Influence of gonadotropins and gonadal hormones on climbing perch thyroid nucleic acids

Climbing perch thyroidal RNA content fluctuated in different phases of the reproductive cycle, highest at spawning (36.08 +/- 3.69 micrograms/mg tissue) and lowest at postspawning (6.88 +/- 0.76 microgram/mg tissue) whereas DNA remained unaltered. Treatment of intact perch with salmon gonadotropin (SG-G100) or ovine LH for 15 days significantly stimulated thyroidal RNA content. Stimulatory effect of SG-G100 was greater (p less than 0.001) than LH (p less than 0.005). FSH had no such effect. Gonadotropin (GtH) treatment could not alter thyroidal DNA. Ovarian steroids, 17 beta-estradiol (E2) and estrone (E1) remarkably elicited RNA content. Ovariectomy of perch caused striking depletion of RNA. Administration of GtH to ovariectomized perch had no effect on thyroid RNA but E1 and E2 supplementation resulted in significant stimulation in comparison to ovariectomized control. Findings indicate that GtH mediated its stimulatory effect on perch thyroidal RNA via the release of ovarian steroids.