in mammals, but the sodium concentration does not change. The failure of the latter
to change may reflect the very low rate of urine formation in these reptiles. The
painted turtle, Chrysemys picta, responds to adrenalectomy in a more classical manner since , after a period of two weeks, the plasma sodium concentration decreases
while the potassium rises (BUTLER and KNOX, 1970). ELIZONDO and LEBRIE (1969)
tied off the blood supplies to the adrenal glands of water snakes, Natrix cyclopion,
and allowed the tissue to atrophy. Urine formation was maintained and both the
sodium and potassium levels in the plasma declined. Change in sodium concentration appeared to reflect a 20% decrease in the rate of sodium reabsorption across
the proximal segment of the renal tubule. Hypophysectomy causes atrophy of
adrenocortical tissues in the lizard, Agama agama, and the grass snake, Natrix natrix, but this is not associated with any significant changes in the electrolyte levels
in the body (WRIGHT and CHESTER JONES, 1957). In mammals hypophysectomy
has since been shown to have little effect on the secretion of aldosterone, so that
the latter observations on the possible role of adrenocorticosteroids in reptilian
mineral metabolism are inconclusive. In addition, it should be remembered that
physiological processes in po ikilotherms are far slower than those in homoiotherrns, so that any derangement in electrolyte metabolism that follows adrenalectomy may be slow to appear, especially if there is littl e turnover of sodium and
potassium . While it appears likely that corticosteroid hormones influence renal sodium and potassium excretion as in other tetrapods, there is little information to
show that this is so . It has recently been show n that th e composition of the urine of
water snakes, Natrix cyclopion, in water diuresis fails to change in response to
injections of aldosterone, corticosterone or the aldosterone inhibitor 'Aldactone'
(ELIZONDO and LE BRIE, 1969). However, when these snakes are in a saline diuresis
du e to the administration of sod ium chloride solutions, aldosterone injections
result in a 20% increa se in the rate of sodium reabsorption across the proximal
renal tubuletLs BRIE and E LIZONDO, 1969).As described pre viously, corticosteroids
also increase the rate of sodium transport across the tortoise urinary bladder and
interference with the adrenal tissue alters the secretion of sodium and potassium
from the salt glands of the green turtle and the desert iguana .
Direct identification of corticosteroids in the blood of reptiles has not been
systematically made , though corticosterone has been found in the blood of the grass
snake, Natrix natrix, (PHILLIPS and CHESTER JONES , 1957) and the lizard, Anolis
carolinensis(LICHTand BRADSHAW, 1969). Identification of such steroids in other
reptiles is based on experiments utilizing in v itro incubation of adrenocortical tissues, sometimes in the presence of the substrate progesterone, and the subsequent
isolation of the products formed . These results (Table 5.9) indicate that diverse reptiles have the ability to form corticosterone, as well as aldosterone, along with a
few other steroids including I l-deoxycorticosterone. It is, of course, not clear from
such experiments whether these steroids are secreted in vivo, but it seems likely
that some of them are.
Information about the regulation of secretion from adrenocortical tissues in
reptiles is sparse. The presence of a corticotrophic principle in the pituitary is implied from the experiments of WRIGHT and CHESTER JONES (1957). Adrenocortical
tissue in Agama agama and Natrix natrixdegenerated following hypophysectomy,
but this could be prevented by injection of mammalian corticotrophin. The alliga155
to change may reflect the very low rate of urine formation in these reptiles. The
painted turtle, Chrysemys picta, responds to adrenalectomy in a more classical manner since , after a period of two weeks, the plasma sodium concentration decreases
while the potassium rises (BUTLER and KNOX, 1970). ELIZONDO and LEBRIE (1969)
tied off the blood supplies to the adrenal glands of water snakes, Natrix cyclopion,
and allowed the tissue to atrophy. Urine formation was maintained and both the
sodium and potassium levels in the plasma declined. Change in sodium concentration appeared to reflect a 20% decrease in the rate of sodium reabsorption across
the proximal segment of the renal tubule. Hypophysectomy causes atrophy of
adrenocortical tissues in the lizard, Agama agama, and the grass snake, Natrix natrix, but this is not associated with any significant changes in the electrolyte levels
in the body (WRIGHT and CHESTER JONES, 1957). In mammals hypophysectomy
has since been shown to have little effect on the secretion of aldosterone, so that
the latter observations on the possible role of adrenocorticosteroids in reptilian
mineral metabolism are inconclusive. In addition, it should be remembered that
physiological processes in po ikilotherms are far slower than those in homoiotherrns, so that any derangement in electrolyte metabolism that follows adrenalectomy may be slow to appear, especially if there is littl e turnover of sodium and
potassium . While it appears likely that corticosteroid hormones influence renal sodium and potassium excretion as in other tetrapods, there is little information to
show that this is so . It has recently been show n that th e composition of the urine of
water snakes, Natrix cyclopion, in water diuresis fails to change in response to
injections of aldosterone, corticosterone or the aldosterone inhibitor 'Aldactone'
(ELIZONDO and LE BRIE, 1969). However, when these snakes are in a saline diuresis
du e to the administration of sod ium chloride solutions, aldosterone injections
result in a 20% increa se in the rate of sodium reabsorption across the proximal
renal tubuletLs BRIE and E LIZONDO, 1969).As described pre viously, corticosteroids
also increase the rate of sodium transport across the tortoise urinary bladder and
interference with the adrenal tissue alters the secretion of sodium and potassium
from the salt glands of the green turtle and the desert iguana .
Direct identification of corticosteroids in the blood of reptiles has not been
systematically made , though corticosterone has been found in the blood of the grass
snake, Natrix natrix, (PHILLIPS and CHESTER JONES , 1957) and the lizard, Anolis
carolinensis(LICHTand BRADSHAW, 1969). Identification of such steroids in other
reptiles is based on experiments utilizing in v itro incubation of adrenocortical tissues, sometimes in the presence of the substrate progesterone, and the subsequent
isolation of the products formed . These results (Table 5.9) indicate that diverse reptiles have the ability to form corticosterone, as well as aldosterone, along with a
few other steroids including I l-deoxycorticosterone. It is, of course, not clear from
such experiments whether these steroids are secreted in vivo, but it seems likely
that some of them are.
Information about the regulation of secretion from adrenocortical tissues in
reptiles is sparse. The presence of a corticotrophic principle in the pituitary is implied from the experiments of WRIGHT and CHESTER JONES (1957). Adrenocortical
tissue in Agama agama and Natrix natrixdegenerated following hypophysectomy,
but this could be prevented by injection of mammalian corticotrophin. The alliga155