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Gen Comp Endocrinol
2000 Apr 01;1181:68-76. doi: 10.1006/gcen.2000.7456.
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Occurrence of immunoreactive Activin/Inhibin beta(B) in thyrotropes and gonadotropes in the bullfrog pituitary: possible Paracrine/Autocrine effects of activin B on gonadotropin secretion.
Uchiyama H
,
Koda A
,
Komazaki S
,
Oyama M
,
Kikuyama S
.
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Occurrence of immunoreactive activin/inhibin beta(B) in the bullfrog (Rana catesbeiana) pituitary was investigated immunocytochemically by use of antibody against Xenopus activin/inhibin beta(B) subunit. Thyrotropes were demonstrated to contain activin/inhibin beta(B)-immunoreactive substances. Moreover, immunoelectron microscopy revealed that in the secretory granules of thyrotropes and, to a lesser extent, in those of gonadotropes, activin/inhibin beta(B)-immunoreactive substances were present. Based on this observation, we investigated the effect of activin B on the release of gonadotropins from dispersed anterior pituitary cells of the bullfrog. Activin B stimulated the release of not only follicle-stimulating hormone (FSH) but also luteinizing hormone (LH) dose dependently. Under the culture conditions used in this experiment, inhibin B, as well as follistatin, did not affect the basal levels of LH and FSH, but they suppressed the activin-induced release of these hormones. This is the first study on the effect of activin on pituitary hormone secretion in lower tetrapods.
FIG. 1. Immunohistochemical staining of the bullfrog pituitary gland with anti-activin/inhibin bB antibody (A,C,D) and anti-TSHb antiserum
(B). In D, anti-activin/inhibin bB antibody was preabsorbed with an excess amount of the antigen peptide prior to reaction on the section.Aand
B, as well as C and D, are the same field of adjacent sections and are at the same magnification. Bar in B 5 160 μm, and bar in D 5 200 μm. Signals
appear brown, and the nuclei appear blue by the counterstaining with hematoxylin. Numbered arrows in Aand B indicate the same cells.
FIG. 2. Electron microscopical immunostaining of the bullfrog pituitary gland. (A)–(F) are at the same magnification. The diameter of the
colloidal gold particles is 15 nm. (A) GH-immunoreactive granules. (B) PRL-immunoreactive granules. (C) ACTH-immunoreactive granules. (D)
TSHb-immunoreactive granules. (E) LHb-immunoreactive granules. (F) Anti-activin/inhibin bB-immunoreactive granules. (Bar, 300 nm.)
FIG. 3. Double staining with anti-LHb (15 nm) and anti-activin/inhibin bB (5 nm). (A) LHb-containing granules. Note the scattered
activin/inhibin bB signals among the LHb signals. (B) TSHb-like granules intensely stained with anti-activin/inhibin bB antibody. (C) GH-like
granules. (Bar, 200 nm)
FIG. 4. Effect of activin B on the release of LH (A) and FSH (B) from dispersed pituitary cells in vitro. Human GnRH was employed as a control
secretagogue. Each column and vertical bar represent the mean of 12 determinations and SEM, respectively. The values with the same
superscript are not significantly different at 5% level.
FIG. 5. Effect of inhibin B on the release of LH (A) and FSH (B) from dispersed pituitary cells in vitro. Human GnRH was employed as a control
secretagogue. Each column and vertical bar represent the mean of 12 determinations and SEM, respectively. The values with the same
superscript are not significantly different at 5% level.
FIG. 6. Effect of inhibin B and follistatin on the activin B-induced release of LH (A) and FSH (B) from dispersed pituitary cells in vitro.
Concentrations of activin, inhibin, and follistatin were 1 ng/ml, 10 ng/ml, and 10 ng/ml, respectively. Each column and vertical bar represent
the mean of 15 determinations and SEM, respectively. The values with the same superscript are not significantly different at 5% level.
