Oxytocin and Bovine Parturition: A Steep Rise in Endometrial Oxytocin Receptors Precedes Onset of Labor1

Fuchs, Anna‐Riitta; Helmer, Hanns; Behrens, Otto K.; Liu, H C; Antonian, Lida; Chang, Soo-Eun; Fields, Michael J.

doi:10.1095/biolreprod47.6.937

Cited by 80 publications

(45 citation statements)

References 29 publications

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“…Because, in vivo, OTR densities can reach up to 1850 and 7300 fmol/mg protein in myometrium and endometrium respectively (Fuchs et al 1992), these levels were well within the physiological range. In addition, when OTR expression levels were lowered by lowering the amount of expression plasmid used for transfection, OTR oligomers remained detectable by the co-immunoprecipitation approach at receptor densities as low as 50 fmol/mg protein.…”

Section: Evidence For Otr Oligomerization By Co-immunoprecipitationmentioning

confidence: 66%

Identification of dimeric and oligomeric complexes of the human oxytocin receptor by co-immunoprecipitation and bioluminescence resonance energy transfer

Devost¹,

Hh²

2003

Journal of Molecular Endocrinology

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The nonapeptide hormone oxytocin exerts many important biological functions, including uterine contractions during parturition and milk ejection during lactation. The manifold effects of oxytocin are mediated by a single oxytocin receptor (OTR) type, a member of the super-family of G-protein-coupled receptors. There is accumulating recent evidence that certain G-protein-coupled receptors exist in the form of oligomeric complexes. Here we demonstrate, using two different co-immunoprecipitation strategies as well as bioluminescence resonance energy transfer techniques, that the OTR is capable of forming oligomeric complexes in vivo and that these complexes exist at the cell surface membrane. The human OTR was N-terminally tagged with either a Myc or Flag epitope and transiently expressed in COS-7 cells. Cell lysates were immunoprecipitated using an anti-Flag antibody and analyzed by SDS-PAGE and Western blotting using an anti-Myc antibody, or vice versa. Either strategy provided evidence for the co-precipitation of Myc-or Flag-tagged OTR respectively.Biochemical characterization of OTR dimers showed that homodimer formation is not dependent on the establishment of disulfide bonds. The existence of OTR dimers and oligomers at the level of the cell surface was demonstrated by exposing intact living cells to an anti-Flag antibody and analyzing the immunoprecipitate by Western blotting with an anti-Myc antibody. This approach demonstrated furthermore that the presence of receptor oligomers at the cell surface is modulated by ligand in a time-dependent fashion. Finally, we obtained evidence that the OTR is forming oligomeric structures in intact living cells by observing the occurrence of bioluminescence resonance energy transfer in cells co-transfected with OTR constructs bearing at their C-terminus either a Renilla luciferase or the yellow fluorescent protein. Taken together, these data show that the OTR can form homodimers and oligomers in the cell model used and that these oligomers are present at the cell surface.

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Section: Evidence For Otr Oligomerization By Co-immunoprecipitationmentioning

confidence: 66%

Identification of dimeric and oligomeric complexes of the human oxytocin receptor by co-immunoprecipitation and bioluminescence resonance energy transfer

Devost¹,

Hh²

2003

Journal of Molecular Endocrinology

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“…They speculated that this effect might be related to an increased myometrial expression of inactivating -adrenoreceptor kinase ( ARK) as previously shown by Ruzycky & DeLoia (1997). A high estrogen level (Fuchs et al 1992) and a fall in circulating progesterone (Thorburn & Challis 1979) are characteristics of parturition in mammals. However, since estrogen induces a modest decrease in ARK and progesterone reverses this effect (Ruzycky & DeLoia 1997), the present data indicate that other mechanisms must contribute to the observed tachyphylaxis.…”

Section: Discussionmentioning

confidence: 87%

Desensitization of beta2-adrenoceptor function in non-pregnant rat myometrium is modulated by sex steroids

Engstrøm

Vilhardt²,

Bratholm³

et al. 2001

Journal of Endocrinology

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The effects of in vivo treatment with estrogen and progesterone on isoproterenol-induced uterine relaxation and 2 -adrenoceptor ( 2 AR) mRNA production in nonpregnant rat myometrium were investigated. Whether homologous myometrial desensitization of 2 AR function was dependent on or modulated by the two steroids was also examined.Estrogen treatment alone or in combination with progesterone reduced maximal relaxation (E max ) of isolated uterine strips subsequently challenged with isoproterenol whereas progesterone alone had no effect on this parameter. The reduction was accompanied by an enhanced 2 AR mRNA concentration. The concentration of isoproterenol giving half-maximal relaxing response (EC 50 ) increased following estrogen treatment and this effect was curbed by progesterone.Isoproterenol had no effect on 2 AR transcription irrespective of the steroid regimes employed. E max of isolated uterine strips was reduced following prolonged in vivo treatment with isoproterenol but the effect was found only when estrogen alone was administered concomitantly. Finally, in vivo treatment with isoproterenol increased EC 50 of uterine strips subsequently stimulated with isoproterenol in vitro. This effect was independent of steroid treatment.We conclude that homologous desensitization of 2 AR function in non-pregnant rat myometrium in terms of sensitivity (EC 50 ) is independent of sex steroids but in terms of maximal response (E max ) occurs only in the presence of estrogen. We speculate whether progesterone withdrawal in connection with the well-known estrogen dominance at rat parturition may strengthen the desensitization induced by 2 AR activation and thus contribute to the transformation of the uterus from a quiescent to a highly contractile organ.

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“…In the uterus, the near-term myometrium is extremely sensitive to oxytocin. This increased uterine responsiveness to oxytocin occurs in parallel with an increase in the number of uterine oxytocin binding sites in rats [3,21], humans [4], rabbits [13,14] and cows [5]. Corresponding increases in uterine oxytocin receptor (OTR) mRNA expression in late pregnancy and parturition have been reported in rats [11,12,19], humans [9], cows [8] and sheep [24,25].…”

mentioning

confidence: 87%

Changes in Uterine Receptor mRNAs for Oxytocin and Estrogen in the Pseudopregnant Rat

Murata

Narita

Higuchi

2008

The Journal of Veterinary Medical Science

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ABSTRACT. This study examined the uterine oxytocin-(OTR) and estrogen-(ER) receptor mRNA levels during and after pseudopregnancy (PSP) in rats. An increased OTR mRNA level was observed from day 14 of PSP, and the maximal level was attained during the following proestrus. The levels of ERα mRNA were low during PSP and significantly increased during the following estrus. The level of ERβ mRNA was significantly decreased during proestrus and then returned to the values observed during days 7-14 of PSP by estrus. These results suggest i) suppression of ERα mRNA during the luteal phase and that ii) the changes in OTR, ERα and ERβ mRNA levels during proestrus and estrus following PSP are similar to those during the normal estrous cycle. KEY WORDS: estrogen receptor, oxytocin receptor, pseudopregnancy.J. Vet. Med. Sci. 70(11): 1253-1256, 2008 Oxytocin (OT) was initially isolated as a neurohypophysial hormone that stimulates contraction of the myometrium and myoepithelium to facilitate parturition and milk ejection, respectively, and is considered to mediate various reproductive functions in the ovary, uterus and brain. In the uterus, the near-term myometrium is extremely sensitive to oxytocin. This increased uterine responsiveness to oxytocin occurs in parallel with an increase in the number of uterine oxytocin binding sites in rats [3,21], humans [4], rabbits [13,14] and cows [5]. Corresponding increases in uterine oxytocin receptor (OTR) mRNA expression in late pregnancy and parturition have been reported in rats [11,12,19], humans [9], cows [8] and sheep [24,25].Estrogen stimulates the number of uterine oxytocin binding sites [3,20,22] and OTR mRNA expression in ovariectomized (OVX) virgin rats [11,12]. However, injection of estrogen does not stimulate oxytocin receptor mRNA expression in late pregnant rats or progesterone-primed OVX virgin rats, but is effective only after ovariectomy and removal of progesterone, respectively [17]. These results suggest that in addition to the increase in serum estrogen level near term in rats, regulation of the uterine responsiveness to estrogen is important for understanding the role of estrogen in the uterus. The actions of estrogen are mediated through estrogen receptors [1], and two types of estrogen receptor (ER), ERα and ERβ, have been cloned from the human uterus [6] and rat prostate [10], respectively.In the rat uterus at the end of pregnancy and during labor, the ERα mRNA level gradually increases simultaneously with the OTR mRNA level, while the ERβ mRNA level does not show any significant changes; during this period, there is a positive correlation between the ERα and OTR mRNA levels [16]. However, while the OTR mRNA level is increased during proestrus and then decreased during estrus in the estrous cycle, the ERα and ERβ mRNA levels decrease during proestrus and return to the levels observed during diestrus at estrus [15,16]. This indicates apparent reciprocal changes between OTR and ER (ERα and ERβ) mRNA levels during proestrus and estrus. Furthermore, injection of 17...

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Oxytocin and Bovine Parturition: A Steep Rise in Endometrial Oxytocin Receptors Precedes Onset of Labor1

Cited by 80 publications

References 29 publications

Identification of dimeric and oligomeric complexes of the human oxytocin receptor by co-immunoprecipitation and bioluminescence resonance energy transfer

Identification of dimeric and oligomeric complexes of the human oxytocin receptor by co-immunoprecipitation and bioluminescence resonance energy transfer

Desensitization of beta2-adrenoceptor function in non-pregnant rat myometrium is modulated by sex steroids

Changes in Uterine Receptor mRNAs for Oxytocin and Estrogen in the Pseudopregnant Rat

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