Characterization of the Primer Pheromone Molecules Responsible for the 'Male Effect' in Ruminant Species

Abstract

Pheromones are chemical signals used among consepcifics for social interactions such as sex attraction, mate selection, modulation of neuroendocrine function, and individual identification (Vandenbergh, 1994; Singh, 2001; Halpern and Martinez-Macros, 2003). The male effect is a representative example of such pheromonal actions in goats and sheep, in which exposure to the male pheromone accelerates the pulsatile gonadotropin-releasing hormone (GnRH)/luteinizing hormone release and thereby the ovarian activity in the female (Schinkel, 1954; Martin et al., 1986). Several attempts have been made to isolate pheromone molecule(s) responsible for the male effect using the induction of ovulation (Knight and Lynch, 1980) or the stimulation of LH release (Claus et al., 1990; Cohen-Tannoudji et al., 1994) as indices for the pheromone activity. These studies found that the male hair but not urine contained the pheromone activity. Therefore, chemical constituents in the male hairs were extracted and processed for further fractionation and analysis. Although the pheromone activity was observed in the fractions of initial steps, it eventually disappeared as the fractionation proceeded. Thus, the chemical identity of the primer pheromone has not yet been determined so far. A major problem of those studies appears to reside in the bioassay systems they employed, which required several time consuming steps to determine whether the sample in question contained the pheromone or not. To overcome this matter, we have established a bioassay system to assess the pheromone activity in a real-time manner with high sensitivity. Utilizing this system, we have been conducting a series of experiments aiming at elucidation of production mechanism and the isolation of chemical molecule (s) of pheromone responsible for the male effect in the Shiba goat, a Japanese indigenous breed.