
hypophysectomy, replacement therapy, and the tolerance of the
euryhaline killifish, fundulus heteroclitus, to hypotonic media
hypophysectomized fundulus heteroclitus, as previously reported, survive only a
few days after transfer from salt to fresh water.  survival time is the same
when fish are tested 2 weeks or 2 months after hypophysectomy.  gradual
dilution of the external medium produces failure at an average salinity of
0.26% (0.67-0.02%).  this salinity is comparable to that causing failure after
abrupt transfer.  although failure is associated with hypochloremia, daily
injections of a balanced salt solution or 0.6% nacl shorten survival.
daily injections of teleostean neurohypophysial peptides, arginine vasotocin
(2.25 and 0.0225 pressor mu per gram) and isotocin (1.32 and 0.026 oxytocic mu
per gram) do not prolong survival.  an extract of caudal neurosecretory tissue
(urophysis) from male tilapia mossambica had no beneficial action at doses of
50 ug per gram every other day.  purified ovine prolactin.  105 mu per gram on
alternate days, maintained survival of 10 of 11 fish for the duration of the
28-day test period in fresh water, irrespective of the period of pretreatment
in salt water.  purified bovine prolactin prolonged survival and 2 of 6 fish
were maintained for 28 days.  purified bovine growth hormone was ineffective.
monkey growth hormone containing 2 u per milligram of prolactin activity,
administered at a dose of 20 ug per gram (equivalent to 40 mu per gram
prolactin activity), prolonged survival.  human growth hormone containing 4 u
per milligram of prolactin activity, at a dose of 20 ug per gram (equivalent to
80 ml per gram prolactin activity) also prolonged survival and 4 of 6 fish
were maintained for 28 days.
the ability of pituitary preparations to protect hypophysectomized
f. heteroclitus from failure in fresh water appears to be related to their
prolactin activity and not to their content of neurohypophysial peptides.
this suggests that an adenohypophysial hormone resembling mammalian prolactin
is essential for survival of this fish in hypotonic external media.  carp
pituitary preparations do not protect hypophysectomized f. heteroclitus
although f. heteroclitus pituitaries are known to be effective.
