meability of the skin and a greatly reduced response to injected neurohypophysial
peptides (LEVINSKY and SAWYER, 1952). This is due mainly to the absence of corticotrophin as injections of this hormone substantially restore the animal to normal,
while additional small doses of th yroxine almost complete the replacement. Such
effects are only manifest after a period of several da ys and do no t occ ur if the fro gs
are tested within a da y or two of the operation. When the latter was done, LEVINSKY
and SAWYER (1953) found that such animals could onl y reh ydrate (after deh ydration) at about 50% the rate of intact frogs. JORGENSEN, WINGSTRAND, and
ROSENKILDE (1956) attempted to destroy the neurohypophysis, leaving the adenohypophysis intact, by cutting the praeoptico-hypophysial tract and allowing the
peripheral neurohypophysial tissue to degenerate over a period of several weeks.
Toads, Bufo bufo, treated in this way continued to form normal quantities of urine,
while their rate of rehydration, after dehydration, was not significantly different
from that of normal toads. A number of objections were made to these experiments
as it seemed possible that release of neurohypophysial peptides from the cut rostral
stump of the praeoptico-hypophysial tract could not be excluded. In order to overcome this difficulty two separate attempts to completely destroy the tissue, by
directly coagulating the praeoptic nucleus, have been made . JORGENSEN, ROSENKILDE, and WINGSTRAND (1969)"repeated their experiments on Bufo bufo and destroyed the praeoptic nucleus. They found evidence for a deficiency in the toads
abilit y to reab sorb water from its urinary bladder, but again found that the operated
toads reh ydrated at the same rate as the normal controls. An examination of their
results , however, shows that the latter control toads only reh ydrated at a ver y slow
rate, very much less than had been reported previously (JORGENSEN and ROSENKILDE, 1956 a). The efficiency of the controls' neurohypophysial function is, therefore, also in doubt. The praeoptic nucleus has also been destroyed in the toad, Bufo
marinus (SHOEMAKER and WARING, 1968), and it was found that in these animal s,
when dehydrated or injected w ith saline, cutaneous water uptake was less and urine
volume greater than in sham-operated controls. Removal of the entire pituitary also
resulted in a reduction of the responses of the skin and kidney, but was similar to
the effect of adenohypophysectom y alone . This presumably reflects the absence
of the adenohypophysial hormones, an effect that was also seen by LEVINSKY and
SAWYER (1952). MIDDLER, KLEEMAN , and EDWARDS (1967) also compared the responses of adenohypophysectomized and totally hypophysectomized Bufo marinus to dehydration and injections of hypertonic saline solutions. They found that
the totally hypophysectomized toads had little ability to reduce their urine flow or
to reabsorb water from their urinary bladders as compared to animals that only had
the adenohypophysis removed. This difference is presumably due to the additional
absence of the neural lobe in the hypophysectomized toads. The variations in the
results from different laboratories probably reflect mainl y the ph ysiological condition of the toads used , both that of the controls and of the operated animals. The
evidence generally sugge sts that the neurohypophysis facilitates the osmoregulatory changes that occur in the skin, kidney and urinary bladder following deh ydrational stresses. Nevertheless, it should be remembered that alterations in the functions of these tissues may still occur even in the absence of any endocrine
stimulation. For example, changes in the circulation and osmotic concentration of
the blood supplying these tissues may have direct effects on their function.
195
peptides (LEVINSKY and SAWYER, 1952). This is due mainly to the absence of corticotrophin as injections of this hormone substantially restore the animal to normal,
while additional small doses of th yroxine almost complete the replacement. Such
effects are only manifest after a period of several da ys and do no t occ ur if the fro gs
are tested within a da y or two of the operation. When the latter was done, LEVINSKY
and SAWYER (1953) found that such animals could onl y reh ydrate (after deh ydration) at about 50% the rate of intact frogs. JORGENSEN, WINGSTRAND, and
ROSENKILDE (1956) attempted to destroy the neurohypophysis, leaving the adenohypophysis intact, by cutting the praeoptico-hypophysial tract and allowing the
peripheral neurohypophysial tissue to degenerate over a period of several weeks.
Toads, Bufo bufo, treated in this way continued to form normal quantities of urine,
while their rate of rehydration, after dehydration, was not significantly different
from that of normal toads. A number of objections were made to these experiments
as it seemed possible that release of neurohypophysial peptides from the cut rostral
stump of the praeoptico-hypophysial tract could not be excluded. In order to overcome this difficulty two separate attempts to completely destroy the tissue, by
directly coagulating the praeoptic nucleus, have been made . JORGENSEN, ROSENKILDE, and WINGSTRAND (1969)"repeated their experiments on Bufo bufo and destroyed the praeoptic nucleus. They found evidence for a deficiency in the toads
abilit y to reab sorb water from its urinary bladder, but again found that the operated
toads reh ydrated at the same rate as the normal controls. An examination of their
results , however, shows that the latter control toads only reh ydrated at a ver y slow
rate, very much less than had been reported previously (JORGENSEN and ROSENKILDE, 1956 a). The efficiency of the controls' neurohypophysial function is, therefore, also in doubt. The praeoptic nucleus has also been destroyed in the toad, Bufo
marinus (SHOEMAKER and WARING, 1968), and it was found that in these animal s,
when dehydrated or injected w ith saline, cutaneous water uptake was less and urine
volume greater than in sham-operated controls. Removal of the entire pituitary also
resulted in a reduction of the responses of the skin and kidney, but was similar to
the effect of adenohypophysectom y alone . This presumably reflects the absence
of the adenohypophysial hormones, an effect that was also seen by LEVINSKY and
SAWYER (1952). MIDDLER, KLEEMAN , and EDWARDS (1967) also compared the responses of adenohypophysectomized and totally hypophysectomized Bufo marinus to dehydration and injections of hypertonic saline solutions. They found that
the totally hypophysectomized toads had little ability to reduce their urine flow or
to reabsorb water from their urinary bladders as compared to animals that only had
the adenohypophysis removed. This difference is presumably due to the additional
absence of the neural lobe in the hypophysectomized toads. The variations in the
results from different laboratories probably reflect mainl y the ph ysiological condition of the toads used , both that of the controls and of the operated animals. The
evidence generally sugge sts that the neurohypophysis facilitates the osmoregulatory changes that occur in the skin, kidney and urinary bladder following deh ydrational stresses. Nevertheless, it should be remembered that alterations in the functions of these tissues may still occur even in the absence of any endocrine
stimulation. For example, changes in the circulation and osmotic concentration of
the blood supplying these tissues may have direct effects on their function.
195