Hiroo Takikawa

Comparative studies on the electric nature of amphibian gonadotropin.

The isoelectric focusing (IEF) profiles of pituitary gonadotropic (GTH) activity in six species of adult male amphibians were examined in addition to the newt and bullfrog. The GTH activity was measured by two radioreceptor assay (RRA) systems; one with Xenopus laevis testicular homogenate as the receptor preparation, and the other with Anolis carolinensis testicular homogenate, both employing 125I-labeled rat FSH as the radioligand, or by a radioimmunoassay (RIA) system for bullfrog basic GTH (LH). The IEF profiles were classified into four groups: (1) Cynops pyrrhogaster pyrrhogaster, Onychodactylus japonicus, (2) X. laevis, (3) Rana japonica, Bufo japonicus formosus, (4) Rana nigromaculata, Hyla arborea japonica, Rana catesbeiana. In Onychodactylus japonicus (Group 1), Anolis RRA-positive peaks and Xenopus RRA-positive peaks were found in almost the same fractions. They were in the alkaline to neutral pH region. This IEF profile was very similar to that of newt pituitary GTH in July when spermatogenesis was active. In X. laevis (Group 2), the IEF profile was similar to that of urodeles. However, the most alkaline peak was found at pH 9.02, which was lower than those of urodeles. These peaks showed some differences in the reactivity to the RRA systems. In R. japonica (Group 3), the major peak obtained by Xenopus RRA was found at pH 10.27, which corresponded to the only positive peak obtained by the RIA system for bullfrog basic GTH. Furthermore, this peak was also recognized by Anolis RRA as one of the eight peaks, which appeared in the alkaline to acidic region. In B. japonicus formosus (Group 3), similar results were observed. In H. arborea japonica, R. nigromaculata and R. catesbeiana (Group 4), Anolis RRA-positive and Xenopus RRA-positive peaks were quite independent, indicating distinct separation of LH and FSH, though pIs of FSH-like GTH in the frogs were not so acidic as those of mammalian and avian FSH.

Effects of OK-432 (Picibanil) on Estrogen Receptor Levels and Tamoxifen Treatment in 7,12-Dimethylbenz[a]anthracene-Induced Rat Mammary Cancers

The effects of OK-432 (Picibanil) on estrogen receptor (ER) levels and subsequent tamoxifen (TAM) treatment were examined in 189 female Sprague-Dawley rats with 7,12-dimethylbenz[a]anthracene (DMBA)-induced mammary cancers. When OK-432 was administered (0.1 KE/kg i.p. once weekly) for 12 weeks to the rats after DMBA, the average ER level of the TAM-responsive tumors in the OK-432-treated group was significantly higher than that in the control group. The antitumor effect of TAM was significantly greater in the OK-432-treated group. When OK-432 was administered to rats with established DMBA tumors, the average ER levels did not change significantly after 2 or 4 weeks of treatment. ER levels in the control group (no treatment) fell significantly after 2 or 4 weeks. These results suggest that hormone dependence of DMBA-induced rat mammary cancers may be maintained or augmented by the administration of OK-432.

Effects of Trilostane on 7,12-Dimethylbenz[α]anthracene-Induced Rat Mammary Cancers and Body Weight of Rats in Relation to Estrogen Receptors

Effects of trilostane (TLS) on 7,12-dimethylbenz[a]anthracene (DMBA)-induced mammary cancers and body weight of rats were examined in relation to estrogen receptors (ER) in 103 female Sprague-Dawley rats with DMBA-induced cancers. The inhibitory effects of the treated groups on the growth of DMBA-induced rat mammary cancers were significantly stronger than those of the control group at many points during the treatment, demonstrating a more remarkable inhibitory effect in the high-dose groups of 300 and 500 mg/kg. In the high-dose groups, the inhibitory effects of TLS tended to be slightly stronger in the ER-negative groups than in the ER-positive groups. These results suggest that the mechanisms of action of TLS are not influenced by the presence or absence of ER, but are due to complicated hormonal changes induced by the inhibition of steroid biosynthesis.

Purification and Characterization of T3-Receptor from Beef Liver Plasma Membrane

Over the past two decades, it has been believed that the transport of thyroid hormones into cells was by simple diffusion. However, recent evidence indicates that the uptake of T3 into the cells occurs by receptor-mediated endocytosis (1), and that this mode of entry is physiologically significant (2). It is also known that the plasma membrane receptor is highly stereospecific for L-T3 (3). Two classes of T3-receptor (high affinity - low capacity and low affinity - high capacity sites) were determined in GH3 cells (3), swiss 3T3 cells (4) and human erythrocytes (5). Using affinity labeling with Bromoacetyl [125I]T3 (BrAc[125I]T3, the binding site of the T3-receptor was identified by SDS-PAGE to be a 55K dalton band (3). However, its structural details and the role of the plasma membrane receptor on the mechanism of T3 action have not been clearly defined.