Effects of calcium entry blockers on KCl- and 5-hydroxytryptamine-induced contractions of human umbilical arteries

The effects of Ca2+ removal and of the calcium entry blockers, nicardipine and nifedipine, on contractions of isolated human umbilical arteries, elicited with KCl and 5-hydroxytryptamine, were investigated. Withdrawal of Ca2+ caused inhibition of both KCl and 5-hydroxytryptamine responses, but the maximum effect of KCl in Ca2(+)-free medium was recuperated by increasing the KCl concentration. The maximum effect of 5-hydroxytryptamine, however, was recuperated only when Ca2+ was restored to the medium. Consistently with an inhibition in Ca2(+)-free medium, calcium entry blockers produced a concentration-dependent relaxation of human umbilical artery strips precontracted with KCl and 5-hydroxytryptamine, and inhibited the concentration-dependent contraction elicited by these stimuli. Our results indicate that contractile responses of the human umbilical arteries are dependent on extracellular Ca2+ for both KCl and 5-hydroxytryptamine. Although Ca2+ entry was sensitive to both nicardipine and nifedipine, the differences between the effects of these dihydropyridines with the two experimental approaches we used were not always conclusive.

Inhibitory effect of GABA on cerebrovascular sympathetic neurotransmission

The possibility that gamma-aminobutyric acid (GABA) could modulate sympathetic neurotransmission in the cerebrovascular bed of the goat has been investigated by means of 3 experimental approaches: measurement of cerebral blood flow in the anesthetized animal, recording of isometric tension in isolated cerebral arteries, and measurement of tritium efflux from cerebral arteries preloaded with [3H]noradrenaline. Electrical stimulation of cervical sympathetic nerve produced reductions in cerebral blood flow which were significantly diminished during continuous infusion of GABA (20-40 micrograms/min) into the internal maxillary artery. Picrotoxin (3 mg) did not change the inhibitory effect of GABA. Exogenously administered noradrenaline (1-9 micrograms) and tyramine (50-500 micrograms) reduced cerebral blood flow as well, but this effect was unchanged by GABA infusion. Transmural electrical stimulation elicited frequency-dependent contractile responses in isolated cerebral arteries which were significantly blocked when GABA was present, at a dose (10(-4) M) which did not modify the contractile response to exogenous noradrenaline (10(-8)-10(-4) M). Moreover, GABA (10(-5)-10(-4) M) inhibited transmural electrical stimulation-evoked tritium efflux from arteries preloaded with [3H]noradrenaline. These results show that GABA inhibits adrenergic neurotransmission in cerebral arteries by a mechanism involving inhibition of transmitter release. Probably, specific presynaptic GABA-B receptors mediate this inhibitory effect.

Bacterial chemistry-III: preliminary studies on trypanosomal activities of Chromobacterium violaceum products

It has been found that the pigment-I from Chromobacterium violaceum, 3-[1,2-dihydro5-(5-hydroxy-1H-indol-3-yl)-2-oxo-3H-pyrrol-3-yli diene] 1,3-dihydro-2H-indol-2-one, has trypanocide activity. The formylated derivatives, pigment-III, immobilized 100% of the Trypanosoma cruzi at a level of 46 microM after 48 h of interaction with a total growth inhibition in the same period. Pigment-I exhibited low toxicity and a DNA synthesis inhibition similar to that of Nifurtimox, a known trypanocide compound.

P1-purinoceptors in the cerebrovascular bed of the goat in vivo

The possible existence and function of specific P1-purinoceptors in the cerebrovascular bed of the unanesthetized goat have been investigated. Blood flow to one cerebral hemisphere (cerebral blood flow) was measured by means of an electromagnetic flow probe previously implanted around the ipsilateral internal maxillary artery. The injection of adenosine, AMP, ADP and ATP (3-30 micrograms) directly into the internal maxillary artery increased cerebral blood flow and decreased cerebrovascular resistance in a dose-dependent manner. Continuous infusion of 8-phenyltheophylline (8-PT), 100 micrograms/min, into the internal maxillary artery did not alter the resting cerebral blood flow or the cerebrovascular resistance, but significantly inhibited the cerebral vasodilation induced by adenosine, AMP, ADP and, to a lesser degree, ATP. The acetylcholine- and histamine-induced cerebral vasodilation was unaffected by 8-PT. These results indicate that adenosine, AMP, ADP and, at least in part, ATP increase cerebral blood flow by acting on specific P1-purinoceptors located in the cerebrovascular wall. These P1-purinoceptors do not appear to be tonically activated under physiological conditions.

New peroxides and their antimicrobial activity

Antimicrobial activity of hydroperoxides and cyclic peroxides has been studied. 2,4-Dihydroperoxy-2,4-dimethylpentane (1) and 2,5-dihydroperoxy-2,5-dimethylhexane (2) were active against microorganism, but 1 showed a large specially against C. albicans, M. luteus and B. subtilis with a MIC value of 31.5 mcg/ml.