Leukotrienes C4, D4, and E4 in fetal lamb tracheal fluid

Previously, we demonstrated that either putative leukotriene receptor antagonists or a synthesis inhibitor markedly decreased pulmonary vascular resistance in the near-term fetal lamb and concluded that leukotrienes may play a role in maintaining the high pulmonary vascular resistance in the fetus. To further investigate the role of leukotrienes, we measured concentrations of leukotriene (LT) C4, LTD4, and LTE4 in 17 tracheal fluid samples from 8 of 9 near-term (129-139 days, term = 145 days), chronically-catheterized, fetal lambs during normoxia to evaluate their possible role in regulating resting tone and in seven of the nine before and during hypoxia to evaluate their possible role in hypoxic vasoconstriction. The tracheal fluid samples collected by gravity over 1-3 min, on ice, were immediately treated with cold ethanol, centrifuged, and the supernatant covered with N2 and stored in a -70 degrees C freezer for a maximum of 3 weeks. Purification and separation of leukotrienes was done by reverse-phase high performance liquid chromatography using a gradient elution method, and fractions corresponding to LTC4, LTD4, and LTE4 standards were quantified immediately by radioimmunoassay. During normoxia (descending aortic PaO2 2.9 +/- 0.3 kPa [21.5 +/- 2.5 mmHg]; mean +/- SD), all 3 leukotrienes were detected in 16 of the 17 samples: LTC4 29 +/- 28 pg/ml (range 0-119 pg/ml); LTD4 66 +/- 51 pg/ml (range 9-177 pg/ml); and LTE4 43 +/- 50 pg/ml (range 0-204 pg/ml).(ABSTRACT TRUNCATED AT 250 WORDS)

The young lamb can increase cardiovascular performance during isoflurane anesthesia

Cardiac output and myocardial blood flow decrease dramatically in a dose-dependent pattern in the young lamb during isoflurane anesthesia. This raises important questions about the ability of the young lamb to increase myocardial performance if oxygen delivery were compromised by a decrease in oxygen content during anesthesia and surgery. To investigate the ability of the young lamb to increase oxygen delivery during isoflurane anesthesia, the response to hypoxemia, which is known to increase myocardial performance, was studied in awake 1-week-old lambs. Mean systemic arterial pressure, heart rate, cardiac output, and regional distribution of blood flow were measured during three states: awake, 1.0 minimum alveolar concentration (MAC) of isoflurane in an FIO2 of 1.0, and 1.0 MAC of isoflurane in an FIO2 of 0.09. Stroke volume, total body and myocardial oxygen consumption, and fractional extraction of oxygen were calculated for the total body and for the myocardium. Isoflurane anesthesia decreased mean systemic arterial pressure (70 +/- 8 mmHg), heart rate (222 +/- 29 beats/min), and cardiac output (277 +/- 72 ml.kg-1.min-1) significantly (43 +/- 11 mmHg, 163 +/- 20 beats/min, 191 +/- 34 ml.kg-1.min-1). Hypoxemia returned heart rate to control (191 +/- 23 beats/min), increased stroke volume (1.71 +/- 0.2 ml/kg) above both control (1.23 +/- 0.2 ml/kg) and 1.0 MAC isoflurane levels (1.19 +/- 0.3 ml/kg), and increased cardiac output (325 +/- 61 ml.kg-1.min-1) above the level during 1.0 MAC isoflurane.

Bradykinin produces pulmonary vasodilation in fetal lambs: role of prostaglandin production

Bradykinin produces pulmonary vasodilation and also stimulates production of other pulmonary vasodilators, including prostaglandin I2 (PGI2) and endothelial-derived relaxing factor. In 12 chronically instrumented fetal lambs, we therefore investigated potential mediation of the bradykinin response by PGI2 or other cyclooxygenase products. A 15-min infusion of bradykinin (approximately 1 microgram/kg estimated fetal wt/min) increased fetal pulmonary blood flow by 522% (P less than 0.05) and decreased pulmonary vascular resistance by 86% (P less than 0.05); plasma 6-ketoprostaglandin F1 alpha (6-keto-PGF1 alpha) concentration also increased (P less than 0.05). After cyclooxygenase inhibition by indomethacin (3 mg), bradykinin increased pulmonary blood flow by only 350% (P less than 0.05) and decreased pulmonary vascular resistance by 83% (P less than 0.05); plasma 6-keto-PGF1 alpha concentrations did not increase. The increase in pulmonary blood flow produced by bradykinin was greater before administration of indomethacin than after (P less than 0.05). These studies demonstrate that bradykinin produces fetal pulmonary vasodilation by at least two mechanisms, one dependent on and the other independent of PGI2 production, the latter mechanism predominating.

Leukotriene antagonists attenuate thromboxane-inducible pulmonary hypertension

Leukotrienes C4 and D4 and thromboxane A2 are potent vasoconstrictors that may mediate pulmonary vasoconstriction in many clinical situations. There is a complex interaction among leukotrienes and thromboxane A2, because inhibition of thromboxane synthesis prevents some of the hemodynamic effects of exogenous leukotrienes. Similarly, if leukotrienes mediate thromboxane A2-induced pulmonary vasoconstriction, then leukotriene antagonists should attenuate the effects of a thromboxane A2-mimetic such as U46619. First, dose response curves for the hemodynamic effects of U46619 were performed on seven spontaneously breathing newborn lambs. Then a putative leukotriene receptor antagonist, FPL57231, 1 mg/kg/min, or a putative leukotriene synthesis antagonist, U60257, 30 mg/kg, was given before infusing U46619 (1 microgram/kg/min). U46619 caused significant dose-dependent increases in pulmonary and systemic arterial pressures (p less than 0.05) and significant dose-dependent decreases in cardiac output and heart rate (p less than 0.05). A 1 microgram/kg/min infusion of U46619 increased pulmonary arterial pressure by 155.4% +/- 8.9 and systemic arterial pressure by 8.9% +/- 7.7 and decreased cardiac output by 19.7% +/- 12.2 and heart rate by 9.9% +/- 10.6. FPL57231 attenuated the effects of U46619. U60257 had similar effects. Therefore, the hemodynamic effects of thromboxane A2, an important mediator of the pulmonary vasoconstriction produced, for example, by group B streptococci and Escherichia coli, may be mediated by the secondary production of leukotrienes.

Influence of increased pulmonary vascular pressures on the closure of the ductus arteriosus in newborn lambs

Neonatal conditions associated with increased pulmonary artery pressure have an increased incidence of patent ductus arteriosus. We operated on 15 near term fetal lambs and placed mechanical occluders into or around both branch pulmonary arteries so that main pulmonary artery blood pressure could be controlled. The lambs were delivered and ventilated for 4 h. In seven lambs, the branch vessels were obstructed so that pulmonary artery pressure increased to equal aortic pressure; in eight lambs (control), the branch vessels were not obstructed. There were no significant differences between the two groups in circulating prostaglandin E2 or 6 keto F1 alpha concentrations, PaO2, pH, or PaCO2. Despite these similarities, ductus resistance in the lambs with elevated pulmonary pressure was significantly less than that in the control lambs. After the 4 h measurements, we studied the ductus in vitro. We have previously found that ductus arteriosus constriction produces ischemia of its muscle wall that limits its ability to dilate or constrict any further. Ductus from lambs with elevated pulmonary pressure had a significantly increased ability to respond to oxygen, prostaglandin E2, and indomethacin compared with ductus from control lambs; these findings are consistent with less ductus constriction in vivo. Thus, the high incidence of patent ductus arteriosus in neonates with elevated pulmonary vascular resistance may be due in part to the increased pulmonary vascular pressure, which opposes ductus constriction and preserves ductus responsiveness. Conversely, the normal drop in pulmonary pressure that occurs in full term infants may facilitate the closure of the ductus after delivery.

Regulation of the pulmonary circulation in the perinatal period and in children

In the fetus, the pulmonary circulation is actively maintained in a constricted state due to low oxygen environment and perhaps leukotrienes. Pulmonary blood flow represents about 8% of fetal cardiac output. Shortly after birth, pulmonary vascular resistance (PVR) and pulmonary arterial pressure fall rapidly, whereas pulmonary blood flow reaches systemic levels. The exact mechanisms by which the dramatic changes in PVR occur with the onset of ventilation at birth are extensively reviewed. They include: oxygen environment and release of vasoactive substances such as bradykinin, PGI2 or PGD2. Thus, regulation of the fetal and immediate postnatal pulmonary circulation reflects a balance between factors producing active pulmonary vasoconstriction and those producing vasodilatation.

Effects of prostaglandin D2 on pulmonary arterial pressure and oxygenation in newborn infants with persistent pulmonary hypertension

We studied the effects of prostaglandin D2 (PGD2) in six newborn infants, 1 to 2 days of age, who had persistent pulmonary hypertension syndrome and a PaO2 less than 75 torr during mechanical hyperventilation with an inspired oxygen concentration of 100%. Tolazoline and dopamine were used to treat some of the patients. No patients had congenital heart disease or sepsis. Catheters were placed to measure pulmonary and systemic arterial blood pressures. PGD2 was infused intravenously at doses of 1 to 25 micrograms/kg/min. Pulmonary and systemic arterial blood pressures, heart rate, and descending aortic blood gas values were measured before each dose change. Only two of six patients had a transient increase in PaO2. All had an increase in heart rate. Two of six patients had an increase in pulmonary arterial blood pressure. No deleterious effects occurred during the infusion. Four of six patients subsequently died. Although PGD2 is a specific pulmonary vasodilator in fetal and newborn animals, it did not lower pulmonary arterial blood pressure nor improve oxygenation in newborn infants with persistent pulmonary hypertension syndrome.

Effect of beta-adrenergic receptor blockade on responses to acute hypoxemia in lambs

We studied the effects of beta-adrenergic receptor blockade on general circulatory and metabolic responses to moderate (FIO2 = 0.09) acute hypoxemia in newborn (protocol 1) and 3-wk-old (protocol 2) lambs, and on regional blood flow distribution in newborn lambs (protocol 1). Via a left thoracotomy we placed an electromagnetic flow transducer around the ascending aorta and inserted various vascular catheters. After 2 days of recovery, the lambs were studied. In protocol 1, we measured cardiovascular variables and regional blood flow distribution during control conditions, after 45 min of acute hypoxemia, and after 0.5 mg/kg of propranolol during acute hypoxemia. In protocol 2, we measured cardiovascular variables during control conditions and after 45 min of acute hypoxemia with and without propranolol pretreatment. In both groups, propranolol limited the increase in cardiac output and heart rate caused by hypoxemia, and thus decreased oxygen delivery. However, propranolol also decreased oxygen consumption so that pulmonary arterial pO2 was either higher (protocol 1) or the same (protocol 2) as during acute hypoxemia alone. Neither metabolic acidosis nor hypothermia ensued. In protocol 1, propranolol decreased renal, carcass, and most importantly, myocardial blood flows. However, myocardial O2 consumption also fell, coronary sinus pO2 increased, and blood was redistributed toward the subendocardium, suggesting that myocardial perfusion improved. Thus, beta-adrenergic receptor blockade during acute moderate hypoxemia may have a beneficial effect by reducing total body and myocardial oxygen demand in excess of the reduction in oxygen delivery.

Indomethacin and patent ductus arteriosus: effects on renal function in preterm lambs

To examine the independent effects of a patent ductus arteriosus and of indomethacin therapy on the renal function of the preterm newborn, we created a preterm lamb model in which ductus diameter could be regulated. We studied 24 preterm newborn lambs. Eight lambs (group 1) had their ductus closed at delivery and received no indomethacin. Eight lambs (group 2) had their ductus closed and then received indomethacin (0.3 mg/kg) at 5.5 h; eight lambs (group 3) had their ductus kept open and then received indomethacin at 5.5 h. Hemodynamic and renal function measurements were made at 5 h (pretreatment) and at 12.5 h. In group 2 lambs there was a significant reduction in inulin clearance (GFR) and osmolal clearance after indomethacin. In contrast, lambs with an open ductus (group 3), when compared with lambs with a closed ductus (groups 1 and 2) at 5 h, already had significantly decreased blood pressure, GFR, urine volume, and osmolal clearance. Following indomethacin treatment, group 3 lambs showed no further decrease in renal function. We suggest that in preterm lambs with patent ductus, the apparent lack of renal dysfunction following indomethacin treatment reflects underlying diminished renal function.

Prostaglandins and leukotrienes in the perinatal period

Arachidonic acid is the precursor of many physiologically active substances. One such group, the prostaglandins, is involved in regulation of the ductus arteriosus, the perinatal pulmonary circulation, and uterine function. Administration of these substances or inhibition of their production or effect has therapeutic benefit in many different circumstances. Another group, the leukotrienes, also appears to be involved in regulation of the perinatal pulmonary circulation; pharmacologic manipulation of these has not yet been tried.

Respiratory effects of a patent ductus arteriosus in premature newborn lambs

We examined the respiratory effects of a patent ductus arteriosus in 29 premature lambs (131-135 days gestational age) after infiltrating the ductal wall with formaldehyde solution (Formalin) and placing a snare around the ductus to regulate its patency. The lambs were given sheep surfactant, paralyzed, and mechanically ventilated at birth. We first compared 8 lambs with open ductus and 13 lambs with closed ductus during the 12 h after birth. Although lambs with open ductus had greater pulmonary blood flow (301 +/- 36 vs. 188 +/- 11 ml.min-1.kg-1, mean +/- SE, at 12 h of age) and mean pulmonary arterial (44 +/- 3 vs. 33 +/- 2 mmHg) and left ventricular end-diastolic (6 +/- 0.6 vs 4 +/- 0.7 mmHg) pressures, we found no differences in dynamic respiratory compliance (Cdyn = 0.55 +/- 0.07 vs. 0.55 +/- 0.03 ml.cmH2O-1.kg-1), midtidal volume resistance (62 +/- 5 X 10(-3) vs. 62 +/- 7 X 10(-3) cmH2O.ml-1.s), or functional residual capacity (FRC = 27 +/- 3 vs. 26 +/- 2 ml.kg-1). Alveolar-arterial PO2 difference was lower in the lambs with open ductus (238 +/- 65 vs. 362 +/- 37 Torr). Next, we challenged eight lambs with two separate saline infusions (50 ml.kg-1 over 3 min), each given with the ductus alternately closed or open. When the ductus was closed, FRC was unchanged, but Cdyn increased by 18% immediately after the infusion. When the ductus was open, FRC decreased by 16% and Cdyn decreased by 12%. We conclude that the premature lamb is surprisingly resistant to changes in respiratory function from ductal patency during the immediate neonatal period.

How a patent ductus arteriosus effects the premature lamb's ability to handle additional volume loads

A model of patent ductus arteriosus in premature lambs was created to examine the lamb's ability to handle the volume load imposed by a patent ductus arteriosus and to determine the lamb's ability to handle any additional volume load. Fifteen preterm lambs [133 +/- 2 (+/- SD) days gestation, term 145 days], whose ductal diameter could be regulated with a mechanical occluder, were studied to determine the independent effects of ductus patency and a saline volume load (50 ml/kg over 3 min) on left ventricular output and its distribution. During a saline infusion, preterm lambs with a closed ductus could only increase their stroke volume by 40% above baseline stroke volume. When challenged with a saline infusion, lambs with an open ductus still were able to increase their stroke volume significantly; the maximal increase in stroke volume during the saline load with the ductus open was 70% above baseline stroke volume. We hypothesize that the associated reduced left ventricular afterload plays a significant role in the preterm lamb's ability to increase its stroke volume when challenged with a patent ductus arteriosus. Even with a patent ductus arteriosus, the lamb still has the ability to handle additional volume loads.

Cardiovascular effects of patent ductus arteriosus in preterm lambs with respiratory distress

We created a model for studying the cardiovascular and pulmonary effects of patent ductus arteriosus (PDA) in premature lambs with respiratory distress. In 47 fetal lambs at 129 to 133 days gestation (term, 145 days), we infiltrated the ductus arteriosus with formalin and placed a mechanical occluder about it so that its patency could be regulated. Two days later the lambs were delivered, given sheep surfactant, paralyzed, and their lungs mechanically ventilated. These premature lambs could more than double their left ventricular output when challenged with increasing degrees of left-to-right shunts through the PDA. This was accomplished by an increase in stroke volume, not by an increase in heart rate. During the 40-minute observation period, there was no change in dynamic compliance or functional residual capacity while the ductus was patent. When the ductus was patent, there was a significant increase in arterial PaO2 (even with small left-to-right shunts) and a decrease in PaCO2 (with large shunts). Despite the heart's ability to handle the increased volume load of a PDA, there were significant alterations in individual organ blood flows, resulting from a combination of decreased perfusion pressure and localized vasoconstriction. The abdominal organs had significant reductions in blood flow even with small PDA shunts. This decrease in organ blood flow may explain some of the pathophysiologic manifestations of PDA in preterm infants.

Redistribution of regional blood flow and oxygen delivery in experimental cyanotic heart disease in newborn lambs

Redistribution of regional blood flow is an important compensatory response to acute hypoxemia which preserves oxygen delivery to the most vital organs. It is not known if this change in blood flow persists when hypoxemia is prolonged, as occurs in cyanotic congenital heart disease. Chronic hypoxemia was produced in newborn lambs by creating pulmonary stenosis and an atrial septal defect. Oxygen saturation was maintained at 60-70% of control for 2 wk. Distribution of cardiac output was then measured with radionuclide-labeled microspheres. As compared with control, chronic hypoxemia did not alter total cardiac output. Regional blood flow was redistributed, however, the pattern of this redistribution was different from that seen during acute hypoxemia. Myocardial and cerebral blood flows, which increase during acute hypoxemia, return to control levels during chronic hypoxemia. Renal, splenic, gastrointestinal, carcass, and skin blood flows remain decreased. Hemoglobin gradually increases so that after 2 wk of hypoxemia total systemic oxygen delivery returns toward control. However, oxygen delivery to all organs except the heart and brain is reduced. Thus, although cardiac output and total systemic oxygen delivery return toward normal during chronic hypoxemia, these measurements may not reflect important regional variations in blood flow and oxygen delivery. Decreased oxygen and substrate delivery to the gastrointestinal tract, liver, and carcass may account for the alterations of metabolism and growth seen in the newborn with cyanotic congenital heart disease.

Piriprost: a putative leukotriene synthesis inhibitor increases pulmonary blood flow in fetal lambs

Leukotrienes may control fetal pulmonary vascular tone since infusions of putative leukotriene receptor antagonists markedly increase pulmonary blood flow and decrease pulmonary vascular resistance in fetal lambs. This hypothesis would be strengthened if inhibition of leukotriene synthesis also produced similar hemodynamic changes. We therefore studied the effects of piriprost (U 60257), a putative leukotriene synthesis inhibitor, on thirteen fetal lambs at 137 to 140 days gestation. In preliminary studies in four fetal lambs, doses of U 60257 greater than 20 mg/kg increased pulmonary blood flow. In the nine other fetal lambs, U 60257 (31.7 +/- 4.1 mg/kg) increased pulmonary blood flow by 502% (p less than 0.05) and decreased pulmonary vascular resistance by 87% (p less than 0.05). Pulmonary arterial and left atrial pressures were unchanged. Descending aortic pressure was increased (p less than 0.05) and heart rate was decreased (p less than 0.05). The abilities of both putative leukotriene synthesis inhibitors and leukotriene receptor antagonists to similarly increase fetal pulmonary blood flow and decrease pulmonary vascular resistance are consistent with the hypothesis that leukotrienes play a role in regulating fetal pulmonary vascular tone.

The cardiovascular effects of isoflurane in lambs

The effects of 1.0 and 1.5 minimum alveolar concentrations (MAC) of isoflurane on mean systemic arterial pressure, heart rate, stroke volume, cardiac output, total body oxygen consumption, myocardial oxygen consumption, and regional distribution of blood flow were studied in newborn lambs. Fractional extraction of oxygen for the total body and for the myocardium were calculated. MAC for isoflurane was first determined in eight lambs less than 10 days old. The mean value obtained was 1.51%. Six different lambs were used for cardiovascular study. Heart rate, stroke volume, cardiac output, and mean systemic arterial pressure decreased significantly during isoflurane anesthesia. Mean systemic arterial pressure and cardiac output decreased in a dose-dependent manner. Heart rate decreased significantly at 1.0 MAC isoflurane, but no further at 1.5 MAC. Stroke volume decreased only at 1.5 MAC. Cardiac output and total body oxygen consumption decreased by similar amounts at 1.0 MAC. Although cardiac output fell further at 1.5 MAC, oxygen consumption did not. Fractional extraction of oxygen increased only at 1.5 MAC. Myocardial blood flow and oxygen consumption decreased in parallel at 1.0 MAC, with no significant change during 1.5 MAC. Myocardial fractional oxygen extraction did not change. Although blood flow to all six body regions decreased significantly from control at both concentrations of isoflurane, blood flow to all organs except the adrenal did not differ significantly during 1.0 and 1.5 MAC. The authors conclude that a decrease in oxygen requirement during isoflurane anesthesia results in an appropriate decrease in oxygen delivery, with no apparent diversion of cardiac output from non-vital to vital organs.(ABSTRACT TRUNCATED AT 250 WORDS)

Postnatal regulation of the pulmonary circulation: a role for lipid mediators?

The action and interaction of many products of arachidonic acid metabolism can affect the pulmonary circulation in the perinatal period. The rapid increase in pulmonary blood flow with the onset of ventilation likely is brought about to a large degree by the production locally of prostaglandin I2 (PGI2). This can be stimulated by purely mechanical factors, by the normally increasing concentrations of angiotension II, by the 02-mediated release of bradykinin, or perhaps by other phenomena. Prostaglandin D2 release from mast cells also may play some role. The opposing pulmonary vascular effect, i.e., pulmonary vasoconstriction, of leukotrienes is likely to play a role in regulating fetal pulmonary blood flow. Inhibition of the production or action of these substances will allow for vasodilatation, and it is probable that perinatal pulmonary vascular tone reflects a balance between local prostaglandin and leukotriene production.

Umbilical cord compression produces pulmonary hypertension in newborn lambs: a model to study the pathophysiology of persistent pulmonary hypertension in the newborn

We investigated the effects of chronic intrauterine hypoxaemia produced by prolonged partial umbilical cord compression on the circulation shortly after birth in lambs. Vascular catheters were inserted in 10 fetal sheep at 120 to 130 days gestation to measure descending aortic blood gases, arterial pH, and arterial O2 saturation. An inflatable silicone rubber balloon cuff was also placed around the umbilical cord. After recovery and the return of descending aortic blood gases to the normal range, the balloon was gradually inflated, decreasing the PaO2 from 21.2 +/- 3.6 to 17.5 +/- 1.3 mm Hg and the arterial O2 saturation from 57.1 +/- 9.2% to 37.2% +/- 5.2. After 14.3 +/- 3.7 days of partial umbilical cord compression, the lambs were delivered by Caesarean section, instrumented to measure systemic and pulmonary arterial, right atrial and pulmonary arterial wedge pressures, pulmonary and systemic blood flows, and mechanically ventilated. Five normal lambs were also studied. From 60 to 120 min after delivery, when compared to normal lambs, the umbilical compression lambs had an increased pulmonary arterial pressure (P less than 0.05) pulmonary vascular resistance (P less than 0.05), and right atrial pressure (P less than 0.05) with similar arterial blood gases. In both groups, hypoxic ventilation produced an increase in pulmonary arterial pressure (P less than 0.05) which on return to room air ventilation decreased to baseline in the normal lambs but not in the umbilical cord compression lambs (P less than 0.05). Prolonged partial umbilical cord compression produces chronic fetal hypoxaemia and pulmonary arterial hypertension after birth. This may represent a model to study the pathophysiology of persistent pulmonary hypertension syndrome.

The differential effects of leukotriene C4 and D4 on the pulmonary and systemic circulations in newborn lambs

Leukotriene (LT) C4 or D4 may mediate pulmonary hypertension induced by hypoxia. LT have also been isolated from patients with persistent pulmonary hypertension of the newborn syndrome and the adult respiratory distress syndrome. To compare the effects of LTC4 and D4 on the pulmonary and systemic circulations, we performed dose-response studies on spontaneously breathing newborn lambs. To determine whether the hemodynamic effects of LT are mediated through alpha-adrenergic stimulation, some lambs were pretreated with the alpha-adrenergic antagonist phentolamine mesylate before LT injection. These results were compared to the effects of pretreatment with the LT receptor antagonist FPL57231. To determine whether the LT-induced decrease in cardiac output was mediated by the decrease in heart rate, other lambs had their heart rate maintained by left atrial pacing. We found that LTC4 and D4 increased systemic arterial pressure and decreased cardiac output and heart rate. However, LTD4, but not LTC4, increased pulmonary arterial pressure. The hemodynamic effects of LTC4 and LTD4 were completely blocked by FPL57231 but not by phentolamine mesylate. Maintenance of heart rate by left atrial pacing did not alter the LT-induced decrease in cardiac output. We conclude that LTC4 and D4 have similar effects on the systemic circulation. However, LTD4 produces more pulmonary vasoconstriction. Because FPL57231 did block the pulmonary vasoconstriction caused by LT, LT antagonists may be useful in treating patients with pulmonary hypertension.

Red blood cell volume of the pig fetus

A non-radioactive fluorescent excitation analysis technique was used to measure total red blood cell volume in 31 unanaesthetised pig fetuses in utero. Red blood cell volume (y in ml) was closely related (r = 0.94) to fetal bodyweight (x in g): where y = 2.92 + 0.0291x. Average red blood cell volume was 34 +/- 1 ml kg-1 fetal bodyweight. Average estimated (total) blood volume was 117 +/- 3 ml kg-1 fetal bodyweight. It was concluded that this non-radioactive indicator dilution measurement of red blood cell volume is a significant advance over the established 51Cr method, and that measurement of red blood cell volume may be used to estimate fetal bodyweight in utero.