Estradiol Affects Prolactin Producing Cells and Calcium levels in a Teleost, Heteropneustesfossilis, Kept in Different Calcium Concentrations

Background: This study investigated the effects of estradiol on plasma calcium and prolactin cells of Heteropneustes fossilis kept in calcium-deficient and normal freshwater. Methods: Fish were deprived of food and divided into groups A-D. Group A and B were kept in artificial freshwater with normal electrolytes. Group C and D were maintained in calcium-deficient freshwater. Vehicle was administered to groups A and C. Groups B and D were injected with estradiol. Plasma calcium levels and prolactin cells were studied after 1, 3, 5, 10 and 15 days. Results: Normal-calcium freshwater: In group A calcium levels remained unaffected. In group B, estradiol provoked hypercalcemia from day 3 to 10 although calcium decreased after day 15. Prolactin cells in group B became degranulated after 10day. Nuclear volume increased from day 10 onwards. Calcium-deficient freshwater: Calcium levels in group C decreased from day 1 to 3 thereafter increased from day 5 to 15. Plasma calcium of group D increased from day 3 to 15. In group C prolactin cells exhibited hyperactivity on day 3 and degranulation on day 5. Nuclear volume increased from day 5 onwards. On day 10 and 15 certain cells became degenerated. In group D degranulation of prolactin cells began on day 3 which proceeded to complete degranulation on day 10. Nuclear volume increased from day 5 onwards. Conclusions: Estradiol enhanced prolactin production and increased blood calcium in food-deprived fishes kept in calcium-deficient medium suggesting that calcium needed for elevation of blood calcium was derived from internal sources.