α-Adrenoceptor subtypes and Ca2+ mobilization the rabbit ear artery†

The mobilization of cellular and extracellular Ca²⁺ pools by selective α₁-adrenoceptor (phenylephrine) and α₂-adrenoceptor (xylazine) agonists as well as noradrenaline was evaluated in rabbit ear artery. Noradrenaline and phenylephrine possess full instrinsic activity for both types of Ca²⁺ mobilization whereas xylazine up to 1 mM had only a limited contractile effect, being more effective in inducing extracellular Ca²⁺-dependent response. However, extracellular Ca²⁺ was mobilized by xylazine in a concentration 20 times higher than that required to stimulate pre-junctional α₂-adrenoceptors. Noradrenaline (5 μM) and xylazine (1 mM) induced cellular and extracellular Ca²⁺-dependent contractions which were prazosin-sensitive and yohimbine-resistant. Xylazine-induced contractile activity, particularly that dependent upon the extracellular Ca²⁺ pool, was markedly reduced by selective adrenergic denervation with 6-hydroxydopamine, but the actions of noradrenaline were unaffected. These results suggest that: (1) rabbit ear artery contain post-junctional α¹-adrenoceptor but not α₂-adrenoceptors; (2) stimulation of these α₁-adrenoceptors can account for the overall contractile activity of exogenously added noradrenaline and (3) stimulation of α₁-adrenoceptors results in mobilization of cellular as well as extracellular Ca²⁺ pools.     

IDENTIFICATION OF DERMORPHIN AND HYP6-DERMORPHIN IN SKIN EXTRACTS OF THE BRAZILIAN FROG PHYLLOMEDUSA RHODEI

Methanol extracts of the skin of the Brazilian frog Phyllomedusa rhodei contain approximately equal amounts of dermorphin and its analogue Hyp⁶-dermorphin, two opiate-like heptapeptides. A unique feature of their sequence is the presence of a D-amino acid residue at position 2. Hyp⁶-dermorphin possesses a spectrum of central and peripheral bioactivity very similar to that of dermorphin.     

Bioorganic stereochemistry. A study of the peptide oxazolones from Z-(Aib)n-OH (n = 2–4) in the solid state*

An investigation of the preferred conformations and modes of self-association of the peptide oxazolones from Z(-Aib-)_n-OH (n = 2–4) in the solid state has been performed by infrared absorption. More detailed information on the peptide oxazolone from Z(-Aib-)₃ OH (2) has been obtained using X-ray diffraction. In this compound the conformations of the first two Aib residues differ substantially, only the N -terminal one being found in the usual 3_10- (or α-) helical region of the Ramachandran map. The C=N-bond of the oxazolone group is not conjugated with the lactone moiety. A very weak intermolecular interaction occurs between the urethane N-H and the carbonyl group of the oxazolone ring.