Effect of insulin, prostaglandin E1 and uptake inhibitors on glucose transport in the perfused guinea-pig placenta

The effects of insulin, prostaglandin E1 (PGE1) and uptake inhibitors on unidirectional D-glucose influx at brush border (maternal) and basal (fetal) sides of the guinea-pig syncytotrophoblast were investigated in the intact, perfused guinea-pig placenta by rapid, paired-tracer dilution. Experiments were performed in either an in situ preparation artificially perfused through the umbilical vessels (intact maternal circulation) or in the fully isolated dually-perfused placenta in which both interfaces were studied simultaneously. Kinetic characterization of unidirectional D-glucose influx gave apparent Km values (mean +/- SEM) at maternal and fetal sides of 70 +/- 6 and 87 +/- 16 mM respectively; corresponding Vmax values were 53 +/- 3 and 82 +/- 6 mumol min-1g-1. At the fetal side (singly-perfused placenta) cytochalasin B (50 microM), ethylidene-D-glucose (100 mM) and PGE1 (1 microM) partially inhibited D-glucose uptake whereas cortisol (50 microM) and progesterone (100 microM) had no effect. Abolition of the sodium gradient across the fetal interface did not modulate the kinetics of influx. In the presence of 150 mu units ml-1 insulin (dually-perfused placenta), unidirectional uptake into the trophoblast and transplacental D-[3H]glucose transfer were unaltered. In contrast, prostaglandin E1 (1 microM) markedly reduced the Km and Vmax for D-glucose at both interfaces and the inhibitory effect was reflected in a reduction in specific transplacental D-glucose transfer. Further experiments showed that the isolated placenta releases prostaglandins (PGE; PGF2 alpha) into both circulations. Bilateral insulin perfusion did not affect either lactate release by the placenta or rapid metabolism of D-[14C]glucose to [3H]lactate (usually less than 10% effluent [14C]lactate in 5 min). An asymmetric degradation of exogenous insulin was observed in the dually-perfused placenta: uterine venous samples contained 24 +/- 7 microunits ml-1 immunoreactive insulin when compared to the arterial concentration (151 +/- 3 microU ml-1 perfusate) while no change was measureable in the fetal circulation within the same time period (152 +/- 5 microU ml-1). This asymmetry was confirmed in experiments employing [125I]insulin. These results demonstrate that glucose transport in the intact guinea-pig placenta occurs by a sodium-independent, cytochalasin B-inhibitable system which is insulin-insensitive. Prostaglandin E1 appeared to be a potent transport inhibitor which suggests that prostaglandins may be involved in the 'down' regulation of placental glucose transport in vivo.     

Ultrastructural study of the permeability of the guinea-pig placenta to horseradish peroxidase

Summary Horseradish peroxidase (HRP) was used to study macromolecule permeation into the guinea-pig placenta perfused in situ. When tissue culture medium 199 (TC 199) was used as fetal-side perfusate, the tracer reaction product was found only lining the fetal endothelium. When a longer period of perfusion with HRP in TC 199 was used, a small amount of reaction product was found in the subendothelial space and syncytiotrophoblastic vesicles, but not in maternal lacunae. In similar experiments using a Krebs bicarbonate Ringer (KRBG) as perfusate the tracer was found (i) lining the fetal endothelium, (ii) in the lateral intercellular spaces of the endothelium, (iii) in the subendothelial space, and (iv) in the maternal lacunae.It is therefore evident that the vehicle influenced the permeability of the guinea-pig placenta to horseradish peroxidase. As other studies have shown that perfusion of the fetal side with salt solution increases pore size, the results with TC 199 are regarded as more representative of the situation in the intact animal. It is therefore suggested that the fetal endothelium of the guinea-pig placenta may be largely impermeable to molecules of the size of horseradish peroxidase (4 nm) or larger.     

Abolition of arteriolar dilation but not constriction to histamine in cremaster muscle of eNOS-/- mice

Histamine increases the permeability of capillaries and venules but little is known of its precapillary actions on the control of tissue perfusion. Using gene ablation and pharmacological interventions, we tested whether histamine could increase muscle blood flow through stimulating nitric oxide (NO) release from microvascular endothelium. Vasomotor responses to topical histamine were investigated in second-order arterioles in the superfused cremaster muscle of anesthetized C57BL6 mice and null platelet endothelial cell adhesion molecule-1 (PECAM-1-/-) and null endothelial NO synthase (eNOS-/-) mice aged 8-12 wk. Neither resting (17 +/- 1 microm) nor maximum diameters (36 +/- 2 microm) were different between groups, nor was the constrictor response (approximately 5 +/- 1 microm) to elevating superfusate oxygen from 0 to 21%. For arterioles of C57BL6 and PECAM-1-/- mice, cumulative addition of histamine to the superfusate produced vasodilation (1 nM-1 microM; peak response, 9 +/- 1 microm) and then vasoconstriction (10-100 microM; peak response, 12 +/- 2 microm). In eNOS-/- mice, histamine produced only vasoconstriction. In C57BL6 and PECAM-1-/- mice, vasodilation was abolished with Nomega-nitro-l-arginine (30 microM); in all mice, vasoconstriction was abolished with nifedipine (1 microM). Vasomotor responses were eliminated with pyrilamine (1 microM; H1 receptor antagonist) yet remained intact with cimetidine (1 microM; H2 receptor antagonist). These findings illustrate that the biphasic vasomotor response of mouse cremaster arterioles to histamine is mediated through H1 receptors on endothelium (NO-dependent vasodilation) as well as smooth muscle (Ca2+ entry and constriction). Thus histamine can increase as well as decrease muscle blood flow, according to local concentration. However, when NO production is compromised, only vasoconstriction and flow reduction occur.     

The effect of zinc levels in fetal circulation on zinc clearance across the in situ perfused guinea pig placenta

Although zinc is essential for normal fetal growth and development, little is known about factors that influence its transfer across the placenta. The in situ perfused guinea pig placenta model was used to study the influence of the zinc concentration of fetal circulation on maternofetal placental zinc transfer. A placenta of the anaesthetized sow was perfused (on the fetal side) with a physiological perfusate via the umbilical vessels, with the fetus excluded. The sow was infused intravenously with 65zinc as a tracer of placental Zn clearance, and with antipyrine as an indirect indicator of maternal placental blood flow. Maternal plasma and placental effluent samples collected at intervals were counted for 65zinc by gamma counter, and the absorbance of nitrosated antipyrine was measured at 350 nm. Varying the mean zinc concentration in the perfusate from 0.176 to 1.87 mg/L had no effect on relative zinc clearance calculated as zinc clearance/antipyrine clearance (mean +/- SEM; 0.085 +/- 0.010 vs. 0.114 +/- 0.018; n = 6; p greater than 0.05). The results suggest that short-term changes in fetal zinc status do not influence placental zinc transfer.     

Lysine and alanine transport in the perfused guinea-pig placenta

The characteristics of L-lysine transport were investigated at brush-border (maternal) and basal (fetal) sides of the syncytiotrophoblast in the term guinea-pig placenta artificially perfused either through the umbilical vessels in situ or through both circulations simultaneously. Cellular uptake, efflux and transplacental transfer were determined using a single-circulation paired-tracer dilution technique. Unidirectional L-[3H]lysine uptake (%) (perfusate lysine 50 microM) was high on maternal (M = 87 +/- 1) and fetal (F = 73 +/- 2) sides. L-[3H]Lysine efflux back into the ipsilateral circulation was asymmetrical (F/M ratio = 2.3) and transplacental flux occurred in favour of the fetal circulation. Unidirectional lysine influx kinetics (0.05-8.00 mM) gave Km values of 1.75 +/- 0.70 mM and 0.90 +/- 0.25 mM at maternal and fetal sides, respectively; corresponding Vmax values were 1.95 +/- 0.38 and 0.87 +/- 0.10 mumol.min-1.g-1. At both sides, lysine influx (50 microM) could be inhibited (about 60-80%) by 4 mM L-lysine and L-ornithine and less effectively (about 10-40%) by L-citrulline, L-arginine, D-lysine and L-histidine. At the basal side: (i) lysine influx kinetics were greatly modified in the presence of 10 mM L-alanine (Km = 6.25 +/- 3.27 mM; Vmax = 2.62 +/- 0.94 mumol.min-1.g-1), but unchanged by equimolar L-phenylalanine or L-tryptophan; (ii) in the converse experiments, lysine (10 mM) did not affect the kinetic characteristics for either L-alanine or L-phenylalanine; (iii) L-lysine and L-alanine influx kinetics were not dependent on the sodium gradient; (iv) the inhibition of L-[3H]lysine uptake by 4 mM L-homoserine was partially (60%) Na+-dependent. At the maternal side the kinetic characteristics for alanine influx were highly Na+-dependent, while lysine influx was partially Na+-dependent only at low concentrations (0.05-0.5 mM). Bilateral perfusion with 2,4-dinitrophenol (1 mM) reduced L-[3H]lysine uptake into the trophoblast and abolished transplacental transfer. It is suggested that lysine transport in the guinea-pig placenta is mediated by a specific transport system (y+) for cationic amino-acids. The asymmetry in the degree of sodium-dependency at both trophoblast membranes may in part explain the maternal-to-foetal polarity of placental amino-acid transfer in vivo.     

H1 and H2 histamine actions on lung vessels; their relevance to hypoxic vasoconstriction.

Pulmonary vasomotor actions of histamine and the possible relationship of histamine to hypoxic pulmonary vasconstriction were studied in anaesthetized cats with one lobe of lung perfused at constant flow and in isolated perfused rat and ferret lungs. In the cat histamine caused dilatation, biphasic responses and constriction with increasing doses. Histamine induced dilatation was better demonstrated during hypoxic vasoconstriction and was reduced by an H2 histamine antagonist; constriction with histamine was abolished by an H1 antagonist. Histamine also caused both vasodilatation and vasoconstriction in ferret lungs. A mast cell stabilizing agent had no effect on hypoxic pulmonary vasoconstriction in cats or rats. This response was unaffected in cats but greatly reduced in rats and ferrets by cyproheptadine, a combined histamine and 5-hydroxy-tryptamine inhibitor. It was unaffected in cats but abolished in ferrets an H1 histamine inhibitor. It was again unaffected in cats but greatly reduced in rats and ferrets by an H2 histamine inhibitor. These species differences may reflect differences in mechanism but more probably reflect non-specific effects of the inhibitors in certain circumstances. However, when drugs nearly abolished hypoxic vasoconstriction, ATP still caused vasoconstriction.     

Transfer of morphine across the human placenta and its interaction with naloxone

The purpose of this investigation was to measure the transfer rate and clearance of morphine across the placenta with and without naloxone. Term human placental cotyledons were perfused in vitro. The placenta was perfused with 50 ng/mL of morphine in the absence (n=4) and presence (n=5) of 100 ng/mL of naloxone. Maternal and fetal samples were collected. Student's t-test or one-way repeated measures ANOVA were used for all comparisons. The maternal-to-fetal morphine transfer rate was 0.73+/-0.44 ng/mL/min in the morphine and 0.69+/-0.26 ng/mL/min in the morphine-naloxone experiments (p=0.89). The clearance of morphine was 0.89+/-0.39 mL/min without naloxone and 0.87+/-0.27 mL/min with naloxone (p=0.92). Final morphine concentrations in the morphine experiments were 9.78+/-6.17 ng/mL (maternal) and 3.43+/-2.14 ng/mL (fetal) and 10.04+/-3.89 ng/mL (maternal) and 4.16+/-1.64 ng/mL (fetal) in the morphine-naloxone experiments. Morphine readily crosses the term human placenta. Naloxone does not alter placental transfer or clearance of morphine, suggesting that transfer across the placental barrier is not altered by changes in vascular resistance. Placental retention of morphine prolongs fetal exposure to morphine.     

Effects of spantide on guinea pig coronary resistance vessels.

Effects of spantide ([D-Arg1,D-Trp7,9,Leu11]substance P) on coronary resistance vessels were studied in isolated guinea pig hearts perfused at constant rate with isotonic buffer containing 20 or 40 mM KCl. Spantide (1 microM) caused a 20-fold rightward shift of the substance P (SP) dose-response curve for vasodilation with no change in maximum (KB = 5.3 x 10(-8) M). Bolus injections of 0.25 to 250 pmol spantide had no effect, but higher doses caused a brief vasodilation followed by a larger, more prolonged vasoconstriction. Histamine produced similar changes in perfusion pressure. Antihistamines (H1 and H2) reduced or blocked responses to spantide and histamine. These findings indicate spantide is a competitive antagonist to SP in guinea pig coronary resistance vessels. In addition, high doses of spantide can cause prominent vascular effects which are mediated by histamine.     

Dopamine production by the isolated perfused rat kidney

We used isolated perfused rat kidneys to examine dopamine (DA) production and its relation to renal function. Both innervated and chronically surgically denervated kidneys perfused with a solution containing neither albumin nor tyrosine, excreted 0.2 +/- 0.1 ng DA X min-1 X g wet weight-1 during the 10-min collection period between 30 and 40 min after starting perfusion. When perfused with 6.7% albumin, without tyrosine, innervated kidneys excreted 1.0 +/- 0.06 ng DA X min-1 X g-1 and denervated kidneys excreted 1.0 +/- 0.07 DA X min-1 X g-1. When 0.03 mM tyrosine was included in the albumin perfusate, innervated kidneys excreted 1.2 +/- 0.1 ng DA X min-1 X g-1 (p less than 0.1). Under these conditions DA excretion continued for at least 100 min at which time it was 0.6 ng X min-1 X g-1 and 86 ng/g kidney weight had been excreted. Denervated kidneys perfused with albumin + tyrosine excreted 0.9 +/- 0.13 ng DA X min-1 X g-1. Renal stores of free DA, conjugated DA, and dihydroxyphenylalanine (DOPA) could have provided at the most 30 ng/g of DA. Carbidopa inhibited DA excretion completely. DA excretion did not correlate with renal vascular resistance, inulin clearance, or fractional sodium excretion. In summary, nonneural tissue in isolated perfused kidneys produced DA at the same rate as denervated kidneys in vivo. Less than one-third of the DA produced by isolated kidneys could have come from intrarenal stores of DOPA, free DA, and conjugated DA; the rest was synthesized from unknown precursors.(ABSTRACT TRUNCATED AT 250 WORDS)     

Rate of disappearance of glycerol from plasma of fetal and newborn sheep

The disappearance of glycerol from plasma was studied after a single intravenous injection to estimate its volume of distribution (Vdist), plasma clearance rate, and rate constant for irreversible loss (kd). Studies were repeated before and after birth of the lamb to test whether loss of the placenta could account for rapidly increasing plasma concentrations in the newborn. The disappearance of glycerol was closely described by a double-exponential model in each instance. In fetal sheep Vdist averaged 0.41 +/- 0.15 (SD) 1/kg fetal wt (n = 15). This volume decreased to 0.33 +/- 0.11 l/kg (n = 8) soon after functionally removing the placenta (by snaring the umbilical cord and maintaining the fetus with intrauterine ventilation), but the change was not significant. In newborn lambs 1-3 days of age, Vdist averaged 0.45 +/- 0.11 l/kg (n = 5, NS). Plasma clearance rate also did not change significantly, averaging 7.9 +/- 2.9, 7.9 +/- 3.8, and 9.0 +/- 5.9 ml.min-1.kg-1 in the fetus, after simulated birth, and in the newborn lamb, respectively, kd also was not altered measurably and averaged 0.020 +/- 0.006, 0.024 +/- 0.007, and 0.019 +/- 0.007 min-1 during the same time periods. Similar results were obtained by using three widely different amounts of infused glycerol. The results indicate that removal of glycerol does not depend on placental function to an appreciable extent. It is concluded that plasma glycerol concentration reflects principally glycerol turnover and, hence, lipolysis before and after birth.     

Pressure-dependent vasoactive effects of histamine in the coronary circulation

Twenty-one isolated, perfused, spontaneously rhythmic guinea pig hearts (Langendorff preparation) were used to investigate the effects of coronary perfusion pressure (CPP) on the coronary vasoactive response to a continuous infusion of histamine. Heart rate (HR), coronary perfusate flow (CPF), left ventricular pressure, dp/dtmax, oxygen extraction, and myocardial oxygen consumption (MVO2) were measured at constant CPP of 40 (n = 9), 53 (n = 6), and 65 cm H2O (n = 6) in the absence and presence of continuous intracoronary infusion of histamine [0.9 +/- 0.2 microgram/(min X g)]. At 40 cm H2O histamine caused significant coronary vasodilation. At 65 cm H2O histamine caused significant coronary vasoconstriction. At an intermediate pressure of 53 cm H2O histamine had no effect on CPF. At all three pressures HR, left ventricular pressure, dp/dtmax, and oxygen extraction increased significantly in response to histamine. MVO2 was unchanged by histamine at 65 cm H2O (flow was reduced but extraction increased. MVO2 increased modestly but significantly at 53 cm H2O (12% increase; flow unchanged but extraction increased), and increased prominently at 40 cm H2O (50% increase; flow and extraction increased). We conclude that the coronary vascular effects of continuously infused histamine are dependent on the preexisting, steady-state level of CPP in the isolated perfused guinea pig heart.     

Participation of mast cell 5-hydroxytryptamine in the vasoconstrictor effect of neurotensin in the rat perfused hindquarter

Neurotensin (NT) (1 X 10(-8) - 1.5 X 10(-6) g ml-1) caused a transient, dose-dependent increase in perfusion pressure in the rat perfused hindquarter. The vasoconstrictor effect of NT was associated with a short-lived, dose-dependent release of histamine and 5-hydroxytryptamine (5-HT) in the hindquarter effluent. Compound 48/80, a classical mast cell secretagogue, also elicited a vasoconstrictor effect in, and release of histamine from, the rat hindquarter. The vasoconstrictor effect and the release of histamine and 5-HT evoked by NT were much smaller in hindquarters derived from rats pretreated with compound 48/80 for 4 days to cause mast cell depletion than in hindquarters derived from control rats. The mast cell inhibitor cromoglycate (4 mg ml-1) inhibited by about 50% the histamine releasing effect and vasoconstriction produced by the lowest concentrations of NT utilized. The histamine releasing effect of compound 48/80 was more sensitive to blockade by cromoglycate than that of NT. The steroidal antiinflammatory and antiallergic drug dexamethasone did not affect the histamine and 5-HT releasing effect of NT. The vasoconstrictor effects of NT, compound 48/80 and 5-HT were markedly reduced by the 5-HT receptor antagonist methysergide (1 X 10(-7) g ml-1). Histamine (1 X 10(-6) - 10(-4) g ml-1) evoked a decrease in perfusion pressure in hindquarters pre-exposed to noradrenaline. The results suggest the participation of mast cell 5-HT in the vasoconstrictor effect of NT in the rat perfused hindquarter.     

Fluid filtration coefficient of isolated goat lungs was unchanged by endotoxin

The Starling fluid filtration coefficient (Kf) of blood-perfused excised goat lungs was examined before and after infusion of Escherichia coli endotoxin. Kf was calculated from rate of weight gain as described by Drake et al. [Am. J. Physiol. 234 (Heart Circ. Physiol. 3): H266-H274, 1978]. These calculations were made twice during base line and then at hourly intervals for 5 h after infusion of 5 mg (approximately 250 micrograms/kg) of E. coli endotoxin or after injection of oleic acid (47 microliter/kg). All lungs were perfused at constant arterial and venous pressure under zone 3 conditions. Base-line Kf averaged 27 +/- 10 and 20 +/- 4 (SD) microliter.min-1.cmH2O-1.g dry wt-1 for endotoxin and oleic acid groups, respectively. It was unchanged in the endotoxin group throughout the experiment but approximately doubled in the oleic acid lungs. Pulmonary arterial and venous pressures were not changed significantly during the course of these experiments in either group. Lung wet-to-dry weight ratios of these lungs were 5.6 +/- 0.6 and 6.1 +/- 0.5 ml/g for the endotoxin and oleic acid groups, respectively. This compares with 4.6 +/- 0.5 ml/g for normal, freshly excised but not perfused goat lungs. The small change in lung water and unchanged pulmonary pressures after both endotoxin and oleic acid suggest that lung injury was minimal. We conclude that 1) endotoxin does not cause a direct injury to the endothelium of isolated lungs during the first 5 h of perfusion, and 2) neutrophils are not sufficient to cause increased Kf after endotoxin infusion in this preparation.     

Priming interactions between platelet activating factor and histamine in the in vivo microcirculation.

To elucidate whether priming exists between platelet-activating factor (PAF) and histamine in the microcirculation, we measured the clearance of FITC-dextran 150 in response to the topical applications of substimulatory concentrations of PAF and histamine. Maximal priming by PAF was observed when a 5-min interval separated the applications of 10(-9) M PAF and 10(-6) M histamine. The mean (+/- SEM) clearance resulting from this sequence of agonist administration was 7529 +/- 659 nl.2 h-1.g-1, representing a 4.5-fold enhancement in FITC-dextran 150 clearance compared with that evoked by 10(-6) M histamine alone (1664 +/- 397 nl.2 h-1.g-1). Lowering the PAF priming dose to 10(-11) M, or reversing the order of agonist addition to the microcirculation, resulted in diminished but significant responses of 3545 +/- 1143 and 4467 +/- 1170 nl.2 hr-1.g-1, respectively. Coapplication of PAF and histamine or increasing the time interval between the agonists to 15 min greatly reduced the responses to 1906 +/- 678 and 2770 +/- 837, respectively. The PAF receptor antagonist WEB 2086 (2 mg/kg i.v.), the H1 blocker pyrilamine (10 mg/kg i.v.), and leukocyte depletion with cyclophosphamide (150 mg/kg i.p.) completely abolished the PAF priming effect. In addition, the 5-lipoxygenase inhibitor RG 5901 (1 or 10 mg/kg i.v.) produced a two-thirds attenuation in PAF priming. We conclude that 1) PAF has the ability to prime the in vivo microvascular actions of histamine in both a concentration and time-dependent fashion; 2) this primed response is receptor mediated; and 3) histamine can prime the microcirculation for enhanced responses to PAF. Our data also demonstrate that leukocytes and the release of leukotrienes participate in PAF priming.     

Bronchial vasodilation by histamine in sheep: characterization of receptor subtype.

Histamine has been shown to mediate features of pulmonary allergic reactions including increased tracheobronchial blood flow. To determine whether the increase in blood flow was due to stimulation of H1- or H2-histamine receptors, we gave histamine base (0.1 micrograms/kg iv) or histamine dihydrochloride as an aerosol (10 breaths of 0.5% "low dose" or 5% "high dose") before and after H1- or H2-receptor antagonists. Blood velocity in the common bronchial branch of the bronchoesophageal artery (Vbr) was continuously measured using a chronically implanted Doppler flow probe. Pretreatment with H2-receptor antagonists cimetidine, ranitidine, or metiamide did not affect the increase in Vbr induced by intravenous histamine [106 +/- 45% (SD)]. Addition of the H1-receptor antagonists diphenhydramine or chlorpheniramine, however, reduced the Vbr response to 16 +/- 22, 21 +/- 28, 23 +/- 23, and 37 +/- 32% of the unblocked responses (P less than 0.05) when intravenous histamine was given at 3, 10, 20, and 30 min, respectively, after the H1 antagonist. At 40, 50, and 60 min the H1-receptor blockade appeared to attenuate, but subsequent continuous infusion of chlorpheniramine (2 mg.kg-1.min-1) then blocked the histamine response for 60 min. Low-dose histamine aerosol did not change mean arterial or pulmonary arterial pressures, cardiac output, or arterial blood gases but increased Vbr transiently from 15.2 +/- 3.4 to 37.6 +/- 8.4 (SE) cm/s. After chlorpheniramine, the Vbr response to histamine, 16.3 +/- 2.2 to 22.6 +/- 3.6 cm/s, was significantly reduced (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Uptake and intracellular routing of peroxidase-conjugated immunoglobulin-G by the perfused human placenta

Summary Selected lobules of term human placenta were extracorporeally perfused and human immunoglobulin-G complexed to horseradish peroxidase (IgG-HRP) was added to the maternal perfusate. After different durations of perfusion IgG-HRP was visualised by use of diamino-benzidine cytochemistry. Within the first 10 min of perfusion IgG-HRP was found bound to microvilli and coated pits of the syncytiotrophoblast; internalisation into coated vesicles and tubulo-vesicular bodies was also observed. Subsequently, IgG-HRP was found in multivesicular bodies and by 30 min appeared in basal vesicles, the frequency of the latter event increasing with time. No routing of IgG-HRP into Golgi regions or lysosomes could be detected. By 60 min IgG-HRP was found in a few caveolae of fetal endothelium of both terminal and intermediate villi. IgG-HRP was not found in intercellular clefts of the endothelium. The pattern of uptake and routing observed suggests a receptor-mediated transcytosis of IgG-HRP across the syncytiotrophoblast and a transcellular pathway through the endothelium.     

Plasma and urinary clearance rates of atrial natriuretic factor during ontogeny in sheep

The present study was designed to determine the plasma clearance rate of atrial natriuretic factor (ANF) during development in chronically-instrumented fetal, newborn and adult non-pregnant sheep. To determine the contribution of the kidney in the metabolism of ANF, urinary clearance of ANF was also measured. Intravenous infusion of ANF (0.025 and 0.1 microgram.min-1.kg-1) produced a significant decrease in mean arterial blood pressure in newborn lambs and in adult non-pregnant sheep. Estimated plasma ANF clearance rate for the 0.025 and 0.1 microgram.min-1.kg-1 ANF infusion rate were respectively 177 +/- 55 and 155 +/- 34 ml.min-1.kg-1 in fetuses, 138 +/- 26 and 97 +/- 13 ml.min-1.kg-1 in newborn lambs and, 148 +/- 33 and 103 +/- 25 ml.min-1.kg-1 in adult nonpregnant ewes. Fetal, newborn and adult ANF plasma clearance rates during high ANF infusion rate (0.1 microgram.min-1.kg-1) were not significantly different. Low or high ANF infusion rate was not associated with significant changes in urinary ANF concentration or urinary ANF excretion rate. Taken together, the present study demonstrates that ANF plasma clearance rate is similar in fetal, newborn and adult non-pregnant sheep and that the excretory function of the kidney contributes only minimally to ANF plasma clearance rate.     

Temporal response of the fetal pulmonary circulation to pharmacologic vasodilators

To determine the temporal response of the fetal pulmonary circulation to pharmacologic vasodilators and to assess vasoreactivity following vasodilation, we infused either acetylcholine, histamine, or bradykinin directly into the left pulmonary artery of 21 chronically prepared fetal sheep. Blood flow (Q) to the left lung was measured by electromagnetic flow transducer. Left pulmonary artery infusion of acetylcholine at 1.5 micrograms.min-1 for 2 hr produced an increase in Q from 59 +/- 8 ml.min-1 to a peak of 113 +/- 10 ml.min-1 at 20 min into the infusion (P less than 0.001). After the peak at 20 min, Q steadily declined toward baseline to 66 +/- 7 ml.min-1 at the end of the 2-hr infusion period (P less than 0.01). Q in the 1/2-hr period following infusion was significantly less than the baseline period (47 +/- 6; P less than 0.04) with no change in pulmonary artery pressure. Similar patterns were seen with 2-hr infusions of histamine (150 ng.min-1) and bradykinin (100 ng.min-1). After a 2-hr infusion of one of the agents, a repeat infusion with that agent or a different one resulted in a diminished response. We conclude that fetal pulmonary vasodilation in response to local infusion of acetylcholine, histamine, or bradykinin is not sustained over a 2-hr period, and that following 2-hr exposure to vasodilators, pulmonary vascular resistance is increased and pulmonary vasoreactivity to pharmacologic vasodilators is decreased.     

Lipopolysaccharide differently affects prostaglandin E2 levels in fetal and maternal compartments of perfused human term placenta

The aim of the present study was to examine the effect of lipopolysaccharide (LPS) on the levels of prostaglandin E(2) (PGE(2)) in the perfusates of the fetal and the maternal compartments of perfused human term placental tissue. Term placentas were perfused for 10h in the absence [control, (n=4)] and presence of LPS [LPS=1 microg/kg perfused placental tissue, (n=4)] in the maternal reservoir. Perfusate samples from the fetal and the maternal circulations were collected every 30 min and examined for PGE(2) levels by radio-immunoassay. PGE(2) levels in the fetal circulation were gradually increased reaching significant peak value of 479+/-159 pg/ml, as compared to PGE(2) levels in the maternal circulation (140+/-146 pg/ml) (p<0.05). After 10 hours of perfusion with control medium, PGE(2) levels in the maternal circulation (347+/-144 pg/ml) were significantly higher as compared to the fetal circulation (150+/-57 pg/ml) (p<0.05). In presence of LPS, PGE(2) levels in the fetal circulation increased reaching a peak value of 1028+/-663 pg/ml after 240 min of perfusion. The levels of PGE(2) in the control group after 240 min of perfusion were significantly lower (156+/-77 pg/ml) (p<0.05). No significant differences were detected in the levels of PGE(2) in the perfusate of the maternal compartment in presence of LPS, as compared to control. Our results suggest that the placenta may play an important role in maintaining high levels of PGE(2) in the fetal circulation and low PGE(2) levels in the maternal circulation during normal pregnancy. Moreover, placental PGE(2) release into the fetal and the maternal circulations may be differently affected in presence of intra-uterine infection/inflammation.     

Lack of effect on human lipoprotein-triacylglycerol on the function of perfused rat kidney

We determined whether addition of human lipoprotein-TG to the perfusate for the isolated rat kidney would increase net Na+ reabsorption or maintain renal tissue K+ content. Rat kidneys (n = 6) were perfused for 75 min with a perfusate containing 6 g% of substrate-free albumin in Krebs-Ringer bicarbonate and a mixture of human chylomicrons and very low density lipoproteins (human lipoprotein-triacylglycerol (HL-TG]. Control kidneys (n = 6) were perfused in the substrate-limited state, i.e., without any exogenous substrates added to the perfusate. Means (n = 6) for function of control kidneys were GFR = 808 +/- 50 microliter g-1 X min-1; %T-Na+ = 63.3 +/- 1.3%. A significant loss of tissue K+ occurred: tissue K+ remaining after 75 min of perfusion = 79.1 +/- 1.9%. Although kidney tissue contains lipoprotein lipase, HL-TG (n = 6) did not increase %Na+ reabsorption (64.3 +/- 2.6%) or maintain tissue K+ content (80.6 +/- 2.0%). Therefore, the TG might have been hydrolyzed and taken up for biosynthesis, the rat kidney lipoprotein lipase might have been inactive, or the rat kidney might not use lipoprotein-TG for biosynthesis or oxidation.