1. THE PITUITARY GLAND
41
and also the similar granules in the postspawning gonadotrop of the
salmon.
The question of whether Poecilia possesses two distinct types of
gonadotrops is unresolved. The behavior and staining properties so far
described apply to all the cells in the gonadotropic zone, and PbH-PAS
has so far been uninformative applied to Poecilia, all the gonadotrops
staining with PAS and none selectively with the PbH. Sometimes it is
possible to distinguish two apparently different cells with Ox-AB-PAS-OG
at times of maximal gonadotropic activity, one type containing more R
granules than the other, but in the absence of functional evidence for a
clear separation there are no reasons for thinking that these are other
than two stages in the activity cycle of one cell type.
The guppy, Poecilia reticulata, exhibits an ovarian cycle essentially
like that of P . latipinnu (Stolk, 1951a; Sokol, 1961), and the gonadotrops
also display a similar cycle (Stolk, 1951b; Sokol, 1961), maximal activity
of the gonadotrops being confined to a period starting in late pregnancy
and finishing a few days after birth (Sokol, 1961), the period when a new
crop of oocytes is undergoing rapid vitellogenic development ( Stolk,
1951a).
Little information is available about reactions of the gonadotrops to
collateral changes in endocrine state. The eel gonadotrops were activated
by treatment with an impure TSH, but this is probably to be attributed
to the known contaminant, LH (Olivereau, 1961), since the gonadotrops
of the eel are greatly stimulated by injections of human chorionic gonadotropin (Olivereau and Herlant, 1960) and carp pituitary homogenates or
purified carp gonadotropin ( Olivereau and Fontaine, 1966; Olivereau,
1967a). It is unexpected that these exogenous gonadotropins, at the same
time as they stimulate the eel gonad, should also cause activation of the
eel pituitary gonadotrops; indeed, one might have expected that the
gonadotrops would regress because of pituitary-gonad negative feedback.
Probably a hypothalamic mechanism is involved, but the nature of this
is not known ( Olivereau and Fontaine, 1966). The quiescent gonadotrops
of the immature eel are not affected by treatment with thyroxine
( Olivereau, 1962a) or by radiothyroidectomy ( Olivereau, 1963a), injections of SU 4885 (Olivereau, 1965), surgical interrenalectomy (Olivereau
and Olivereau, 196S), sojourn in deionized water (Olivereau, 196%) or
seawater ( Olivereau and Olivereau, 1968). Older work suggested that
stress produced alterations in the gonadotrops of Astyanax and the goldfish resembling the changes following injections of ACTH or corticosteroids; such treatments generally lead also to inhibition of oocyte
growth, suggesting failure of gonadotropin secretion (see Ball, 1960, for
review of literature). Atz (1953) presented in detail data showing that
41
and also the similar granules in the postspawning gonadotrop of the
salmon.
The question of whether Poecilia possesses two distinct types of
gonadotrops is unresolved. The behavior and staining properties so far
described apply to all the cells in the gonadotropic zone, and PbH-PAS
has so far been uninformative applied to Poecilia, all the gonadotrops
staining with PAS and none selectively with the PbH. Sometimes it is
possible to distinguish two apparently different cells with Ox-AB-PAS-OG
at times of maximal gonadotropic activity, one type containing more R
granules than the other, but in the absence of functional evidence for a
clear separation there are no reasons for thinking that these are other
than two stages in the activity cycle of one cell type.
The guppy, Poecilia reticulata, exhibits an ovarian cycle essentially
like that of P . latipinnu (Stolk, 1951a; Sokol, 1961), and the gonadotrops
also display a similar cycle (Stolk, 1951b; Sokol, 1961), maximal activity
of the gonadotrops being confined to a period starting in late pregnancy
and finishing a few days after birth (Sokol, 1961), the period when a new
crop of oocytes is undergoing rapid vitellogenic development ( Stolk,
1951a).
Little information is available about reactions of the gonadotrops to
collateral changes in endocrine state. The eel gonadotrops were activated
by treatment with an impure TSH, but this is probably to be attributed
to the known contaminant, LH (Olivereau, 1961), since the gonadotrops
of the eel are greatly stimulated by injections of human chorionic gonadotropin (Olivereau and Herlant, 1960) and carp pituitary homogenates or
purified carp gonadotropin ( Olivereau and Fontaine, 1966; Olivereau,
1967a). It is unexpected that these exogenous gonadotropins, at the same
time as they stimulate the eel gonad, should also cause activation of the
eel pituitary gonadotrops; indeed, one might have expected that the
gonadotrops would regress because of pituitary-gonad negative feedback.
Probably a hypothalamic mechanism is involved, but the nature of this
is not known ( Olivereau and Fontaine, 1966). The quiescent gonadotrops
of the immature eel are not affected by treatment with thyroxine
( Olivereau, 1962a) or by radiothyroidectomy ( Olivereau, 1963a), injections of SU 4885 (Olivereau, 1965), surgical interrenalectomy (Olivereau
and Olivereau, 196S), sojourn in deionized water (Olivereau, 196%) or
seawater ( Olivereau and Olivereau, 1968). Older work suggested that
stress produced alterations in the gonadotrops of Astyanax and the goldfish resembling the changes following injections of ACTH or corticosteroids; such treatments generally lead also to inhibition of oocyte
growth, suggesting failure of gonadotropin secretion (see Ball, 1960, for
review of literature). Atz (1953) presented in detail data showing that