083P Institute of Education, London
Winter Meeting December 2005

 

Investigation of the in vitro effect of vasopressin and oxytocin in the rat and Guinea-pig uterus

G. Mayer, M.B. Princivalle, V. Goddard, D.J. Corkill, R.M. Haigh, C.M. Yea & R.L.C. Handy, Biology Department, Ferring Research Ltd, Chilworth Science Park, 1 Venture Road, Southampton, SO16 7NP.

In-vitro and in-vivo non-pregnant human uteri contract in response to arginine vasopressin (AVP) via the vasopressin V1a receptor (Akerlund et al., 1986; Bossmar et al., 1995 & 1997; Melin et al., 1981; Steinwall et al., 2004). A great deal of evidence supports the contractile role of the V1a rather than the oxytocin (OT) receptor in human uteri, including reports that AVP is 20 times more potent than OT in inducing contractions of human uterine strips in vitro (Bossmar et al., 1995 & 1997; Melin et al., 1981). The aim of this study was to investigate if the same occurs in rat and guinea pig and thus whether either of these species could be used as models of human V1a receptor mediated uterine activity. Current literature suggests that the OT rather than the V1a receptor mediates vasopressin induced contractions in rat (Chan et al., 1996) and in mouse (Kawamata et al, 2004).

Two cylinders from each uterine horn of adult Wistar rats (~ 210 g) and guinea pigs (~ 440 g) were mounted between two stainless steel triangles in an organ bath. Uteri were mounted singly under 1.0 g or 1.5 g tension respectively, in 10 ml baths with a modified ionic composition of Krebs Ringer bicarbonate buffer (pH 7.5) gassed with 95 % O2, 5 % CO2 at 37 ° C, which was optimised in order to reduce spontaneous contractions. Stock solutions of [Arg8]-vasopressin (AVP), OT, the selective OT receptor antagonist barusiban (FE 200440, Nilsson et al., 2003), and the selective peptidic V1a agonist F-180 (Andres et al., 2002) were prepared at 1 x 10-2 M in 100 % dimethyl sulfoxide (DMSO) and then serially diluted in Krebs Ringer buffer. Barusiban was used to confirm if the contractions obtained with OT and AVP in rats were the result of OT or V1a receptor activation.

AVP and OT, but not F-180, were able to induce contractions in rat uteri (EC50 values are shown in Table 1) with OT being 18-fold more potent than AVP. Barusiban was able to inhibit both the OT and AVP-induced contractions. Therefore, we conclude that the contraction of the rat uterus induced by both AVP and OT in vitro are OT receptor mediated. Likewise, in the guinea pig uteri, AVP and OT (but not F-180) were able to induce contractions with EC50 values of 5.43 x 10-9 M and 4.80 x 10-8 M for OT and AVP respectively, again consistent with an OT rather than a V1a mediated response. The rat and the guinea-pig are therefore not suitable in vitro models of human V1a receptor mediated uterine activity.

Table 1: EC50 data for rat uterine contractions with and without barusiban (1 x 10-8 M)(n = 4)

 

EC50 without barusiban
EC50 with barusiban
OT
6.24 x 10-10 M
(2.45 x 10-10 to 1.59 x 10-9 M)
3.34 x 10-7 M
(1.76 x 10-7 to 6.31 x 10 -7 M)
AVP
1.15 x 10-8 M
(4.68 x 10-9 to 2.81 x 10-8 M)
4.34 x 10-6 M
(2.10 x 10-7 to 9.04 x 10-5 M)
F-180
No response up to 10 μM
No response up to 10 μM

 

 

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Bossmar et al., (1995). Br. J. Obstet. Gynaecol., 102, 907-912.
Bossmar et al., (1997). Br. J. Obstet. Gynaecol., 104, 471-477.
Chan et al., (1996). Am. J. Obstet. Gynaecol., 175(5), 1331-5.
Kawamata et al., (2003). Eur. J. Pharmacol., 472(3),229-34.
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Steinwall et al., (2004). Acta. Obstet. Gynecol Scand., 83, 12-18.