Dietary nucleotide supplementation raises erythrocyte 2, 3-diphosphoglycerate concentration in neonatal rats.

The present study was designed to test if dietary intake of nucleotides increases erythrocyte 2,3-diphosphoglycerate (2,3-DPG) in neonatal rats. To this end, rat pups were fed a nucleotide-supplemented formula (S, n = 14) from d 9 until d 16 after birth. The results were compared with those obtained from a group of breast-fed pups (C, n = 14) and a group of pups artificially fed with nucleotide-free formula (NS, n = 14). Neonatal weight, 2,3-DPG concentration, hematocrit (Hct) and hemoglobin concentration (Hb) were determined before the experiment (d 9) and after 7 d of treatment (d 16). In all groups, 2,3-DPG concentration was greater at d 16 than d 9, and the increase was greater in the S group than in the NS group. Alterations in neonatal weight, Hct and Hb concentration did not differ among the groups. On d 16 the 2, 3-DPG/Hb ratio, reflecting the affinity of hemoglobin for oxygen, was significantly higher in the C and S groups than in the NS group. We conclude that in neonatal rats, dietary nucleotides increase erythrocyte 2,3-DPG concentration. Studies need to be conducted in humans to assess the effect of this increase on both neonatal peripheral hemodynamics and metabolism in this species.

Mechanism of volume adaptation in the awake early pregnant rat.

The objective of the present study was to determine whether the increase in plasma volume (PV) during pregnancy is established by fluid retention or by a shift within the extracellular fluid volume (ECFV) from the interstitium toward the intravascular compartment. To this end, we simultaneously, measured total body water, (TBW), ECFV, and PV together with the hematocrit (Hct) and plasma osmolality 4, 8, and 12 days postsurgery in chronically instrumented pregnant (P) and nonpregnant (NP) rats. The P rats were instrumented with a catheter in the femoral artery on day 1 postconception. In the NP group, neither TBW nor ECFV and PV had changed consistently on days 8 and 12 postsurgery relative to day 4. In contrast, in the P animals, TBW, ECFV, and PV had increased by 16, 24, and 20%, respectively, by day 12 relative to day 4. To evaluate whether PV had increased in concert with an overall rise in TBW or as a result of a fluid shift at the cost of the interstitial fluid volume, we calculated the relative size of each fluid compartment on three consecutive measurement sessions. In the NP group, TBW, presented as percentage of maternal weight (%MW) as well as ECFV (%TBW) and PV (%ECFV) had not changed consistently throughout the measurement period. In the P animals, TBW (%MW) was slightly higher on day 12 compared with day 4, but ECFV (%TBW) and PV (%ECFV) had not changed significantly. Finally, in the NP group, Hct had not changed, whereas, in the P animals, Hct was 10% lower on days 8 and 12 compared with day 4. Plasma osmolality did not change consistently in either group during the course of the experimental period. The gradual synchronous increase in all fluid compartments, without consistent change in their relative distribution, suggests that, in normal rat pregnancy, PV expansion is primarily achieved by fluid retention rather than by a redistribution of the ECFV.

The extent of trophoblast invasion in the preplacental vasculature of the guinea-pig.

Pregnancy-induced structural changes in spiral arteries seem to be a prerequisite for successful fetal outcome in humans. It is unknown whether these changes also occur in other preplacental vessels (radial and arcuate arteries) in normal pregnancies. Since the radial and arcuate arteries need to dilate in order to accommodate the increase in placental blood flow during pregnancy, it is expected that they are also invaded by trophoblast and respond with structural changes. The objective of the present study was to evaluate the extent of trophoblast invasion in the guinea-pig preplacental vasculature and its effect on the vascular structure of mesometrial, myometrial and arcade arteries. Under general anaesthesia the vascular system of non- (n = 4), mid- (n = 4) and late- (n = 8) pregnant guinea-pigs was fixed by immersion or perfusion. Cross-sections of immersion-fixed mesometrial and arcade arteries were stained with toluidine blue. Cross-sections of perfusion-fixed mesometrial, myometrial and arcade arteries were stained with haematoxylin-eosin, Elastica van Gieson staining and antibodies against alpha-smooth-muscle-actin (ASMA), cytokeratin and factor VIII, to detect vascular smooth muscle, trophoblastic, and endothelial cells, respectively. In addition, the external and internal vascular circumference of sections from perfusion-fixed tissue was determined. All cross-sections were evaluated by light microscopy. In the course of pregnancy, progressive endothelial swelling, disappearance of the elastic lamina interna and disarrangement of the tunica media were observed in the myometrial and throughout the mesometrial arteries up to the junction with the arcade arteries. These changes coincided the migration of keratin-positive staining giant cells. It is concluded that in normal guinea-pig pregnancy, structural changes occur in the entire mesometrial artery and at least a part of the myometrial artery, although such changes were not seen in the arcade artery.

Hemodynamic changes in pseudopregnancy in chronically instrumented conscious rats.

It is unclear whether the trophoblast is needed for the normal early-pregnancy hemodynamic adaptation. In this study we tested the hypothesis that the presence of trophoblast is not essential for the initial hemodynamic adaptation in pregnancy. To this end, we measured systemic hemodynamics in conscious pseudopregnant rats and compared the results with those obtained in a concomitantly studied control group of virgin rats as well as with a previously studied group of pregnant rats. The rats were studied daily from day 4 postmating until day 10 and on days 12, 14, 18, and 20. In pseudopregnant rats, cardiac output (CO) increased from day 5 onward, to 14 +/- 3% above the initial value by day 8. This rise in CO was entirely accomplished by a rise in stroke volume (21 +/- 4% by day 8). Mean arterial pressure did not change appreciably. Therefore, total peripheral resistance also decreased by 21 +/- 4% by day 8. Meanwhile, peak flow, aortic flow acceleration, and stroke work, indicators of myocardial performance, had increased, and the hematocrit had decreased (15 +/- 1% by day 8). Between day 10 and day 20 the hemodynamic parameters gradually returned to baseline. We conclude that systemic hemodynamic changes do take place in pseudopregnancy. They consist of a rise in CO by a rise in stroke volume, an increase in myocardial performance, and hemodilution. The observed changes closely resemble those in early normal pregnancy. Therefore, we accept our hypothesis that trophoblast is not essential for the initial hemodynamic changes in rat pregnancy.

Hemodynamic changes in early pregnancy in chronically instrumented, conscious rats.

To explore the onset of and the interrelationship between maternal hemodynamic changes in pregnancy, serial hemodynamic measurements were performed in chronically instrumented, conscious rats using electromagnetic flow probes around the ascending aorta and arterial catheters. The rats were studied daily from day 4 to day 12 and on days 14, 18, and 20 of pregnancy. Nonpregnant (NP) rats matched for age and days postsurgery served as controls. In the pregnant (P) group, the hematocrit started to decrease by postconceptional day 6 (day of implantation) to reach a value of 9 +/- 3% below the initial level by day 8. In these 2 days, cardiac output (CO) increased by 9 +/- 4%, as a result of a rise in stroke volume (SV). No changes in mean arterial pressure were observed. In both groups, heart rate (HR) had decreased by day 7. Aortic flow acceleration and peak aortic flow, indicators of myocardial contractility, increased from day 10 on only in the P group. In this context, it should be emphasized that the results of this study do not allow differentiation between the contractile properties of the cardiac muscle and the contractile changes as a result of the altered preload and afterload. By days 12 and 18, CO had increased by 20 +/- 5 and 29 +/- 9%, respectively, above the initial value and by 25 and 40%, respectively, above the value observed in the NP group. The rise in CO after day 14 was accomplished by a concomitant increase in HR and SV and was accompanied by a further increase in myocardial performance. We conclude that hemodynamic changes can already be identified by day 8 of rat pregnancy, 2 days after implantation. The rise in CO in early pregnancy results from a selective increase in SV and is accompanied by a rise in myocardial performance.

Lack of positive correlation between placental blood flow and mean arterial pressure in the non-anaesthetised guinea pig near term; an indication for autoregulation?

The objective of the present study was to evaluate whether placental blood flow (PBF) decreases or increases, in response to a fall or rise in mean arterial pressure (MAP), respectively, in an unanaesthetised animal model with a haemochorial placenta. Such a response would support the absence of autoregulation of placental blood flow for changes in mean arterial pressure. To this end, 31 late-pregnant guinea pigs were subjected to isovolemic haemodilution, a sham procedure or isovolemic haemoconcentration, after adequate recovery from instrumentation. The percentage change from baseline in PBF (delta PBF, %), was compared between animals with a fall in MAP, in response to haemodilution or the sham procedure (MAP-fall, n = 8, mean delta MAP -11 +/- 7%) and those with a rise in MAP, following haemoconcentration (MAP-rise, n = 10, mean delta MAP +15 +/- 8%). In addition, the percentage change in the blood flow to the myocardium, gastrointestinal tract, adrenals, kidneys, brain, skin, carcass and myometrium was compared between the MAP-fall and the MAP-rise group. The direction of the change in PBF did not differ between the MAP-fall and the MAP-rise group. In this respect, the distribution of delta PBF over the two groups was comparable with that observed for the myocardium, gastrointestinal tract, adrenals, skin, carcass and myometrium. The blood flow to the kidneys and the brain varied in response to the change in haematocrit. The results of this study show that PBF varies independently from MAP. This observation supports the idea that the blood flow to the labyrinthine placenta of the awake and healthy guinea pig near term may be autoregulated for hydrostatic inflow pressure, at least over the spectrum of arterial pressures observed in the present study.

The effect of labetalol on maternal haemodynamics and placental perfusion in awake near term guinea pigs.

The effect of labetalol (20 micrograms/kg/min) on maternal haemodynamics in general, and absolute placental perfusion in particular, was studied in eight chronically instrumented hypertensive guinea pigs near term. One day before drug testing, all experimental animals were subjected to haemoconcentration (haematocrit was gradually raised from 35.9 +/- 2.9 to 49.4 +/- 5.6 vol%, mean +/- S.D.) to establish a prolonged and stable state of hypertension. This procedure increased mean arterial pressure from 59.7 +/- 7.2 to 70.3 +/- 8.6 mmHg, and was paralleled by mild foreseeable systemic haemodynamic effects (redistribution of cardiac output away from intestines and brain), without consistent changes in the maternal placental blood flow. The hypotensive effect of labetalol was paralleled by a selective reduction in placental perfusion as reflected by a consistent fall in weight-specific cardiac output fraction (from 55.5 +/- 26.6 to 40.9 +/- 12.5%/100 g, P < 0.05) and blood flow (from 155 +/- 76 to 112 +/- 44 ml/min/100 g, P < 0.05) to the placentas. The concomitant placental resistance had increased consistently from 0.55 +/- 0.26 to 0.62 +/- 0.32 mmHg.min.100 g/ml, P < 0.05. We conclude that in awake late-pregnant hypertensive guinea pigs, labetalol reduces uteroplacental blood flow selectively. We speculate that the latter selective effect is secondary to the fall in blood pressure.

Increased red cell aggregation does not reduce uteroplacental blood flow in the awake, hemoconcentrated, late-pregnant guinea pig.

The effect of increased red blood cell aggregation on uteroplacental blood flow was studied in 11 awake, late-pregnant guinea pigs. The aggregation of the red cells was increased by administering high molecular weight dextran (HMWD) to the previously hemoconcentrated animal. The purpose of the hemoconcentration before HMWD was 1) to use a preeclampsia model in which the hemorheology may be impaired because of the combined effect of polycythemia, an increased red cell aggregation, and an increased plasma viscosity and 2) to potentiate the aggregation-increasing effect of HMWD. Relative to the pre-HMWD condition, arterial blood pressure and systemic vascular resistance increased by 10 and 26%, respectively. The cardiac output fraction shunted across the systemic circulation and the arterial hematocrit decreased by 30 and 4%, respectively. Neither cardiac output nor the weighted organ flows, including those to the placentas, changed in response to the rise in red cell aggregation. We conclude that an imposed increase in red cell aggregation has no appreciable effect on uteroplacental blood flow in the awake and healthy late-pregnant guinea pig. These data do not exclude the possibility that increased red blood cell aggregation potentiates the negative effects on uteroplacental blood flow, e.g. in pregnancy-induced hypertension or preeclampsia, where the placenta is not only marginally perfused but also frequently damaged histologically.

Hemodynamic response to volume stress in awake late-pregnant and nonpregnant rats.

The present study was designed to determine whether the often observed gestational rise in blood volume alters the hemodynamic response to volume stress relative to the nonpregnant state. Late-pregnant and nonpregnant Wistar rats, prepared with an electromagnetic flow probe around the ascending aorta and/or intravascular catheters were used for this study. One of the following sets of measurements were performed either before and after volume loading or before and after volume depletion (24 h thirst): 1) continuous monitoring of cardiac output, blood pressure, heart rate, and fluid balance (only during volume loading); 2) measurement of cardiac output and regional blood flows (microspheres); and 3) measurement of the inferior vena cava diameter (x-ray). Both rapid (bolus) and slow volume loading (infusion) led to a rise in cardiac output. The generated surplus in cardiac output was distributed to the kidneys, skeletal tissues, and intestines (only in nonpregnant rats), and was paralleled in the pregnant rats by a consistent fall in placental blood flow. Slow volume depletion had neither a consistent effect on cardiac output nor on its distribution, with even a preserved maturational rise in placental blood flow during the 24 h of thirst. Slow volume loading and depletion led to an increase and decrease of the caliber of the inferior vena cava, respectively. The nonnuterine hemodynamic response to all forms of volume stress had not changed in pregnancy.(ABSTRACT TRUNCATED AT 250 WORDS)

Nondeformable red blood cells do not interfere with uteroplacental blood flow in the awake, late-pregnant guinea pig.

The fractional entrapment of rigidified [relative to control (labeled)] red cells after the intravascular bolus injection of a cocktail of these cells, and the concomitantly induced changes in cardiac output and its distribution (microspheres) were studied in 14 awake, late-pregnant guinea pigs. In a preceding validation study in eight nonpregnant guinea pigs, it was demonstrated that with this technique reproducible data could be generated on the fractional entrapment of rigidified red cells in all organs in this species except for lungs, liver, and spleen. In response to a bolus injection with rigidified and control red cells, only the brain showed preferential entrapment of rigidified red cells, together with a small but consistent increase in blood flow. In other organs (lungs, liver, and spleen excluded), neither preferential entrapment of rigidified red blood cells nor a consistent change in blood flow could be demonstrated. The results of our study suggest that circulating nondeformable red cells have no measurable adverse effect on the perfusion of the nondiseased hemochorial placenta in the awake, late-pregnant guinea pig. This does not exclude the possibility that rigidified red cells may increase the resistance to flow in a microcirculation that has been pathologically changed by some underlying disease.

The effect of volume expansion on placental blood flow in awake hypovolemic rats in late pregnancy.

Symptomatic hypovolemia in preeclampsia is often treated by volume expansion. However, the effect of this treatment on placental blood flow is unclear. In the present study the hypothesis was tested that slow volume expansion, imposed on volume-depleted rats, does not compromise placental blood flow. Mild hypovolemia was induced in rats in late pregnancy by 24 hours' thirsting. The resulting gradual dehydration was associated with a 7% reduction in blood volume. These rats were then subjected to blood volume expansion by a continuous infusion with a plasma substitute. Volume expansion increased blood volume by 32% and cardiac output by 73%. The extra cardiac output was distributed to kidneys, carcass, and portal bed. Placental blood flow decreased by 31%. The pattern of response was comparable to the one previously observed in normovolemic rats. However, the magnitude of the changes was larger, probably associated with a delayed or impaired diuretic response. These data suggest that volume expansion therapy in mildly hypovolemic pregnant rats elicits an exaggerated hemodynamic response as compared with normovolemic rats, including placental compromise.

Systemic leakage of 15 micron radioactive microspheres over a period of 24 hours, in awake late-pregnant guinea pigs.

The present study was designed to determine the reliability of regional blood flow measurements with 15 microns radioactive microspheres, when 24 h have elapsed between reference sampling and sacrifice. The study was performed in 12 chronically-instrumented late-pregnant guinea pigs. The fraction of microspheres recovered from the lungs was consistently higher, by about 2% of the cardiac output after such a 24-h period, as compared to microsphere experiments performed immediately prior to sacrifice. This finding suggests dislodgement of radioactive particles from the systemic circulation between the time of completion of reference sampling and the subsequent 24 h. No correlation could be demonstrated between the change in lung fraction and the change in any organ fraction in particular. Therefore, it is highly unlikely that the microspheres accumulated in the lungs over this period originate from the placenta or any other specific organ. It is concluded that in the awake late-pregnant guinea pig, the 2% loss of microspheres from the systemic circulation during the 24 h following reference sampling, does not invalidate the cardiac output distribution derived.

Role of maternal glucose as a metabolic substrate for the guinea pig conceptus.

Our study in pregnant guinea pigs was designed to determine whether the modest fractional contribution of glucose to the late-pregnant uterine caloric uptake was due to inadequate uterine glucose supply or to diminished uterine glucose demand. To this end, uterine uptake of glucose, O2, and lactate was measured in 27 late-pregnant guinea pigs with a wide range of litter sizes. A group of 11 mid-pregnant guinea pigs served as a reference. The fractional uterine uptake of glucose in mid- and late-pregnancy was 90 and 45%, respectively, confirming the indirect data calculated from different studies. In late pregnancy, uteroplacental blood flow (microspheres, -40%) as well as arterial glucose concentration (-30%) had decreased relative to mid-gestation, giving rise to a 60% lower wt-specific uterine glucose supply and a 21% lower wt-specific uterine glucose uptake. Inasmuch as fetal and placental glycogen stores become rapidly depleted after the 50th day of pregnancy, the lower uterine glucose uptake in late pregnancy appears to reflect inadequate uterine glucose supply rather than diminished fetal glucose demands. In late pregnancy, uterine caloric demand per kg is about 60% more than in mid-gestation, most likely associated with accelerated fetal fat accretion. Inasmuch as the latter appears to be mostly fueled by nonglucose fat precursors, it could explain why the glucose fraction of the uterine caloric uptake in late pregnancy has decreased by 50% instead of 21% as compared to mid-gestation. The reduction in arterial glucose concentration in late pregnancy was independent of litter size suggesting this phenomenon is to be a maturational adaptation rather than a sign of inadequate maternal glucose production.

Relationship between maternal hemodynamics and hematocrit and hemodynamic effects of isovolemic hemodilution and hemoconcentration in the awake late-pregnant guinea pig.

The relationship between the spontaneous hematocrit (Hct) and maternal hemodynamics and the hemodynamic effects of experimentally induced changes in this Hct were studied in the awake late-pregnant guinea pig. In animals with a relatively low Hct, cardiac output fractions and blood flows to brain and heart determined with microspheres were higher and those to kidneys lower than in animals with a relatively high Hct. The O2 flows to the kidneys and skin in the former animals were also lower. Cardiac output, heart rate, systemic blood pressure, and blood flows to the other organs, including the placenta, were not related to the Hct. Placental blood flow was found to vary in proportion to cardiac output. Both hemodilution and hemoconcentration induced changes in the cardiac output distribution and organ flows which resembled those observed in the spontaneous relation with Hct. In addition, hemodilution decreased systemic blood pressure. Both hemodilution and hemoconcentration increased placental blood flow; the magnitude of this flow increase was twice as high after hemodilution. The changes in oxygen flows after experimentally induced hemodilution and hemoconcentration appears to be directly related to the concomitant change in whole blood oxygen capacity. It is concluded that in the awake late-pregnant guinea pig, only brain, heart, and kidney perfusion vary in relation to the arterial Hct. The higher placental blood flow after isovolemic hemodilution may be a result of better blood rheology in the porous-like intervillous space of the placentas in a state of reduced systemic blood pressure. The modest rise in placental blood flow after isovolemic hemoconcentration appears to be mostly related to the methodology employed.

Placental transfer of Org 10172, a low-molecular weight heparinoid, in the awake late-pregnant guinea pig.

The placental transfer of Org 10172, a low-molecular weight heparinoid, was determined in 12 awake late-pregnant guinea pigs. Nine animals receiving placebo served as controls. After 5 days i.v. treatment with Org 10172 (2 x 300 anti-Xa U/kg/day), anti-Xa activity in fetal plasma amounted to 2.4% of the maternal concentration. The Org 10172 transfer across the placenta was also evaluated with 3H-labelled Org 10172. One hour after the administration of the latter compound, fetal Org 10172-bound 3H-activity had reached 1.5% of the maternal value. The associated extremely low placental Org 10172 transfer indicates that the Org 10172 transport across the placenta of the guinea pig is membrane-limited and that the placental permeability is negligibly low. Since the hemochorial placenta of the guinea pig closely resembles that of the human, it is likely that similar transplacental transfer properties of Org 10172 apply to man.

Antiarrhythmic action and protection of ischaemia myocardium after beta-blockade with bevantolol.

In the present study 12 of 13 untreated pigs died of ventricular fibrillation during three 10 min episodes of left anterior descending coronary artery occlusion interrupted by 20 min of reperfusion. The selective beta-adrenoceptor antagonist bevantolol in a dose of 1.5 mg X kg-1, but not 0.5 mg X kg-1, offered nearly complete protection against this fatal arrhythmia. Evidence is also presented that bevantolol enhanced the recovery of regional myocardial function after these ischaemic events.

Is nisoldipine capable of reducing left ventricular preload?

In ten anesthetized pigs, nisoldipine (2-4 micrograms X kg-1 X min-1), a calcium channel blocker structurally related to nifedipine, reduced left ventricular systolic pressure (40%) and systemic vascular resistance (35%), whereas maxLVdP/dt decreased by 20% and cardiac output was unchanged. Left ventricular end-diastolic volume (15%) and end-diastolic pressure (40%) decreased, while ejection fraction slightly increased (13%). In normal hearts, nisoldipine reduces left ventricular pre- and afterload, without a depression of myocardial contractility, which results in a more efficient emptying of the left ventricle.