Effects of Etiocholanolone Glucuronide, a Putative Pheromone on Brain and Plasma Vasotocin Levels in the Catfish Heteropneustes fossilis

Abstract

Teleost gonads have been demonstrated to be an active source of sex (reproductive) pheromones having releaser or primer functions. Steroid hormones, prostaglandins and their metabolites have received considerable attention in this regard. Etiocholanolone glucuronide (EG) is a natural metabolite of etiocholanolone generated in the liver by UDP gluconyl transferase. Etiocholanolone (or 5-isoandrosterone) is a metabolite of testosterone, classified as a ketosteroid; it causes fever, immunostimulation and leukocytosis. Glucuronidation is a means of excretion of toxic substances, drugs or other substances that cannot be used as an energy source. In teleosts, EG is secreted by males (testis and seminal vesicle) and exerts pheromonal roles via olfactory stimulation of females [1]. This steroid has got pheromonal properties and is responsible for regulation of spawning behavior and reproduction. Vasotocin (VT) is the basic neurohypophysial nonapeptide in nonmammalian vertebrates and is involved in diverse functions like osmoregulation, reproduction and behavior [2]. The administration of VT has been shown to influence or modify reproductive/seasonal behavioral activities (spawning, courtship, egg laying, clasping and song production) in a variety of vertebrates like fish, amphibians, reptiles and birds [3, 4, 5]. The reproductive role of VT was investigated in the catfish and ovarian steroids were found to modulate VT secretion in vitro [6]. We, therefore, hypothesize that pheromone exposure may induce brain VT release and influence catfish reproductive behavior. To test this hypothesis we perfused female catfish with different concentrations of EG and measured brain and plasma vasotocin levels.