4. THYROID FUNCTION AND ITS CONTROL IN FISHES
247
section of this chapter, that it deserves confirmation and publication in
full detail for better evaluation. This appears to confirm earlier data of
Olivereau (1954) and Vivien (1941) who observed histological stimulation of Scyliorhinus caniculus thyroids after injection of crude suspensions
of Scyliorhinus pituitary tissue.
Eight days after hypophysectomy of late-embryo sharks by decapitation, thyroidal l3l1 uptake was apparently reduced in experiments by
Vivien and Rechenmann (1954). However, these authors judged the lalI
uptake by the use of radioautography of tissue sections, and this is not a
technique that yields reliable quantitative data. Dodd and Goddard (unpublished work cited by Dent and Dodd, 1961 ) hypophysectomized adult
Scylwrhinus caniculus, and in specimens that survived as long as 2 years
they found no histological changes in the thyroid. In earlier work Waring
et al. (1942) found no histological changes in the thyroids of Scyliorhinus
1 month after hypophysectomy. More recently, Vivien (1963) found
that in younger Scyliorhinus embryos hypophysectomized by decapitation,
thyroidal differentiation is incomplete.
Unlike the cyclostomes and elasmobranchs, for the teleosts there is an
abundance of evidence which indicates that the pars distalis contains a
thyroid stimulating hormone and that surgical removal of this gland leads
to involutional changes in the thyroid and reduction of its function (M.
Fontaine et al., 1953; Pickford, 1959). The earliest literature is exhaustively reviewed by Pickford and Atz (1957) as well as by Dodd et al.
(1963) and Dodd and Matty ( 1964). Emphasis of the newer phases of
this field will be made here. It may be concluded from the earlier and
more recent work that the pars distalis of numerous teleosts contains cells
which are responsive to and along with changes in thyroid state of the
fish (Olivereau and Ball, 1964; Sage, 1967; Mattheij and van Oordt, 1967),
and these may be considered TSH cells. B. I. Baker (1965, 1967) even
finds these cells directly responsive to thyroxine in tissue cultures (of
Salmo gairdneri pituitary), raising again the question of direct feedback
responsiveness versus hypothalamic control of TSH secretion. In this context reference should be repeated to the papers of Ball et ab ( 1963,1965) ;
these workers found that pituitary glands transplanted into a site away
from the hypothalamus can secrete more TSH than in the normal site,
while gonadotropic and ACTH secretion are reduced. The obvious inference from this work is that TSH secretion is under inhibitory control of
the brain when the normal anatomical relationships of the Poecilia
pituitary obtain.
It is quite possible that in fish, as in mammals, both levels of feedback
control of TSH secretion, hypothalamic and direct TSH-cell responsiveness are effective. It is of interest that bioassay procedures reveal an
247
section of this chapter, that it deserves confirmation and publication in
full detail for better evaluation. This appears to confirm earlier data of
Olivereau (1954) and Vivien (1941) who observed histological stimulation of Scyliorhinus caniculus thyroids after injection of crude suspensions
of Scyliorhinus pituitary tissue.
Eight days after hypophysectomy of late-embryo sharks by decapitation, thyroidal l3l1 uptake was apparently reduced in experiments by
Vivien and Rechenmann (1954). However, these authors judged the lalI
uptake by the use of radioautography of tissue sections, and this is not a
technique that yields reliable quantitative data. Dodd and Goddard (unpublished work cited by Dent and Dodd, 1961 ) hypophysectomized adult
Scylwrhinus caniculus, and in specimens that survived as long as 2 years
they found no histological changes in the thyroid. In earlier work Waring
et al. (1942) found no histological changes in the thyroids of Scyliorhinus
1 month after hypophysectomy. More recently, Vivien (1963) found
that in younger Scyliorhinus embryos hypophysectomized by decapitation,
thyroidal differentiation is incomplete.
Unlike the cyclostomes and elasmobranchs, for the teleosts there is an
abundance of evidence which indicates that the pars distalis contains a
thyroid stimulating hormone and that surgical removal of this gland leads
to involutional changes in the thyroid and reduction of its function (M.
Fontaine et al., 1953; Pickford, 1959). The earliest literature is exhaustively reviewed by Pickford and Atz (1957) as well as by Dodd et al.
(1963) and Dodd and Matty ( 1964). Emphasis of the newer phases of
this field will be made here. It may be concluded from the earlier and
more recent work that the pars distalis of numerous teleosts contains cells
which are responsive to and along with changes in thyroid state of the
fish (Olivereau and Ball, 1964; Sage, 1967; Mattheij and van Oordt, 1967),
and these may be considered TSH cells. B. I. Baker (1965, 1967) even
finds these cells directly responsive to thyroxine in tissue cultures (of
Salmo gairdneri pituitary), raising again the question of direct feedback
responsiveness versus hypothalamic control of TSH secretion. In this context reference should be repeated to the papers of Ball et ab ( 1963,1965) ;
these workers found that pituitary glands transplanted into a site away
from the hypothalamus can secrete more TSH than in the normal site,
while gonadotropic and ACTH secretion are reduced. The obvious inference from this work is that TSH secretion is under inhibitory control of
the brain when the normal anatomical relationships of the Poecilia
pituitary obtain.
It is quite possible that in fish, as in mammals, both levels of feedback
control of TSH secretion, hypothalamic and direct TSH-cell responsiveness are effective. It is of interest that bioassay procedures reveal an