SUSTAINED ADMINISTRATION OF GNRHA INCREASES MILT VOLUME WITHOUT ALTERING SPERM COUNTS IN THE SEA BASS

The role of gonadotropin-releasing hormone (GnRH) in spermiogenesis an d spermiation is not well understood. This study examined the effects of different modes of administration of a GnRH analog (GnRHa; [D-Ala(6 ),Pro(9)NEt]-mGnRH) on spermiation in the sea bass, Dicentrarchus Labr ax. Groups of sea bass received either GnRHa injection in saline (I; 2 5 mu g/kg body weight [BW] or one of three types of GnRHa sustained re lease polymeric device: a fast-releasing implant (ethylene-vinyl aceta te copolymer [EVAc]; 100 mu g/kg BW), a slower-releasing implant (ethy lene-vinyl acetate copolymer [EVSL]; 100 mu g/kg BW), or biodegradable microspheres (M; 50 mu g/kg BW). Total expressible milt was collected and assessed for volume, motility, and counts at various intervals fo r 44 days. Untreated males produced a total of 9.4 +/- 3.4 ml/kg BW (m ean +/- SEM) of milt over the 44-day experimental period, with milt pr oduction ending by day 28. All GnRHa treatments stimulated a significa nt increase in total milt volume (ml/kg BW) peaking by day 2 (I: 11.8 +/- 1.8) or day 7 (EVAc: 20.0 +/- 1.5; M: 26.8 +/- 2.7; EVSL: 27.9 +/- 4.3) posttreatment. While milt volumes in injected males returned to control values by day 14, all groups treated with sustained GnRHa deli very systems maintained significantly elevated milt volumes for 21 day s (EVAc group) or 35 days (EVSL and M groups). Sperm motility was cons istently good to excellent (70-100% vigorously active) in all groups w hen expressible milt volume was above 1.0 ml, and there were no signif icant differences in sperm counts (averaging 5.5 +/- 0.1 x 10(9) sperm atozoa/ml). These data show that sustained administration of GnRHa sig nificantly increases and prolongs spermiation in the sea bass without altering sperm concentration or quality. (C) 1996 Wiley-Liss, Inc.