Maternal hemodynamics and uteroplacental blood flow throughout gestation in conscious rats.

The present studies were conducted to develop experimental methods for obtaining cardiovascular measurements in conscious, pregnant rats. Methods were then used to establish key quantitative measurements of (a) placental and fetal development, (b) maternal hemodynamics and (c) uteroplacental blood flow throughout gestation. A progressive and significant enhancement in fetal weight occurs during the later one-third of gestation, commencing at day 15 of pregnancy. Fetal mass increases from 100 mg to 6,500 mg over this time period. Placental weight increases concurrently; however, over the last one-third of gestation, fetal growth and development outstrips placental augmentation such that each placental unit supports 10 fetal units near-term. As late gestation proceeds, a progressive reduction in mean arterial blood pressure is accompanied by enhancement in cardiac output. Total peripheral resistance is significantly reduced. Starting at day 15 of gestation, progressive and significant enhancement in blood flow to uterine tissue occurs. Moreover, significantly greater percentage of cardiac output is directed toward uterine tissue, especially near term. Percentage uterine blood flow directed to placenta is less than 10% at day 15 gestation, but placental perfusion is preferentially enhanced as late gestation continues. Near-term, 90% of uterine blood flow perfuses the placenta. Blood flows to nonreproductive visceral organs (kidney, liver, gut and spleen) and skeletal muscles (gastrocnemius, plantaris, tibialis anterior and soleus) are unaltered by pregnancy and gestation. Therefore, late gestational rat fetal development is supported by cardiovascular adaptations, including specific regional control mechanisms, qualitatively similar to those occurring during human gestation.

Decreased ovarian blood flow may confound the tocolytic effect of ritodrine.

Pregnancies ending before 37 weeks gestation are the leading cause of infant morbidity and death. A recent study involving over 2,000 patients concluded that the beta-adrenergic agonist, ritodrine (Yutopar), the only tocolytic agent currently approved for clinical use, had no significant beneficial effect on perinatal mortality, the frequency of prolongation of pregnancy to term, or birth weight despite proven efficacy in suppressing uterine smooth muscle contraction for 24-48 h. Our previous studies in anesthetized, pregnant rats found that both isoproterenol and ritodrine decreased blood flow to the ovary, apparently via a 'vascular steal' phenomenon. Because decreased ovarian blood flow and blood flow-mediated decrease in progesterone secretion represents one potential mechanism to explain the long-term ineffectiveness of beta-agonist tocolysis, ovarian blood flow studies were conducted in conscious, pregnant rats. Our results indicate that, indeed, ritodrine infusion significantly decreases ovarian blood flow (40%) in the conscious, near-term pregnant rat.

Uteroplacental blood flow at rest and during exercise in late-gestation conscious rats.

The present studies were conducted to achieve three specific aims. First, techniques and procedures were developed to allow tissue and organ blood flow measurements by radioactive microsphere methodology in the conscious female rat. Second, technical aspects of the methodology were evaluated with emphasis on potential uteroplacental shunting of microspheres in the late-gestational period. Third, the above techniques and procedures were utilized to assess uteroplacental blood flow at rest and during exercise in conscious pregnant rats during the late stages of gestation, i.e., days 15, 19, and 22 of pregnancy. Results established the validity of tracer blood flow technical assumptions, and no significant increase in arteriovenous shunting of 15-microns microspheres either as pregnancy progressed or during superimposed exercise in near-term pregnant animals was detected. During the stages of pregnancy studied, cardiac output was enhanced approximately 20% near term. Marked and progressive increases in uterine blood flow were noted both in milliliters per minute and as percentage of cardiac output. Preferential placental perfusion during late-stage gestation was indicated by increased tissue flow (7 +/- 1, 84 +/- 12, 232 +/- 32 ml.min-1 x 100 g-1), increased percent cardiac output (1.7 +/- 0.1, 5.1 +/- 0.7, 11.0 +/- 1.7% cardiac output), and increased percent uterine blood flow (10 +/- 1, 59 +/- 3, 87 +/- 2% uterine flow) at days 15, 19, and 22 of gestation, respectively. Progressive maternal body weight increase during gestation enhanced exercise work intensity, as shown by heart rate and cardiac output at the end of 30 min of treadmill running at 8.5 m/min, 0% incline.(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma catecholamine measurements in resting and stressed conscious rats, using high performance liquid chromatography with electrochemical detection.

Plasma epinephrine (EPI) and norepinephrine (NE) were measured in conscious, unrestrained rats at rest, and following exercise, cold stress and hemorrhage. Heart rate and mean arterial pressure were monitored at all points. Minor modifications of a standard, commercially available methodology achieved good chromatographic separation of both EPI and NE. Sensitivity was sufficient for all NE measurements and for EPI measurements in the stress conditions. Estimates of EPI by this procedure were somewhat higher than those in other reports. Absolute values of NE, as well as the selective, qualitative changes found in both EPI and NE under each stress condition, were consistent with those found in other studies which used the radioenzymatic method. Blood withdrawal of two 1.5 ml samples, 3 hours apart, had no detectable effect on EPI, NE, mean arterial pressure or heart rate in otherwise non-stressed rats.

Covariation of distributions of callosal cell bodies and callosal axon terminals in layer III of cat primary auditory cortex.

Primary auditory cortex in the cat is both the source and target of callosal fibers. Injection of horseradish peroxidase (HRP) in the high frequency representation of AI in one hemisphere retrogradely labels callosal cell bodies and anterogradely labels callosal axon terminals in AI of the opposite hemisphere. In tissue sections cut through layer III parallel to the cortical surface, elongated patches composed of dense aggregates of callosal cell bodies and callosal axon terminals alternate with regions containing lower concentrations of these elements. Labeling in AI is most dense in regions corresponding to the frequency representation of the injected site. In layer III of the densely labeled region, patches of high concentrations of labeled callosal axon terminals correspond with high concentrations of labeled callosal cell bodies. On the other hand, little correspondence is apparent between the distributions of the two elements in layer III in the surrounding area of lighter labeling. Layers V and VI contain relatively few labeled callosal axon terminals and cell bodies, and our data do not suggest whether the two distributions covary in these layers.