A sensitive and easy bioassay for teleost gonadotropin depending on the ovarian-free cholesterol depletion in vitro

Abstract

Ovarian tissues from murrel (Channa punctatus Bloch) were incubated in vitro to obtain discrete effect regarding free cholesterol (f-cholesterol) depletion in response to salmon gonadotropin (SG-G100). To select the best responsive ovarian stage, ovarian tissues containing 30-40% or 40-50% or 60-70% or 80-90% of mature oocytes were incubated separately with SG-G100 (400 ng/incubation). Maximum response was evident in tissue containing 40-50% matured oocytes. With increasing concentrations of SG-G100 like 1.5 and 10 μg/incubation, a distinct linear profile for ovarian f-cholesterol depletion was observed. The linear slope of f-cholesterol depletion was checked for individual variations and striking uniformity and parallelism was observed among the different individuals of murrel. Carp and murrel pituitary extracts were tested in the present system and gonadotropin content was expressed as nanograms of SG-G100 equivalent. Efficacy of fish hypothalamic extract (HE) and gonadotropin releasing hormone (GnRH) was also judged by coincubating ovary and pituitary. Findings clearly indicate that the present in vitro system is not only highly sensitive as a bioassay of teleost gonadotropin but also very convenient since the whole procedure can be done within 10 hr.