Effects of Iskedyl and its two constituents raubasine and dihydroergocristine on the release of [3H]noradrenaline and [3H]serotonin in canine basilar arteries

Release of 3H-5-hydroxytryptamine from isolated rabbit aorta

The main aim of the present investigation was to study systematically the passive and stimulation-evoked release of 3H-5-hydroxytryptamine (3H-5-HT) from rabbit isolated aorta. This was accomplished by preloading rings of aorta with 3H-5-HT (10(-6)M) and then monitoring by fractional collection the basal 3H-outflow and stimulation-evoked 3H-overflow. The basal 3H-outflow from aorta preloaded with 10(-6)M of either 3H-5-HT or (-)-3H-noradrenaline (3H-NA) leveled off about 100 min. after the onset of wash-out and remained almost constant thereafter (100-240 min.). The basal 3H-outflow from tissue preloaded with 3H-5-HT was almost 3-fold higher (70-240 min.) than that seen after preloading with 3H-NA. Cocaine (3 x 10(-5)M) did not alter the basal 3H-outflow (15-240 min.) from tissue preloaded with 3H-5-HT, while pargyline (5 x 10(-4)M) decreased it by about 66% (100-240 min.). Electrical-field stimulation (S1-S7, 200 mA, 600 pulses, 0.5 msec., 3 Hz) were applied to the tissue. The initial stimulation-evoked 3H-overflow from aorta preloaded with 3H-5-HT was higher than the subsequent ones (S1-S7; 100, 35, 35, 35, 35, 37, and 40%). Similar results to these were obtained with tissues preloaded with 3H-NA. The stimulation (S1-S7; 200 mA). 600 pulses, 0.5 msec, 3 Hz)-evoked 3H-overflow increased in an apparent linear manner with the amount of current used (50-200 mA).(ABSTRACT TRUNCATED AT 250 WORDS)

Innervation of cerebral arteries by nerves containing 5-hydroxytryptamine and noradrenaline

Noradrenaline (NA)-containing nerves, mainly originating in the sympathetic superior cervical ganglia, supply large and small cerebral arteries. In large cerebral arteries, nerves containing serotonin (5-hydroxytryptamine, 5-HT) may represent neuronal uptake of circulating 5-HT by sympathetic nerves. 5-HT-containing nerves supplying small pial vessels probably have a central origin in the dorsal raphe nucleus. In most species, NA is a weak vasoconstrictor (alpha 1- or alpha 2-adrenoceptors), while 5-HT is a potent vasoconstrictor (5-HT2 or 5-HT1-like receptors) of large cerebral arteries. In contrast, both NA and 5-HT tend to cause vasodilatation in small pial vessels and arterioles. Adrenergic and serotonergic transmission can be modulated by pH, a range of putative neurotransmitters and neuromodulators, and by the endothelium. Sumatriptan, a 5-HT1-like receptor agonist, has been shown to be effective in the treatment of migraine. Changes in NA- or 5-HT-containing nerves and/or in the responses of cerebral vessels to NA and 5-HT have been observed in a variety of vascular disorders, including cerebral vasospasm following subarachnoid haemorrhage, hypertension, and atherosclerosis.

Changes in the adrenergic mechanisms of cerebral arteries after subarachnoid hemorrhage in goats

We have examined the effects of experimental subarachnoid hemorrhage (SAH), induced by delivering autologous blood into the subarachnoid space, on the adrenergic mechanisms of the goat cerebrovascular bed. To achieve this, the response to noradrenaline was recorded both in vivo, by measuring cerebral blood flow in unanesthetized animals, and in vitro, by recording isometric tension in isolated cerebral arteries. In addition, we checked the function of adrenergic innervation by measuring the tritium efflux evoked by electrical stimulation in cerebral arteries preloaded with [3H]-noradrenaline, and we examined this innervation by using both fluorescent and electron transmission microscopy. All studies were performed before and 3, 7, and 14 days after SAH. Injections of noradrenaline (0.1-10 micrograms) directly into the cerebro-arterial supply produced reductions in cerebral blood flow, with no concomitant changes in mean arterial blood pressure and heart rate, which were significantly enhanced (P < 0.01) 3 and 7 days after SAH and returned to control values 14 days after hemorrhage induction. In isolated cerebral arteries, noradrenaline (10(-8)-10(-4) mol/L) produced concentration-dependent contractions, which were also significantly enhanced (P < 0.05) 3 and 7 days after SAH and returned to control values in cerebral arteries obtained 14 days after SAH. On the other hand, increases in the release of tritium induced by electrical stimulation in cerebral arteries preloaded with [3H]-noradrenaline were significantly lower (P < 0.01) after SAH. Moreover, microscopical studies showed a reduction in catecholamine fluorescence and signs of sympathetic degeneration in some perivascular axons after SAH.(ABSTRACT TRUNCATED AT 250 WORDS)

Diet-induced atherosclerosis inhibits release of noradrenaline from sympathetic nerves in rabbit arteries

Contractile responses to sympathetic nerve stimulation and exogenous noradrenaline were compared in aortas and pulmonary arteries of control rabbits and rabbits fed a cholesterol-rich diet (0.3%) for 16 or 30 weeks. The diet-induced atherosclerosis reduced the contractions to increasing concentrations of exogenous noradrenaline (0.1 nM to 10 microM) in both arteries, and the reduction was more pronounced after 30 weeks of the hypercholesterolemia. The contractions produced with increasing frequencies of electrical stimulation (1-32 Hz) were nearly abolished in the atherosclerotic arteries. Labeling of the aorta and the pulmonary arteries with [3H]noradrenaline resulted in accumulation of radioactivity in both control and atherosclerotic blood vessels. After mounting the labeled blood vessels for superfusion, a basal efflux of [3H]noradrenaline and of 3H-metabolites was detected. In the atherosclerotic arteries, a decreased efflux of the intraneuronal deaminated metabolites 3,4-dihydroxyphenyl glycol (DOPEG) and 3,4-dihydroxymandelic acid (DOMA) was detected. Electrical stimulation at 1 Hz (pulmonary artery) or 2 Hz (aorta) caused an augmented efflux of total 3H from the control arteries; this was mostly due to release of intact [3H]noradrenaline. The electrical impulses evoked significantly less (16 weeks) or no (30 weeks) release of [3H]noradrenaline in the atherosclerotic arteries. These data illustrate that diet-induced atherosclerosis exerts an inhibitory action on the sympathetic nerve terminals in the aorta and the pulmonary artery of the rabbit. This effect, together with an inhibitory effect at the postjunctional level results in a loss of the responsiveness to nerve stimulation. The atherosclerotic process also inhibits the intraneuronal deamination of the sympathetic transmitter.

Direct and neuromodulatory effects of histamine on isolated goat cerebral arteries

1. The effects of histamine on isolated goat middle cerebral artery were examined using two experimental approaches: recording of isometric tension and measurement of [3H]-noradrenaline efflux. 2. Cumulative addition of histamine (10(-7)-3 x 10(-2)M) and 2-pyridylethylamine (2-PEA, 10(-6)-3 x 10(-2)M) produced concentration-dependent contractile responses. Preincubation with diphenhydramine (10(-7), 10(-6)M) or cimetidine (10(-7), 10(-6)M) competitively inhibited the histamine-induced contractile response. 3. Endothelium denudation enhanced the contractile effects of histamine. 4. Transmural electrical stimulation elicited contractions which were enhanced by histamine (10(-7)M), 2-PEA (10(-6)M) and dimaprit (10(-4)M). Diphenhydramine (10(-5)M) inhibited the action of histamine, but cimetidine did not. 5. Noradrenaline (10(-8)-10(-4)M) elicited concentration-dependent contractions which were unaffected by histamine (10(-7)M). 6. In arteries preloaded with [3H]-noradrenaline, transmural electrical stimulation induced an increase in the tritium efflux, which was enhanced in the presence of histamine (10(-7)M). 7. Therefore, histamine contracts cerebral arteries via specific non-endothelial H1-receptors, and enhances perivascular adrenergic neurotransmission through specific presynaptic H1-receptors by a mechanism involving increases in noradrenaline release.

Modulatory action of acetylcholine on cerebrovascular sympathetic neurotransmission

1. Acetylcholine (10 micrograms/min) diminished the electrically-induced cerebral blood flow reductions. Atropine (1-2 mg) partially blocked this inhibitory effect. 2. Exogenously administered noradrenaline (1-10 micrograms) and tyramine (50-500 micrograms) reduced cerebral blood flow but this effect was unchanged by acetylcholine infusion. 3. Acetylcholine inhibited the nonadrenergic component of the electrically-induced contraction at a concentration greater than or equal to 10(-6) M and potentiated the adrenergic component at a concentration greater than or equal to 10(5) M. Atropine 10(-7) M) inhibited both of these effects. In addition, acetylcholine (10(-4) M) enhanced the electrically-evoked [3H]noradrenaline overflow. 4. These results show that: (a) acetylcholine modulates cerebrovascular sympathetic neurotransmission by acting on muscarinic receptors; and (b) the potentiating effect of acetylcholine is achieved by a mechanism involving increases in noradrenaline release.

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.

Modification of glycosylation of renin in sodium-depleted and captopril-treated rats

Concanavalin A (con A) chromatography of rat plasma revealed the presence of three differently glycosylated forms of renin, including the con A unbound form (renin C), the loosely bound form (renin A), and the tightly bound form (renin B). Rat renal cortical slices in vitro secreted all these forms. They had a different half-life in the plasma after ligation of both renal artery and vein (half-life of 21 +/- 1, 14 +/- 3, and 35 +/- 4 min for renin A, B, and C, respectively). Thus differently glycosylated forms of renin are released from the kidney into the blood circulation and disappear, with a different half-life. Rats were sodium-depleted and captopril-treated (40-60 mg.kg-1.day-1) for 2 wk, and the effects of these treatments on relative proportions of renin A, B, and C were investigated. These treatments elevated plasma renin concentration approximately 60-fold (from 24 +/- 3 to 1,406 +/- 128 ng angiotensin I.h-1.ml-1; P less than 0.01), in association with an increase in the relative percent of renin C in the plasma from 22 +/- 2 to 39 +/- 3% (P less than 0.01). Moreover, the relative proportion of renin C released from the renal cortical slices was significantly higher in the treated than in the control rats (42 +/- 9 vs. 16 +/- 3% of secreted renin, respectively; P less than 0.02). These results show that the predominant release of renin C, with the longest half-life (35 min) in the plasma, contributes to the increased plasma renin concentration in sodium-depleted and captopril-treated rats.