in which a decreased lymph flow rate plays a significant role in interstitial fluid retention.

Effect of whole-body pH changes on thoracic duct lymph flow in anesthetized sheep

Physiologic alterations of pH in vitro produce alterations of the oncotic pressure of both plasma and interstitial proteins, the effect being more marked in the latter. Therefore we postulated that by changing an animal's pH we could produce alterations in fluid distribution and affect the whole-body lymph flow rate. To test this hypothesis, we infused seven acutely nephrectomized anesthetized sheep with 2% body weight/volume isosmotic lactated Ringer's solution and bicarbonate (200 mEq) after a 30-minute control period. The fluid was infused over a 10-minute period with 20-minute recovery intervals. To another group of seven ewes, we infused the same volume of lactated Ringer's solution and hydrochloric acid (40 mEq). Throughout the experiment, we continuously measured arterial and venous pressures and lymph flow rate. Every 10 minutes we obtained samples for arterial pH, for hematocrit, and for plasma and lymph protein and osmolality. The infusion of bicarbonate was associated with a comparatively lower peak lymph flow rate (383% over baseline compared with 757% for acid infusion). Also the lymph flow rate after acid infusion started to increase approximately 5 minutes after the beginning of the infusion, as compared with approximately 10 minutes after the base infusion. Acid infusion did not increase arterial pressure, in contrast to the other infusions. The changes in pH obtained with the infusions were insignificant for the Ringer's infusion, +0.17 for the base, and -0.16 for the acid. The plasma/lymph protein concentration ratios at the end of the infusion were no different for acid or base: 112.4% +/- 4.4% and 101.9% +/- 5% (difference from control, mean +/- SEM) respectively (p greater than 0.1). In conclusion, minimal alterations of pH produced alterations in the cardiovascular and lymph flow rate responses to fluid challenge in anesthetized animals.

Is a decrease in plasma oncotic pressure enough to explain the edema of pregnancy?

The balance of fluid across capillaries is given by the Starling equation. Because the plasma protein concentration (one of its components) is decreased in pregnancy, we decided to explore the question as to whether hypoproteinemia with intact protein mass (produced by blood volume expansion) or hypoproteinemia with decreased total protein mass (produced by removal of circulating proteins) alters the oncotic pressure differences across capillaries. We calculated the oncotic pressure difference obtained in seven nonpregnant ewes during periods of normoproteinemia and hypoproteinemia; the influence of fluid infusion under both conditions was also observed. There was an increase in the oncotic pressure difference across the capillary wall during hypoproteinemia produced by a decrease in the total protein mass (p less than 0.01); however, the response to hypoproteinemia produced by fluid infusion was similar (p greater than 0.1). The venous pressure (used as an index of interstitial fluid pressure changes) did not differ in either hypoproteinemia or fluid infusion. Capillary permeability was decreased during hypoproteinemia, as evidenced by a higher lymph/protein ratio of labeled albumin during the control period (p less than 0.05). In conclusion, during a state of decreased plasma protein concentration similar to that of pregnancy, the difference in the oncotic pressure and hydrostatic pressure forces acting to prevent transfer of fluid to the interstitium is increased. Therefore other factors that influence fluid transfer across the capillaries must be investigated to explain the edema of pregnancy.

Effects of sustained lymph drainage on cardiovascular function and thoracic duct lymph in sheep

We studied the effect of lowering the plasma protein concentration on the cardiovascular function and thoracic duct lymph in awake adult sheep. Hypoproteinemia was induced in seven nonpregnant, splenectomized sheep by drainage of the thoracic duct lymph over a 5-day period. The plasma protein went from a mean of 6.4 +/- 0.2 (SE) to 4.9 +/- 0.2 g/dl on day 5, and the lymph-to-plasma protein concentration ratio decreased from 0.74 +/- 0.01 on day 1 to 0.48 +/- 0.04 on day 5. The percentage composition of the protein fractions in plasma and lymph remained unchanged. Lymph flow was 1.79 +/- 0.37 and 1.28 +/- 0.10 ml/min for days 1 and 5, respectively. Renin concentration in plasma increased 50-fold by day 5. Arterial pressure fell from 102.9 +/- 5.4 to 72.7 +/- 4.4 mmHg by day 5. Mean hematocrit was 28.9 +/- 1.7 at day 1, which was not significantly different than 24.6 +/- 2.9 at day 5 and indicated that the plasma volume did not decrease. Body weight also did not change significantly. There was a decrease in the transcapillary protein escape rate, determined as the thoracic lymph flow rate multiplied the lymph protein concentration, that suggests adaptations in the microcirculation to decrease vascular-to-interstitial protein transfer during hypoproteinemia. Hypoproteinemic animals also demonstrated greater vascular retention of a fluid volume challenge. In conclusion, the sheep adaptations to sustained hypoproteinemia produced by lymph drainage were a significant decrease in arterial pressure, large increases in vascular compliance and renin concentration, and reduced transcapillary escape rate of protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Atrial natriuretic peptide, plasma renin activity, and aldosterone in women on estrogen therapy and with premenstrual syndrome

Estrogens are known to increase the renin-angiotensin-aldosterone system and to produce fluid retention, while atrial natriuretic peptide (ANP) induces an increase of the urinary output and tends to return the fluid balance to normal. The aim of this study was to test whether the levels of ANP were decreased during chronic estrogen and progestin administration, thereby possibly decreasing the amount of fluid excreted. The authors also studied women with premenstrual syndrome (PMS), because of the associated fluid retention often described with this syndrome. Levels of ANP, plasma renin activity (PRA), and aldosterone were determined in premenopausal women in the early follicular phase (EFP) and on low-dose oral contraceptives (OC), in postmenopausal patients with and without estrogen replacement therapy (ERT), and in women with PMS associated with fluid retention. The concentrations of ANP and PRA were enhanced in the women on OC, but those of aldosterone were unchanged. No differences were observed in the women on ERT or with PMS. It is concluded that the levels of PRA and ANP are affected by estrogen or progesterone therapy or the combination of the two and this response is dose dependent or additive. Furthermore, ANP and PRA do not seem to play a direct role in PMS.

Clinical management of patients with cystic fibrosis and pulmonary insufficiency

Management of a patient with cystic fibrosis who started her pregnancy in a state of pulmonary insufficiency, as defined by arterial blood gas values and a chest x-ray film, is described. A systematic approach to evaluation of patients with cystic fibrosis, including serial assessments of pulmonary functions, screening for diabetes, maintenance of adequate nutrition (including hyperalimentation), and cardiac function evaluation is described.

Oxytocin augmentation of labor: a comparison of 15- and 30-minute dose increment intervals

Two different regimens for oxytocin augmentation of labor were compared retrospectively in two institutions. In one regimen, the interval between dose increments was 15 minutes; in the other it was 30 minutes. All study patients were nulliparous and had uncomplicated pregnancies in spontaneous active labor; the 15-minute group consisted of 92 patients and the 30-minute group had 82 patients. No differences were demonstrated in age, dilation when oxytocin administration started, length of oxytocin administration, cesarean section rate, complications of delivery, birth weight, or Apgar scores. The maximal oxytocin dose in the 30-minute interval group was significantly lower. This group also had the oxytocin infusion stopped for evidence of uterine hyperstimulation and/or abnormal fetal heart rate tracing significantly less often (6.9% for the 30-minute interval versus 17.8% for the 15-minute interval; P = .0017). Overall, these results suggest that the longer interval does not increase the length of labor but decreases the incidence of uterine hyperstimulation.

Time-dependent changes in bone, placental, intestinal, and hepatic alkaline phosphatase activities in serum during human pregnancy

To measure changes in bone alkaline phosphatase (EC 3.1.3.1) activity in serum as a function of duration of pregnancy, we adapted our existing alkaline phosphatase (ALP) isoenzyme assay (which has been used to measure bone, hepatic, and intestinal ALP activities in serum, in the absence of placental ALP) to allow quantification of individual ALP isoenzyme activities in the presence of placental ALP. The resulting CV for repeat measurements of bone ALP activity in artificial isoenzyme mixtures ranged from 23% for samples in which the bone isoenzyme represented 7% of total ALP activity to 11% for samples in which bone ALP accounted for 48% of total ALP activity. Values for repeat determinations of bone ALP activity in human serum samples (i.e., including samples obtained from pregnant women and from nonpregnant controls) varied by an average of 18%. We find, in initial applications of this method, that (a) the amount of bone ALP activity in serum is increased during pregnancy (P less than .001), and remains increased at six weeks postpartum, in non-lactating women (P less than .001), and (b) bone ALP activity at term was not significantly different in pregnant women with pre-eclampsia, diabetes, premature rupture of membranes, or premature labor, compared with normal pregnancies at term. Our data support the hypothesis that maternal bone formation may be increased during pregnancy.

Time-dependent changes in bone, placental, intestinal, and hepatic alkaline phosphatase activities in serum during human pregnancy

To measure changes in bone alkaline phosphatase (EC 3.1.3.1) activity in serum as a function of duration of pregnancy, we adapted our existing alkaline phosphatase (ALP) isoenzyme assay (which has been used to measure bone, hepatic, and intestinal ALP activities in serum, in the absence of placental ALP) to allow quantification of individual ALP isoenzyme activities in the presence of placental ALP. The resulting CV for repeat measurements of bone ALP activity in artificial isoenzyme mixtures ranged from 23% for samples in which the bone isoenzyme represented 7% of total ALP activity to 11% for samples in which bone ALP accounted for 48% of total ALP activity. Values for repeat determinations of bone ALP activity in human serum samples (i.e., including samples obtained from pregnant women and from nonpregnant controls) varied by an average of 18%. We find, in initial applications of this method, that (a) the amount of bone ALP activity in serum is increased during pregnancy (P less than .001), and remains increased at six weeks postpartum, in non-lactating women (P less than .001), and (b) bone ALP activity at term was not significantly different in pregnant women with pre-eclampsia, diabetes, premature rupture of membranes, or premature labor, compared with normal pregnancies at term. Our data support the hypothesis that maternal bone formation may be increased during pregnancy.

Estrogen, progesterone, prolactin, prostaglandin E2, prostaglandin F2 alpha, 13,14-dihydro-15-keto-prostaglandin F2 alpha, and 6-keto-prostaglandin F1 alpha gradients across the uterus in women in labor and not in labor

Before or during labor in humans, changes in peripheral levels of estrogen and progesterone are not evident. Local alterations of estrogen, progesterone, and prolactin concentrations may be present and be accompanied by prostaglandin changes. The purpose of this study was to investigate the differences in concentrations of these hormones across the uterus and to evaluate their interrelationships in patients at term gestation with and without labor. Blood samples were obtained from a radial artery and a uterine vein in 22 women without and in 10 with labor. The difference between levels in the two blood vessels was designated as the gradient. Neither levels nor gradients were different between the two groups for estrone, estradiol, estriol, progesterone, or prolactin. The plasma levels of prostaglandin F2 alpha, 13,14-dihydro-15-keto-prostaglandin F2 alpha, and prostaglandin E2 were significantly increased in labor. Prostacyclin levels, as indicated by the 6-keto-prostaglandin F1 alpha metabolite, were not altered. The gradients for prostaglandin F2 alpha and E2 were significantly increased in labor. The results of the study also suggested that, in gestation at term, serum prolactin is produced mainly by the pituitary and that estrone may originate from peripheral conversion of estradiol. We conclude that in humans prostaglandin gradients of the E and F groups are increased in labor. These increases are not associated with changes in sex steroids or prolactin. Prostacyclin metabolite gradients also appear not to be altered in labor, suggesting that some prostaglandins are selectively increased in early labor either by enhanced production or decreased metabolism or both.

Lymphatic and vascular responses to fluid infusion in castrated and noncastrated sheep

Estrogen administration produces blood volume expansion and interstitial fluid retention. We decided to study the effect of estrogen withdrawal on blood volume and determine whether oophorectomy has an effect on lymph flow or protein concentration. The rate of left thoracic duct lymph flow averaged 0.041 +/- 0.005 (SE) and 0.071 +/- 0.008 ml X min-1 X kg-1 in castrated (n = 9) and noncastrated (n = 9) female sheep, respectively (P = 0.006). After three serial intravenous infusions of Ringer lactate solution (2% body wt/infusion) the thoracic duct lymph flow in the castrated animals increased 358, 457, and 498% over the base-line rate, compared with increase of 200, 235, and 353% in the nonpregnant ewes. However, with the lower control values in the castrated animals, the lymph flow rate reached the same absolute values as those seen in the noncastrated ewes. Lymph protein concentration and the lymph-to-plasma protein concentration ratio, as well as arterial and venous pressures, were unaltered by oophorectomy. Base-line whole blood volumes were 58.2 +/- 1.9 (n = 9) and 64.8 +/- 2.6 ml/kg (n = 9) in the castrated and noncastrated ewes, respectively (P less than 0.05). Systemic vascular compliance averaged 4.5 +/- 0.7 and 7.1 +/- 1.7 ml X kg-1 X mmHg-1 in the castrated and noncastrated ewes, respectively (P less than 0.05), whereas interstitial fluid compliance values were 12 and 32 ml X kg-1 X mmHg-1, respectively. The capillary filtration coefficients were not different in the two groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin II infusion increases thoracic duct lymph flow in chronically catheterized sheep

Both pregnancy and estrogen administration are associated with a decrease in the systemic vasculature pressor response to angiotensin II infusion; however, the lymphatic vessel system response is not clear. In the present study we infused angiotensin II to nine nonpregnant splenectomized ewes with 0.1, 10, or 1,000 ng X kg-1 X min-1 for a 5-min period at each dose. At the lowest dose the mean arterial pressure increased from 10 to 20% over base line. At the highest dose, the left thoracic duct flow rate peaked at 361% 10 min after the infusion was started, whereas arterial pressure peaked at 183% of the control value. Peak lymph flow occurred 4-6 min after the maximal increase in mean systemic arterial pressure. Neither hematocrit nor venous pressure were altered at any of the doses administered. This suggests that the interstitial fluid space pressure remained unchanged and that the increase in lymph flow was not secondary to fluid transfer from the intravascular system. We postulate, therefore, that the effect of angiotensin II in the increase of lymph flow rate is by direct action on the lymphatic vessels themselves.

Uteroplacental unit as a source of elevated circulating prorenin levels in normal pregnancy

Circulating levels of inactive renin, that is, prorenin, are increased in normal pregnant women. To determine whether the uteroplacental unit secretes prorenin into the maternal circulation, we measured enzymatically active and inactive renin in plasma simultaneously obtained from the radial artery and uterine vein of 12 normotensive, nonlaboring patients undergoing elective cesarean section at term. We also measured these forms of renin in the umbilical arterial and venous blood of these patients. Our data reveal that the levels of inactive renin in both arterial and uterine venous blood of normal pregnant women are significantly higher than in peripheral venous blood of nonpregnant, normotensive control subjects; normotensive term patients have a ratio of plasma inactive to active renin of 9:1 in contrast to the 1:1 ratio in normotensive nonpregnant subjects; there is a significant uterine arteriovenous difference of prorenin (66.2 +/- 24.4 ng/ml/hr, p less than 0.05) but not of active renin (1.8 +/- 1.5 ng/ml/hr, not significant). These results suggest that the uteroplacental unit contributes to the elevated prorenin levels at term pregnancy.