Inter-relationships between plasma luteinizing hormone, testosterone and cortisol as revealed by frequent blood sampling of mature bulls
1987; Elsevier BV; Volume: 143; Issue: 5 Linguagem: Inglês
10.1016/0007-1935(87)90023-6
ISSN1879-3606
Autores Tópico(s)Animal Behavior and Welfare Studies
ResumoPlasma LH and testosterone were measured in four mature bulls which were bled hourly for 8 h once a week for 3 consecutive weeks on 3 occasions. One 8 h period was not representative for a given bull but 3 weekly periods were more acceptable. In 3 of the 4 bulls there was a stress-related deterioration in LH and testosterone profiles characterized by early maximum testosterone concentrations. Cortisol concentrations were very high (>8 ng/ml) in one bull, and paralleled testosterone release in another. Basal values of cortisol ranged from 0·5 to 4 ng/ml. Very frequent sampling (every 2 min) during spontaneous increases in LH and testosterone revealed pulsatile release of both hormones at 10–15 min intervals. Initial rises in LH were followed 30–45 min later by measurable increases in testosterone. A decline from maximum LH values (10–18 ng/ml) occurred at least l h before maximum testosterone concentrations (8–12 ng/ml). GnRH (20 μg iv) increased LH values within 2 min resulting in raised pulsatile LH and testosterone profiles for the first hour very similar to spontaneous release. However LH then spontaneously increased to 25–47 ng/ml approximately 2 h after GnRH. A second 20 μg GnRH injection 3 h after the first resulted immediately in even higher LH values (55–70 ng/ml). Testosterone concentrations were not further increased after the first hour but remained steady at 12·5–25 ng/ml for 6 h after the first GnRH (basal testosterone 1–4 ng/ ml). In conclusion, pulsatile release of LH causes increases in gonadal steroidogenesis in bulls but the precise control mechanism appears to be different from that in cows. Increased adrenal activity appears to influence pituitary-gonadal relationships.
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