Iodide induced suppression of thyrotropin-stimulated adenosine 3',5'-monophosphate production in cat thyroid slices.

Cat thyroid slices were studied to investigate their responsiveness to thyrotropin stimulation of cyclic AMP accumulation. Ovine and bovine thyrotropin, in the presence of 2.5 mM aminophylline, induced a dose-dependent increase in the cyclic AMP content of cat thyroid tissue. Half-maximal stimulation of cyclic AMP accumulation was obtained at a thyrotropin concentration of 1-2 mU/ml. The maximal effect of thyrotropin was observed at 10 mU/ml, and was associated with a mean 77 +/- 19-fold increase in thyroidal cyclic AMP. Preincubation of cat thyroid tissue for 2 h with 50 micron NaI resulted in an impairment in the subsequent ability of thyrotropin to enhance cyclic AMP accumulation, without altering the level of cyclic AMP in tissues not exposed to the hormone. Preincubation alone was without effect on thyrotropin stimulation of cyclic AMP, and the inhibitory effect of iodide was prevented by addition of 3 mM methimazole to the preincubation medium. In addition, the time course of thytrotropin stimulation of cyclic AMP accumulation in cat thyroid slices was not significantly altered by the preincubation with excess iodide. These studies provide additional evidence that excess iodide inhibits the adenylate cyclase-cyclic AMP system in thyroid tissue.     

Vessel origin in Cabomba

Tracheary elements of the nodal plexus in stems of Cabomba aquatica and C. caroliniana have pores in the primary wall as seen with scanning electron microscopy (SEM); these pores are adjacent to the helical thickening bands. Presence of the pores qualifies these tracheary elements as vessel elements, in agreement with our previous criteria in Nymphaeaceae, but the vessel elements differ from any hitherto described for vascular plants and thereby enhance the likelihood of polyphylesis of vessels in dicotyledons.     

Characterization of hemoglobin from the lizard Uromastix hardwickii

Hemoglobin from the tropic lizard Uromastix hardwickii was isolated. Chain separations were studied, and the whole carboxymethylated globin was cleaved with trypsin. Peptides were pre-fractionated by exclusion chromatography and finally purified by reversed phase high-performance liquid chromatography. Amino acid sequence analysis permitted ordering of peptides in alpha- and beta-chains by homology with known structures in other hemoglobins. Results show large structural variations (about 50% homology between Uromastix and viper alpha-chains) and suggest chain heterogeneity with the presence of at least two types of both the alpha- and beta-chains in the preparations.     

Therapeutic Abortion—Attitudes and Practices of California Physicians

A questionnaire about attitudes and practices regarding therapeutic abortion was sent to 943 diplomates of the American Board of Obstetrics and Gynecology listed in California. In the 748 replies received, certain disparities between the views and practices of the specialists on the one hand and current California statutes on the other were noted. The responses to the questions strongly suggested that current California laws governing the performance of therapeutic abortion are in need of modernization and liberalization if they are to accord with the views and practices of California obstetrician-gynecologists.     

Errata

The pH-dependent control of the rate of protein synthesis in the fertilized sea urchin egg has suggested that pH may have an important role in cell activation at fertilization. We looked for similar changes of intracellular pH during meiotic maturation of the Xenopus oocyte. The basal pH of the oocyte is in the range 7.4–7.8. The higher values were found mostly in oocytes from animals with recent hormonal stimulation, suggesting a correlation with the elevated metabolism of such oocytes. Regardless of basal pH, progesterone-induced maturing oocytes alkalize an average of 0.18 pH unit. Beginning shortly before germinal vesicle breakdown, intracellular pH then decreases to near the original value. The same program is observed when maturation is induced by an injection of “maturation promoting factor.” Maturation is delayed or inhibited if intracellular pH is driven acidic. It is induced in the absence of progesterone by trimethylamine, a weak base which may act via an imposed alkalization. However, maturation still occurs when net alkalization is prevented. These data suggest that the alkalization during maturation is a form of metabolic “insurance” and that there may be both pH-dependent and pH-independent pathways for maturation. There is some evidence suggesting that pH changes are related to movement of other ions.