In vivo and in vitro effects of prolactin (PRL) and growth hormone (GH) on plasma levels of lysozyme and ceruloplasmin were examined
in the rainbow trout (Oncorhynchus mykiss). Hypophysectomy had no effect on the plasma lysozyme level. Implantation of PRL- or GHcontaining
cholesterol pellets increased the lysozyme level in a dose-related manner. After hypophysectomy and sham operation, plasma
ceruloplasmin was elevated above the level in intact fish, suggesting inflammation caused by the surgery. PRL or GH treatment significantly
attenuated the increased level of ceruloplasmin in the operated fish. Expression of lysozyme mRNA was detected in the leucocytes isolated
from the peripheral blood by RT-PCR. In vitro administration of PRL or GH showed no effect on the proliferation of isolated leucocytes or on
the total protein content; however, lysozyme activity in the medium increased in a dose-related manner. These results suggest that PRL and
GH directly stimulate lysozyme production without affecting the proliferation of leucocytes, and the attenuated ceruloplasmin level increased
in response to inflammation