3. FISH PROLACTIN AND GROWTH HORMONE
223
more rapidly after hypophysectomy than after castration, suggesting that
they may be partially maintained by some pituitary hormone(s) other
than gonadotropins. In a detailed investigation, Sundararaj and Goswami
(1965) showed that prolactin by itself did not stimulate the atropic seminal vesicles of intact ( regressed), castrated, or hypophysectomized fish,
but they showed that prolactin did stimulate growth and secretory activity of the seminal vesicles of intact fish primed with HCG (human
chorionic gonadotropin), Similarly, androgen priming of the vesicles of
castrated or hypophysectomized catfish allowed prolactin to exert a
stimulatory effect on the growth and secretory activity of these structures.
Growth hormone also synergized in the same way after androgen priming
of hypophysectomized fish, and the maximum response was obtained by
simultaneous treatment with androgen, prolactin, and growth hormone
( Sundararaj and Goswami, 1965). These results suggest that endogenous
fish prolactin may participate in the maintenance and activity of the seminal vesicles, although the physiological status of the observed effects of
mammalian prolactin is not completely certain. Similarly, it is not clear
that the various recorded actions of exogenous prolactin on male accessory structures in mammals have any physiological validity (Meites and
Nicoll, 1966).
In the only report of an effect of prolactin on reproduction in fish other
than teleosts, Carlisle (1954) reported that spermiation, which was interrupted by starvation, was resumed in dogfish following treatment with
prolactin or with gonadotropins. As usual, the physiological meaning of
this observation is obscure, although the presence of fish prolactin in the
elasmobranch pituitary is attested by a positive response in the red eft
water-drive test (Grant, 1961, 1962) and the negative performance of
elasmobranch material in pigeon crop and mammary gland tests (Nicoll
and Bern, 1964, 1968; Nicoll et al., 1966).
Several effects of prolactin have been demonstrated in fishes that seem
to have no relation to osmoregulation or reproductive processes. Thus,
Olivereau (1966) found that chronic injections of ovine prolactin resulted
in marked histological activation of the thyroid in intact eels, Anguilla
anguilla, but not in hypophysectomized animals, the TSH cells in the
pituitary becoming highly active after prolactin treatment. As Olivereau
suggested, these results could be explained either by prolactin acting as a
goitrogen at the thyroid level or by prolactin somehow stimulating TSH
output by a hypothalamic or pituitary action in the presence of a normally functioning thyroid. In amphibians, exogenous prolactin appears to
act as a goitrogen in Rana catesbiana ( Gona, 1967), and there is some
evidence from pituitary transplantation experiments that endogenous prolactin may have an antithyroid action in this frog (Etkin et d., 1967).
223
more rapidly after hypophysectomy than after castration, suggesting that
they may be partially maintained by some pituitary hormone(s) other
than gonadotropins. In a detailed investigation, Sundararaj and Goswami
(1965) showed that prolactin by itself did not stimulate the atropic seminal vesicles of intact ( regressed), castrated, or hypophysectomized fish,
but they showed that prolactin did stimulate growth and secretory activity of the seminal vesicles of intact fish primed with HCG (human
chorionic gonadotropin), Similarly, androgen priming of the vesicles of
castrated or hypophysectomized catfish allowed prolactin to exert a
stimulatory effect on the growth and secretory activity of these structures.
Growth hormone also synergized in the same way after androgen priming
of hypophysectomized fish, and the maximum response was obtained by
simultaneous treatment with androgen, prolactin, and growth hormone
( Sundararaj and Goswami, 1965). These results suggest that endogenous
fish prolactin may participate in the maintenance and activity of the seminal vesicles, although the physiological status of the observed effects of
mammalian prolactin is not completely certain. Similarly, it is not clear
that the various recorded actions of exogenous prolactin on male accessory structures in mammals have any physiological validity (Meites and
Nicoll, 1966).
In the only report of an effect of prolactin on reproduction in fish other
than teleosts, Carlisle (1954) reported that spermiation, which was interrupted by starvation, was resumed in dogfish following treatment with
prolactin or with gonadotropins. As usual, the physiological meaning of
this observation is obscure, although the presence of fish prolactin in the
elasmobranch pituitary is attested by a positive response in the red eft
water-drive test (Grant, 1961, 1962) and the negative performance of
elasmobranch material in pigeon crop and mammary gland tests (Nicoll
and Bern, 1964, 1968; Nicoll et al., 1966).
Several effects of prolactin have been demonstrated in fishes that seem
to have no relation to osmoregulation or reproductive processes. Thus,
Olivereau (1966) found that chronic injections of ovine prolactin resulted
in marked histological activation of the thyroid in intact eels, Anguilla
anguilla, but not in hypophysectomized animals, the TSH cells in the
pituitary becoming highly active after prolactin treatment. As Olivereau
suggested, these results could be explained either by prolactin acting as a
goitrogen at the thyroid level or by prolactin somehow stimulating TSH
output by a hypothalamic or pituitary action in the presence of a normally functioning thyroid. In amphibians, exogenous prolactin appears to
act as a goitrogen in Rana catesbiana ( Gona, 1967), and there is some
evidence from pituitary transplantation experiments that endogenous prolactin may have an antithyroid action in this frog (Etkin et d., 1967).