Critical Time Period for the Vagino-cervical Stimulus to Induce Pseudopregnancy in the Dioestrous Rat

Abstract

Groups of rats experienced mechanical stimulation of the vagino-cervical region to induce pseudopregnancy at various intervals from 0900 h on dioestrus - 1 (D - 1) to 1800 h on D - 2. Twentyfour of 26 rats which were stimulated on D - I experienced immediate pseudopregnancy whereas when the stimulus was given on D-2, 39 of 45 rats continued to cycle and the latest time when such mechanical stimulation would reliably induce immediate pseudopregnancy was 2400 h on D-l. Abolition of the dark phase between 1800 h D-l and 0600 h D-2 did not alter this critical time period (2400 h on D-I). Stimulation as late as 1200 h on D-2 caused alterations in the normal pattern of 4-day cyclicity in 8 of 11 rats.