other animals . Th e po ssibility that a tissue may onl y assume ph ysiolo gical importance in
certai n situations should be kept in mind. Prol actin promotes the survival of teleost fish
in fresh water, but is apparently unn ecessary when th ey are in salt water. A high salt diet
can often con siderabl y ameliora te the effects of adrenalecto my, while diab etes insipidus,
du e to the absence of the neurohypophysis, is no t appa rent if the adenohypophysis is also
removed.
2. The biological activity of the putative gland sho uld also be present in the circulation ,
under appropriate physiolo gical or environmental conditions.
3..The suspe cted effector tissue should respond to extracts f rom the blood and putativ e
gland, and exhibit a sensitivity consistent with the concentrations present , especially tho se
in th e circulation. Th e reaction s of the end ocrin e gland and the hormon e(s), including the
facto rs initiating release of the secretion and th e nature of the effector response , sho uld be
consistent when they are viewed as an integrated hom eostatic mechani sm. The respon se of
the supposed effecto r or gan should be direct ed towards correcting the conditions that
brought about the release of th e ho rmone, and such ph ysiolo gical compensation should then
reduce (' feed- back' ) subsequent secretion.
b) Endocrine Extirpation - Surgical and Chemical
Surgical skills play a large role in establishing the end ocrin e significance and function of
a tissue. Such pro cedures include removal of the putative gland and the alteration of its vascular and neural connections, either directly in situ, or by the manoeuvre of tr ansplantin g
it elsewhere . The basic surgical aim is to perform such tasks in a manner that leaves a minimum of residu al tissue, and with as littl e ph ysiological disruption and incon venience to
the animal as po ssible. It is ofte n difficult to separate the adverse effects of a sur gical pro cedure per se, from the specific endocrine changes that are the experimental aim. Nonspecific
surgical tr aum a and discomf ort to the animal can be reduc ed by the acquisition of th e relevant skill by an investigator , as well as by selectin g the most appropriate route and method
for approaching the tissue in question. Such pro cedu res vary consider ably in different species, depending on the anato mical site of the gland and the suitability and sensitivity of the
animal to surge ry. Th ere are special problems associated with surgery in fishes, as compared
to terrestrial tetrapods, du e principally to differences in th e mod es of respiration, bu t also
to their generally different morpholo gical arrangement. Endocrine tissues like the thyroid
and int errenals are mor e diffuse and no t as comp actly arran ged in the fishes as in tetrapod s,
but even amon g the latt er con siderabl e differences exist. In the rept iles and the Amphibia,
adrenocortical tissue is not as compact or discrete as in mammal s. O sseous differences mak e
removal of th e pituitary a far mor e difficult operation in the guinea pig than in the rat. Such
variations make it necessary to modify sur gical methods in different species in ord er to do
the job and to minimize surg ical stress. Special pr e-operative and post-operative tr eatm ent
may assist these aims. Thus, antithyroid drugs can be given prior to sur gery, in order to
reduce the possibility of an 'explosive' release of th yroid horm one during manipulation of
this gland. Adrenocortical hormones may be inject ed during adrenalecto my , in order to alleviate any acute requirement s for such hormones as a result of th e operation.
Special problems associated with sur gical extirpation include th e difficulty of separating
closely associated endo crine glands, like the adr enocortical and chromaffin tissue, th e
th yroids and parathyroids, and the adenohypophysis and neurohypophysis. In addition
most endocrin e tissues produce more than on e hormone which surgically cannot be dissociated. Some of these difficult ies may be partly overcome by subsequently administering
some of the hormones kno wn to be missin g. Wh en several secretions are involved this may
tak e th e form of serially successive hormone sub stitutions , in ord er to find the parti cular
secretion which is responsible for an ob served deficiency. Thus the teleost fish, Fundulus
heteroclitus, living in fresh water dies after remo val of its pituitary, but survives if prolactin
is injected (PICKFORD and PHILLIPS, 1959), administration of other pitu itar y hormones being
ineffective in this respect. Another problem associated with att empts at endo crine extirpa tion involve the question of how compl etely th e tissue has been removed, and whether
or not any regeneratio n has occurred; careful histol ogical postmortem examination may
be necessary in order to rule out such po ssibilities.
41
certai n situations should be kept in mind. Prol actin promotes the survival of teleost fish
in fresh water, but is apparently unn ecessary when th ey are in salt water. A high salt diet
can often con siderabl y ameliora te the effects of adrenalecto my, while diab etes insipidus,
du e to the absence of the neurohypophysis, is no t appa rent if the adenohypophysis is also
removed.
2. The biological activity of the putative gland sho uld also be present in the circulation ,
under appropriate physiolo gical or environmental conditions.
3..The suspe cted effector tissue should respond to extracts f rom the blood and putativ e
gland, and exhibit a sensitivity consistent with the concentrations present , especially tho se
in th e circulation. Th e reaction s of the end ocrin e gland and the hormon e(s), including the
facto rs initiating release of the secretion and th e nature of the effector response , sho uld be
consistent when they are viewed as an integrated hom eostatic mechani sm. The respon se of
the supposed effecto r or gan should be direct ed towards correcting the conditions that
brought about the release of th e ho rmone, and such ph ysiolo gical compensation should then
reduce (' feed- back' ) subsequent secretion.
b) Endocrine Extirpation - Surgical and Chemical
Surgical skills play a large role in establishing the end ocrin e significance and function of
a tissue. Such pro cedures include removal of the putative gland and the alteration of its vascular and neural connections, either directly in situ, or by the manoeuvre of tr ansplantin g
it elsewhere . The basic surgical aim is to perform such tasks in a manner that leaves a minimum of residu al tissue, and with as littl e ph ysiological disruption and incon venience to
the animal as po ssible. It is ofte n difficult to separate the adverse effects of a sur gical pro cedure per se, from the specific endocrine changes that are the experimental aim. Nonspecific
surgical tr aum a and discomf ort to the animal can be reduc ed by the acquisition of th e relevant skill by an investigator , as well as by selectin g the most appropriate route and method
for approaching the tissue in question. Such pro cedu res vary consider ably in different species, depending on the anato mical site of the gland and the suitability and sensitivity of the
animal to surge ry. Th ere are special problems associated with surgery in fishes, as compared
to terrestrial tetrapods, du e principally to differences in th e mod es of respiration, bu t also
to their generally different morpholo gical arrangement. Endocrine tissues like the thyroid
and int errenals are mor e diffuse and no t as comp actly arran ged in the fishes as in tetrapod s,
but even amon g the latt er con siderabl e differences exist. In the rept iles and the Amphibia,
adrenocortical tissue is not as compact or discrete as in mammal s. O sseous differences mak e
removal of th e pituitary a far mor e difficult operation in the guinea pig than in the rat. Such
variations make it necessary to modify sur gical methods in different species in ord er to do
the job and to minimize surg ical stress. Special pr e-operative and post-operative tr eatm ent
may assist these aims. Thus, antithyroid drugs can be given prior to sur gery, in order to
reduce the possibility of an 'explosive' release of th yroid horm one during manipulation of
this gland. Adrenocortical hormones may be inject ed during adrenalecto my , in order to alleviate any acute requirement s for such hormones as a result of th e operation.
Special problems associated with sur gical extirpation include th e difficulty of separating
closely associated endo crine glands, like the adr enocortical and chromaffin tissue, th e
th yroids and parathyroids, and the adenohypophysis and neurohypophysis. In addition
most endocrin e tissues produce more than on e hormone which surgically cannot be dissociated. Some of these difficult ies may be partly overcome by subsequently administering
some of the hormones kno wn to be missin g. Wh en several secretions are involved this may
tak e th e form of serially successive hormone sub stitutions , in ord er to find the parti cular
secretion which is responsible for an ob served deficiency. Thus the teleost fish, Fundulus
heteroclitus, living in fresh water dies after remo val of its pituitary, but survives if prolactin
is injected (PICKFORD and PHILLIPS, 1959), administration of other pitu itar y hormones being
ineffective in this respect. Another problem associated with att empts at endo crine extirpa tion involve the question of how compl etely th e tissue has been removed, and whether
or not any regeneratio n has occurred; careful histol ogical postmortem examination may
be necessary in order to rule out such po ssibilities.
41