Biomedical subjects

G E Rice

Publications and source records attributed to G E Rice.

At least 109 records · Page 6Linked to original sources

PubMed1990

Analysis of the responses of the fetal vessels of human perfused placental lobules to acute infusions of arachidonic acid.

The vasodilatory response to arachidonic acid by the fetal vessels of human perfused placental lobules, in which tone had been increased by infusion of the thromboxane A2 mimetic U46619, was significantly reduced in the presence of the prostacyclin (PGI2) synthetase inhibitor tranylcypromine compared with saline infusion controls. HPLC analysis of the fetal effluent from human perfused placental lobules, in which radiolabelled arachidonic acid had been infused, identified two peaks of activity. The first peak displayed an elution profile similar to that of a 6-keto-PGF1 alpha standard; the presence of 6-keto-PGF1 alpha in this peak was confirmed by RIA. The second peak had an elution profile similar to that of an arachidonic acid standard. These results suggest that the vasodilatory response to the fetal vessels of human perfused placental lobules to acute infusions of arachidonic acid is mediated, at least in part, by the synthesis of PGI2. These data are consistent with the hypothesis that PGI2 may be involved in the maintenance of low vascular resistance of the fetal placenta in utero.

6-Ketoprostaglandin F1 alpha↗

PubMed1990

Is human labour triggered by an increase in the rate of synthesis of prostaglandin G/H synthase?

The increase in the synthesis of prostaglandins by intrauterine tissues which occurs at the time of parturition may be the consequence of periparturient changes in several regulatory pathways. The aim of this study was to determine whether changes in the rate of synthesis of prostaglandin G/H synthase (PGHS) contribute to the labour-associated increase in prostaglandin synthesis by human chorioamnion and placenta. The rate of recovery of prostaglandin E2 (PGE2) synthesis following inhibition of PGHS by aspirin was used as an estimation of PGHS resynthesis. In tissues obtained following spontaneous delivery, the half-time recovery of PGE2 synthesis was 3.5 to 6.0-fold less (P less than 0.001; n = 5) than the half-time recovery observed in tissues obtained before the onset of labour. These data suggest that a periparturient increase in the rate of synthesis of PGHS contributes to enhanced prostaglandin synthesis at term.

Amnion↗

PubMed1990

Regulation of oxytocin secretion by the ovine corpus luteum: effect of activators of protein kinase C.

The effect of protein kinase C activation and dibutyryl cyclic AMP on oxytocin secretion by ovine luteal tissue slices was investigated. Several putative regulators of luteal oxytocin secretion were also examined. Oxytocin was secreted by luteal tissue slices at a basal rate of 234.4 +/- 32.8 pmol/g per h (n = 24) during 60-min incubations. Activators of protein kinase C: phorbol 12, 13-dibutyrate (n = 8), phorbol 12-myristate, 13-acetate (n = 4) and 1,2-didecanoylglycerol (n = 5), caused a dose-dependent stimulation of oxytocin secretion in the presence of a calcium ionophore (A23187; 0.2 mumol/l). Phospholipase C (PLC; 50-250 units/l) also caused a dose-dependent stimulation of oxytocin secretion by luteal slices. Phospholipase C-stimulated oxytocin secretion was potentiated by the addition of an inhibitor of diacylglycerol kinase (R59 022; n = 4). These data suggest that the activation of protein kinase C has a role in the stimulation of luteal oxytocin secretion. The results are also consistent with the involvement of protein kinase C in PLC-stimulated oxytocin secretion. The cyclic AMP second messenger system does not appear to be involved in the control of oxytocin secretion by the corpus luteum.

Animals↗

PubMed1990

Prostaglandin G/H synthase activity in ovine cotyledons: a gestational profile.

A polarographic oxygen electrode technique was used to quantify the activity of prostaglandin G/H synthase present in microsomes prepared from cotyledons of ewes at 74 to 147 days of gestation (n = 25). Microsomal oxygen consumption was stimulated by arachidonic acid and suppressed significantly (p less than 0.0001) by indomethacin, a specific inhibitor of prostaglandin G/H synthase. A residual indomethacin-incentive oxygen consumption was identified but the magnitude of this component did not change during gestation. During gestation prostaglandin G/H synthase (PGHS) activity, present in ovine cotyledons, increased 22-fold, from 0.6 +/- 0.19 at 70-80 days (n = 3) to 13.22 +/- 2.08 nmol O2/min/mg protein at greater than 145 days of gestation (n = 8; p less than 0.001). This gestational increase in the PGHS activity present in ovine cotyledons was not observed when fetal hypophysectomy was performed at 70-80 days of gestation. The data obtained in this study are consistent with the hypothesis that cotyledonary PGHS activity is increased during the second half of gestation and that this increase may be dependent upon fetal pituitary factors.

Animals↗

PubMed1989

An inducible endothelial cell surface glycoprotein mediates melanoma adhesion.

Hematogenous metastasis requires the arrest and extravasation of blood-borne tumor cells, possibly involving direct adhesive interactions with vascular endothelium. Cytokine activation of cultured human endothelium increases adhesion of melanoma and carcinoma cell lines. An inducible 110-kD endothelial cell surface glycoprotein, designated INCAM-110, appears to mediate adhesion of melanoma cells. In addition, an inducible endothelial receptor for neutrophils, ELAM-1, supports the adhesion of a human colon carcinoma cell line. Thus, activation of vascular endothelium in vivo that results in increased expression of INCAM-110 and ELAM-1 may promote tumor cell adhesion and affect the incidence and distribution of metastases.

Animals↗

PubMed1989

Effects of calcium availability on the release of ovine choriomammotropin from cotyledonary cells incubated in vitro.

1. In this study, we examined the basal release of choriomammotropin (oCM) from monolayer cultures of cotyledonary cells obtained from ewes at different gestational ages. 2. oCM release increased with gestational age and displayed a similar profile to the concentration of oCM observed in maternal plasma. 3. Release of oCM was significantly (P less than 0.05; n = 9) increased in calcium-depleted medium, and by treatment with either phospholipase C (0.125 units/ml) or KCl (50 mM). 4. The calcium antagonist MgCl (12 mM) and the calcium channel-blocking agents verapamil (50 microM) and nefidipine (10 microM) all significantly stimulated oCM release. 5. These data are consistent with the suggestion that oCM release is inversely related to extracellular calcium concentration.

Animals↗

PubMed1989

Effects of subacute opioid administration during late pregnancy in the rat on the initiation, duration and outcome of parturition and maternal levels of oxytocin and arginine vasopressin.

1. The effects, on parturition in the rat, of subacute and acute opioid administration were studied. Further experiments investigated the role of modulation of maternal plasma and pituitary oxytocin (OXY) and arginine vasopressin (AVP) levels in these effects. 2. Subacute opioid (M320, buprenorphine or bremazocine) administration prolonged the gestation of rats. This was accompanied by toxic effects on the offspring. Acute subcutaneous (s.c.) M320 (10 micrograms/kg) administration was accompanied by prolonged gestation without toxic effects. 3. Subacute M320 (10 micrograms/kg, s.c., twice daily) treatment was accompanied by increased interbirth intervals in parturient rats. 4. Maternal OXY but not AVP release, as assessed by measurement of plasma and pituitary immunoreactivity, was elevated during and up to 1 h after the completion of parturition. Subacute M320 treatment did not inhibit this elevated OXY release.

Animals↗

PubMed1989

mu- and K-opiate receptor agonists reduce plasma neurohypophysial hormone concentrations in water-deprived and normally hydrated rats.

1. The effects of mu- and K-opiate receptor agonists on plasma concentrations of immunoreactive (ir) oxytocin (OXY) and arginine vasopressin (AVP) in normally hydrated and water-deprived rats were studied. 2. Water-deprivation for 36 h elevated both plasma ir-OXY and ir-AVP concentrations of Long-Evans rats. These elevated levels were lowered in a dose-dependent manner after subcutaneous administration of bremazocine (3-10 micrograms/kg), M320 (10-100 micrograms/kg) or morphine (0.1-10 mg/kg). Comparable reductions of plasma concentrations of ir-AVP and ir-OXY were observed. 3. Plasma concentrations of ir-OXY and ir-AVP of normally hydrated Long-Evans rats were lower after subcutaneous administration of bremazocine (10 micrograms/kg), M320 (10 micrograms/kg) and morphine (1.0 mg/kg). 4. These data suggest that both mu- and K-opiate receptor agonists inhibit both OXY and AVP release from the neurohypophysis of rats.

Animals↗

PubMed1989

Gestational profile of prostaglandin E2 synthesis by porcine placenta and fetal membranes.

The capacity of the diffuse, epitheliochorial porcine placenta (chorioamnion plus endometrium: AMCE and chorioallantois plus endometrium: ALCE) and allantoamnion (ATA), obtained from sows at 47-112 days of gestation (n = 12), to release PGE2, during in vitro explant incubation, was determined. There was no significant difference between PGE2 release from AMCE and ALCE, and the data obtained from these two tissues were pooled. The release of PGE2 from ATA was, at all stages of gestation, significantly less (8-50 fold; p less than 0.01, n = 12) than that released from AMCE/ALCE. During gestation, the basal release of PGE2 from AMCE/ALCE increased from 13.7 +/- 2.8 pmol/100 mg per incubation (n = 8; mean +/- S.E.M.) at less than 80 days to a maximum of 176.5 +/- 30.9 pmol PGE2/100mg per incubation (n = 10) at greater than 109 days of gestation. Basal PGE2 release from ATA increased from 1.6 +/- 0.6 pmol PGE2/100 mg per incubation (n = 3) at less than 80 days to 3.5 +/- 0.5 pmol PGE2/100 mg per incubation at greater than 109 days gestation. At all stages of gestation and in all tissues, the addition of sodium arachidonate significantly stimulated PGE2 release, indicating that during gestation prostaglandin synthesis by porcine placenta and fetal membranes is, at least partly, substrate limited. The observed increase in the release of prostaglandin E2 from placenta and fetal membranes that occurred from 90 days of gestation and rapidly increased at term may reflect an increase in substrate availability, an increase in the activity of prostaglandin endoperoxide H synthase- E isomerase or a combination of these processes.

Animals↗

PubMed1988

Studies of the effects of subacute treatment with N-(cyclopropylmethyl)-19-isopentylnororvinol (M320) on timing of parturition in the rat.

1. Administration of 10 micrograms kg-1 of the long lasting potent kappa- and weaker mu-opioid agonist N-(cyclopropylmethyl)-19-isopentylnororvinol (M320) twice daily from day 20 of gestation prolonged the internal gestation period of the rat and retarded the development of the offspring in the perinatal period. 2. The capacities of myometrial, placental and cervical tissues to produce prostaglandin E2 (PGE2) were not affected by M320 treatment. 3. During the period in which parturition normally occurred in saline-treated rats, foetal pituitary levels of immunoreactive oxytocin (ir-OXY) but not immunoreactive arginine-vasopressin (ir-AVP) were greater in M320-compared to saline-treated animals. Following the completion of parturition, foetal pituitary ir-OXY and ir-AVP levels continued to rise in saline-treated rats, but fell dramatically in rats treated subacutely with M320. 4. These data indicate that subacute treatment with M320 may inhibit foetal oxytocin release at term. This foetal OXY release may be a stimulus for the initiation of labour.

Animals↗

PubMed1988

Control of oxytocin secretion by ovine corpora lutea: effects of arachidonic acid, phospholipases, and prostaglandins.

The involvement of arachidonic acid and arachidonic acid metabolites in the control of oxytocin secretion by ovine corpus luteum was investigated, using slices of luteal tissue incubated in vitro. Oxytocin was secreted at steady rates by luteal slices, during 60-min incubations (315.0 +/- 45.3 pg/mg.h). The secretion of oxytocin was stimulated by arachidonic acid, phospholipase A2 (PLA2), and phospholipase C (PLC) in a dose-dependent manner. The highest doses of arachidonic acid, PLA2, and PLC used stimulated oxytocin secretion by 145.8 +/- 23.0% (P less than 0.01; n = 6), 331.5 +/- 42.4% (P less than 0.02; n = 4), and 955.5 +/- 278.6% (P less than 0.01; n = 4), respectively. Oxytocin secretion by luteal slices was not affected by either prostaglandin F2 alpha (PGF2 alpha) or PGE2 over a concentration range from 3-3000 nM. Furthermore, inhibitors of the cyclo-oxygenase pathway of arachidonic acid metabolism did not consistently affect arachidonic acid and PLA2-stimulated oxytocin secretion. Nordihydroguaiaretic acid, which inhibits 5-lipoxygenase, however, totally abolished arachidonic acid- and reduced PLA2-stimulated oxytocin secretion. The presence of CoCl2 in the incubation medium also significantly reduced basal and PLA2- and PLC-stimulated oxytocin secretion [P less than 0.05 (n = 5), P less than 0.05 (n = 5), and P less than 0.01 (n = 6), respectively]. We have shown that oxytocin secretion from slices of ovine corpus luteum incubated in vitro is stimulated by exogenous and endogenously released arachidonic acid. The data show that PGF2 alpha and PGE2 do not have a role in luteal oxytocin secretion in vitro and PG formation does not appear to be involved in the stimulation of oxytocin secretion elicited by arachidonic acid or PLA2. Arachidonic acid may have its effect via the lipoxygenase pathway.

Animals↗

PubMed1988

Biophysical characteristics of oxytocin secretory granules isolated from ovine corpora lutea.

Luteal oxytocin-containing secretory granules have been isolated and characterized in terms of their physicochemical parameters. The isopynic sedimentation density (1.03 +/- 0.003 g/ml) and sedimentation coefficient (1670 S, 0.32 mol sucrose/l, 4 degrees C) of these granules have been estimated. Based upon these estimates, the average vesicle diameter (258 +/- 17 nm) and vesicle weight (9.92 +/- 0.67 fg/vesicle) were calculated. The exchangeable water content (58.2%) of these granules was determined using density gradients prepared with deuterium oxide. Luteal oxytocin-containing granules displayed similar physicochemical characteristics to those reported for neurohypophysial peptide-containing granules, with the exception of particle size. Luteal granules were 1.3 times greater in diameter than neurohypophysial granules.

Animals↗

PubMed1988

Gestational changes in prostaglandin synthase activity of ovine cotyledonary microsomes.

The capacity of cotyledonary microsomes, prepared from pregnant ewes (20-145 days of gestation), to metabolize exogenous arachidonic acid was quantified using a radiolabel technique. During gestation, the capacity of microsomes to metabolize arachidonic acid increased 25-fold, from 0.36 +/- 0.06 mumol arachidonic acid/incubation (n = 8) at less than 100 days of gestation to 9.06 +/- 1.02 mumol arachidonic acid/incubation at 130-145 days of gestation (n = 5; P less than 0.05). Arachidonic acid was metabolized to prostaglandin E2 and F2 alpha, as determined by thin-layer chromatography and reverse-phase high performance liquid chromatography. The profile of prostaglandins synthesized by cotyledonary microsomes did not change throughout gestation. These data suggest that the increase in cotyledonary prostaglandin synthesis that occurs during late gestation and at term may reflect an increase in the tissue content of prostaglandin H2 synthase.

Animals↗

PubMed1988

Tumor cell-endothelial interactions. Increased adhesion of human melanoma cells to activated vascular endothelium.

The authors examined the adhesion of seven human melanoma cell lines to cultured human umbilical vein endothelial cells (HEC) that were activated by cytokines or bacterial endotoxin. The adhesion of Hs 294T and MEL-24 cells was markedly increased (approximately 2 to 12-fold) after pretreatment of HEC monolayers for 6 hours with tumor necrosis factor, interleukin-1, or endotoxin. Smaller increases were noted with the cell lines RPMI 7951, HT 144, Malme-3M, MEL-2, and no significant increase was observed with MEL-5. Cytokine and endotoxin effects on melanoma-HEC adhesion were concentration- and time-dependent, with onset by 2 hours, peak at 6-8 hours and maintenance through 48 hours. Cytokine induction of increased HEC adhesiveness for melanoma cells was blocked by actinomycin-D or cycloheximide, suggesting the requirement for RNA and protein synthesis. Interaction of melanoma cells with subendothelial matrix did not appear to play a primary role because: 1) phase contrast and electron microscopy revealed direct contact between tumor cells and endothelial cells in standardized monolayer adhesion assays; 2) increased adhesion (rosette formation) of tumor cells to activated HEC was also observed after nonenzymatic resuspension of HEC, and 3) the matrix peptide GRGDSP partially blocked (approximately 45%) Hs 294T cell adhesion to subendothelial matrix, but had little or no effect on adhesion to activated HEC monolayers. Taken together, these data suggest that inducible HEC surface changes may mediate the adhesion of certain melanoma cells, thereby exerting an active influence over the metastatic process.

Biomechanical Phenomena↗

PubMed1987

Ovine myometrial cytosol inhibits phospholipase A activity, in vitro.

Myometrium obtained from pregnant ewes (30-80 days gestation) contains a factor which inhibits phospholipase A2 (PLA2) activity. The activity of this moiety was assessed using an in vitro porcine pancreatic PLA2 assay system. Inhibitory activity was associated with a 35-45000 dalton molecular weight fraction, heat-labile, sensitive to protease degradation and did not partition into organic solvents. These data are indicative that PLA2-inhibitory activity resides in a protein moiety. Dixon-plot analysis of myometrial-inhibitory activity was indicative that the inhibition of PLA2 activity was of a non-competitive nature (Ki = 4.1 +/- 0.7 micrograms/ml, ca 118 nmol/l). Myometrial phospholipase-inhibitory protein(s) may be involved in the suppression of eicosanoid biosynthesis by the uterine tissues throughout gestation thus inhibiting uterine contractile activity.

Animals↗

PubMed1987

Ovine allantoic fluid inhibition of prostaglandin synthesis in cotyledonary microsomes.

Inhibition of microsomal prostaglandin (PG) biosynthesis by allantoic fluid, obtained from ewes at 80-120 days of gestation, was examined. Inhibition of cotyledonary microsomal PGE2 and PGF2 alpha biosynthesis by lyophilized allantoic fluid occurred in a dose-dependent manner. The concentration of allantoic fluid required to inhibit PGE2 and PGF2 alpha production by 50% averaged 17.9 +/- 3.2 (S.E.M.) mg dry weight/ml (n = 5). Microsomal PG biosynthesis was markedly enhanced by the addition of arachidonic acid (30 mumol/l). Synthesis of PGE2 and PGF2 alpha was increased to 245 +/- 65% and 184 +/- 14% of control (P less than 0.05, n = 5) respectively. Treatment of cotyledonary microsomes with porcine phospholipase A2 (PLA2; 0.125 units/ml) also stimulated PG synthesis, PGE2 increasing to 216 +/- 27% and PGF2 alpha to 172 +/- 14% of control (P less than 0.05, n = 5) respectively. Allantoic fluid (20 mg dry weight/ml) inhibited arachidonic acid-stimulated PG synthesis (PGE2 by 48.6 +/- 13.8% and PGF2 alpha by 44.2 +/- 7.7%) and PLA2-stimulated PG synthesis (PGE2 by 60.6 +/- 11.6% and PGF2 alpha by 74.8 +/- 8.5%). Allantoic fluid, however, did not affect PLA2-stimulated release of arachidonic acid from microsomes, thus negating the possibility that allantoic fluid suppresses PG synthesis by inhibiting PLA2 activity. These data indicate that allantoic fluid inhibits PG production at the level of PG synthase enzymes. Prostaglandin inhibitor(s) in allantoic fluid may play a role in maintaining uterine quiescence throughout gestation and its withdrawal, at term, may be involved in the initiation of labour.

Allantois↗

PubMed1986

Plasma levels of arginine vasotocin, prolactin, aldosterone and corticosterone during prolonged dehydration in the domestic fowl: effect of dietary NaCl.

Three groups of White Plymouth Rock laying hens were adapted to three levels of dietary NaCl: low-NaCl food with tap water (LOW), high-NaCl food (1% NaCl w/w added) with tap water (HT), and high-NaCl food with 0.5% NaCl for drinking (HS). The birds were subjected to water deprivation (dehydration) for 18 days. Blood sampling was done at 2-4 day intervals. Plasma concentrations of arginine vasotocin (AVT), prolactin (PRL), aldosterone (ALDO) and corticosterone (CS) were determined by radioimmunoassay. Plasma osmolality, sodium, chloride, and potassium were also determined. In the normally hydrated hens fully adapted to the diets, there was a stepwise increase from LOW to HS in plasma osmolality (305, 315, 332 mOsm, for LOW, HT and HS, respectively), [Na+] (144, 153, 161 mM) and [Cl-] (109, 119, 127 mM) as well as in [AVT] (6, 14, 18 pg/ml) and [PRL] (16, 24, 34 ng/ml). Regressing [AVT] on osmolality gave a slope of 0.30 pg . ml-1/mOsm and a threshold of 273 mOsm. The slope of [PRL] on osmolality was 0.73 ng . ml-1/mOsm. The correlation coefficient of [AVT] and [PRL] was 0.67. LOW had high [ALDO] (165 pg/ml) which was suppressed to low levels in HT and HS (5-8 pg/ml), while [CS] was the same in all groups (0.9-1.1 ng/ml). Plasma [K+] was decreased in the high-NaCl groups (5.8 mM in LOW, 4.4 and 4.7 mM in HT and HS). Dehydration resulted within 2 days generally in a sharp (5-15%) increase in osmolality, [Na+] and [Cl-], which thereafter increased more slowly during the remaining 16 days in all groups, with the slowest increase in LOW. The levels of osmolality [Na+] and [Cl-] were 5% lower in LOW than in HT and HS, which showed the same levels during the dehydration period. Plasma [AVT] and [PRL] increased 2-4 fold within 2 days of dehydration; [AVT] reached a plateau at 29 pg/ml in all groups, but [PRL] continued to rise in all groups, fastest in LOW, reaching similar levels in all groups after 14-18 days of dehydration, about 85 ng/ml. The correlation coefficient of [AVT] and [PRL] was decreased by half (to 0.32) during dehydration. Plasma [ALDO] increased in all groups with dehydration, 1.7 fold in LOW and 3-6 fold in HT and HS, but the levels reached in HT and HS were only 15-30% of that seen in LOW.(ABSTRACT TRUNCATED AT 400 WORDS)

Adrenal Cortex Hormones↗

PubMed1986

Osmotic stimuli and NaCl-intake in the fowl; release of arginine vasotocin and prolactin.

White Plymouth Rock hens were fed a high- and a low-NaCl content of the diet. The two groups were exposed to moderate dehydration, to intra-arterial hyperosmotic NaCl-loading, or to injection of physiological doses of arginine vasotocin (AVT). The plasma levels of AVT and prolactin were measured by accurate and sensitive radioimmunoassay and the osmolality and Na, K (and Cl) concentrations also measured for 48 h after dehydration, and for 60-90 min after NaCl-loading or AVT-injection. The plasma concentration of AVT after a given increase of plasma osmolality was in all experiments found higher in the low- as compared to the high-NaCl diet group. The average difference was 0.2 pg/ml X mOsm. The intra-arterial injection of AVT resulted in a strictly mono-exponential fall over the next hour with an average half-life of 6.3 min without any difference between the high- and the low-NaCl diet groups. It is concluded (a) that the release of prolactin after osmotic stimulation is most likely caused by a direct effect of osmolality (or Na concentration) and not by AVT, (b) that the release of AVT is influenced by the NaCl-intake in a direction which tends to maintain extracellular volume.

Animals↗