262
AUBREY GORBMAN
lates the conversion of I4C-labeled gluconate to CO, by as much as 125%.
He has concluded that this in vitro action represents a possible activation
of the pentose cycle.
Increased ammonia excretion by goldfish is another metabolic function
of thyroxine that has been claimed (Hoar, 1958). Thornburn and Matty
(1963) have shown that thyroxine affects nitrogen metabolism in the
brown trout as well as in goldfish and it stimulates incorporation of 14Clabeled leucine into protein. Numerous authors have observed the silvering of the skin, especially in salmonids, that results from thyroxine treatment ( e.g., Sage, 1968). It seems clear that thyroxine may therefore affect
integumentary guanine metabolism, and some evidence to this effect was
furnished recently by Matty and Sheltawy (1967) who report that prolonged thyroxine treatment increases the guanine content of teleost skin
and also increased incorporation of I4C-labeled glycine into newly
synthesized guanine.
A relation to salt and water movement in teleost tissues, and therefore
to osmoregulation, also has been claimed frequently for thyroxine. There
appears to be little question that environmental salinity may have some
effect on thyroid function (Hickman, 1959) in fishes. However, whether
thyroid hormone has an important influence in osmoregulation remains to
be proved. Some of the older research (reviewed by Pickford and Atz,
1957; Hickman, 1959) showing apparently reduced thyroid function in
seawater merely showed the influence of increased iodide in the environment (Gorbman and Berg, 1955; Hickman, 1959). Research such as that
cited by M. Fontaine (1956) from his laboratory, which showed that
thyroxine has a protective action for eels transferred from saltwater to
freshwater, will have to be reevaluated in terms of simultaneous action of
prolactin, which has an important role under these circumstances in teleosts (Pickford and Phillips, 1959; see Dharmamba et al., 1967, for more
recent bibliography). Other hormones that may play a larger role in
water-electrolyte regulation than thyroxine are the corticosteroids and
the neurohypophysial peptides.
Srivastava (1963a,b) has studied patterns of influence on isotopically
labeled phosphate uptake by goldfish by hypophysectomy, and by thiourea administration. He concluded that such uptake of 32P from the surrounding aquatic medium is favored by TSH since it is reduced by
hypophysectomy, but increased by thiourea.
Conversion of retinene to vitamin A in young fish has been found
apparently inhibited by triiodothyronine ( Naito and Wilt, 1962; Beatty,
1965 ) ,
Endocrine control of growth of teleosts has concerned several investigations but has not resulted in a clear definition the role of thyroid hor-
AUBREY GORBMAN
lates the conversion of I4C-labeled gluconate to CO, by as much as 125%.
He has concluded that this in vitro action represents a possible activation
of the pentose cycle.
Increased ammonia excretion by goldfish is another metabolic function
of thyroxine that has been claimed (Hoar, 1958). Thornburn and Matty
(1963) have shown that thyroxine affects nitrogen metabolism in the
brown trout as well as in goldfish and it stimulates incorporation of 14Clabeled leucine into protein. Numerous authors have observed the silvering of the skin, especially in salmonids, that results from thyroxine treatment ( e.g., Sage, 1968). It seems clear that thyroxine may therefore affect
integumentary guanine metabolism, and some evidence to this effect was
furnished recently by Matty and Sheltawy (1967) who report that prolonged thyroxine treatment increases the guanine content of teleost skin
and also increased incorporation of I4C-labeled glycine into newly
synthesized guanine.
A relation to salt and water movement in teleost tissues, and therefore
to osmoregulation, also has been claimed frequently for thyroxine. There
appears to be little question that environmental salinity may have some
effect on thyroid function (Hickman, 1959) in fishes. However, whether
thyroid hormone has an important influence in osmoregulation remains to
be proved. Some of the older research (reviewed by Pickford and Atz,
1957; Hickman, 1959) showing apparently reduced thyroid function in
seawater merely showed the influence of increased iodide in the environment (Gorbman and Berg, 1955; Hickman, 1959). Research such as that
cited by M. Fontaine (1956) from his laboratory, which showed that
thyroxine has a protective action for eels transferred from saltwater to
freshwater, will have to be reevaluated in terms of simultaneous action of
prolactin, which has an important role under these circumstances in teleosts (Pickford and Phillips, 1959; see Dharmamba et al., 1967, for more
recent bibliography). Other hormones that may play a larger role in
water-electrolyte regulation than thyroxine are the corticosteroids and
the neurohypophysial peptides.
Srivastava (1963a,b) has studied patterns of influence on isotopically
labeled phosphate uptake by goldfish by hypophysectomy, and by thiourea administration. He concluded that such uptake of 32P from the surrounding aquatic medium is favored by TSH since it is reduced by
hypophysectomy, but increased by thiourea.
Conversion of retinene to vitamin A in young fish has been found
apparently inhibited by triiodothyronine ( Naito and Wilt, 1962; Beatty,
1965 ) ,
Endocrine control of growth of teleosts has concerned several investigations but has not resulted in a clear definition the role of thyroid hor-