MYOMETRIAL ACTIVITY IN THE PREGNANT GUINEA-PIG

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Abstract
SUMMARY: 1. Observations are reported on the effect of gestagens, oxytocin and Infonutrol on pregnancy in the guinea-pig. 2. In mid-pregnancy a series of oxytocin injections (each of 5 i.u.) was required in most animals to produce abortion but this treatment was not always effective. Abortion occurred several hours after an injection and often not all the foetuses were extruded on the same day. 3. Towards the end of pregnancy the myometrium became more sensitive and within 2 days of term a small dose of oxytocin resulted in the prompt delivery of the entire litter. 4. Neither progesterone nor 6α-methyl 17α-hydroxyprogesterone acetate were effective in delaying spontaneous or oxytocin-induced delivery in the doses tried (2·5 mg. 12-hourly i.m. or 10 mg. daily s.c.). 5. In a small number of experiments Infonutrol was not effective in disturbing pregnancy. 6. The significance of these findings is discussed in relation to the mechanisms for the control of the myometrium which have been established in the rabbit. There seems no reason to believe the basic mechanisms are necessarily different in the guinea-pig.