The Effect of Oxytocics on the Human Cervix During Midtrimester Pregnancy

Abstract

Observations of the effects of oxytocics on the human pregnant cervix have been made in vivo using a double open ended catheter technique. Prostaglandin E,, prostaglandin F,a and oxytocin had similar but no specific effects upon the intracervical canal pressure; ergometrine caused contractions of the cervix. The significance of these findings is discussed in relation to cervical rupture and cervico-vaginal fistulae that have been reported following second trimester abortion induced with prostaglandins.

Mechanical Responses of the Isolated Cervix and Uterine Horn of Pregnant Rats Near Term to Drugs

“…Contractile responses to PGE2 at low concentrations and inhibitory actions at high concentrations suggest two receptor systems which display differing sensitivities to PGE2. PGE2 has been shown to in- duce relaxations of the cervix of the non-pregnant human in vitro (Najak et al, 1970) and in vivo (Coutinho & Darze, 1976) but generally contracts the uterus of the non-pregnant human and both tissues during pregnancy (Mackenzie, 1976). The inhibitory action of PGE2 was not blocked by propranolol demonstrating it was not a ,B-adrenoceptor-mediated effect.…”

“…This is in contrast to these tissues from the non-pregnant rat which exhibited similar sensitivities to methacholine, oxytocin, isoprenaline and phenylephrine (Hollingsworth, 1974). Oxytocin has been shown to be less potent on the cervix of the pregnant cow in vivo than the uterus (Fitzpatrick, 1957) while ergometrine is more potent on the human cervix than the uterus (Schild et al, 1951;Mackenzie, 1976). The reasons for these differences in drug potencies between the cervix and uterine horn are not as yet explained.…”

“…In the nonpregnant rat, some thickening of the circularly arranged smooth muscle at the uterine horn end of the cervix has been noted (Hollingsworth, 1974). Cervical tissue in vitro and in vivo of several species can exhibit spontaneous mechanical activity and will respond to drugs with both contractions and relaxations (Newton, 1934;Bonnycastle & Ferguson, 1941;Adler, Bell & Knox, 1944;Schild, Fitzpatrick & Nixon, 1951;Schofield, 1952;Fitzpatrick, 1957;1958;Najak, Hillier & Karim, 1970; Hollingsworth, 1974;Coutinho & Darze, 1976;Mackenzie, 1976).…”

Cervical contractions: the response of the cervix to oxytocic stimulation in the latent phase of labour

“…These data show that the cervix has more than a passive function, particularly in early labour when the cervix is still relatively uneffaced and undilated. Contractions of the cervix have been demonstrated in animals (Newton 1934, 1937; Bonnycastle & Ferguson 1941; Adler et al 1944) and in humans (Karlson 1949; Schild et al 1951; Mackenzie 1976). Studies in pregnant women have shown that in the first and second trimesters of pregnancy the human cervix can contract in response to oxytocic agents (Schild et al 1951; Mackenzie 1976) and at term the cervix can contract rhythmically, sometimes independently of activity in the uterine body (Karlson 1949).…”

Quantitative Ultrasound Detects Smooth Muscle Activity at the Cervical Internal Os in Vitro

“…Although the IHC, imaging and functional studies described above are recent, the concept of a functional cervical sphincter is more than a century old; in 1872, Lott described a "sphincter isthmii interni based on cadaver studies, and in 1924, Oertel suggested that it was functional, as reported in Youssef (1958). Studies from the 1930s through 1990s reported that the cervix and uterus of pregnant and non-pregnant women contract independently in response to hormones or oxytocin in vivo and that cervical tissue contracts when exposed to adrenoreceptor agonists or oxytocin in organ baths (Karlson 1949;Schild et al 1951;Youssef 1958;Mackenzie 1976;Bryman et al 1984;Olah 1993).…”