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Biomedical subjects

R E Garfield

Publications and source records attributed to R E Garfield.

At least 145 records · Page 8Linked to original sources
PubMed1987

Cellular and molecular bases for dystocia.

In this review I have briefly outlined some of the cellular and molecular reasons for dystocia. I have described the myogenic, that may control the normal progression of labor and explain inadequate uterine contractility associated with dystocia. I have placed particular emphasis on our studies of gap junctions and their regulation. These studies show that there are specific physiologic mechanisms for regulating structural and functional coupling between myometrial cells during labor. The integration of these control mechanisms probably operates to ensure appropriate activation and maintenance of synchronous contractility of the myometrium and effective delivery.

Animals↗
PubMed1987

Functional characterization of cell-to-cell coupling in cultured rat aortic smooth muscle.

Gap junction (GJ) occurrence and function was studied in cultured rat aortic smooth muscle cells, since cell-to-cell coupling is proposed to coordinate smooth muscle function but is difficult to study in the intact tissue. Cell proliferation in vitro formed a multilayered structure 10-15 cells thick. GJs connected cells to lateral and vertical neighbors, appearing in freeze fracture as P-face particles aggregated into circular plaques but also as linear arrays. The membrane potential was 58 +/- 3 mV. From quantification of the spread of electrotonic potentials according to a two-dimensional model, the intercellular resistivity was 900-1,400 omega X cm, whereas the nonjunctional membrane resistivity was 10(4) omega X cm2. Intercellular spread of 5(6)-carboxyfluorescein (CF; mol wt 376) in aortic cultures suggests that metabolic coupling is an important consequence of GJs in smooth muscle. CF transfer was not blocked by A23187 (10(-5) M), although rat fibroblasts became uncoupled by 10(-6) M. Ultimately uncoupled by the more potent ionophore ionomycin (10(-5) M), aortic cells seem more able to maintain GJ permeability during challenge from increased intracellular Ca than cells of noncontractile origin.

Animals↗
PubMed1986

Electrical and mechanical uterine activity and gap junctions in estrogen-treated oophorectomized sheep.

The effects of a single dose (0.1 mg) of 17 beta-estradiol on myometrial electrical activity, intrauterine pressure, and myometrial gap junctions were studied in six chronically instrumented oophorectomized ewes. The intrauterine pressure cycles were analyzed for the maximum rate of rise, peak pressure, and active pressure area, together with the frequency of the cycles and the burst frequency, and related to the gap junction area. 17 beta-estradiol temporarily depressed uterine activity. The period of quiescence was followed by a pronounced increase in all variables of electrical and mechanical activity and also by a rise in gap junction area. The greatest increase in the maximum rate of rise of the intrauterine pressure cycles occurred 24 hours after estrogen and was associated with the maximum increase in gap junction area. These results indicate that a single dose of 17 beta-estradiol induces formation of myometrial gap junctions, which may facilitate the spread of electrical activity over the myometrium and improve coordination of uterine contractility.

Animals↗
PubMed1986

Effects of 17 beta-estradiol on myometrial gap junctions and pregnancy in the rat.

The effects of estradiol treatment on the development of myometrial gap junctions and premature labour were investigated using timed pregnant rats. In control animals myometrial gap junctions were infrequent between days 17 and 20 of pregnancy, but began to develop on day 21 and were at maximum frequency, size, and membrane area on day 22 during delivery. Gap junctions were completely absent from the myometrium 48 h after delivery. Animals treated with 500 micrograms 17 beta-estradiol/day starting on day 16 of pregnancy developed numerous myometrial gap junctions and delivered their pups prematurely on day 19. Similarly, treatment with 50 micrograms estradiol/day resulted in the development of myometrial gap junctions on day 20 of pregnancy and premature labour. However, treatment with various doses of estradiol up to and including 500 micrograms/day for 3 days beginning 1 day before delivery was not able to maintain the presence of myometrial gap junctions during the postpartum period. These results support the hypothesis that estradiol stimulates the development of myometrial gap junctions and that the presence of gap junctions in the myometrium is a requirement for the occurrence of term, as well as preterm labour. Furthermore, it is evident from this study that the postpartum regression of myometrial gap junctions is not dependent on the decrease in estradiol.

Animals↗
PubMed1986

Effects of tamoxifen citrate and cycloheximide on estradiol induction of rat myometrial gap junctions.

Longitudinal muscle of myometrial tissues from immature rats were examined by quantitative thin section electron microscopy for the presence of gap junctions after treatment with estradiol with and without tamoxifen, and cycloheximide for 1-6 days. Gap junctions were present between myometrial cells on days 4, 5, and 6 after treatment with estradiol (500 micrograms/day). Tamoxifen administered concomitantly with estradiol over the 6-day period completely prevented induction of the junctions. Gap junctions were not detected in the myometrium after treatment with tamoxifen alone. Administration of cycloheximide together with estradiol on day 0 of the 6-day period had no effect on gap junction frequency but resulted in a reduction in gap junction size in the myometrium after continued treatment with the hormone. Treatment with cycloheximide on day 1, however, significantly suppressed the effect of further estradiol treatment on the induction of gap junctions in the myometrium. Junctions were not visible in the tissues from animals treated with cycloheximide alone or in the control groups treated with sesame oil. These results indicate that estradiol influences the presence of gap junctions in the myometrium by regulating the synthesis of gap junction proteins through the steroid receptor mechanism.

Animals↗
PubMed1986

Structural studies of innervation on nonpregnant rat uterus.

Whole-mount preparations of the uterus and mesentery from nonpregnant rats were examined after staining with glyoxylic acid or acetylcholinesterase to demonstrate the innervation. Some uterine tissues were also evaluated by electron microscopy. Glyoxylic acid fluorescent nerves were present in the mesentery, mesometrium, and uterine wall exclusively around blood vessels. Acetylcholinesterase positive nerve fibers from Frankenhäuser's plexus (cervical ganglia) were associated with blood vessels and muscle in the uterine wall but not in the mesentery. Electron microscopy revealed nerve varicosities with granular vesicles associated with blood vessels and varicosities with agranular vesicles located near blood vessels and muscle cells. Treatment of animals for 3 days with 5- and 6-hydroxydopamine, respectively, increased granular size and damaged the varicosities with granular vesicles but did not change nerves with agranular vesicles or induce the presence of gap junctions. The results of this study suggest that blood vessels in the uterus are highly innervated by both adrenergic and other types of nerves that probably control blood flow. Nonadrenergic but not adrenergic nerves may also directly control myometrial contractility.

Acetylcholinesterase↗
PubMed1986

Evidence for physiological regulation of myometrial gap junction permeability.

We have investigated whether direct intercellular communication between uterine smooth muscle cells of delivering rats is influenced by intracellular adenosine 3',5'-cyclic monophosphate concentration ([cAMPi]) and agents relevant to the hormonal control of pregnancy and parturition. The rate of diffusion of phosphorylated 2-[3H]deoxy-D-glucose (2-DG) in strips of longitudinal myometrium from rats in labor, indicated by the apparent diffusion coefficient for this molecule, was observed to be significantly reduced in tissues with elevated [cAMPi] (after treatment with dibutyryl cAMP, 8-bromo cAMP, forskolin, and theophylline) in the absence of any change in the area of gap junctions (GJs). Similarly, several agonists that elevate [cAMPi] in this tissue (e.g., isoproterenol, relaxin, carbacyclin, prostaglandin E2) also reduced 2-DG diffusion. These data suggest that the permeability of GJs in uterine smooth muscle may be regulated by [cAMPi] and physiologically relevant agonists. Control of GJ permeability may be important for the physiological regulation of intercellular communication and the extent of synchronous contractile activity in the uterine wall during pregnancy and parturition.

5,8,11,14-Eicosatetraynoic Acid↗
PubMed1986

Myometrial activity related to gap junction area in periparturient and in ovariectomized oestrogen treated sheep.

Propagation of electrical (EMG) activity in the myometrium may be facilitated by the presence of gap junctions (GJ), leading to improved synchronization of contractility. EMG and mechanical (IUP) activity in relation to GJ area were studied in 9 periparturient and in 2 ovariectomized (OVX) oestradiol-17 beta (E2) treated ewes, chronically instrumented with bipolar electrodes and intrauterine sponge-tip catheters. Myometrial biopsies were taken under epidural anaesthesia at various time intervals around delivery and after intra-arterial administration of 0.1 mg of E2. In pregnant ewes we found a significant increase in the rate of rise and area of IUP cycles during labour. Both were closely related to a significant increase in GJ area. In E2 treated OVX sheep we found a significant increase in GJ area, with a maximum at 24 hours after injection. The increase in GJ area was associated with a significant increase in the rate of rise of IUP cycles. The results of our study support the hypothesis that gap junctions facilitate the spread of EMG activity across the myometrium, which may improve synchronization of uterine contractility during labour.

Animals↗
PubMed1985

Electrical and mechanical uterine activity and gap junctions in peripartal sheep.

In 10 chronically instrumented pregnant ewes myometrial electrical activity and intrauterine pressure were measured and plasma levels of 17 beta-estradiol and progesterone were determined in late pregnancy and during and after labor. Myometrial biopsies were obtained to determine gap junction area. Plasma progesterone levels fell 4 days before delivery, and 17 beta-estradiol levels rose sharply 12 hours before delivery. Toward delivery the myometrial electrical pattern changed from infrequent bursts of long duration to frequent bursts of short duration, and the active pressure area of the intrauterine pressure cycles, the apparent conduction velocity, and the rate of rise of intrauterine pressure cycles increased associated with the changes in hormone levels. These changes were related to an increase in gap junction area. It is concluded that these results support the hypothesis that changes in concentrations of steroid hormones lead to an increase in myometrial gap junction area, which improves the coordination of contractile activity of the uterus during labor.

Animals↗
PubMed1985

Modulation of spontaneous myometrial activity in chronically instrumented ovariectomized sheep.

The uterine electromyogram (EMG) and intrauterine pressure curves (IUP) were investigated as indicators of myometrial activity in chronically instrumented, ovariectomized ewes. Spontaneous electrical activity was characterized by rhythmic patterns of trains of bursts accompanied by IUP waves. Administration of adrenergic (propranolol or phentolamine) or cholinergic (atropine) blocking agents had no effect on spontaneous uterine activity. Both oxytocin and PGF2 alpha appeared to stimulate spontaneous myometrial activity. 17beta-Estradiol temporarily depressed uterine activity in a dose-dependent fashion. The period of relaxation was followed by a pronounced increase in activity. Progesterone treatment resulted in long-term suppression of myometrial activity. Oxytocin and PGF2alpha increased EMG and IUP activity during estradiol suppression but not after progesterone treatment. These results indicate that the myometrium is active in chronically instrumented, ovariectomized ewes. The autonomic nervous system or its receptors do not play a role in the maintenance of spontaneous myometrial activity, estradiol and progesterone suppress myometrical activity but by different mechanisms.

Action Potentials↗
PubMed1985

Hormonal control of gap junctions in the myometrium.

Myometrial tissues from immature, ovariectomized mature, and pregnant rats were examined by thin-section or freeze-fracture electron microscopy for the presence of gap junctions following treatment with steroid hormones and inhibitors of prostaglandin synthesis. Gap junctions were present in the myometrium of immature rats after repeated injections of estradiol or diethylstilbestrol (500 micrograms/day). The frequency of gap junctions in immature rats after estradiol treatment was similar to that found during delivery. Concomitant administration of indomethacin or meclofenamate with estradiol (50 and 500 micrograms/day) for 3 or 4 days enhanced the effect of estradiol on gap junctions. Progesterone depressed the response of 500 micrograms/day estradiol and both 50 and 500 micrograms/day doses of estradiol when administered together with the inhibitors of prostaglandin synthesis. Gap junctions were also present in the myometria of ovariectomized mature rats after treatment with estradiol by itself or together with indomethacin, and these effects were suppressed by concomitant progesterone administration. These results indicate that the steroid hormones and prostaglandins may interact to modulate the presence of gap junctions in the myometrium.

Animals↗
PubMed1985

Gap junctions and direct intercellular communication between rat uterine smooth muscle cells.

We have tested the hypothesis that an increase in direct intercellular communication accompanies the development of gap junctions (GJs) between rat uterine smooth muscle cells at parturition. Intercellular communication in these tissues was studied by exposing one portion of small strips of myometrium to 2-[3H]deoxy-D-glucose (2-DG) and determining the longitudinal distribution of tracer after a 5-h period of diffusion. The distribution of 2-DG was greater in parturient compared with ante- and postpartum tissues. Similarly, the apparent diffusion coefficient of 2-DG was almost 10-fold greater in delivering tissues (1.86 X 10(-6) cm2/s) than before (0.199 X 10(-6) cm2/s) or after (0.296 X 10(-6) cm2/s) parturition. Control experiments indicated that the redistribution of 2-DG was dependent on the presence of GJs and was the result of intracellular and direct cell-to-cell diffusion. The appearance of GJs is the myometrium at term facilitates direct intercellular communication between uterine smooth muscle cells during labor. This improved communication may be responsible for synchronizing and coordinating electrical, metabolic, and contractile activity in the uterine wall and, hence, the effective expulsion of fetuses.

Animals↗
PubMed1985

Structural and functional studies of myometrial gap junctions.

Gap junctions are believed to be sites of metabolic and electrical coupling between cells. These contacts are present between myometrial cells immediately prior to and during parturition. We report the results of studies to investigate the control and the function of myometrial gap junctions. Injection of estradiol (500 micrograms/day) with or without progesterone into immature and ovariectomized mature rats demonstrated that estradiol stimulated whereas progesterone suppressed gap junction formation. Indomethacin treatment was also shown to potentiate the action of estradiol. Also, pregnant rats treated with oestradiol developed numerous myometrial gap junctions and aborted their fetuses. These results suggest that the steroid hormones and prostaglandins may control myometrial gap junction development. Diffusion studies of 3H-2-deoxyglucose in longitudinal myometrial strips revealed a significant increase in the diffusion coefficient in delivering versus ante-partum rat tissues. This indicates that there is increased metabolic transfer during parturition when gap junctions are present. The results of these studies show that steroid hormones and prostaglandins may regulate myometrial gap junctions and that metabolic, as well as electrical coupling, of uterine smooth muscle cells increase at parturition concomitant with the development of gap junctions.

Animals↗
PubMed1984

Myometrial electrophysiologic activity and gap junctions in the pregnant rabbit.

Electromyographic activity of the myometrium, intrauterine pressure, and myometrial gap junctions were examined in rabbits at various stages of pregnancy and during parturition. Electromyographic activity occurred throughout pregnancy and was characterized by electromyographic bursts lasting up to 5 minutes at a frequency of one to four per hour. The gap junction area of plasma membrane showed a significant increase at delivery at a time when electromyographic activity changed to rhythmic bursts of short duration at a frequency of about one per minute. This study shows that the rabbit uterus is active throughout pregnancy; furthermore, the development of large numbers of gap junctions between myometrial cells occurs at a time when uterine activity changes to the expulsive activity required for labor.

Animals↗
PubMed1984

Myometrial ultrastructure and innervation in Myotis lucifugus, the little brown bat.

Uteri from hibernating bats, Myotis lucifugus, collected periodically from Renfrew County, Ontario, were fixed in 2% glutaraldehyde and processed for electron microscopy or incubated in glyoxylic acid to show adrenergic nerves by fluorescence. The bat uterus is structurally typical of mammalian species; although the right uterine horn is permanently enlarged in parous bats due to hypertrophy of both myometrium and endometrium. Nerves were abundant between both longitudinal and circular layers of muscle cells. Unmyelinated, and some myelinated, axons, ranging from few to many, coursed generally parallel to the uterine long axis. Numerous axonal varicosities containing small dense-cored (adrenergic) vesicles or, less often, small agranular (cholinergic) vesicles, were found forming close nerve-muscle contacts between myometrial cells and blood vessels. Fluorescent microscopy showed a dense network of adrenergic nerves in parous uteri, but a sparse network in nulliparous uteri. A specific adrenergic nerve marker, 5-hydroxydopamine, greatly increased the density and in some instances, the size of granular vesicles, while 6-hydroxydopamine, which depletes adrenergic neutrotransmitter, reduced the number of dense-cored vesicles. Nulliparous uteri appeared unchanged by six daily injections of 0.1 microgram estradiol-17 beta; 0.25 mg progesterone, or both; but parous uteri were greatly enlarged by all regimes. Nerve ultrastructure, however, appeared unaffected by steroid treatment; nor, despite the absolute dextral bias in implantation, were left-right differences observed. Gap junctions were not found between muscle cells in myometria of any bat uteri. Based on this study, we suggest that M. lucifugus may provide a most useful model for examination of neurogenic regulation of the uterus.

Animals↗
PubMed1984

Uterotropic action of indomethacin on the rat uterus.

Administration of indomethacin (10 mg/kg body weight, twice daily for 6 days) resulted in a significant (P less than 0.01) increase in the weight, and cross-sectional area of uteri of ovariectomized rats, whereas no such effects were observed following indomethacin administration to normal cycling rats. Prostaglandin F2 alpha (PGF2 alpha) content (ng/uterus) and concentration (ng/g wet weight) in the uterus of indomethacin-treated animals were reduced 40.4% and 60.8%. Simultaneous administration of either estradiol-17 beta (E2), progesterone testosterone with indomethacin to ovariectomized rats failed to reduce the uterine weight increase. On the contrary, concomitant administration of E2 (25 or 100 ng/day) and indomethacin resulted in uterine weight increases which were greater than those associated with indomethacin alone. Uterine E2 content was significantly higher in animals treated with indomethacin plus E2 as compared to those given estradiol alone. Uterine uptake of 2,4,6,7-[3H]E2 following i.v. administration was greater in animals pretreated with indomethacin (5 mg/kg, twice daily) for 3 days than in ovariectomized controls. These results suggest that prostaglandins may be involved in the regulation of uterine growth.

Animals↗