Effects of 3',5' cyclic nucleotides on membrane transport in isolated thyroid cells

Stimulation of cartilage macromolecule synthesis by adenosine 3',5'-monophosphate

The role of cyclic AMP in the regulation of cartilage macromolecule synthesis in vitro was studied in pelvic cartilage from 10-12 day chick embryos. Incubation of cartilages in medium containing 0.5 mM cyclic AMP resulted in a 30% inhibition of 35SO4-2, [3H]leucine and [3H]uridine incorporation into proteoglycan, total protein and RNA, respectively. Higher concentrations of cyclic AMP had no greater effects. In contrast, butyrylated cyclic AMP derivatives (0.5-5.0 mM) added to the incubation medium stimulated (50-100%) the incorporation of these radiolabeled precursors into cartilage macromolecules. Theophylline, in concentrations (0.1-0.5 mM) which raise intracellular cyclic AMP, also increases the incorporation of radiolabeled precursors into macromolecules. The data indicate that exogenous cyclic AMP and butyrylated cyclic AMP derivatives have paradoxical effects on cartilage macromolecule synthesis. Butyrylated cyclic AMP derivatives, not exogenous cyclic AMP, mimic the effects of intracellular cyclic AMP. Incubation of embryonic chicken cartilage with exogenous cyclic AMP results in the extracellular degradation of the cyclic AMP to adenosine. Adenosine (0.125 mM) inhibits precursor incorporation into cartilage macromolecules. The metabolism of exogenous cyclic AMP generates sufficient adenosine to account for the observed inhibitory effects of exogenous cyclic AMP on cartilage macromolecule synthesis. Butyrylated cyclic AMP derivatives are not degraded during incubation with cartilage. The data indicate that cartilage is a tissue in which the effect of cyclic AMP is to stimulate anabolic processes.

Stimulatory effects of induced phagocytosis on the function of isolated thyroid cells

Stimulation of endocytosis is a very early effect of thyrotropin on thyroid. However, the relationship of the endocytotic process to the many other thyrotropin effects on thyroid is not clearly defined. Since phagocytosis in isolated thyroid cells is a presumed model for in vivo endocytosis of colloid, we induced phagocytosis in isolated thyroid cells by incubating them at 37 degrees C with 0.109-mu diameter polystyrene microbeads; phagocytosis was confirmed in each experiment by electron microscopy and/or spectrophotometric analysis of dioxane cell extracts. Cells incubated with 50-100-mu diameter polystyrene macrobeads (too large to ingest) served as controls. Microbead-induced phagocytosis in isolated thyroid cells was consistently accompanied by increases in: (a) cyclic 3',5'-adenosine monophosphate-(14)C formation from adenine-8-(14)C (66%); (b) iodide-(131)I trapping (40%); (c) protein and RNA synthesis (30%); (d) phospholipogenesis (50%); (e) alpha-aminoisobutyric acid-1-(14)C uptake (15%). 50- to 100-mu diameter polystyrene macrobeads did not influence cell function in any of these experiments. Aminotriazole, 5 x 10(-3) (M), a peroxidase inhibitor, blocked the stimulatory effect of microbead-induced phagocytosis on phospholipogenesis only. These studies indicate that in isolated thyroid cells the phagocytotic process, per se, may alter activity of the membrane-bound adenyl cyclase enzyme. The resultant increase in cyclic 3',5'-adenosine monophosphate may be a triggering mechanism for (some) subsequent metabolic changes occuring during phagocytosis. Since these changes mimic those induced by thyrotropin, it is suggested that a variety of thyrotropin effects on thyroid may be secondary to stimulation of colloid resorption and hormone secretion.