240
CHARLES S. THORNTON
by the traumatic action of hemorrhage. The adrenal glucocorticoids have
a negative feedback effect on ACTH production in Rana
catesbiana
(Piper and DeRoos, 1967) so that it is possible that, in the intact frogs
used by Schotte and Wilber (1958), the adrenal implants inhibited ACTH
production in the pituitary. The glucogenic adrenal cortical hormones
would then remain at normal levels in these frogs. Glucogenic adrenal
hormones should be even lower than normal in the hypophysectomized
frogs with adrenal implants. The adrenal cortical hormones concerned
with electrolyte and water metabolism are influenced by ACTH, renin,
and plasma levels of Na and K in mammals (Mulrow and Ganong, 1961)
and in the frog (Carstensen et al, 1961), but much higher levels of ACTH
must be used to increase aldosterone production than are needed to
increase cortisone. If a similar interaction should be found in the urodele,
as seems likely, then it is important to investigate the possible interrelation of amputational trauma, aldosterone or deoxycorticosterone, and
limb regeneration in the hypophysectomized newt. Indeed, Lindberg and
Schotte (1955) and Pellman and Schotte (1955) have reported that
trauma, due to repeated amputation or repeated anesthesia, could induce
limb regeneration in hypophysectomized
newts. Since Schotte and Bierman (1956) have already reported some success in stimulating a regenerative response in hypophysectomized newts with injections of
deoxycorticosterone, the possibility that the mineralocorticoids may be
involved (without a necessary intervening action of the pituitary) in a
stress-initiated action on limb regeneration should receive careful attention.
The action of the pituitary gland in limb regeneration was considered
by Schotte and Hall (1952) to be particularly significant for the processes
of wound healing and tissue dedifferentiation. However, the best regenerative response in hypophysectomized newts was obtained by implanting
frog adrenals IS days after amputation
(Schotte and Lindberg, 1954)
or by beginning the injection of growth hormone H days after
amputation (Wilkerson, 1963). The dedifferentiation phase of regeneration is
ending at this time and the growth phase is beginning so that, as Hay
(1966) suggests, the hormonal influence may be on cell proliferation
rather than on tissue dedifferentiation. Of interest, therefore, is the fact
that Inoue (1956) has noted a diminished mitotic proliferation in
epidermal cells of amputated limbs of hypophysectomized adult newts.
Further work, however, is needed before we can specify the phase of
regeneration on which the pituitary acts, and whether this action is
focused directly on the regenerate or is indirect, as Schotte suggests, by
CHARLES S. THORNTON
by the traumatic action of hemorrhage. The adrenal glucocorticoids have
a negative feedback effect on ACTH production in Rana
catesbiana
(Piper and DeRoos, 1967) so that it is possible that, in the intact frogs
used by Schotte and Wilber (1958), the adrenal implants inhibited ACTH
production in the pituitary. The glucogenic adrenal cortical hormones
would then remain at normal levels in these frogs. Glucogenic adrenal
hormones should be even lower than normal in the hypophysectomized
frogs with adrenal implants. The adrenal cortical hormones concerned
with electrolyte and water metabolism are influenced by ACTH, renin,
and plasma levels of Na and K in mammals (Mulrow and Ganong, 1961)
and in the frog (Carstensen et al, 1961), but much higher levels of ACTH
must be used to increase aldosterone production than are needed to
increase cortisone. If a similar interaction should be found in the urodele,
as seems likely, then it is important to investigate the possible interrelation of amputational trauma, aldosterone or deoxycorticosterone, and
limb regeneration in the hypophysectomized newt. Indeed, Lindberg and
Schotte (1955) and Pellman and Schotte (1955) have reported that
trauma, due to repeated amputation or repeated anesthesia, could induce
limb regeneration in hypophysectomized
newts. Since Schotte and Bierman (1956) have already reported some success in stimulating a regenerative response in hypophysectomized newts with injections of
deoxycorticosterone, the possibility that the mineralocorticoids may be
involved (without a necessary intervening action of the pituitary) in a
stress-initiated action on limb regeneration should receive careful attention.
The action of the pituitary gland in limb regeneration was considered
by Schotte and Hall (1952) to be particularly significant for the processes
of wound healing and tissue dedifferentiation. However, the best regenerative response in hypophysectomized newts was obtained by implanting
frog adrenals IS days after amputation
(Schotte and Lindberg, 1954)
or by beginning the injection of growth hormone H days after
amputation (Wilkerson, 1963). The dedifferentiation phase of regeneration is
ending at this time and the growth phase is beginning so that, as Hay
(1966) suggests, the hormonal influence may be on cell proliferation
rather than on tissue dedifferentiation. Of interest, therefore, is the fact
that Inoue (1956) has noted a diminished mitotic proliferation in
epidermal cells of amputated limbs of hypophysectomized adult newts.
Further work, however, is needed before we can specify the phase of
regeneration on which the pituitary acts, and whether this action is
focused directly on the regenerate or is indirect, as Schotte suggests, by