Characterization of late-pregnant rat uterine contraction via the contractility ratio in vitro - Significance of alpha(1)-adrenoceptors

The aim of this study was to characterize the ability of late-pregnant (day s 15-22) rat uterine tissue rings to contract in response to electric field stimulation in vitro. For this purpose, maximum rhythmic contractions were elicited by optimum choice of the period time and the pulse width, the two main parameters of electric field stimulation. In parallel, the plasma 17 beta -estradiol and progesterone levels were determined. It was found that the contractility ratio, i.e, the quotient of the optimum pulse width and t he period time, is a good parameter with which to express the contractility . The larger the contractility ratio, the better the ability to contract. E valuation of the area under the curve did not furnish information relating to the contractility in this method. A very close correlation was observed between the contractility ratio and the quotient of the 17 beta -estradiol and progesterone levels on different days, demonstrating that the in vitro ability characterized by the contractility ratio is in keeping with the phy siological regularity. There was also a very close correlation between the contractility ratio and the quotient of the alpha (1)- and beta -adrenergic receptors, suggesting the main role of the numbers of alpha1(-)receptor in pregnant uterine contractility. It is believed that this is the first in v itro model to give a numerical measure concerning the ontogeny of uterine c ontractility in late pregnancy. (C) 2001 Elsevier Science Inc. All rights r eserved.