212
J. N. BALL
cells remain active during life in freshwater (Ball, 1969; see chapter by
Ball and Baker, Volume 11). In summary, it appears that the prolactinlike
activity originates from a single distinct cell type which behaves as if
this activity were involved physiologically in sodium conservation in
freshwater.
There is some evidence from Gambusia and Fundulus kansae that prolactin in these species may act like ACTH in stimulating the interrenal
(Chambolle, 1967a,b; Ball and Fleming, 1967; see Ball and Ensor, 1969),
but considerable experimental evidence has been adduced which shows
that ovine prolactin does not stimulate the interrenal in Fundulus heteroclitus or Poeciliu latipinna (Pickford and Kosto, 1957; Ball and Ensor,
1969), and of course in both species ACTH did not mimic prolactin in
promoting electrolyte conservation. This is additional evidence, adding
to that from mammalian hormone specificity screening and pituitary
histophysiology, that ovine prolactin really does imitate a specific and
distinct fish hormone in the conditions of the work on these species. This
fish hormone is physiologically involved in electrolyte conservation, and
its kinship to tetrapod prolactin is attested by the unique ability of prolactin to mimic its action. It may appropriately be called “fish prolactin”
or “paralactin” ( Ball, 1965a, 1969).
Thus far, we have considered only teleosts which require the pituitary
gland for survival in freshwater, from which the paralactin-based mechanism could appear to be of only limited distribution within these fishes.
However, evidence from other teleosts which tolerate hypophysectomy in
freshwater points to a more widespread osmoregulatory role for fish
prolactin.
Although the eel, Anguilla anguilla, does not fail in freshwater after
hypophysectomy (Callamand et al., 1950); it nevertheless suffers a slow
reduction in plasma sodium, potassium, and calcium, which can be retarded by maintenance therapy with ovine prolactin (Olivereau and
Chartier-Baraduc, 1966). Chan et al. ( 1968) found that while sodium and
calcium decreased slightly following hypophysectomy of the eel in freshwater, plasma potassium increased slightly, recalling the more pronounced
increase in deionized water found by Olivereau and Chartier-Baraduc
(19sS). Chan et al. (1968) were not able to influence the decline in
sodium and calcium with bovine prolactin treatment, although this hormone did reduce the elevation of plasma potassium. Butler (1967) also
could not demonstrate an effect of a very low dose of ovine prolactin on
electrolyte levels in the hypophysectomized eel. However, Chan et al.
(1968) found that bovine prolactin prevented the excessive hydration of
eel muscle that occurs after hypophysectomy in freshwater, and they
suggested that fish prolactin might act in the intact animal to maintain
J. N. BALL
cells remain active during life in freshwater (Ball, 1969; see chapter by
Ball and Baker, Volume 11). In summary, it appears that the prolactinlike
activity originates from a single distinct cell type which behaves as if
this activity were involved physiologically in sodium conservation in
freshwater.
There is some evidence from Gambusia and Fundulus kansae that prolactin in these species may act like ACTH in stimulating the interrenal
(Chambolle, 1967a,b; Ball and Fleming, 1967; see Ball and Ensor, 1969),
but considerable experimental evidence has been adduced which shows
that ovine prolactin does not stimulate the interrenal in Fundulus heteroclitus or Poeciliu latipinna (Pickford and Kosto, 1957; Ball and Ensor,
1969), and of course in both species ACTH did not mimic prolactin in
promoting electrolyte conservation. This is additional evidence, adding
to that from mammalian hormone specificity screening and pituitary
histophysiology, that ovine prolactin really does imitate a specific and
distinct fish hormone in the conditions of the work on these species. This
fish hormone is physiologically involved in electrolyte conservation, and
its kinship to tetrapod prolactin is attested by the unique ability of prolactin to mimic its action. It may appropriately be called “fish prolactin”
or “paralactin” ( Ball, 1965a, 1969).
Thus far, we have considered only teleosts which require the pituitary
gland for survival in freshwater, from which the paralactin-based mechanism could appear to be of only limited distribution within these fishes.
However, evidence from other teleosts which tolerate hypophysectomy in
freshwater points to a more widespread osmoregulatory role for fish
prolactin.
Although the eel, Anguilla anguilla, does not fail in freshwater after
hypophysectomy (Callamand et al., 1950); it nevertheless suffers a slow
reduction in plasma sodium, potassium, and calcium, which can be retarded by maintenance therapy with ovine prolactin (Olivereau and
Chartier-Baraduc, 1966). Chan et al. ( 1968) found that while sodium and
calcium decreased slightly following hypophysectomy of the eel in freshwater, plasma potassium increased slightly, recalling the more pronounced
increase in deionized water found by Olivereau and Chartier-Baraduc
(19sS). Chan et al. (1968) were not able to influence the decline in
sodium and calcium with bovine prolactin treatment, although this hormone did reduce the elevation of plasma potassium. Butler (1967) also
could not demonstrate an effect of a very low dose of ovine prolactin on
electrolyte levels in the hypophysectomized eel. However, Chan et al.
(1968) found that bovine prolactin prevented the excessive hydration of
eel muscle that occurs after hypophysectomy in freshwater, and they
suggested that fish prolactin might act in the intact animal to maintain