Biomedical subjects

S N Caritis

Publications and source records attributed to S N Caritis.

79 records · Page 5Linked to original sources

PubMed1977

Effects of dexamethasone on maternal and fetal hemodynamic states and fetal oxygenation.

The effects of dexamethasone on maternal and fetal hemodynamic states and fetal oxygenation were determined in chronically instrumented unanesthetized pregnant ewes and fetal lambs. Intravenous injections of pharmacologic doses of dexamethasone to the mother failed to alter maternal blood pressure, heart rate, blood flow in the uterine artery supplying the pregnant horn, or uterine vascular resistance. Direct administration of dexamethasone to the fetus had no effect on fetal blood pressure, heart rate, acid-base state, or oxygenation. Furthermore, direct fetal administration of dexamethasone did not produce premature parturition.

Animals↗

PubMed1977

Effects of terbutaline on the pregnant baboon and fetus.

The effects of terbutaline on the mother and fetus were evaluated in 8 near-term pregnant baboons. Significant suppression of postoperative spontaneous and oxytocin-augmented uterine activity was achieved with infusion rates of 0.36 and 0.56 microgram/kg/min, respectively. Maternal and fetal blood pressure and acid-base states as well as fetal heart rate were unaffected by the administration of terbutaline to the mother, but a mild maternal tachycardia was observed. Both maternal and fetal blood glucose increased during terbutaline infusion. Direct administration of terbutaline to the fetus did not alter the fetal cardiovascular or acid-base state. It is concluded that in the baboon, terbutaline is an effective tocolytic agent with minimal untoward effects on either mother or fetus.

Acid-Base Equilibrium↗

PubMed1977

Effect of terbutaline on cardiovascular state and uterine blood flow in pregnant ewes.

The cardiovascular and uterine hemodynamic effects of terbutaline, a beta-adrenergic receptor stimulant and labor inhibiting agent, were evaluated in the chronically instrumented, near-term pregnant ewe. The administration of terbutaline in the dose range required for labor inhibition in this species resulted in a mild maternal tachycardia and increase in pulse pressure without significant changes in uterine blood flow; uterine vascular resistance; or systolic, diastolic, or mean blood pressures. With infusion rates of terbutaline in excess of those required for labor inhibition, significant increases in maternal heart rate, pulse pressure, and systolic blood pressure were observed. Diastolic blood pressure decreased significantly during the higher infusion rates; however, uterine blood flow was unaffected. The minimal cardiovascular and uterine blood flow was unaffected. The minimal cardiovascular and uterine hemodynamic effects noted with the administration of terbutaline in the dose range necessary for labor inhibition indicate that this agent may possess advantages over several others currently in use for the treatment of premature labor.

Animals↗

PubMed1976

Umbilical vein occlusion and transient acceleration of the fetal heart rate. Experimental observations in subhuman primates.

Transient acceleration of the fetal heart rate is commonly seen in the cardiotachometer tracing of the human fetus during labor. A likely cause appeared to be partial occlusion of the umbilical cord. On the basis of this hypothesis, fetal cardiovascular responses to partial occlusion of the umbilical cord or isolated intra-abdominal portion of umbilical vein were studied in near-term pregnant baboons and rhesus monkeys prior to and following sympathetic blockade with dibenzyline and propranolol. The responses were of two types. In the well-oxygenated fetus, partial occlusion resulted in transient acceleration of heart rate and a decrease in pulse pressure. This response was abolished with dibenzyline or propranolol. In the hypoxic fetus, partial occlusion resulted in either bradycardia and hypotension or hypotension with no alteration in heart rate. Thus, transient acceleration of the fetal heart rate can be explained on the basis of a sympathetic response to diminished venous return. It would appear to be an early sign of a potential cord complication. This response will not be seen if the fetus becomes asphyxiated and hypoxic.

Animals↗

PubMed1976

Prolonged infusion of diazoxide in the management of premature labor in the baboon.

The management of premature labor by the prolonged infusion of diazoxide was evaluated in 33 pregnant baboons. The drug was administered intravenously to the mother with an average rate of 0.065 mg/kg/min for 4 hours. Mild to moderate spontaneous labors were significantly inhibited by diazoxide without jeopardizing the fetus. Diazoxide produced a significant increase in maternal heart rate, but its effect on fetal circulation was minimal. Fetal acid-base state and arterial oxygenation remained essentially unchanged throughout the period of observation. Intravenous administration of this drug to the fetuses caused only mild cardiovascular changes irrespective of its preexisting conditions. Thus, a slow intravenous infusion of diazoxide to the mother in a low dosage appears to be of value for inhibiting the uterine activity in early labor, without interfering with the fetal well-being.

Amniotic Fluid↗

PubMed1976

The effect of diazoxide on uterine blood flow in pregnant sheep.

Diazoxide, a labor inhibiting agent, was administered intravenously at various rates to seven pregnant, near-term sheep to evaluate its effect on cardiovascular and uterine hemodynamics. Uterine blood flow was measured with electromagnetic flow transducers. Rapid administration of diazoxide resulted in a profound maternal tachycardia with hypotension, an increase in uterine vascular resistance, and a significant decrease in uterine blood flow. With slow infusion of the drug, the changes in heart rate and blood pressure were minimized, uterine vascular resistance was decreased, and uterine blood flow was maintained. Therefore, slow infusion appears to be the preferred method for inhibiting labor with diazoxide.

Animals↗

PubMedDate not supplied

Alterations in ovine myometrial beta-adrenergic cascade do not mediate tachyphylaxis to ritodrine.

The purpose of this study was to determine in vivo the dose response relationship between beta-adrenergic receptor (BAR) agonist concentration and various elements of the BAR cascade: receptor density, hormone-stimulable adenylyl cyclase activity, and contraction inhibition. A previously described, chronically-catheterized ovine model was used. Ritodrine was infused continuously over 24 h in 22 mixed-breed sheep. Each animal received a single, constant infusion rate. Myometrial biopsies were obtained before and after the drug infusions. BAR density was determined using tritiated dihydroalprenolol. Adenylyl cyclase activity was determined using the Gilman competitive protein-binding assay. Intermittent oxytocin boluses were given into the maternal aorta and contractile response was determined. Infusion rates of 0.06-4.0 micrograms/kg/min yielded steady-state ritodrine serum concentrations of 5-168 ng/ml. No significant correlation was found between the ritodrine concentration and the magnitude of decrease in BAR density. Significant correlations existed, however, between the ritodrine concentration and both the magnitude of decrease in adenylyl cyclase activity and the loss of contraction inhibition. There was no correlation noted between the BAR cascade alterations and the loss of contraction inhibition. Despite significant reductions in receptor density (down regulation) and dose-related reductions in hormone-stimulable adenylyl cyclase activity (uncoupling), ritodrine at low concentrations was still able to inhibit oxytocin-induced contractions, i.e., tachyphylaxis did not occur. Tachyphylaxis appeared to correlate only with the serum ritodrine concentration. Hence, alterations in the BAR cascade do not necessarily equate with a loss of end-organ response (tachyphylaxis). Previous concepts based on in vitro studies about the interaction of the BAR agonist with its receptor, the subsequent generation of intracellular messengers, and the resultant end-organ response may not apply in the intact animal.

Adenylyl Cyclases↗