Effects of prolactin and growth hormone on strategies of hypoosmotic adaptation in a marine teleost, Sparus sarba

Silver seabream (Sparus sarba) held in seawater (33 parts per thousand) or acclimated to a hypoosmotic environment of 6 parts per thousand were given intraperitoneal injections of saline (0.8% NaCl), recombinant bream growth hormone (rbGH, 1 mu g/g), or ovine prolactin (oPRL, 6 mu g/g) for 7 consecu tive days. Serum Na+ levels were unaffected by hypoosmotic acclimation and rbGH and oPRL treatment. Treatment of seawater fish with oPRL resulted in h yperchloremia. In 6 parts per thousand, saline-treated fish exhibited eleva ted branchial chloride cell (CC) numbers and exposure indices, all of which were markedly reduced by oPRL. CC numbers and morphometrics were unaffecte d by oPRL in seawater fish. In contrast, rbGH treatment of seawater fish re sulted in elevated CC numbers, apical area, and fractional area and, in 6 p arts per thousand fish, elevated CC fractional area and exposure numbers. B ranchial Na+-K+-ATPase activity reduced in saline-treated fish adapted to 6 % but was unaffected by rbGH regardless of salinity, oPRL reduced activity in both seawater and 6 parts per thousand-adapted fish. Neither hypoosmotic adaptation nor oPRL had any effect on renal Na+-K+-ATPase activity whereas rbGH reduced activity in both 33 and 6 parts per thousand. Saline-treated fish adapted to 6 parts per thousand exhibited reduced Na+-K+-ATPase activi ty in most regions of the intestine. Treatment with rbGH did not change int estinal Na+-K+-ATPase activity of seawater fish but elevated activity in th e anterior regions (esophagus and stomach) of 6 parts per thousand-adapted fish. Treatment with oPRL elevated Na+-K+-ATPase activity throughout the ga strointestinal tract of seawater fish and in the anterior reaches of 6 part s per thousand-adapted fish. The data indicated that the as yet uncharacter ized osmoregulatory roles of PRL and GH in seabream may warrant further att ention as the present study connoted differing responses to that of other t eleosts studied. (C) 1999 Academic Press.