Effects of hypophysectomy and replacement therapy with ovine prolactin on serum calcium levels, and calcification in otoliths and scales in goldfish.

Abstract

The effects of hypophysectomy and replacement therapy using ovine prolactin on serum calcium and sodium levels, as well as on calcium incorporation into otoliths and scales, were examined in goldfish. Hypophysectomized fish were given ovine prolactin (0.3IU/g body weight) 3 times at intervals of 48h. Subsequently, fish were transferred to water labelled with 45Ca and administered the fourth dose of prolactin the following day. After 2 days in this radioactive environment, fish were sacrificed in order to perform 45Ca analyses. Hypophysectomy resulted in marked hypocalcemia and hyponatremia, which were completely corrected by prolactin therapy. Serum 45Ca levels were lowered in the hypophysectomized fish but were only partially corrected by prolactin. The incorporation of 45Ca into otoliths was reduced by hypophysectomy and exogenous prolactin had no effect on restoring this incorporation. Hypophy-sectomy also reduced the rate of 45Ca incorporation into scales but in this tissue, prolactin partially restored this incorporation rate to normal. In terms of μg Ca/mg tissue weight, hypophysectomy resulted in a marked reduction in calcium incorporation into otoliths, which was not restored by prolactin therapy. In scales, however, hypophysectomy and prolactin exhibited no effect on the incorporation of calcium. These results were discussed in relation to the presence of physiologically labile calcium pool in scales.