Sex-steroid hormone receptors in human medullary thyroid carcinoma

Three complementary techniques were used to detect sex-steroid hormone receptors in tumor tissues from seven patients with medullary thyroid carcinoma: steroid binding analysis, enzyme immune assay, and immunohistochemistry. The presence of estrogen receptors was detected by steroid binding analysis in one of seven patients, although in very low concentrations (3.17 to 5.06 fmol/mg protein). These results were confirmed by enzyme immune assay (6.35 to 9.32 fmol/mg protein). Progesterone receptors were found in five of seven patients by steroid binding analysis (11.1 to 47.9 fmol/mg protein), and progesterone receptor results were confirmed by enzyme immune assay (8.1 to 34.1 fmol/mg protein). By immunohistochemistry, progesterone receptors were focally detected in all cases, whereas all tumors were negative for estrogen receptors. In summary, our results confirm the presence of sex-steroid hormone receptors, particularly progesterone receptors in medullary thyroid carcinoma. The presence of progesterone receptors in medullary thyroid carcinoma apparently does not require the continuous presence of estrogen receptors.

Na+,K(+)-ATPase expression during the early phase of liver growth after partial hepatectomy

Na+,K(+)-ATPase expression has been studied in the early phase of liver growth after partial hepatectomy to ascertain whether its increased activity is due to stable effects, involving de novo synthesis and insertion of pumps into the plasma membrane. Na+,K(+)-ATPase activity progressively increases after partial hepatectomy, reaching a three-fold induction above basal values 12 h after surgery. mRNA amounts of both alpha 1 and beta 1 subunits are rapidly increased up to two-fold for alpha 1 and nearly three-fold for beta 1, at 9 and 12 h post-hepatectomy, respectively. This correlates with increased abundance of both subunit proteins. The results prove that the increase of Na+,K(+)-ATPase activity correlates with higher expression of both subunit proteins and mRNAs, although the characteristics of the induction suggest that some translational and post-translational events may be equally involved in the increased activity of the pump.

Up-regulation of system A activity in the regenerating rat liver

System A activity for neutral amino acid transport, measured as the MeAIB-sensitive Na(+)-dependent L-alanine uptake, is induced 6 h after partial hepatectomy in plasma membrane vesicles from rat livers. Other Na(+)-dependent transporters, like system ASC (MeAIB-insensitive Na(+)-dependent L-alanine transport) and the nucleoside carrier show similar inductions. Up-regulation of system A is not explained by changes in the dissipation rate of the Na+ transmembrane gradient, as deduced from uptake measurements performed in the presence of monensin. To determine whether induced system A shared any similarity with the activity found in hepatoma cell lines, we analyzed the N-ethylmaleimide (NEM) sensitivity of system A in both regenerating and control rat liver plasma membrane vesicles. NEM treatment was equally effective in inhibiting system A in both experimental groups. Thus, during the prereplicative phase of liver growth, a transport activity similar to basal system A is up-regulated in liver parenchymal cells, by a stable mechanism that does not involve changes in the Na+ transmembrane gradient.