216
J. N. BALL
seen in the example of the plains killifish, FunduZus kansae. Unlike F .
heteroclitus, F. kansae is able to survive without its pituitary in freshwater, and even in deionized water provided sufficient calcium is added;
whereas calcium will not protect F. heteroclitus from failure in deionized
water or even in freshwater ( Pickford et al., 19eSb). Fundulus kansae
will survive for weeks in a calcium-rich freshwater after hypophysectomy,
although in negative sodium balance; such fish display a reduced serum
and total body sodium despite normal or higher than normal extrarenal
sodium influx, because of enhanced sodium loss via the kidneys (Stanley
and Fleming, 1967b). These workers concluded that hypophysectomy,
which reduced urine flow (Stanley and Fleming, 1966a), must actually
reduce the permeability of the integument to water. A low dose of prolactin increased urine flow in hypophysectomized fish in freshwater, but
ACTH was not effective ( Stanley and Fleming, 1967a). The renal loss of
sodium after hypophysectomy in freshwater resulted from impairment
of renal sodium resorption which was not compensated by reduced urine
flow (Stanley and Fleming, 1966a,b). Prolactin reduced the sodium content of the urine of hypophysectomized F. kansae, but because of the
associated increase in urine flow the actual sodium loss remained elevated. Thus, although prolactin probably enhanced the resorption of
sodium by the renal tubule in this fish, it had no net result in terms of the
total sodium economy. In intact F. kansae, however, prolactin did reduce
sodium loss via the kidney (Stanley and Fleming, 1967a). These workers
concluded (1967a) that prolactin acts in both freshwater and seawater
to increase the permeability of the integument, resulting in freshwater in
increased passage of water into the body and hence in increased urine
flow. The effects they had demonstrated on sodium metabolism were
minor or equivocal. However, more recent work has indicated that prolactin at higher doses does have extrarenal effects in F. k a w e , in that it
stimulates the active uptake of sodium in hypophysectomized fish in
freshwater, while having no effect on the outfiux (Fleming and Ball,
1967). These findings are very different from the effects of prolactin on
sodium outflux in F. heteroclitus and P . latipinnu and may be related to
the fact that in F. kansae, but not in the other two species, prolactin has
an ACTH-like action on the interrenal (Ball and Fleming, 1967; Ball and
Ensor, 1969).
It is difficult to generalize about the site of action of prolactin in these
fishes. We have seen that the evidence points largely to an extrarenal action of prolactin in the eel and F. heteroclitus, although it is not impossible that some sodium loss could take place across the eel skin and be
reduced by prolactin (Potts and Evans, 1966; Maetz et al., 1967a,b), An
extrarenal action of prolactin is probably paramount in P. Zutipinna,
J. N. BALL
seen in the example of the plains killifish, FunduZus kansae. Unlike F .
heteroclitus, F. kansae is able to survive without its pituitary in freshwater, and even in deionized water provided sufficient calcium is added;
whereas calcium will not protect F. heteroclitus from failure in deionized
water or even in freshwater ( Pickford et al., 19eSb). Fundulus kansae
will survive for weeks in a calcium-rich freshwater after hypophysectomy,
although in negative sodium balance; such fish display a reduced serum
and total body sodium despite normal or higher than normal extrarenal
sodium influx, because of enhanced sodium loss via the kidneys (Stanley
and Fleming, 1967b). These workers concluded that hypophysectomy,
which reduced urine flow (Stanley and Fleming, 1966a), must actually
reduce the permeability of the integument to water. A low dose of prolactin increased urine flow in hypophysectomized fish in freshwater, but
ACTH was not effective ( Stanley and Fleming, 1967a). The renal loss of
sodium after hypophysectomy in freshwater resulted from impairment
of renal sodium resorption which was not compensated by reduced urine
flow (Stanley and Fleming, 1966a,b). Prolactin reduced the sodium content of the urine of hypophysectomized F. kansae, but because of the
associated increase in urine flow the actual sodium loss remained elevated. Thus, although prolactin probably enhanced the resorption of
sodium by the renal tubule in this fish, it had no net result in terms of the
total sodium economy. In intact F. kansae, however, prolactin did reduce
sodium loss via the kidney (Stanley and Fleming, 1967a). These workers
concluded (1967a) that prolactin acts in both freshwater and seawater
to increase the permeability of the integument, resulting in freshwater in
increased passage of water into the body and hence in increased urine
flow. The effects they had demonstrated on sodium metabolism were
minor or equivocal. However, more recent work has indicated that prolactin at higher doses does have extrarenal effects in F. k a w e , in that it
stimulates the active uptake of sodium in hypophysectomized fish in
freshwater, while having no effect on the outfiux (Fleming and Ball,
1967). These findings are very different from the effects of prolactin on
sodium outflux in F. heteroclitus and P . latipinnu and may be related to
the fact that in F. kansae, but not in the other two species, prolactin has
an ACTH-like action on the interrenal (Ball and Fleming, 1967; Ball and
Ensor, 1969).
It is difficult to generalize about the site of action of prolactin in these
fishes. We have seen that the evidence points largely to an extrarenal action of prolactin in the eel and F. heteroclitus, although it is not impossible that some sodium loss could take place across the eel skin and be
reduced by prolactin (Potts and Evans, 1966; Maetz et al., 1967a,b), An
extrarenal action of prolactin is probably paramount in P. Zutipinna,