Disappearance of Inhibin‐like Activity in Bull Seminal Plasma Following Castration

Abstract

Ejaculates from normal and castrated bulls were evaluated for the presence of inhibin‐like activity. Inhibin activity found in the seminal plasma of normal bulls became undetectable after castration. Crude protein concentrates prepared from the ejaculates of castrated bulls failed to produce inhibition of FSH secretion as measured by in vivo and in vitro tests: a) hCG‐induced uterine weight test in mice and b) LH‐RH‐induced FSH secretion in 34‐day‐old male mouse pituitary. The concentrates also lacked the ability to inhibit the binding of iodine‐125 (125I)‐labeled inhibin fraction from normal bull seminal plasma to ovine pituitary membranes. Chromatographic and electrophoretic analyses of the ejaculate from castrated bulls revealed the absence of the band corresponding to inhibin of normal bull seminal plasma.