Studies on closure of the ductus arteriosus. XI. Ductal closure in utero by a prostaglandin synthetase inhibitor

Intrauterine contraction of the ductus arteriosus in fetuses followed a single oral dose of 15 mg/kg indomethacin to pregnant rats 12 or 18 h prior to delivery. This ductal contraction studied by the whole-body freezing technique was markedly pronounced up to 30 min after delivery. Blood gas measurements showed a low pH at 30 min which returned to normal at 120 min. Cyanosis was persistant in the indomethacin groups. Intrauterine ductal closure may be a danger to the fetus and subsequent postnatal adjustment. The present results need confirmation in other species to predict a similar risk in the human fetus.     

Chronic exposure to nicotine alters endothelium-dependent arteriolar dilatation: effect of superoxide dismutase.

The first goal of this study was to determine whether chronic injection of nicotine alters endothelium-dependent arteriolar dilatation. We measured the diameter of cheek pouch resistance arterioles (approximately 50 microm in diameter) in response to endothelium-dependent (acetylcholine and ADP) and -independent (nitroglycerin) agonists in control hamsters and hamsters treated with nicotine (2 microg. kg-1. day-1 for 2-3 wk). In control hamsters, acetylcholine (0.1 and 1.0 microM) dilated arterioles by 13 +/- 2 and 31 +/- 3%, respectively, and ADP (1.0 and 10 microM) dilated arterioles by 18 +/- 1 and 30 +/- 1%, respectively. In contrast, acetylcholine (0.1 and 1.0 microM) dilated arterioles by only 5 +/- 2 and 12 +/- 3%, respectively, and ADP (1.0 and 10 microM) dilated arterioles by only 7 +/- 2 and 13 +/- 3%, respectively, in animals treated with nicotine (P < 0.05 vs. response in control hamsters). Nitroglycerin produced similar dose-related dilatation of cheek pouch arterioles in control and nicotine-treated hamsters. Our second goal was to examine a possible mechanism for impaired endothelium-dependent arteriolar dilatation during chronic treatment with nicotine. We found that superfusion of the cheek pouch microcirculation with superoxide dismutase (150 U/ml) restored impaired endothelium-dependent, but did not alter endothelium-independent, arteriolar dilatation in hamsters treated with nicotine. Superfusion with superoxide dismutase did not alter endothelium-dependent or -independent arteriolar dilatation in control hamsters. We suggest that chronic exposure to nicotine produces selective impairment of endothelium-dependent arteriolar dilatation via a mechanism related to the synthesis/release of oxygen-derived free radicals.     

Studies on closure of the ductus arteriosus. X. effect of prostaglandin

The effect of prostaglandins F_2∝, E₁ and of 7-oxa-13-prostynoic acid on the newborn rat and rabbit ductus can be studied using the whole-body freezing technique. PGF_2∝ and PGE₁ were able to re-open the closing ductus arteriosus in adequately oxygenated animals. PGF_2∝ administration was accompanied by a strong physical reaction in the rat but less in the rabbit. PGF₁ had sedative effects in both animals. A prostaglandin antagonist, 7-oxa-13-prostynoic acid had no effect on normal ductal closure nor did it counteract the effects of PGF_2∝ and PGE₁. The role of prostaglandins in homeostasis during the fetal and newborn period may be to modify ductal tone.     

Influence of hydrocarbon-stapling on membrane interactions of synthetic antimicrobial peptides

Cyclization has been recognized as a valuable technique for increasing the efficacy of small molecule and peptide therapeutics. Here we report the application of a hydrocarbon staple to a rationally-designed cationic antimicrobial peptide (CAP) that acquires increased membrane targeting and interaction vs. its linear counterpart. The previously-described CAP, 6K-F17 (KKKKKK-AAFAAWAAFAA-NH₂) was used as the backbone for incorporation of an i to i?+?4 helical hydrocarbon staple through olefin ring closing metathesis. Stapled versions of 6K-F17 showed an increase in non-selective membrane interaction, where the staple itself enhances the degree of membrane interaction and rate of cell death while maintaining high potency against bacterial membranes. However, the higher averaged hydrophobicity imparted by the staple also significantly increases toxicity to mammalian cells. This deleterious effect is countered through stepwise reduction of the stapled 6K-F17’s backbone hydrophobicity through polar amino acid substitutions. Circular dichroism assessment of secondary structure in various bacterial membrane mimetics reveals that a helical structure may improve – but is not an absolute requirement for – antimicrobial activity of 6K-F17. Further, phosphorus-31 static solid state NMR spectra revealed that both non-toxic stapled and linear peptides bind bacterial membranes in a similar manner that does not involve a detergent-like mechanism of lipid removal. The overall results suggest that the technique of hydrocarbon stapling can be readily applied to membrane-interactive CAPs to modulate how they interact and target biological membranes.