Pseudopregnancies from Electrical Stimulation of the Cervix in the Diestrum. ∗

The artificial induction of a pseudopregnant state in the rat by means of electrical or mechanical stimulation of the cervix uteri is a common laboratory procedure. It has long been supposed that these stimuli to be effective must be applied at or near the time when the female is in a sexually receptive mood (i. e., late proestrus or estrus). We wish to report some observations on the application of an electrical stimulus to the cervix of adult female rats during the diestrous phase of the cycle.

The cervix was exposed with a speculum and the electrodes, spaced at 2 mm, were applied at any place on the body of the cervix. The stimulus, a faradic current taken from an induction coil, was moderately intense and always produced convulsive contractions in the hind quarters The stimulus was applied continuously over a period of 5 to 10 sec.

In a group of 26 virgin females known to be having regular 4 to 5 day cycles 13 were stimulated on the 1st day of diestrous, and 13 on the second day. The number of animals becoming immediately pseudopregnant, those showing one additional estrus before becoming pseudopregnant and those showing no disturbance of the estrous cycle are listed in Table I.

The total number of pseudopregnancies obtained in the above groups in which the stimulus was applied during the interval was 20 or 76%. Thirty-six females in late proestrus or estrus were stimulated in the same manner: 31 or 86% became pseudopregnant immediately and the remaining 5 continued to show cycles of normal length. The above figures are all on the basis of a single stimulation for each animal.