1. THE PWITARY GLAND
47
the S cells to treatment with the antithyroid agent thiourea, administered in solution in the tank water, Results are summarized in Table IV
and clearly demonstrate the strong response of the S cell to thioureainduced blockage of thyroid hormone synthesis. None of the other cell
types responded to the treatment. Unexpectedly, treatment of adult hh
with thyroxine produced no obvious regression of the 6 cells, although
reducing thyroidal 24-hr l3II uptake to 0.5% (cf. Table IV) . This lack of
effect of thyroxine on TSH cell morphology in Poecilia latipinnu agrees
with the failure of thyroxine treatment to affect the TSH cells of the
guppy (Sage, 1967), but contrasts with the distinct effects in the eel and
Mugil (Olivereau, 1%2a, 19f38), and with the rather slight changes in the
thyroid and thyrotrops of Astyanux ( Atz, 1953). Clearly the time course
of the TSH cell response to different doses of thyroxine should be
explored in Poecilia.
Leray and Blanc (1!367a,b) showed that treatment of young Mugil
auratus with the thyroid inhibitor propylthiouracil (PTU) reduced levels
of plasma protein-bound iodine (PB1)-that is, impaired the production
of thyroid hormone-and produced signs of histological stimulation in
the thyroid itself (i.e., raised levels of TSH) . Correspondingly, the 6 cells
of the pars distalis became strongly activated, marking them as thyrotrops
since no other pituitary cells were affected. Olivereau (1968) confirmed
these observations in this same species, thiourea activating -md thyroxine
inhibiting the 6 cells.
Other evidence bearing on the function of the 6 cells comes from their
marked activation in response to thiourea or thiouracil treatment in
Phoxinus (Barrington and Matty, 1955), Astyanux ( Atz, 1953), and the
guppy (Sokol, 1955; Sage, 1967). Thyroxine administered with thiourea
to the guppy reversed the activation of the 6 cells induced by thiourea
Table IV
Effects of Thiourea Treatment on the 6 Cells of Juvenile Poecilia Zatininna
Group
n
Thyroida
6 Cellsb
A. Controls in fresh- 14 Low activity, epithelial Low activity, well granulated,
water + 0.2% potaseium iodide
0.2% potassium iohyperplasia, epithelial
nucleolus large, cells invaddide + 0.03% thioing neurohypophysis; mean
urea, 28 days
nuclear area 15.6 f 0.33 pa
cell height ca. 2.5 p
B. In freshwater and 13 Very active, marked
Very active, degranulated,
cell height ca. 9.0 p
nucleolus small; mean
nuclear area 9.7 f 0.35 pa
a In parallel experiments with adult fish, this treatment reduced 24 hr 1811 uptake by
the thyroid region from 24 f 3.2% (controls n = 11) to 1.4 f 0.6% (thiourea, TZ = 6).
The t test comparison of mean nuclear areas of group A and group B, p < 0.001.
47
the S cells to treatment with the antithyroid agent thiourea, administered in solution in the tank water, Results are summarized in Table IV
and clearly demonstrate the strong response of the S cell to thioureainduced blockage of thyroid hormone synthesis. None of the other cell
types responded to the treatment. Unexpectedly, treatment of adult hh
with thyroxine produced no obvious regression of the 6 cells, although
reducing thyroidal 24-hr l3II uptake to 0.5% (cf. Table IV) . This lack of
effect of thyroxine on TSH cell morphology in Poecilia latipinnu agrees
with the failure of thyroxine treatment to affect the TSH cells of the
guppy (Sage, 1967), but contrasts with the distinct effects in the eel and
Mugil (Olivereau, 1%2a, 19f38), and with the rather slight changes in the
thyroid and thyrotrops of Astyanux ( Atz, 1953). Clearly the time course
of the TSH cell response to different doses of thyroxine should be
explored in Poecilia.
Leray and Blanc (1!367a,b) showed that treatment of young Mugil
auratus with the thyroid inhibitor propylthiouracil (PTU) reduced levels
of plasma protein-bound iodine (PB1)-that is, impaired the production
of thyroid hormone-and produced signs of histological stimulation in
the thyroid itself (i.e., raised levels of TSH) . Correspondingly, the 6 cells
of the pars distalis became strongly activated, marking them as thyrotrops
since no other pituitary cells were affected. Olivereau (1968) confirmed
these observations in this same species, thiourea activating -md thyroxine
inhibiting the 6 cells.
Other evidence bearing on the function of the 6 cells comes from their
marked activation in response to thiourea or thiouracil treatment in
Phoxinus (Barrington and Matty, 1955), Astyanux ( Atz, 1953), and the
guppy (Sokol, 1955; Sage, 1967). Thyroxine administered with thiourea
to the guppy reversed the activation of the 6 cells induced by thiourea
Table IV
Effects of Thiourea Treatment on the 6 Cells of Juvenile Poecilia Zatininna
Group
n
Thyroida
6 Cellsb
A. Controls in fresh- 14 Low activity, epithelial Low activity, well granulated,
water + 0.2% potaseium iodide
0.2% potassium iohyperplasia, epithelial
nucleolus large, cells invaddide + 0.03% thioing neurohypophysis; mean
urea, 28 days
nuclear area 15.6 f 0.33 pa
cell height ca. 2.5 p
B. In freshwater and 13 Very active, marked
Very active, degranulated,
cell height ca. 9.0 p
nucleolus small; mean
nuclear area 9.7 f 0.35 pa
a In parallel experiments with adult fish, this treatment reduced 24 hr 1811 uptake by
the thyroid region from 24 f 3.2% (controls n = 11) to 1.4 f 0.6% (thiourea, TZ = 6).
The t test comparison of mean nuclear areas of group A and group B, p < 0.001.