J.P. Figueroa

Power spectrum analysis of myometrial electromyogram and intrauterine pressure changes in the pregnant rhesus monkey in late gestation

Various methods have been used to quantify myometrial activity in the pregnant rhesus monkey during the last third of gestation. A precise definition of activity must retain the characteristics of epoch duration, amplitude, and the repetitive frequencies of active epochs. We used Fast Fourier Transform and power spectrum analysis to determine whether the patterns of myometrial contractility consist predominantly of contractions or contractures. This analysis allows quantification of activity represented by each of these patterns of activity. We applied these methods to myometrial electromyogram and intrauterine pressure recordings in pregnant rhesus monkeys to characterize the changes in myometrial activity that occur after surgery, after intravenous indomethacin administration, and when food is withdrawn for 48 hours. We conclude that changes in the frequency pattern of myometrial activity provide important information in relation to labor and delivery contractions.

Effect of a 48-hour intravenous Δ4-androstenedione infusion on the pregnant rhesus monkey in the last third of gestation: Changes in maternal plasma estradiol concentrations and myometrial contractility

Increased myometrial activity in the pregnant rhesus monkey occurs in situations in which plasma estrogen concentrations are elevated. Examples of such situations are after laparotomy, with or without hysterotomy, and before delivery. The increased activity occurs primarily in the hours of darkness. To investigate the possibility of a causal relationship between the rise in estrogens and myometrial activity, we infused androstenedione intravenously for 48 hours to the rhesus monkey in the last third of gestation. Myometrial activity was quantified either as an increase in the number of individual contraction events or as a change in the power spectrum at high frequencies characteristic of contractions. Androstenedione infusion was followed by increased myometrial activity. Maternal plasma 17 beta-estradiol concentration was significantly elevated at 10 AM on the second day of androstenedione infusion. We conclude that, in the rhesus monkey late in gestation, estradiol may play a role in the regulation of the contraction activity observed during the hours of darkness in several different situations.

Modification of maternal and fetal oxygenation with the use of tracheal gas infusion

A new technique is described for producing changes in fetal blood gases in the chronically instrumented pregnant sheep. Gas mixtures were infused directly into the maternal trachea. Maternal and fetal carotid arterial blood gases and pH were measured. Air infusion at 16 L X min-1 produced no change. Oxygen infusion caused significant increases in maternal PaO2 at 2 L X min-1 and in fetal PaO2 at 4 L X min-1. Nitrogen infusion significantly decreased maternal anf fetal PaO2 at 4 L X min-1. During 4 L X min-1 oxygen infusion, maternal PaO2 rose rapidly to plateau at 314 +/- 47 mm Hg at 4 minutes and fetal PaO2 rose to plateau at 28.7 +/- 2.8 mm Hg after 7 to 8 minutes. Maternal PaO2 fell to 56.4 +/- 4.3 mm Hg during nitrogen infusion (4 L X min-1) while fetal PaO2 fell to 15.9 +/- 1.8 mm Hg. Continuous infusion for 5- to 6-hour periods produced a consistent rise in maternal PaO2 during oxygen infusion and a consistent decrease during nitrogen infusion. Tracheal infusion of gases can be used to change maternal and fetal PaO2 rapidly and predictably.

Alteration of 24-hour rhythms in myometrial activity in the chronically catheterized pregnant rhesus monkey after a 6-hour shift in the light-dark cycle

We determined the effect of a 6-hour phase shift in the light-dark cycle on the 24-hour rhythm of myometrial activity with 15 chronically catheterized pregnant rhesus monkeys during the last third of gestation. Monkeys were housed indoors in constant temperature on a 14-hour-light/10-hour-dark photoperiod in two groups based on the time the lights were turned on (group A lights on at 6 AM and group B lights on at midnight). The power spectra were calculated for periods of 512 readings (1.138 hours) starting at the time the lights were turned on for continuous periods of 25.03 hours of data showing well-developed contraction-type activity at any time during that period. The power spectra data for contractures and contractions were analyzed separately from myometrial electromyographic data. During the 14 hours of light, myometrial activity was primarily composed of contractures. In all experimental animals the switch from contractures to contractions occurred around the time the lights were turned off. The proportion of contraction-type activity in each 1.138-hour analysis interval expressed as a percentage of the total contraction power for the whole 25.03-hour analysis period for all monkeys increased around the time the lights were turned off in both groups. The increase in contractions was observed 12 to 15 hours after the lights were turned on. No systematic change in the proportion of contracture activity was observed. Peak contraction activity was 22.6 +/- 0.60 hours (16.6 hours after lights on), and was at 18.3 +/- 1.4 hours (18.31 hours after lights on) in groups A and B, respectively. This difference was statistically significant (22.6 +/- 0.6 vs 18.3 +/- 1.4 hours, p less than 0.05). Seven of eight monkeys in group A and six of seven in group B had switched from contractures to contractions before lights were turned off. We have confirmed a 24-hour rhythm in myometrial activity in the pregnant rhesus monkey and provided new evidence to support the endogenous nature of this rhythm and its direct relationship to the light-dark cycle.

Effect of food withdrawal on arterial blood glucose and plasma 13,14-dihydro-15-keto-prostaglandin F2α concentrations and nocturnal myometrial electromyographic activity in the pregnant rhesus monkey in the last third of gestation: A model for preterm labor?

Pregnant rhesus monkeys were studied between 109 and 149 days of gestation. Food withdrawal for 48 hours (with free access to water) was accompanied by a decrease in maternal whole blood glucose concentration and an increased maternal arterial plasma 13,14-dihydro-15-keto-prostaglandin F(2α) concentration. On successive nights of the 48-hour period of food withdrawal, there was an increase in the frequency of myometrial contractions as recorded by uterine electromyogram. In the period after food was returned, blood glucose, arterial 13,14-dihydro-15-keto-prostaglanding F(2α) concentration, and contraction frequency returned to baseline. Because of food withdrawal results in the appearance of the nocturnal contraction pattern seen at term, we suggest that this experimental paradigm may be used as a model for preterm labor.

Neuropeptide Cells and Fibers in the Hypothalamus and Pituitary of the Fetal Sheep: Comparison of Oxytocin and Arginine Vasopressin

Both oxytocin (OXY) and arginine vasopressin (AVP) enhance the effects of corticotropin-releasing factor on ACTH release by the pituitary. One of these, AVP, plays a role in the control of fluid balance and responses to hypoxemic stress in the fetal sheep. To determine the possibility that OXY also participates in fetal neuroendocrine events, OXY-containing neuronal structures must first be demonstrated within the fetal endocrine hypothalamus. OXY-immunoreactive elements were examined in fetal sheep hypothalami late in gestation and compared to AVP-containing structures using immunocytochemical procedures. Six fetal sheep ranging from 126 to 144 days gestational age were delivered via cesarian section from timed pregnant Rambouillet-Columbia ewes and killed by an overdose of anesthesia. The fetal head was perfused via bilateral carotid catheters and processed for immunocytochemical localization of OXY or AVP using the avidin-biotin complex procedure. At all fetal ages examined, OXY- and AVP-containing neurons were found within the paraventricular nuclei (PVN), supraoptic nuclei (SON) and accessory magnocellular hypothalamic nuclei. OXY-containing neurons were found principally in the SON and PVN. They were generally less numerous and less intensely stained than the AVP neurons. In the SON, they concentrated along the dorsal borders of the nucleus above the AVP neurons. In PVN, clusters of OXY cells were located along the dorsal and lateral borders of the nucleus surrounding the AVP neurons; in the periventricular division, they were intermingled with the AVP neurons. Small numbers of OXY axons were located in the external zone of the median eminence; whereas most OXY axons extended into the hypothalamo-neurohypophyseal tract and posterior lobe of the pituitary. A few of the OXY axons in the pituitary stalk were diverted to the pars intermedia. Likewise, some of the OXY fibers from the external zone of the median eminence entered the pars tuberalis but were rarely found in the distal lobe of the pituitary. In contrast, AVP axons richly innervated the external zone of the median eminence, and neural lobe. Like OXY, AVP axons from the median eminence and the pituitary stalk sent projections to the adenohypophysis. AVP fibers in the pars distalis frequently contacted corticotropes and were more numerous than OXY fibers in this region. These data provide anatomical evidence that OXY and AVP may directly regulate the fetal adenohypophysis. Of these two neuropeptides, AVP predominates anatomically.

An analysis of the characteristics of the electromyogram recorded from the mesometrium in the ovariectomized nonpregnant ewe and its similarities with and differences from the electromyogram obtained from the myometrium: The effect of estrogens☆☆☆

Mesometrial and myometrial electromyograms have been recorded from ovariectomized nonpregnant ewes. After infusion with saline solution, the frequency of electromyographic events lasting less than 180 seconds in the myometrium was not different from the frequency of their occurrence in the mesometrium. During infusion of estradiol at 100 micrograms/24 hours, the frequency of events less than 180 seconds increased significantly in the myometrium but was unchanged in the mesometrium. Contracture activity (electromyographic events lasting more than 180 seconds) was significantly greater in the mesometrium than in the myometrium before estradiol administration. During estradiol infusion, contracture activity remained unchanged. These findings suggest that the mesometrial muscle may be a useful model to study the effects of various stimulators and inhibitors of uterine muscle function in the absence of stretch and local paracrine effects that occur in the uterus itself.

Validation of thermal techniques for measurement of pelvic organ blood flows in the nonpregnant sheep: Comparison with transit-time ultrasonic and microsphere measurements of blood flow

Data obtained from a thermal system capable of measuring changes in organ temperature as well as tissue thermal clearance in the uterus and vagina have been compared with blood flow measured continuously with a transit-time ultrasound volume-flow sensor placed around the common internal iliac artery and intermittently with radioactive microspheres in the chronically instrumented nonpregnant sheep. Temperature changes in both the uterus and the vagina correlated well with blood flow changes measured by both techniques after intravenous administration of estradiol or norepinephrine. Thermal clearance did not correlate well with blood flow in the vagina or uterus. These methods may have value in the investigation of blood flow patterns in various clinical situations such as the pelvic pain syndrome and early pregnancy.

Inhibition of arachidonic acid metabolism by antipyrine and 4-aminoantipyrine

Antipyrine and 4-aminoantipyrine are used to determine uterine and umbilical blood flows. When administered in vivo, these compounds produce a decrease in uterine contracture activity and maternal uterine vein 13,14-dihydro-15-keto-prostaglandin F2 alpha concentrations. In this paper we report that they also inhibit in vitro activity of prostaglandin synthase in bovine seminal microsomes.