Accumulation of cyclic AMP in neurohypophyses in response to angiotensin

Angiotensin II (10⁻¹⁰ to 10⁻⁸ M) increases cyclic AMP content in isolated rat neurohypophyses but only when incubated in the presence of theophylline (10⁻² M). The stimulatory effect of 10⁻⁹ M angiotensin II is inhibited by 8-Gly-angiotensin II (10⁻⁷ M) a specific inhibitor of the peripheral effects of the natural octapeptide. The angiotensin antagonist alone did not exhibit any intrinsic effect on cyclic AMP accumulation at the dose used.     

Some implications of helical fibres in worm cuticles

The cuticles of many worms contain a cylindrical trellis made of layers of collagen fibres wound round the body in left- and right-hand helices. This kind of extensible skeletal structure imposes various constraints on a worm's behaviour, and some of these are examined, using the nematomorph Parachordodes woltersforffii as the main example. Upon extension or shortening of the cuticle, neighbouring fibres in one layer will eventually touch and so limit further movement; this in turn affects the extent of shortening, elongation, bending and coiling of the whole worm. Simple equations relate: the angle between a fibre and the worm's long axis; fibre spacing and radius; worm body radius and radius of curvature. The relevance to the life of the worm of fibre arrangement, matrix properties and volume changes is discussed.     

Parallel Induction of Nitric Oxide and Tetrahydrobiopterin Synthesis by Cytokines in Rat Glial Cells

Abstract: Activation of monocyte-derived macrophages with cytokines leads to the induction of nitric oxide synthase. Much less is known about the effects of cytokines on microglia, resident brain macrophages, or on astrocytes. In this study, we compared the induction by lipopolysaccharide, interferon-γ, and tumor necrosis factor-α of nitric oxide production and synthesis of tetrahydrobiopterin, the required cofactor for nitric oxide synthase, in microglia and peritoneal macrophages. Activation of microglia induced parallel increases in nitric oxide and intracellular tetrahydrobiopterin levels, although induction of the latter appears to be somewhat more sensitive to diverse stimulators. As with macrophages, inducible nitric oxide production in microglia was blocked by inhibitors of tetrahydrobiopterin biosynthesis. Interleukin-2, an important component of the neuroimmunomodulatory system, was only a weak activator of microglia by itself but potently synergized with interferon-γ to stimulate production of both nitric oxide and tetrahydrobiopterin. Astrocytes were also activated by lipopolysaccharide and combinations of cytokines but showed a somewhat different pattern of responses than microglia. Biopterin synthesis was increased to higher levels in astrocytes than in microglia, but maximal induction of nitric oxide production required higher concentrations of cytokines than microglia and the response was much lower. These results suggest that tetrahydrobiopterin synthesis in glial cells is a potential target for therapeutic intervention in acute CNS infections whose pathology may be mediated by overproduction of nitric oxide.