16
J. N. BALL AND BRIDGET I. BAKER
(Follenius and Porte, 1961a). The prolactin cells do not appear to undergo marked activity changes during the monthly cycle of oocyte growth
and pregnancy in viviparous cyprinodonts ( Xiphophorus, Schreibman,
1964; Poecilia, Ball, 1967); but in Zoarces viuiparw, an unrelated viviparous form with a totally different mode of gestation, ultrastructural
studies indicated that these cells are hyperactive during pregnancy
(Oztan, 1966a). In the male Hippocampus, which incubates the eggs in
a brood pouch or marsupium, the prolactin cells undergo an annual cycle
in correlation with the development and functions of the marsupium,
being especially active during the first half of the incubation period.
These changes correlate with experimental evidence that prolactin is
concerned in maintaining the marsupium ( Boisseau, 1967)- The 7 cells of
salmon, Salmo saZur, are fairly active in the freshwater parr and smolt and
appeared to be reorganizing after degeneration in adult fish ascending
the river from the sea in the spring, eventually becoming stimulated and
hyperplastic. Their activity seemed to be depressed in spawning fish in
freshwater, particularly in the female (Olivereau, 1954). The 7 cells in
hybrid Xiphophorus bearing melanomas were extremely large and hyperactive (Schreibman, l W ) , an interesting correlation in view of evidence
that prolactin can promote melanogenesis in Fundulus heteroclitus ( Pickford and Kosto, 1957; Kosto et al., 1959).
In view of all the evidence for the part played by fish prolactin in
sodium conservation in freshwater (see chapter by Ball, this volume),
one might expect the 7 cells to be maximally active in deionized water;
but this is not so, at least in the case of the eel, in which a sojourn in
deionized water reduced the cells to a state of inactivity comparable to
that in seawater (Olivereau, 1967b), with marked concomitant changes
in other cell types described elsewhere (Sections 11, B, 3 and 11, B, 6).
Deionized water is obviously a highly artificial medium, and in its effects
on electrolyte metabolism it does not act simply as a highly dilute freshwater (Section 11, B, 3).
There are indications of interactions between the prolactin cells and
other endocrine glands. The cells are activated after radiothyroidectomy
in the eel and goldfish (Olivereau, 196213, 1963a), but not distinctly so
in the trout (Olivereau et al., 1964). However, thyroxine had no very
clear effect on the cells in the eel (Olivereau, 196%) apart from inducing
a retention of 7 granules (Olivereau, 1969a). Doses of thiourea or thyroxine, both of which inhibited thyroidal 13*1 uptake, had no obvious
effects on the prolactin cells in P. lutipinna; nor did propyl thiouracil
affect the prolactin cells of Mugil, although inducing pronounced alterations in the TSH-thyroid axis (Leray and Blanc, 196713). Surgical interrenalectomy did not alter the prolactin cells in the eel (Olivereau and
J. N. BALL AND BRIDGET I. BAKER
(Follenius and Porte, 1961a). The prolactin cells do not appear to undergo marked activity changes during the monthly cycle of oocyte growth
and pregnancy in viviparous cyprinodonts ( Xiphophorus, Schreibman,
1964; Poecilia, Ball, 1967); but in Zoarces viuiparw, an unrelated viviparous form with a totally different mode of gestation, ultrastructural
studies indicated that these cells are hyperactive during pregnancy
(Oztan, 1966a). In the male Hippocampus, which incubates the eggs in
a brood pouch or marsupium, the prolactin cells undergo an annual cycle
in correlation with the development and functions of the marsupium,
being especially active during the first half of the incubation period.
These changes correlate with experimental evidence that prolactin is
concerned in maintaining the marsupium ( Boisseau, 1967)- The 7 cells of
salmon, Salmo saZur, are fairly active in the freshwater parr and smolt and
appeared to be reorganizing after degeneration in adult fish ascending
the river from the sea in the spring, eventually becoming stimulated and
hyperplastic. Their activity seemed to be depressed in spawning fish in
freshwater, particularly in the female (Olivereau, 1954). The 7 cells in
hybrid Xiphophorus bearing melanomas were extremely large and hyperactive (Schreibman, l W ) , an interesting correlation in view of evidence
that prolactin can promote melanogenesis in Fundulus heteroclitus ( Pickford and Kosto, 1957; Kosto et al., 1959).
In view of all the evidence for the part played by fish prolactin in
sodium conservation in freshwater (see chapter by Ball, this volume),
one might expect the 7 cells to be maximally active in deionized water;
but this is not so, at least in the case of the eel, in which a sojourn in
deionized water reduced the cells to a state of inactivity comparable to
that in seawater (Olivereau, 1967b), with marked concomitant changes
in other cell types described elsewhere (Sections 11, B, 3 and 11, B, 6).
Deionized water is obviously a highly artificial medium, and in its effects
on electrolyte metabolism it does not act simply as a highly dilute freshwater (Section 11, B, 3).
There are indications of interactions between the prolactin cells and
other endocrine glands. The cells are activated after radiothyroidectomy
in the eel and goldfish (Olivereau, 196213, 1963a), but not distinctly so
in the trout (Olivereau et al., 1964). However, thyroxine had no very
clear effect on the cells in the eel (Olivereau, 196%) apart from inducing
a retention of 7 granules (Olivereau, 1969a). Doses of thiourea or thyroxine, both of which inhibited thyroidal 13*1 uptake, had no obvious
effects on the prolactin cells in P. lutipinna; nor did propyl thiouracil
affect the prolactin cells of Mugil, although inducing pronounced alterations in the TSH-thyroid axis (Leray and Blanc, 196713). Surgical interrenalectomy did not alter the prolactin cells in the eel (Olivereau and