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The present experiments sought to characterize the particular stimuli received during mating in the female rat which induce acute increases in luteinizing hormone (LH) and prolactin (PRL) following copulation. Comparisons were made between cycling females mated on the evening of proestrus in partitioned chambers in which spontaneous patterns of approach/withdrawal toward the male served to pace copulatory stimulation (paced), in non-partitioned chambers in which female regulation of intervals between copulatory mounts was prevented (non-paced), or under conditions in which they received mounts-without-intromission (mounts-only). Frequent blood samples were withdrawn via surgically implanted intra-atrial catheters. In experiment 1, blood samples for LH determinations were taken at 15-min intervals for 1 h prior to and for 2 h after mating on the evening of proestrus. In experiment 2, samples for PRL determinations were taken at 10-min intervals for 30 min prior to and for 90 min after mating on proestrus and at 0300, 0400 and 0500 h on the day of estrus (reported times corrected for reversed light cycle). LH levels were significantly higher in paced animals 15 min after initiation of mating than in non-paced and mounts-only females; no differences in LH were seen between females who subsequently became or did not become pregnant/pseudopregnant (P/PSP). PRL values were not different between groups receiving the different mating treatments at any time; however, P/PSP animals showed significantly higher levels of PRL between 20 to 60 min after mating than did non-P/PSP females. No differences in PRL were seen between mating treatments or pseudopregnancy condition at 0300 to 0500 h on estrus. Paced females in both experiments received intromissions at a significantly slower rate than did non-paced females. There was a significant positive correlation (r = 0.619, P<0.001) between LH concentration at 15 min and the inter-intromission interval (in seconds) in paced and non-paced groups of females. These data suggest that an LH response to mating is dependent upon the particular characteristics of mating stimulation received. In addition, they demonstrate that PRL increases acutely after mating stimulation in animals destined to become P/PSP but does not increase in response to those characteristics of mating stimulation which induced increases in LH.

Six experiments were carried out to determine whether dihydrotestosterone (5 alpha-androstan-17 beta-ol-3-one; DHT) acts to inhibit oestradiol (OE2)-induced lordosis behaviour after its metabolic conversion to 5 alpha-androstane-3 alpha,17 beta-diol (3 alpha-androstanediol, 3 alpha-Adiol). In experiments 1 and 2, ovariectomized rats were treated with several doses of DHT or 3 alpha-Adiol, injected with OE2 and progesterone, and tested for lordosis responsiveness. Significant inhibition of lordosis occurred after a dose of 3 alpha-Adiol which was approximately threefold less than the effective DHT dose. In experiments 3 and 4, plasma concentrations of DHT and 3 alpha-Adiol were measured after the injection of these steroids to ovariectomized rats at doses shown to be both sufficient or insufficient to inhibit lordosis. Behaviourally effective dosages of DHT and 3 alpha-Adiol produced circulating concentrations of 3 alpha-Adiol greater than those produced by behaviourally ineffective doses of DHT or 3 alpha-Adiol. At 30 min after injection of DHT (experiment 3), 78.8% of plasma androgens were in the form of 3 alpha-Adiol, while after injection of 3 alpha-Adiol, only 7.4% were DHT. When plasma DHT and 3 alpha-Adiol were measured at 3, 6, 9 and 12 h after steroid injection (experiment 4), plasma levels of 3 alpha-Adiol produced by the behaviourally subthreshold dose of DHT were significantly lower than levels produced by behaviourally sufficient dosages of DHT or 3 alpha-Adiol. In experiments 5 and 6, concentrations of DHT and 3 alpha-Adiol were measured in five brain regions 1 and 6 h after injection of behaviourally sufficient doses of these steroids to ovariectomized females. At 1 h after injection, similar levels of DHT and 3 alpha-Adiol were measured in DHT- and 3 alpha-Adiol-injected females, and DHT concentrations in the preoptic area were significantly higher in both groups than in any other brain area. At 6 h, animals injected with DHT had significantly higher levels of DHT in all brain areas combined than did 3 alpha-Adiol- or vehicle-injected animals. Brain concentrations of 3 alpha-Adiol were not different between groups injected with DHT, 3 alpha-Adiol or vehicle at this time. In brain, 34.6% of DHT had been converted to 3 alpha-Adiol after 1 h and 53.0% of 3 alpha-Adiol had been converted to DHT.(ABSTRACT TRUNCATED AT 400 WORDS)