An Examination of the Quantitative Relationship Between Progesterone and the Maintenance of Pregnancy

The effects of oestradiol benzoate, progesterone, relaxin and ovariectomy on cervical extensibility in the late pregnant rat

“…There is only limited information on the possible hormonal control of the increase in cervical extensibility during late pregnancy in the rat (see 'Introduction')· The present results and those of others (Csapo & Wiest, 1969;Cátala & Deis, 1973;Buckle & Nathanielsz, 1975) show that parturition after ovariectomy in late pregnancy in the rat is protracted, fetal and neonatal deaths occur and often fetuses are lodged in a cervical canal. This could be due to a lack of an ovarian hormone to provide the terminal increase in cervical extensibility.…”

“…In the present work, oestradiol benzoate and progesterone had no effect on cervical extensibility when given to intact rats but the combination of progesterone and oestradiol benzoate produced a small increase when given to ovariectomized rats. The dosages of progesterone and oestradiol benzoate used are similar to those which will, respectively, return plasma progesterone concentrations to normal values following ovariectomy (Csapo & Wiest, 1969) and produce normal delivery following ovariectomy near term (Cátala & Deis, 1973). Also, the increases in extensibility during pregnancy described here and by Harkness & Nightingale (1962) and Rundgren (1974) precede the rise in plasma oestradiol concentrations near term (Shaikh, 1971).…”

“…As peripheral plasma concentrations of progesterone decline in the late pregnant rat from about Day 17 or 18 (Csapo & Wiest, 1969;Buckle & Nathanielsz, 1975) increased cervical extensibility could be a direct consequence of progesterone withdrawal. However, cervical extensibility decreases following ovariectomy when plasma progesterone concentrations will have fallen (Csapo & Wiest, 1969) and extensibility could not be significantly increased with the progesterone-withdrawal treatment used in the present study. Fitzpatrick (1977a, b) Another hormone synthesized and stored in rat ovaries is relaxin (Anderson & Long, 1978).…”

Calmodulin concentration in the uterus during pregnancy and influence of sex steroids.

“…Estrogen is shown to increase the response of uterine contraction and progesterone to decrease it (Csapo and Wiest 1969). The present results indicate that the increase in calmodulin contents produced by estrogen may be one of the factors to increase the uterine contractile response.…”

A critical period in the onset of parturition in rats and uterine sensitivity to estradiol and progesterone

“…A change in the balance of uterine epinephrine and norepinephrine has been previously reported by Maltier and CavaiII6 (1975) in association with these abnormal deliveries. The impairment observed after both treatments was similar to that described after ovariectomy (delayed parturition, partial delivery or no delivery ; Csapo and Wiest, 1969), suggesting that some disorders in ovarian steroids might be implicated in abnormal parturition. Wilcox and Wiest (1966) and Kuhn and Briley (1970) and then applied by Lacy et al, (1976 (anti-progesterone-11a [succinyl] -bovine serum albumin), used at a final dilution of 1:3 000, had no significant cross-reactivity with 20a-HP (1 %), 5a-pregnan-3,20-dione (2.5 %), 50-pregnan-3,20-dione (2 %) or deoxycorticosterone (3.5 %).…”