3. FISH PROLACTIN AND GROWTH HORMONE
217
although not actually demonstrated, and in the goldfish (Lahlou and
Sawyer, 1967; Donaldson et al., 1968). On the other hand, prolactin appears to have distinct renal actions in F. kansae, possibly normally in synergism with other pituitary factors (Stanley and Fleming, 1963, 1967a),
and in addition probably stimulates active sodium uptake at the gills
even in hypophysectomized F. kansae (Fleming and Ball, 1967). At least
part of the action of prolactin in osmoregulation in the winter stickleback
transferred to freshwater appears to be on the kidney (Lam and Hoar,
1967). Possibly in teleosts in general prolactin potentially acts on both
the kidney and the integument (especially the gills), and its main locus
of action differs with species. The epidermal mucous cells have been put
forward as important factors in fish osmoregulation, in maintaining a layer
of nonstirred mucus over the surface of the skin, and especially of the gills
(Potts and Evans, 1966; see Ball, 1969), and effects of prolactin on these
cells have been described (see Section I, D).
Fish prolactin, or paralactin, is certainly only one of several hormones
implicated in electrolyte regulation in teleosts, and its importance in the
maintenance of homeostasis appears to vary with species. The physiological status of this fish hormone in teleosts is well established by the
work on F. heteroclitus and P. latipinnu. In the only reported effect of
prolactin on electrolyte regulation in a nonteleostean “fish,” Chester Jones
et al. (1962) found that prolactin, when injected daily for 8 days, Iowered
the muscle sodium concentration in the cyclostome Myxine kept in 60%
seawater. A similar effect could be produced by corticosteroids or ACTH,
and the authors were inclined to think that the injected ovine prolactin
acted as a mimic of endogenous ACTH and stimulated interrenal secretion. We have seen that this possibility is in line with the effects of prolactin in F. kunsae and Gambusia, but that in other teleosts prolactin
appears to have no ACTH-like properties. Implications of these differences have been briefly discussed elsewhere (Ball and Ensor, 19ss).
C. Prolactin and Melanogenesis in Teleosts
Work on this aspect of effects of prolactin in fishes is virtually confined to one species, Fundulus heteroclitus. After hypophysectomy this
fish becomes noticeably pale, owing to loss of melanin pigmentation, the
effect being particularly marked on the normally dark dorsal surface
(“dorsal paling”) (Pickford and Kosto, 1957). Treatment of pale hypophysectomized fish with a variety of purified mammalian pituitary
preparations demonstrated that darkening of the dorsal surface, with the
reappearance of melanin in the depigmented melanophores, was elicited
217
although not actually demonstrated, and in the goldfish (Lahlou and
Sawyer, 1967; Donaldson et al., 1968). On the other hand, prolactin appears to have distinct renal actions in F. kansae, possibly normally in synergism with other pituitary factors (Stanley and Fleming, 1963, 1967a),
and in addition probably stimulates active sodium uptake at the gills
even in hypophysectomized F. kansae (Fleming and Ball, 1967). At least
part of the action of prolactin in osmoregulation in the winter stickleback
transferred to freshwater appears to be on the kidney (Lam and Hoar,
1967). Possibly in teleosts in general prolactin potentially acts on both
the kidney and the integument (especially the gills), and its main locus
of action differs with species. The epidermal mucous cells have been put
forward as important factors in fish osmoregulation, in maintaining a layer
of nonstirred mucus over the surface of the skin, and especially of the gills
(Potts and Evans, 1966; see Ball, 1969), and effects of prolactin on these
cells have been described (see Section I, D).
Fish prolactin, or paralactin, is certainly only one of several hormones
implicated in electrolyte regulation in teleosts, and its importance in the
maintenance of homeostasis appears to vary with species. The physiological status of this fish hormone in teleosts is well established by the
work on F. heteroclitus and P. latipinnu. In the only reported effect of
prolactin on electrolyte regulation in a nonteleostean “fish,” Chester Jones
et al. (1962) found that prolactin, when injected daily for 8 days, Iowered
the muscle sodium concentration in the cyclostome Myxine kept in 60%
seawater. A similar effect could be produced by corticosteroids or ACTH,
and the authors were inclined to think that the injected ovine prolactin
acted as a mimic of endogenous ACTH and stimulated interrenal secretion. We have seen that this possibility is in line with the effects of prolactin in F. kunsae and Gambusia, but that in other teleosts prolactin
appears to have no ACTH-like properties. Implications of these differences have been briefly discussed elsewhere (Ball and Ensor, 19ss).
C. Prolactin and Melanogenesis in Teleosts
Work on this aspect of effects of prolactin in fishes is virtually confined to one species, Fundulus heteroclitus. After hypophysectomy this
fish becomes noticeably pale, owing to loss of melanin pigmentation, the
effect being particularly marked on the normally dark dorsal surface
(“dorsal paling”) (Pickford and Kosto, 1957). Treatment of pale hypophysectomized fish with a variety of purified mammalian pituitary
preparations demonstrated that darkening of the dorsal surface, with the
reappearance of melanin in the depigmented melanophores, was elicited