Plasma and pituitary prolactin levels in rainbow trout during adaptation to different salinities

Abstract

The development of a highly specific radioimmunoassay for salmonid prolactin (PRL) using chinook salmon PRL allowed us to study plasma and pituitary PRL profiles in large sedentary rainbow trout (Salmo gairdneri) transferred from fresh water to seawater and vice versa. Plasma osmotic pressure and chloride levels were also measured for 3 weeks following change of salinity. Within 1 day after transfer to full seawater we observed a plasma PRL decrease, which stayed significantly lower (3-5 ng/ml) than the fresh water control group (10-15 ng/ml) during the entire experiment. Pituitary PRL content showed an initial abrupt increase, but after 3 weeks in seawater pituitary PRL content had decreased to the same level as in the fresh water control group. On the contrary, transfer from seawater to fresh water was followed within 1 day by a rise in plasma PRL levels, which stayed high (10-15 ng/ml) after 3 weeks in fresh water. Simultaneously, pituitary PRL content decreased significantly. These results may indicate an important role of PRL in fresh water adaptation of sedentary rainbow trout.

Immune localization of prolactin receptor in the mitochondria‐rich cells of the euryhaline teleost (Oreochromis mossambicus) gill

“…Plasma prolactin levels are reportedly higher in fish kept in FW than in ones adapted to a hyperosmotic environment [8][9][10][11]14]. Following transfer of teleosts into SW, a drastic reduction in PRL secretion has been demonstrated [8,10]. This phenomenon has also been observed in the gills of rainbow trout [31] and coho salmon [32], in which the high cortisol levels down-regulate the corticosteroid receptors.…”

“…First, the tiPRL receptors may be down-or up-regulated by various levels of tiPRL in waters of different salinity. Plasma prolactin levels are reportedly higher in fish kept in FW than in ones adapted to a hyperosmotic environment [8][9][10][11]14]. Following transfer of teleosts into SW, a drastic reduction in PRL secretion has been demonstrated [8,10].…”

“…In addition, several studies have shown that PRL has a hypercalcémie effect in a variety of teleosts [3][4][5][6][7]. Plasma levels of PRL are higher in fish kept in FW than in ones adapted to a hyperosmotic environment [8][9][10][11]. In tilapia pituitary, two different PRL molecules have been found with a sequence identity of 69%, one variant (tiPRL I, 188 amino acids) being more similar to other fish PRLs than to the other variant (tiPRL II, 177 amino acids) [12,13].…”

Absence of direct regulation of prolactin cells by estradiol-17β in rainbow trout (Oncorhynchus mykiss)

“…Pituitary and plasma PRL levels were determined using a specific radioimmunoassay (RIA) for salmonid PRL (Prunet et al, 1985).…”

Immunohistochemical Study of Growth Hormone and Prolactin Cells in the Pituitaries of Anguilliform Leptocephali Captured in the Atlantic Sargasso Sea.

“…Injection of GH to juvenile rainbow trout actually resulted in acceleration of growth.1-3) Meanwhile, PRL delayed flounder metamorphosis which was stimulated by thyroid hormone.4) Furthermore, PRL facilitates regulation of water and electrolyte balance in fresh water teleosts, so that it is referred to as fish fresh water hormone. [5][6][7][8][9] As is very well known, leptocephali of anguilliform fish which arrive at coastal brackish sea areas metamorphose into glass eels and acquire fresh water adaptability.…”