220
J. N. BALL
that Bliim and Fiedler (1965) were not able to demonstrate an effect on
the mucous cells of PterophyZZum because the number of cells vary
greatly from one part of the body to another. Attempts to demonstrate
a reduction in mucous cells of Tilapia mossambica after hypophysectomy,
and stimulation of the cells by prolactin, have so far been unsuccessful
(Bern, 1967). To date it has been impossible to detect any consistent effects of hypophysectomy or prolactin treatment on the gill mucous cells
in P. Iatipinnu (Ball, 1968). On the other hand, as in the case of the goldfish (Ogawa and Johansen, 1967), we have repeatedly observed that
hypophysectomized PoeciZia secrete less mucus than intact fish, in that
they feel distinctly less slimy to the hand. Furthermore, not only prolactin
treatment but also (and more noticeably) TSH and thyroxine restore the
normal sliminess to the skin. These rather subjective data (which nevertheless are consistently borne out by our records of the condition of the
skin on fish in many different experiments) require backing by more objective methods of assessment, but they do suggest that in this species the
effects of prolactin on sodium movements are not mediated by alterations
in general skin mucus secretion, since neither thyroxine nor TSH has the
same effects on sodium metabolism as prolactin (Ball and Ensor, 1967;
Ball, 1968). Similarly, our failure to detect effects of hypophysectomy or
prolactin on gill mucous cells may cast doubt on the hypothesis that these
cells mediate the action of prolactin on sodium movements. However, it
remains true that increased mucus secretion need not necessarily be accompanied by histologically detectable increases in the number of mucous
cells in the skin or gills, and it is quite possible that the secretion of
mucus on the gills of P. latipinnu may be altered by experimentation even
though the number of mucous cells showed no definite changes,
One important and curious point is that none of the workers who have
demonstrated an effect of prolactin on mucous cells has employed hypophysectomized animals; thus, contributions from the in situ pituitary
cannot be excluded until more rigorous experimentation has been
reported.
E. Miscellaneous Effects of Prolactin in Fishes
Several different categories of prolactin effects have been described
following the administration of mammalian prolactin to (usually intact)
fishes. It should be said at once that the physiological status of most of
these effects is uncertain. Some are related to reproductive phenomena
and may be considered at this point. It is well known that in birds prolactin generally seems to act to promote care of the young, being impli-
J. N. BALL
that Bliim and Fiedler (1965) were not able to demonstrate an effect on
the mucous cells of PterophyZZum because the number of cells vary
greatly from one part of the body to another. Attempts to demonstrate
a reduction in mucous cells of Tilapia mossambica after hypophysectomy,
and stimulation of the cells by prolactin, have so far been unsuccessful
(Bern, 1967). To date it has been impossible to detect any consistent effects of hypophysectomy or prolactin treatment on the gill mucous cells
in P. Iatipinnu (Ball, 1968). On the other hand, as in the case of the goldfish (Ogawa and Johansen, 1967), we have repeatedly observed that
hypophysectomized PoeciZia secrete less mucus than intact fish, in that
they feel distinctly less slimy to the hand. Furthermore, not only prolactin
treatment but also (and more noticeably) TSH and thyroxine restore the
normal sliminess to the skin. These rather subjective data (which nevertheless are consistently borne out by our records of the condition of the
skin on fish in many different experiments) require backing by more objective methods of assessment, but they do suggest that in this species the
effects of prolactin on sodium movements are not mediated by alterations
in general skin mucus secretion, since neither thyroxine nor TSH has the
same effects on sodium metabolism as prolactin (Ball and Ensor, 1967;
Ball, 1968). Similarly, our failure to detect effects of hypophysectomy or
prolactin on gill mucous cells may cast doubt on the hypothesis that these
cells mediate the action of prolactin on sodium movements. However, it
remains true that increased mucus secretion need not necessarily be accompanied by histologically detectable increases in the number of mucous
cells in the skin or gills, and it is quite possible that the secretion of
mucus on the gills of P. latipinnu may be altered by experimentation even
though the number of mucous cells showed no definite changes,
One important and curious point is that none of the workers who have
demonstrated an effect of prolactin on mucous cells has employed hypophysectomized animals; thus, contributions from the in situ pituitary
cannot be excluded until more rigorous experimentation has been
reported.
E. Miscellaneous Effects of Prolactin in Fishes
Several different categories of prolactin effects have been described
following the administration of mammalian prolactin to (usually intact)
fishes. It should be said at once that the physiological status of most of
these effects is uncertain. Some are related to reproductive phenomena
and may be considered at this point. It is well known that in birds prolactin generally seems to act to promote care of the young, being impli-