When estrous female rats regulate or pace (P) the timing of vaginal intromissions
received from males during mating, the stimulation is more effective in inducing luteal
function and abbreviating the period of receptivity than is nonpaced (NP) stimulation.
The present studies examined whether the coital stimuli necessary for each of these
functional consequences are similar. In Experiment 1, estrous females received either
5 or 10 intromissions from males in P or NP tests; control animals received mounts-without-intromission
(MO). The duration of estrus was not affected by 5P, 5NP, or 10NP stimulation, but
was significantly abbreviated in 10P animals. In contrast, activation of prolonged
luteal function occurred in 70% of 5P females compared to only 10% of 5NP females;
luteal activation was similar in 10P and 10NP females (74% for both groups combined).
In Experiment 2, male copulatory behaviors were compared in tests with P and NP females.
Males tested with P females exhibited significantly longer intromission durations
(616 +/- 21 msec) than did males tested with NP females (527 +/- 30 msec). Other measures
of male copulatory performance such as the number of intromissions to ejaculation
and the ejaculation latency did not differ between groups. These studies demonstrate
that luteal activation is more readily induced by paced coital stimulation than is
abbreviation of estrus. In addition, they suggest that differences between P and NP
females in the behavioral and neuroendocrine responses to coital stimulation may result
from differences in intromission duration displayed by males under these test conditions.