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Environmental
physiology and comparative endocrinology of estuarine fish
The neuroendocrine system regulates development and physiology in
fish and coordinates their interactions with their environment.
Our studies are based on the idea that reproduction, development,
immune function and environmental adaptation are regulated through
the orderly release of hormones by the neuroendocrine system, which
integrates information from genes and the environment. Such studies
can improve the way we utilize and protect the marine organisms,
the renewable resources of marine environments. Studies in developmental
endocrinology can be used to increase the food supply through aquaculture
without compromising environmental health. These studies can also
provide new avenues for restoring populations of endangered species,
for limiting noxious organisms and for clarifying the effects of
endocrine-disrupting chemicals. These chemicals enter the environment
through human activity. Their negative impact on marine animals,
including fish, can be profound because hormones play a crucial
role in controlling development.
The regulation of salt and water balance is a fundamental requirement
of life. The structure and function of macromolecules depend closely
on their interactions with water and its solutes. Few factors affect
the distribution and evolution of an organism as extensively as
osmoregulation. Thus, organisms invest considerable energy in controlling
precisely the composition of both intracellular and extracellular
fluids. In fish, osmoregulation typically consumes 25-50% of the
total metabolic output, possibly the largest single component. Osmotic
equilibrium is maintained only through the precise interplay of
a major portion of the neuroendocrine array. Indeed, the maintenance
of osmotic balance in seriously ill patients is among the most difficult
challenges in medicine. In view of the cost and importance of osmoregulation,
it may seem ironic that the mechanisms that monitor and regulate
osmotic balance are so poorly understood. Closer attention reveals
the impediment, the typically complex structure and arrangement
of osmoreceptive cells and tissues. These problems are obviated
by the use of the osmosensitive prolactin cell of a fish pituitary.
Prolactin plays a fundamental role in freshwater osmoregulation,
and prolactin cells are directly sensitive to extracellular osmolality.
Our studies are aimed at elaborating the cellular mechanisms that
mediate this osmoreceptive response. The information these studies
provide has found useful application in such diverse areas as biotechnology,
medicine and aquaculture.
Representative
publications
Seale, A. P., Riley, L. G., Leedom, T. A., Kajimura, S., Dores,
R. M., Hirano, T., and Grau, E. G. 2001. Effects of environmental
osmolality on release of prolactin, growth hormone and ACTH from
the tilapia pituitary. Gen. Comp. Endocrinol. in press.
Seale, A. P., Itoh, T., Moriyama, S., Takahashi, A., Kawauchi, H.,
Sakamoto, T., Fujimoto, M., Riley, L. G., Hirano, T., and Grau,
E. G. 2001. Isolation and Characterization of a Homologue of Mammalian
Prolactin-Releasing Peptide from the Tilapia Brain and Its Effect
on Prolactin Release from the Tilapia Pituitary. Gen. Comp. Endocrinol.
Accepted for publication.
Basu, N., Nakano, T., Grau, E. G. and Iwama, G. K. 2001. The effects
of cortisol on heat shock protein 70 levels in two fish species.
General and Comparative Endocrinology, in press.
Hirano, T., Leedom, T. A., Seale, A. P., and Grau, E. G., 2001.
Angiotensin II and plasma osmolality modulate prolactin secretion
from the tilapia pituitary in concert, "Drink or Die"
Society for Experimental Biology Satellite Meeting (14th International
Congress of Comparative Endocrinology), Sorrento, Italy. Accepted
for publication.
Yada, T., Azuma, T., Hirano, T. and Grau, E. G. 2001. Effects of
hypophysectomy on immune functions in channel catfish, Proceedings
of the 14th International Congress of Comparative Endocrinology.
In press.
Leedom T. A., Uchida K., Yada T., Richman N. H. III, Byatt J. C.,
Collier R. J., Hirano T., Grau, E. G. 2001. Recombinant bovine growth
hormone treatment of tilapia: growth response, metabolic clearance,
receptor binding and immunoglobulin production. Aquaculture, in
press.
Sparks, R. T., Ron, B., Shepherd, B. S., Shimoda, S. K., Iwama,
G.K. and Grau, E. G. 2001. Effects of 17(-methyltestosterone and
salinity on growth and metabolic rate in the euryhaline tilapia,
Oreochromis mossambicus. Comp. Biochem. Physiol. Accepted for publication.
Eckert, S. M., Yada, T., Shepherd, B.S., Stetson, M. H., Hirano,
T. and Grau E.G., 2001. Hormonal Control of Osmoregulation in the
Channel Catfish, Ictalurus punctatus. General and Comparative Endocrinology,
122: 270-286.
Eckert, S. M. Yada, T., Shepherd, B. S., Stetson, M. H., Hirano,
T. and Grau, E. G. 2001. Hormonal control of osmoregulation in a
stenohaline catfish, Ichtalurus punctatus. Proceedings of 4th Congress
of Asia and Oceania Society of Comparative Endocrinology, in press.
Park, R., Shepherd, Brian S., Nishioka, R. S., Grau, E. G. and Bern,
H. A. 2000. Effects of homologous pituitary hormone treatment on
serum insulin-like growth factor-binding proteins (IGFBPs) in hypophysectomized
tilapia, Oreochromis mossambicus, with special reference to a novel
IGFBP-20K. Gen. Comp. Endocrinol. 117: 404-412.
Shepherd, B., Eckert, S., Parhar, I., Vijayan, M., Wakabayashi,
I, Hirano, T., Grau, E. and Chen, T. (2000) The Hexapeptide KP-102
(D-Ala-D-b-Nal-Ala-Trp-D-Phe-Lys-NH2) Stimulates Growth Hormone
Release in a Cichlid Fish (Oreochromis mossambicus). Journal of
Endocrinology 167: R7-R10
Shepherd BS, Sakamoto T, Hyodo S, Nishioka RS, Ball C, Bern HA,
Grau EG. 1999. Is the primitive regulation of pituitary prolactin
(tPRL177 and tPRL188) secretion and gene expression in the euryhaline
tilapia (Oreochromis mossambicus) hypothalamic or environmental?
J Endocrinol 161:121-129.
Morrey C, Nakamura M, Kobayashi T, Grau EG, Nagahama Y. 1998. P450scc-like
immunoreactivity throughout gonadal restructuring in the protogynous
hermaphrodite, Thalassoma duperrey. Int J Devel Biol 42:811-816.
Shepherd BS, Sakamoto T, Mori I, Nishioka RS, Richman NH III, Madsen
S, Hirano T, Bern HA, Grau EG. 1997. Somatotropic actions of the
homologous growth hormone (tGH) and prolactins in the euryhaline
tilapia, Oreochromismossambicus. PNAS 94:2068-2072.
Weber GM, Powell JFF, Park M, Fisher WH, Rivier JE, Nanakorn U,
Parhar IS, Grau EG, Sherwood NM. 1997. Primary structures for three
gonadotropin-releasing hormone (GnRH) molecules and evidence that
GnRH functions as a prolactin-releasing factor in tilapia. J Endocrinol
155:121-132.
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