1. THE PITUITARY GLAND
29
for the functions of the other pars distalis cell types, the a cells have come
to be accepted as somatotrops, as it were by a process of elimination.
More specifically, when the cellular source of gonadotropin( s ) , TSH and
ACTH were known, the two acidophils, a and 7 cells, remained as the
producers of prolactin and growth hormone; we have seen that the 9 cells
secrete fish prolactin, which leaves the cells as the source of growth
hormone. The functional distinction between the two acidophils was
clinched by partial hypophysectomy in Poecilia latipinnu, which showed
that removal of most of the rostra1 pars distalis (7 cells), while impairing
prolactin secretion, had no deleterious effect on growth. This meant that
growth hormone must be produced in the proximal pars distalis, and
knowing the gonadotrops, TSH cells, and ACTH cells, this leaves the a
cells as somatotrops (Ball, 1965b). The scarcity and degranulation of a
cells in the ectopic pituitary transplants that secreted little growth hormone in P . formosa is in agreement with this conclusion (Olivereau and
Ball, 1966).
Unfortunately, little information is available about alterations in the
(Y cells during the life history. The relationship of these cells to periods
of rapid growth in salmon has already been mentioned. The a cells of the
guppy, Poecilia reticulata, differentiate and attain their adult condition
later than in the 7 cells (Follenius and Porte, 1961a); they are present
and active in newly born and rapidly growing P . latipinna fry, and they
have been described as staining more intensely in the elver than in the
adult yellow eel (Knowles and Vollrath, 1966~). The a cells were
enlarged and particularly active in melanoma-bearing hybrid Xiphophorus (Schreibman, 1964), a suggestion of a possible tumorogenic action
of fish growth hormone.
Concerning the response of the a cells to collateral endocrine changes,
Olivereau (1962a, 1963a) detected no action of thyroxine or radiothyroidectomy on these cells in the eel, and female P. latipinna display no
marked a cell reactions to thyroxine or thiourea treatment, Radiothyroidectomy did not affect the CY cells in trout (Olivereau et al., 1964).
However, Sage (1967), while agreeing that thyroxine alone had no action
on the a cells of male guppies, Poecilia reticulata, found that thiourea
caused increased storage of granules in the cells, indicating retention of
growth hormone, and that thyroxine given in combination with thiourea
reduced this storage of granules. Since thyroxine increased the growth
of thiourea-treated guppies, Sage interpreted his findings as evidence
that thyroxine in some way is necessary for the release of growth hormone
from the a cells. However, on this hypothesis and with this type of
evidence, the enhanced growth produced by thyroxine alone (and repeatedly observed in thyroxine-treated female P . latipinna also) cannot
29
for the functions of the other pars distalis cell types, the a cells have come
to be accepted as somatotrops, as it were by a process of elimination.
More specifically, when the cellular source of gonadotropin( s ) , TSH and
ACTH were known, the two acidophils, a and 7 cells, remained as the
producers of prolactin and growth hormone; we have seen that the 9 cells
secrete fish prolactin, which leaves the cells as the source of growth
hormone. The functional distinction between the two acidophils was
clinched by partial hypophysectomy in Poecilia latipinnu, which showed
that removal of most of the rostra1 pars distalis (7 cells), while impairing
prolactin secretion, had no deleterious effect on growth. This meant that
growth hormone must be produced in the proximal pars distalis, and
knowing the gonadotrops, TSH cells, and ACTH cells, this leaves the a
cells as somatotrops (Ball, 1965b). The scarcity and degranulation of a
cells in the ectopic pituitary transplants that secreted little growth hormone in P . formosa is in agreement with this conclusion (Olivereau and
Ball, 1966).
Unfortunately, little information is available about alterations in the
(Y cells during the life history. The relationship of these cells to periods
of rapid growth in salmon has already been mentioned. The a cells of the
guppy, Poecilia reticulata, differentiate and attain their adult condition
later than in the 7 cells (Follenius and Porte, 1961a); they are present
and active in newly born and rapidly growing P . latipinna fry, and they
have been described as staining more intensely in the elver than in the
adult yellow eel (Knowles and Vollrath, 1966~). The a cells were
enlarged and particularly active in melanoma-bearing hybrid Xiphophorus (Schreibman, 1964), a suggestion of a possible tumorogenic action
of fish growth hormone.
Concerning the response of the a cells to collateral endocrine changes,
Olivereau (1962a, 1963a) detected no action of thyroxine or radiothyroidectomy on these cells in the eel, and female P. latipinna display no
marked a cell reactions to thyroxine or thiourea treatment, Radiothyroidectomy did not affect the CY cells in trout (Olivereau et al., 1964).
However, Sage (1967), while agreeing that thyroxine alone had no action
on the a cells of male guppies, Poecilia reticulata, found that thiourea
caused increased storage of granules in the cells, indicating retention of
growth hormone, and that thyroxine given in combination with thiourea
reduced this storage of granules. Since thyroxine increased the growth
of thiourea-treated guppies, Sage interpreted his findings as evidence
that thyroxine in some way is necessary for the release of growth hormone
from the a cells. However, on this hypothesis and with this type of
evidence, the enhanced growth produced by thyroxine alone (and repeatedly observed in thyroxine-treated female P . latipinna also) cannot