Up-regulation of oxytocin receptors in non-pregnant rat myometrium by isoproterenol: effects of steroids

The objective of the present study was to further elucidate our previous observation that beta2-adrenoceptor activation induces oxytocin receptor (OTR) expression in rat myometrium. We wanted to investigate whether the mechanism behind this effect was under the influence of gonadal steroids. Ovariectomized non-pregnant rats were treated with estrogen, progesterone or a combination of both for 3 days. Some rats were concomitantly treated with isoproterenol. Estrogen treatment increased both OTR mRNA production and maximal binding of [3H]-oxytocin to isolated myometrial plasma membranes, but it did not affect contractility of isolated uterine strips challenged with oxytocin. When the estrogen regimen was combined with isoproterenol treatment, an augmented maximal contractile response (Emax) to oxytocin was observed although no further increase in OTR mRNA and binding was seen. Progesterone treatment did not in itself alter OTR mRNA, OTR binding or Emax. However, OTRs were induced at the level of gene expression when progesterone was supplemented with isoproterenol infusion. Finally, progesterone suppressed the effect of estrogen on OTR mRNA production and binding when the two compounds were administered together. However, when isoproterenol treatment was added this effect was abolished and Emax was enhanced more than that seen following treatment with estrogen alone. These data suggest that beta2-adrenoceptor activation represents an important regulator of OTR expression/function in estrogen- and progesterone-dominated rat myometrium.

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Beta2-adrenoceptor desensitization in non-pregnant estrogen-primed rat myometrium involves modulation of oxytocin receptor gene expression

Journal of Molecular Endocrinology ◽

10.1677/jme.0.0200261 ◽

1998 ◽

Vol 20 (2) ◽

pp. 261-270 ◽

Cited By ~ 12

Author(s):

T Engstrom ◽

P Bratholm ◽

H Vilhardt ◽

NJ Christensen

Keyword(s):

Gene Expression ◽

Contractile Response ◽

Receptor Gene ◽

Mrna Levels ◽

Oxytocin Receptor Gene ◽

Pregnant Rat ◽

Homologous Desensitization ◽

Stimulation Of

The nona-peptide oxytocin (OT) induces contraction of the myometrium by interaction with specific plasma membrane associated OT receptors (OTR), whereas stimulation of beta2-adrenoceptors (beta2AR) causes relaxation. Homologous desensitization of the myometrium to both hormones has been described. However, a possible interaction between the two systems has not been investigated. In the present study, long-term in vivo treatment of non-pregnant estrogen-primed rats with isoproterenol decreased maximal relaxation of isolated uterine strips challenged with isoproterenol. Increased EC50 values of similarly treated animals suggest that the coupling between receptor occupancy and contractile response was impaired. Since beta2AR mRNA levels were left unchanged, we conclude that the homologous desensitization to beta2 stimulation is not due to changes in beta2AR gene expression. OT infusion did not alter beta2AR mRNA levels or isoproterenol-induced relaxation of isolated uterine strips. Treatment with OT had no effect on the amount of myometrial OTR mRNA. We have previously found that OT down-regulates OTR in the non-pregnant rat myometrium, but this therefore does not appear to take place at the level of mRNA production. Isoproterenol treatment resulted in a three-fold increase in OTR mRNA. This was accompanied by a 91% rise in OTR binding and an augmented contractile response of isolated uterine strips to OT, suggesting that the increased production of mRNA reflects formation of active receptors. Neither OTR affinity nor EC50 of in vitro strips was affected by isoproterenol treatment. We conclude that stimulation of beta2AR causes heterologous up-regulation of OTR in the non-pregnant estrogen-primed rat myometrium.

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Expression of rat hepatic multidrug resistance-associated proteins and organic anion transporters in pregnancy

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.00126.2002 ◽

2002 ◽

Vol 283 (3) ◽

pp. G757-G766 ◽

Cited By ~ 60

Author(s):

Jingsong Cao ◽

Bruno Stieger ◽

Peter J. Meier ◽

Mary Vore

Keyword(s):

Multidrug Resistance ◽

Plasma Membranes ◽

Organic Anion ◽

Liver Homogenate ◽

Pregnant Rats ◽

Pregnant Rat ◽

Western Analysis ◽

Anion Transporters ◽

Intracellular Compartments ◽

In Pregnancy

The expression of hepatic multidrug resistance-associated protein (Mrp)1, 2, 3, and 6 and organic anion transporting polypeptides (Oatp)1 and 2 were examined in control and 20- to 21-day pregnant rats. Western analysis showed that expression of Oatp2 was decreased 50% in pregnancy, whereas expression of Oatp1 did not change. Expression of Mrp2 protein determined by Western analysis of total liver homogenate decreased to 50% of control levels in pregnant rats, consistent with studies using plasma membranes. Confocal immunohistochemistry showed that Mrp2 expression was confined to the canalicular membrane in both control and pregnant rats and was not detectable in intracellular compartments. In isolated perfused liver, the biliary excretion of 2,4-dintrophenyl-glutathione was significantly decreased in pregnancy, consistent with decreased expression of Mrp2. The expression of the basolateral transporter Mrp1 was not altered in pregnancy, whereas expression of Mrp6 mRNA was decreased by 60%. Expression of Mrp3 was also decreased by 50% in pregnant rat liver, indicating differential regulation of Mrp isoforms in pregnancy. These data also demonstrate that decreased Mrp2 expression is not necessarily accompanied by increased Mrp3 expression.

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Use of a novel and highly selective oxytocin receptor antagonist to characterize uterine contractions in the rat

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.00057.2007 ◽

2007 ◽

Vol 293 (1) ◽

pp. R299-R305 ◽

Cited By ~ 13

Author(s):

Gerald P. McCafferty ◽

Mark A. Pullen ◽

Charlene Wu ◽

Richard M. Edwards ◽

Michael J. Allen ◽

...

Keyword(s):

Receptor Antagonist ◽

Intravenous Administration ◽

Plasma Concentrations ◽

Oxytocin Receptor ◽

Pregnant Rats ◽

Uterine Contractions ◽

Oxytocin Receptors ◽

Dose Dependent Decrease ◽

Dose Dependent ◽

Similar Affinity

Spontaneous and induced uterine contractions in the rat were found to be inhibited by a novel and selective oxytocin receptor antagonist GSK221149A (3 R,6 R)-3-Indan-2-yl-1-[(1 R)-1-(2-methyl-1,3-oxazol-4-yl)-2-morpholin-4-yl-2-oxoethyl]-6-[(1 S)-1-methylpropyl]-2,5-piperazinedione. GSK221149A displayed nanomolar affinity ( Ki = 0.65 nM) for human recombinant oxytocin receptors with >1,400-fold selectivity over human V1a, V1b, and V2 receptors. GSK221149A had similar affinity ( Ki = 4.1 nM) and selectivity for native oxytocin receptors from rat and produced a functional, competitive block of oxytocin-induced contractions in isolated rat myometrial strips with a pA2 value of 8.18. Intravenous administration of GSK221149A produced a dose-dependent decrease in oxytocin-induced uterine contractions in anesthetized rats with an ID50 = 0.27 ± 0.60 mg/kg (corresponding plasma concentrations were 88 ng/ml). Oral administration of GSK221149A (5 mg/kg) was effective in inhibiting oxytocin-induced uterine contractions after single and multiple (4-day) dosing. Spontaneous uterine contractions in late-term pregnant rats (19–21 days gestation) were significantly reduced by intravenous administration of 0.3 mg/kg of GSK221149A. These results provide further evidence that selective oxytocin receptor antagonism may offer an effective treatment for preterm labor.

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Gonadal steroids effect similar regulation of gonadotrophin subunit mRNA expression in both male and female rats

Journal of Endocrinology ◽

10.1677/joe.0.1320039 ◽

1992 ◽

Vol 132 (1) ◽

pp. 39-45 ◽

Cited By ~ 14

Author(s):

A. C. Dalkin ◽

S. J. Paul ◽

D. J. Haisenleder ◽

G. A. Ortolano ◽

M. Yasin ◽

...

Keyword(s):

Gene Expression ◽

Steady State ◽

Gnrh Antagonist ◽

Gonadal Steroids ◽

Female Rats ◽

Plasma Testosterone ◽

Subunit Gene ◽

Gnrh Secretion ◽

Male And Female Rats ◽

Males And Females

ABSTRACT Gonadal steroids can act both indirectly via gonadotrophin-releasing hormone (GnRH) and directly on the pituitary to regulate gonadotrophin subunit gene expression. Recent studies to assess a possible direct action at the pituitary have shown that testosterone, when given to males in the absence of endogenous GnRH action, selectively increases FSH-β mRNA concentrations. Conversely, in females, oestradiol appears to regulate gonadotrophin subunit mRNAs primarily via GnRH. The present study was designed to determine whether these differing results reflect specific actions of the gonadal steroids themselves or different responses of the pituitary gonadotroph cells in males and females. Rats which had been castrated 7 days earlier were given silicone elastomer implants (s.c.) containing oestradiol (plasma oestradiol 68 ± 4 ng/l) in males or testosterone (plasma testosterone 3·5 ± 0·3 μg/l) in females in the absence or presence of a GnRH antagonist. Seven days later pituitaries were removed and steady-state mRNA concentrations measured by dotblot hybridization. In males, oestradiol reduced LH-β and FSH-β but not α mRNA. The antagonist reduced levels of all three subunit mRNAs in males and the addition of oestradiol had no further effect, suggesting that oestradiol regulates gonadotrophin subunit gene expression in males by suppressing GnRH secretion. In females, testosterone reduced all three subunit mRNAs though FSH-β remained threefold higher than in intact animals. The GnRH antagonist was as effective as testosterone alone and reduced α and LH-β to levels found in intact animals. FSH-β mRNA was partially reduced by antagonist alone in ovariectomized females but the addition of testosterone increased FSH-β twofold versus antagonist alone (as has been observed in males). These findings, together with earlier data, suggest that testosterone increased FSH-β twofold versus antagonist alone (as has been observed in males). These findings, together with earlier data, suggest that testosterone reduces gonadotrophin subunit mRNAs by inhibiting GnRH secretion and also acts directly on the gonadotroph to increase steady-state FSH-β mRNA concentrations in both males and females. Journal of Endocrinology (1992) 132, 39–45

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Regulation of oxytocin receptor gene expression in sheep: tissue specificity, multiple transcripts and mRNA editing

Reproduction ◽

10.1530/jrf.0.1200187 ◽

2000 ◽

Vol 120 (1) ◽

pp. 187-200 ◽

Cited By ~ 1

Author(s):

H. Feng ◽

M Bhave ◽

R. Fairclough

Keyword(s):

Gene Expression ◽

Tissue Specificity ◽

Receptor Gene ◽

Oxytocin Receptor ◽

Mrna Editing ◽

Oxytocin Receptor Gene ◽

Multiple Transcripts ◽

Receptor Gene Expression

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PLASMA PROLACTIN AND PROGESTERONE RESPONSES TO MATING ARE ALTERED IN AGED RATS

Journal of Endocrinology ◽

10.1677/joe.0.0900179 ◽

1981 ◽

Vol 90 (2) ◽

pp. 179-191 ◽

Cited By ~ 3

Author(s):

S. HENDRICKS ◽

C. A. BLAKE

Keyword(s):

Plasma Concentrations ◽

External Jugular Vein ◽

Female Rats ◽

Plasma Prolactin ◽

Aged Rats ◽

Pregnant Rats ◽

Pregnant Rat ◽

Plasma Progesterone ◽

The One ◽

The Right

The effects of varying amounts of copulatory stimulation on patterns of plasma concentrations of prolactin and progesterone were evaluated in 3- and 12-month-old female rats. The 12-month-old group included rats which still exhibited oestrous cycles and rats in persistent vaginal oestrus (PVO). The extent of copulatory stimulation was defined by the number of intromissions received during mating: ≤5,15 or > 50. Blood samples were drawn over the 8 days after mating through a cannula inserted into the right external jugular vein. Plasma from the samples was assayed for prolactin and progesterone. In aged but still cyclic rats, pregnancy rates were positively correlated with the number of intromissions received during mating. Only one rat in PVO became pregnant. All animals which became pregnant and rats in PVO which, after mating, exhibited a disruption of the pattern of PVO, showed the nocturnal surge of plasma prolactin characteristic of pregnant and pseudopregnant rats. While these surges persisted until day 8 after mating in pregnant animals, they were absent by this time in the rats in PVO. Prolactin surges were present in some but not all of the aged rats which did not become pregnant. Progesterone concentrations were raised in all pregnant animals except the one pregnant rat in PVO and, while not related to the number of intromissions, concentrations were higher 8 days after mating in young compared with those in aged pregnant rats. Plasma progesterone was low in rats in PVO regardless of disruption of the pattern of PVO. We have concluded that the failure of limited copulatory stimulation to induce pregnancy in older rats results, at least in part, from its failure to initiate nocturnal prolactin surges. Nevertheless, our data suggest that matings which are not experimentally limited should provide ample stimulation to establish such surges. Although reduced plasma concentrations of prolactin and progesterone at pro-oestrus and reduced plasma progesterone through part of gestation may contribute to decreasing fertility in aged rats, other unidentified factors appear to be involved in mediating the capacity of extensive copulatory stimulation to induce pregnancy in these animals.

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Effect of chronic hypoxia on myometrial responsiveness in the pregnant rat

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.1996.270.3.e477 ◽

1996 ◽

Vol 270 (3) ◽

pp. E477-E482 ◽

Cited By ~ 2

Author(s):

J. W. Rhee ◽

L. D. Longo ◽

W. J. Pearce ◽

N. H. Bae ◽

G. J. Valenzuela ◽

...

Keyword(s):

Binding Sites ◽

Chronic Hypoxia ◽

Contractile Response ◽

Plasma Concentrations ◽

Hypoxic Exposure ◽

Normal System ◽

Pregnant Rat ◽

Near Term ◽

Air Control

Mechanisms involving the timing of normal parturition are not well understood in most animal species. To gain a greater understanding of the mechanisms, we employed hypoxia to perturb the normal system of parturition. The present study was designed to investigate the effects of chronic hypoxia on myometrial contractility in the near-term pregnant rat. Rats were exposed to room air (control) or to continuous hypoxia (10.5% O2) either from experimental days 19 through 21 (2-day exposure) or from experimental days 15 through 21 (6-day exposure). On day 21, blood was collected for hormone assays, and the uterine horns were collected from each dam. One horn was snap-frozen in liquid nitrogen for oxytocin (OT) receptor analysis, and the other was used for in vitro assessment of myometrial contractile responses to cumulative doses of OT or arginine vasopressin (AVP). Hypoxic exposure resulted in approximately 60% reduction of the maximal myometrial contractile response to OT and a significant reduction in OT binding sites from 256.9 +/- 34.9 to 84.9 +/- 21.3 fmol/mg protein (P<0.01). In contrast, the contractile response to AVP was unaffected after exposure to chronic hypoxia (P> 0.05). Additionally, we observed no difference in the plasma concentrations of estrogen, progesterone, and corticosterone. We conclude that chronic hypoxia decreased the effectiveness of OT-specific contractile mechanisms, at least partially through a decrease in OT binding sites.

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Glucose uptake and oxidation in fat cells of trained and sedentary pregnant rats

Journal of Applied Physiology ◽

10.1152/jappl.1986.60.5.1704 ◽

1986 ◽

Vol 60 (5) ◽

pp. 1704-1709 ◽

Cited By ~ 6

Author(s):

B. W. Craig ◽

J. Treadway

Keyword(s):

Glucose Uptake ◽

Exercise Program ◽

Cell Number ◽

Fat Cells ◽

Sedentary Control ◽

Pregnant Rats ◽

Pregnant Rat ◽

Fed State ◽

Exercise Period ◽

Fat Pads

The purpose of this investigation was to examine the relationship between an exercise program and fetal development to determine whether training could influence insulin sensitivity in the pregnant rat. Prior to impregnation one group of animals was exercise trained on a Quinton shock-stimulus rodent treadmill. The exercised group was trained to run 5 days/wk, for 2.0 h/day at 31 m/min up an 8 degree incline for 8 wk before mating. Following mating the training intensity was reduced to 27 m/min up a 5 degree incline, and the exercise period decreased to 1 h/day. On day 19 of gestation, 24 h postexercise for the trained mothers, the animals were killed in the fed state and the parametrial fat pads were removed. The parametrial depot of the trained mother was smaller than the sedentary control dam. This was due to a change in cell size and did not involve alterations in cell number. Isolated adipocytes of the parametrial fat pads were used to measure the rates of 2-deoxy-D-[3H]glucose uptake and D-[1–14C]glucose oxidation to 14CO2. The results indicated that the adipocytes from the dam trained prior to and during pregnancy were significantly (P less than 0.05) more responsive to insulin than those of animals remaining sedentary during the same period. At the maximal insulin concentration tested, the fat cells from trained mothers were able to take up and metabolize approximately twice as much glucose as the sedentary control dams. However, the increase in insulin responsiveness induced by the training program did not match the changes observed in trained nonpregnant rats of prior investigations.

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MORPHOLOGICAL CHANGES IN THE ENDOCRINE PANCREAS IN PREGNANT RATS WITH EXPERIMENTAL DIABETES

Journal of Endocrinology ◽

10.1677/joe.0.0800175 ◽

1979 ◽

Vol 80 (2) ◽

pp. 175-179 ◽

Cited By ~ 14

Author(s):

F. A. VAN ASSCHE ◽

L. AERTS ◽

W. GEPTS

Keyword(s):

Endocrine Pancreas ◽

Experimental Diabetes ◽

Morphological Changes ◽

Normal Pregnancy ◽

Β Cells ◽

Pregnant Rats ◽

Pregnant Rat ◽

Human Pregnancy ◽

The Individual

This present study has demonstrated that during normal pregnancy in the rat the number of β-cells is increased (hyperplasia) and the volume of the individual β-cells is increased (hypertrophy). During experimental diabetes, however, the endocrine pancreas has an impaired capacity to compensate during pregnancy. In the experimental diabetic pregnant rat the β-cells cannot replicate due to the unfavourable metabolic environment. This could reflect the complications caused by diabetes during human pregnancy.

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