Temporal Aspect of Uterine Sensitivity in the Pseudopregnant or Pregnant Rat

Abstract

The duration of uterine sensitivity (ability to produce a deciduoma) was determined for several strains of pseudopregnant rats using the method of endometrial scratching. The day of maximal sensitivity was found to be related to the last ovulation and not to the day on which the pseudopregnancy was initiated. It occurred on Day 4, a day associated with increased uterine weight and water content, and was markedly reduced or absent 24 hr later, depending on the strain of rat. It was not possible to prolong sensitivity to Day 5 by: a) physiologic lengthening of pseudopregnancy, b) administration of hormones associated with pseudopregnancy, or c) daily blockade of the CNS by pentobarbital. It is concluded that, once maximal sensitivity has been acquired, the endometrium loses its capacity for another response during pseudopregnancy or pregnancy. This concept of maximal sensitivity contributes to our understanding of some of the results obtained by earlier investigators.