Department of Physiology and Environmental Studies, University of Nottingham School of Agriculture, Sutton Bonington, Loughborough LE12 5RD, Leicestershire, U.K.
As part of a study on pituitary-testicular feedback mechanisms, the plasma hormone levels of 9 Friesian bulls, 6-8 months old, were examined at the time of unilateral castration. Blood (10 ml) was taken from indwelling jugular cannulae at 30 min intervals for 48 hr, a testis being removed under local anaesthesia (Lignocaine, Pharmaceutical Man. Co.) from each animal after 24 hr. Testosterone concentrations in plasma were measured by the radioimmunoassay method of Haynes, Hafs, Waters, Manns & Riley (1975) and LH concentrations by the radioimmunological procedure described by Oxender, Hafs & Edgerton (1972). One bull had no detectable testosterone after unilateral castration and was not included in the analysis.
A summary of the results for 8 animals is given in Table 1. Hormone concentrations before castration were in accord with previous
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