Osmoregulatory action of PRL, GH, and cortisol in the gilthead seabream (Sparus aurata L).

The osmoregulatory actions of ovine prolactin (oPRL), ovine growth hormone (oGH), and cortisol were tested in the euryhaline gilthead seabream Sparus aurata. Acclimated to sea water (SW, 40 ppt salinity, 1000 mOsm/kg H(2)O) or brackish water (BW, 5 ppt, salinity, 130 mOsm/kg H(2)O), injected every other day for one week (number of injections, 4) with saline (0.9% NaCl), oPRL (4 microg/g body weight), oGH (4 microg/g body weight) or cortisol (5 microg/g body weight), and transferred from SW to BW or from BW to SW 24h after the last injection. Fish were sampled before and 24h after transfer. Gill Na(+), K(+)-ATPase activity, plasma osmolality, plasma ions (sodium and chloride), plasma glucose, and muscle water moisture were examined. SW-adapted fish showed higher gill Na(+), K(+)-ATPase activity, plasma osmolality, and plasma ions levels than BW-adapted fish. Transfer from SW to BW decreased plasma osmolality and ions levels after 24h, while transfer from BW to SW increased these parameters, whereas gill Na(+),K(+)-ATPase activity was unaffected. oPRL treatment significantly decreased gill Na(+),K(+)-ATPase activity and increased plasma osmolality and ions in SW- and BW-adapted fish. This treatment minimizes loss of osmolality and ions in plasma after transfer to BW and increased these values after transfer to SW. No significant changes were observed in gill Na(+),K(+)-ATPase activity, plasma osmolality, and plasma ions in oGH-treated group with respect to saline group before or after transfer from SW to BW or from BW to SW. Treatment with cortisol induced, in SW-adapted fish, a significant increase of gill Na(+),K(+)-ATPase activity and decrease of plasma osmolality and plasma ions. In BW-adapted fish this treatment induced a significant increases in gill Na(+),K(+)-ATPase activity, plasma osmolality, and plasma ions. After transfer to SW cortisol-treated fish had higher plasma osmolality than the saline group. Our results support the osmoregulatory role of PRL in the adaptation to hypoosmotic environment in the gilthead seabream S. aurata. Further studies will be necessary to elucidate the osmoregulatory role of GH in this species. Cortisol results suggest a "dual osmoregulatory role" of this hormone in S. aurata.

Ontogeny of adenohypophyseal cells in the pituitary of the American shad (Alosa sapidissima).

The distribution and ontogeny of adenohypophyseal cells have been studied in the pituitary gland of embryos, larvae, and juveniles of the clupeid American shad (Alosa sapidissima) using immunocytochemical techniques. In juvenile specimens, adenohypophysis was composed of rostral pars distalis (RPD), formed by cavities lined by prolactin (PRL), adrenocorticotropic hormone (ACTH), and gonadotropic hormone (GTH) cells; proximal pars distalis (PPD), containing growth hormone (GH), GTH, and putative thyroid stimulating hormone (TSH) cells; and pars intermedia (PI) with somatolactin (SL) and melanophore stimulating hormone (MSH) cells. At 3 days post-fertilization (3 days pre-hatching) the pituitary of embryos consisted of an oval mass of cells, close to the ventral margin of the diencephalon, divided in rostral and caudal regions. At this time PRL and ACTH cells appeared in the rostral region of the adenohypophysis, while SL cells were observed in the caudal region where MSH cells showed reactivity 1 day before hatching. At variance, GH cells showed a weak immunoreactivity in the rostral portion at hatching that increased 2 days latter. GTH cells also showed weak immunoreactivity in the rostral region of the adenohypophysis at hatching time. Two days later GTH cells were located in the rostral and central regions of the adenohypophysis. At hatching, the neurohypophysis was very small and no nerve processes were seen to penetrate the adenohypophysis tissue. After hatching, the pituitary gland elongated and in 7 days old larvae, the RPD showed a small lumen surrounded by a palisade of PRL, ACTH, and GHT cells; the PPD showed GH and GTH cells while the PI contained SL and MSH cells. The adenohypophysis and neural lobe increased in size with development and, in 42 days old larvae, they were similar to those of juvenile specimens.