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GENDER-SPECIFIC GROWTH AND HEPATIC NEOPLASIA IN MEDAKA (ORYZIAS LATIPES). (R825433)
Citation:
Teh, S. J. AND D. E. Hinton. GENDER-SPECIFIC GROWTH AND HEPATIC NEOPLASIA IN MEDAKA (ORYZIAS LATIPES). (R825433). AQUATIC TOXICOLOGY 41(1-2):141-159, (1998).
Description:
Brief exposure of hatchling medaka (Oryzias latipes), to diethylnitrosamine (DEN), resulted in hepatic tumor formation in female medaka at an incidence of 2–3-fold higher than that of their male cohorts. Spontaneous liver tumor incidence was reported in unexposed 3–5 year old medaka. Gender differences were seen; higher incidence was in the females. Aspects of gender-specific growth in hatchling, immature and sexually mature control medaka are reported and studies sought to determine whether growth enhanced tumorigenesis in females. From a pool of 2000 mixed-sex, 3 week old medaka hatchlings, 1350 were exposed to an aqueous bath of 250 ppm DEN for 48 h. Another 650 hatchlings served as controls. For each fish, body- and liver-weights were recorded (BW and LW, respectively) and LW to BW ratio (hepatosomatic index—HSI) was estimated. Next, livers and carcasses were processed for histopathology. BWs of control females were significantly greater than that of males at weeks 8, 20, 32 and 44 (P<0.05). LWs and HSIs were significantly greater in females versus males at all ages (P<0.05). In the DEN-treated medaka, female BWs were significantly more than their male counterparts at weeks 8, 16, 20 and 32 (P<0.05). Female LWs were greater than male values at all weeks except 4 and 6 (P<0.05). Female HSIs were significantly greater than male HSIs at all times (P<0.05). A higher incidence of foci of cellular alteration (40%) distinguished females from males (10%) at week 4 and these values reached 100% incidence (females) and 90% (males) at week 12. Tumor latency periods for adenomas and carcinomas were significantly shorter in females than in males. At week 20, the incidence of tumors was significantly higher in females than in males (P<0.05). Results indicate that gender-specific differences appear in BW, but especially LW and HSI as a function of larval development, ovarian maturation and age in control and DEN-treated medaka. Tumor incidence and time to endpoint (latency period) demonstrate that female growth is a promotional-stimulus, positively modulating DEN hepatocarcinogenesis.
Author Keywords: Medaka (Oryzias Latipes); Diethylnitrosamine (DEN); Tumor formation