246
AUBREY CORBMAN
cedure as the bioassay, the high levels of activity in neurohypophysis
tissue must be considered indicative of the background or meaningless
level of the assay technique; hence, the results could be interpreted to
show that no TSH activity was extractable from cyclostome pituitary, and
the question remains open.
Two other direct approaches to the question of TSH in cyclostome
pituitary have been made. Knowles ( 1941 ) hypophysectomized larval
lampreys ( ammocoetes), and Larsen ( 19ss) has hypophysectomized
young adult lampreys; in neither set of experiments was there any observable effect upon endostylar or thyroid histology, or upon rate of I3*I
accumulation by the thyroid. On the other hand, although TSH injections by Knowles (1941) into larval Lampetra pkaneri were without effect,
both Olivereau (1956) and Clements-Merlini (1962), using other species
of ammocoetes, found that mammalian TSH evoked morphological
changes in the endostyle and a slight stimulation of 1311 metabolism.
Under these circumstances, as long as hypothalamic control of the
cyclostome pituitary remains dubious, and as long as definitive proof of
TSH production still is lacking, it is difficult to interpret claims of thyrotropic cells in the cyclostome pars distalis (van de Kamer and Schreurs,
1959; and others).
The use of adult temperate zone selachians in laboratory experiments,
particularly when this requires keeping them for extended periods of time,
presents numerous practical difficulties and high mortality rates. For this
reason there are relatively few studies of the effects of hypophysectomy,
or of the effects of repeated injections of TSH. Furthermore, these studies
are conducted at marine laboratories where available facilities and techniques modify experimental design, and somewhat less than definitive experiments result. These difficulties are mentioned at this point in explanation of the fragmentary and imperfect experiments to be described in the
following paragraphs. This also explains why several of the studies have
utilized embryonic or newly hatched sharks; these are much more easily
used in laboratory experiments.
If we examine the evidence based on pituitary tissue extraction, and
on hypophysectomy, we must admit that definitive proof of a TSH-like
principle in elasmobranch pituitaries also remains to be provided, The
pituitary extraction and bioassay experiments of Ferguson, Dodd, and
Hunter (unpublished, but extensively cited by Dodd et al., 1963) show by
the use of the McKenzie TSH bioassay that the ventral lobe of the
Scyliorhinw caniculu pars distalis contains a concentration of TSH
activity about equal to that of a salamander and higher than that in a
teleost, Pleuronectes, pituitary. This important observation opens so many
questions, including that of hypothalamic control raised in the previous
AUBREY CORBMAN
cedure as the bioassay, the high levels of activity in neurohypophysis
tissue must be considered indicative of the background or meaningless
level of the assay technique; hence, the results could be interpreted to
show that no TSH activity was extractable from cyclostome pituitary, and
the question remains open.
Two other direct approaches to the question of TSH in cyclostome
pituitary have been made. Knowles ( 1941 ) hypophysectomized larval
lampreys ( ammocoetes), and Larsen ( 19ss) has hypophysectomized
young adult lampreys; in neither set of experiments was there any observable effect upon endostylar or thyroid histology, or upon rate of I3*I
accumulation by the thyroid. On the other hand, although TSH injections by Knowles (1941) into larval Lampetra pkaneri were without effect,
both Olivereau (1956) and Clements-Merlini (1962), using other species
of ammocoetes, found that mammalian TSH evoked morphological
changes in the endostyle and a slight stimulation of 1311 metabolism.
Under these circumstances, as long as hypothalamic control of the
cyclostome pituitary remains dubious, and as long as definitive proof of
TSH production still is lacking, it is difficult to interpret claims of thyrotropic cells in the cyclostome pars distalis (van de Kamer and Schreurs,
1959; and others).
The use of adult temperate zone selachians in laboratory experiments,
particularly when this requires keeping them for extended periods of time,
presents numerous practical difficulties and high mortality rates. For this
reason there are relatively few studies of the effects of hypophysectomy,
or of the effects of repeated injections of TSH. Furthermore, these studies
are conducted at marine laboratories where available facilities and techniques modify experimental design, and somewhat less than definitive experiments result. These difficulties are mentioned at this point in explanation of the fragmentary and imperfect experiments to be described in the
following paragraphs. This also explains why several of the studies have
utilized embryonic or newly hatched sharks; these are much more easily
used in laboratory experiments.
If we examine the evidence based on pituitary tissue extraction, and
on hypophysectomy, we must admit that definitive proof of a TSH-like
principle in elasmobranch pituitaries also remains to be provided, The
pituitary extraction and bioassay experiments of Ferguson, Dodd, and
Hunter (unpublished, but extensively cited by Dodd et al., 1963) show by
the use of the McKenzie TSH bioassay that the ventral lobe of the
Scyliorhinw caniculu pars distalis contains a concentration of TSH
activity about equal to that of a salamander and higher than that in a
teleost, Pleuronectes, pituitary. This important observation opens so many
questions, including that of hypothalamic control raised in the previous