280
AUBREY GORBMAN
iodine in 13 S and 29 S fractions is seen after longer intervals following
1311 injection. Long time estivation (3 months at 2 5 O C ) produced a shift
in distribution of 1311 among the three fractions.
V. ACTIONS OF THYROID HORMONES IN FISH
Much has been written concerning peripheral tissue responsiveness
in fish to thyroid hormone, but only a few of the observations have established a f i r m causal relationship between thyroid hormone and the particular functional feature discussed. It is useful also to remember in the
following discussion that certain of the thyroxine effects claimed are relatively modest ones and that other known mechanisms may affect the same
phenomena in a much more potent manner. This last comment applies
in particular to the relationship of thyroid hormone to carbohydrate
metabolism, osmoregulation, and perhaps also to growth in fish.
Practically nothing is known of the action of thyroid hormones in
cyclostomes or in elasmobranchs. Some interest exists in the question
whether thyroxine can precipitate metamorphic changes in ammocoetes
larvae of lampreys. Stokes (1939) long ago showed that thyroxine does
not have this action. This finding has been confirmed by a number of
workers (e.g., Leach, 1946) but such confirmations usually remain unpublished because of their negative character. Furthermore, Leach
(1946) found that thyroid hormone treatment had no effect on oxygen
consumption either in ammocoetes or in adult lampreys.
Elasmobranchs likewise have no clear respiratory response (oxygen
consumption) to thyroidectomy or administered thyroid hormone ( Matty,
1954). Pritchard and Gorbman (1960) treated late embryos (pups) of
the shark, Squalus suckleyi, with repeated injections of triiodothyroacetic
acid, thyroxine, or propylthiouracil over periods of several weeks and
measured respiratory oxygen consumption during this time. There was a
rise in oxygen consumption for 8-10 days, and then a fall despite continued hormone treatment. The goitrogen had no apparent effect. Dogfish
pups of the same species were injected with thyroxine by Gorbman and
Ishii ( 1960) who found that hypothalamic neurosecretory material was
caused to appear precociously. This may be an expression of thyroxine
sensitivity of the central nervous system discussed below more extensively
for the teleosts.
There seems ,to be a general parallelism of thyroid and reproductive
functions in elasmobranchs. This is more fully reviewed by Pickford and
Atz ( 1957), Dodd and Matty ( 1964), and Woodhead (1966).
AUBREY GORBMAN
iodine in 13 S and 29 S fractions is seen after longer intervals following
1311 injection. Long time estivation (3 months at 2 5 O C ) produced a shift
in distribution of 1311 among the three fractions.
V. ACTIONS OF THYROID HORMONES IN FISH
Much has been written concerning peripheral tissue responsiveness
in fish to thyroid hormone, but only a few of the observations have established a f i r m causal relationship between thyroid hormone and the particular functional feature discussed. It is useful also to remember in the
following discussion that certain of the thyroxine effects claimed are relatively modest ones and that other known mechanisms may affect the same
phenomena in a much more potent manner. This last comment applies
in particular to the relationship of thyroid hormone to carbohydrate
metabolism, osmoregulation, and perhaps also to growth in fish.
Practically nothing is known of the action of thyroid hormones in
cyclostomes or in elasmobranchs. Some interest exists in the question
whether thyroxine can precipitate metamorphic changes in ammocoetes
larvae of lampreys. Stokes (1939) long ago showed that thyroxine does
not have this action. This finding has been confirmed by a number of
workers (e.g., Leach, 1946) but such confirmations usually remain unpublished because of their negative character. Furthermore, Leach
(1946) found that thyroid hormone treatment had no effect on oxygen
consumption either in ammocoetes or in adult lampreys.
Elasmobranchs likewise have no clear respiratory response (oxygen
consumption) to thyroidectomy or administered thyroid hormone ( Matty,
1954). Pritchard and Gorbman (1960) treated late embryos (pups) of
the shark, Squalus suckleyi, with repeated injections of triiodothyroacetic
acid, thyroxine, or propylthiouracil over periods of several weeks and
measured respiratory oxygen consumption during this time. There was a
rise in oxygen consumption for 8-10 days, and then a fall despite continued hormone treatment. The goitrogen had no apparent effect. Dogfish
pups of the same species were injected with thyroxine by Gorbman and
Ishii ( 1960) who found that hypothalamic neurosecretory material was
caused to appear precociously. This may be an expression of thyroxine
sensitivity of the central nervous system discussed below more extensively
for the teleosts.
There seems ,to be a general parallelism of thyroid and reproductive
functions in elasmobranchs. This is more fully reviewed by Pickford and
Atz ( 1957), Dodd and Matty ( 1964), and Woodhead (1966).