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Diurnal Variation of Plasma Testosterone in Wild Stallions

1976; Oxford University Press; Volume: 15; Issue: 1 Linguagem: Inglês

10.1095/biolreprod15.1.98

1529-7268

J. F. Kirkpatrick, R. Vail, S. Devous, S. Schwend, C. B. Baker, Lubbe Wiesner,

Pharmacological Effects and Assays

Three wild horse stallions from the Pryor Mountain National Wild Horse Range in Montana were captured and blood samples collected over a 24 h period. Androgens were extracted from the plasma, testosterone was isolated by Sephadex LH-20 column chromatography and quantitated by a competitive-protein-binding assay. All three horses exhibited similar qualitative changes in testosterone concentrations during the 24 h, with the nadir occurring at 2300 (1.37 ± 0.75 ng/ml) and a peak at 0800 (3.48 ± 0.12 ng/ml). One of the horses, an eight year old bachelor stallion which has never made an effort to gather a harem since sexual maturity, had a significantly lower (P<0.01) 24 h mean testosterone concentration (1.52 ± 0.89 ng/ml) than either of the two stud stallions (2.68 ± 0.59 ng/ml and 3.20 ± 0.68 ng/ml), both of which have possessed harems and sired colts. It is concluded that all three stallions possessed a diurnal testosterone rhythm. Whether the lower testosterone concentrations in the bachelor stallion are a cause or an effect of sexual disinterest remains unanswered.