Endocrine correlates of partner preference behavior in rams.
Level 5 - mechanism / opinion, no new human data
Animal research without human data
PubMed 8793066 · doi:10.1095/biolreprod55.1.120
What was done
Researchers compared endocrine and neurochemical profiles between 6 male-oriented rams (rams that preferred courting males over estrous ewes in 30-minute tests) and 7 female-oriented rams (proven breeders). After behavioral testing, animals were killed and tissues collected under blinded conditions to measure: (1) serum concentrations of testosterone (T), dihydrotestosterone (DHT), androstenedione, estrone (E1), and estradiol-17β (E2) by radioimmunoassay; (2) in vitro testicular biosynthesis of 17α-hydroxyprogesterone and T from 3H-progesterone; and (3) aromatase activity (AA) across 10 brain regions, including the preoptic area (POA).
What was found
Female-oriented rams showed significantly higher serum T (1559 ± 228 vs. 874 ± 196 pg/ml), E1 (46 ± 2 vs. 40 ± 2 pg/ml), and E2 (15 ± 3 vs. 8 ± 1 pg/ml) compared to male-oriented rams (all p < 0.05). Serum DHT and androstenedione did not differ. Testicular biosynthesis was significantly higher in female-oriented rams for T (28.8 ± 8.1 vs. 12.1 ± 2.3 µmol·h⁻¹·mg protein⁻¹) and 17α-hydroxyprogesterone (416.9 ± 100.8 vs. 186.3 ± 30.7 µmol·h⁻¹·mg protein⁻¹; p < 0.05). Preoptic area aromatase activity was significantly higher in female-oriented rams (472 ± 34 vs. 296 ± 24 fmol 3H2O·h⁻¹·mg protein⁻¹, p < 0.05), with no differences observed in the other nine brain regions.
Why it matters
This paper demonstrates that naturally occurring male-oriented partner preference in rams is associated with decreased testicular steroidogenic capacity and lower preoptic aromatase activity.
Limits
The sample size is very small (n = 13 total rams). The cross-sectional, post-mortem design identifies biological correlates rather than causal drivers, and animal behavioral models cannot be directly extrapolated to human sexual orientation.
Cited by
- supports A small percentage of domestic rams exclusively court and mount other rams and show no sexual interest in females even after prolonged exposure.