Effects of prolactin and fish pituitary extract on plasma calcium levels in common carp, Cyprinus carpio.

The effects of prolactin (PRL) from both mammalian and piscine sources on plasma calcium levels in common carp, Cyprinus carpio, were investigated. Injections of ovine prolactin (oPRL) or homologous fish pituitary extract or partially purified prolactin of murrel, Channa punctatus pituitary (mPRL), caused significant increases in total and ultrafiltrable plasma calcium. Larger hypercalcemic responses were observed in fish kept in high-calcium fresh water and normal tap water than in fish in low-calcium fresh water. Injections of oPRL caused dose-dependent increases in plasma calcium level. The highest dose (1 mg/kg body wt) of oPRL had a reduced hypercalcemic effect. Administration of EGTA (200 microM/kg body wt) reduced the stimulatory effects of daily injections of oPRL or mPRL on plasma calcium in freshwater common carp under laboratory conditions. These results indicate that PRL may be involved in regulating plasma calcium levels in fish.