Sympathetic neurotransmission in the rabbit isolated central ear artery is affected as early as one week following a single dose of X-irradiation

Reduced sympathetic noradrenergic neurotransmission in the tail artery of Donryu rats fed with high cholesterol-supplemented diet

1. Sympathetic neurotransmission and noradrenaline content of the tail artery of Donryu rats fed for 2 months with a cholesterol-supplemented diet enriched with 4% cholesterol, 1% cholic acid, 0.5% thiouracil (CCT), were examined. 2. Total serum cholesterol level of CCT fed rats (7.05 +/- 1.77 mg ml(-1), n = 8) was significantly greater than lab-chow fed controls (2.58 +/- 0.32 mg ml(-1), n = 8). Low density lipoprotein level was also significantly increased in CCT-fed (1.79 +/- 0.26 mg ml(-1), n = 8) compared with control fed rats (1.35 +/- 0.25 mg ml(-1), n = 8) but plasma levels of triglyceride and high density lipoproteins did not differ significantly between the two groups. 3. Contractile responses of the arterial rings to transmural nerve stimulation (65 V, 0.1 ms, 4-64 Hz, 1 s), were markedly attenuated in the CCT fed animals compared with the controls. This reduction involved the noradrenergic rather than purinergic component of sympathetic transmission. 4. Vasoconstrictor responses to exogenous noradrenaline (0.01-300 microM) and adenosine 5'-triphosphate (0.3-1000 microM) were unaffected by CCT diet, indicating prejunctional alteration of sympathetic neurotransmission during CCT-induced hyperlipidaemia. 5. The noradrenaline content of the tail arteries of CCT fed animals (2.64 +/- 0.36 ng mg(-1), n = 6) was significantly lower than that of controls (3.82 +/- 0.32 ng mg(-1), n = 6). 6. These findings show that chronic treatment of Donryu rats with a cholesterol-supplemented diet led to altered levels of circulating lipid fractions accompanied by attenuated sympathetic noradrenergic neurotransmission and reduced noradrenaline content of the rat tail artery.

Effect of gamma knife irradiation on relaxation and contraction responses of the common carotid artery in the rat

This report concerns a pilot study of the short- and long-term effects of gamma knife radiosurgery on vascular responses. The investigation was carried out on male Sprague-Dawley rats, and the relaxation and contraction responses of the right common carotid artery (CCA) were assessed following irradiation (100 Gy). The non-treated CCA of the same animals served as internal controls. Non-irradiated rats were used to control the effect of normal aging on vascular function. Isometric tension was determined on in vitro preparations of arterial rings. Acetylcholine-mediated, endothelium-dependent relaxation was impaired one month after radiosurgery, as was endothelium-independent relaxation induced by sodium nitroprusside, but the effect on the latter was minimal. The irradiated CCA was also impaired with respect to contraction responses induced by norepinephrine, endothelin-1 or phorbol dibutyrate. This impairment appeared to be biphasic, as it was evident one day after radiosurgery, followed by a partial recovery one week later, and again manifest after one month. At the light microscope level, the carotid arteries appeared to be well preserved throughout the experiment. However, obvious ultrastructural changes were noted in endothelial and smooth muscle cells of specimens obtained three months after radiosurgery. The present data indicate that high dose gamma knife radiosurgery affects the functions of both, the vascular endothelium and the vascular smooth muscles in an apparent time-dependent fashion. Because of its increasing application to patients, there is the need for studying the effects of gamma knife radiosurgery on cerebral arteries, since functional vascular changes may occur in the absence of obvious histological alterations. Our results on CCAs point to the feasibility of such experimental investigations.

Patterns of peptide-containing perivascular nerves in the circle of Willis: their absence in intracranial arteriovenous malformations

Using standard immunohistochemical techniques and an improved procedure for whole-mount vascular preparations, the authors describe the pattern and density of innervation of calcitonin gene-related peptide (CGRP)-like, neuropeptide Y (NPY)-like and vasoactive intestinal polypeptide (VIP)-like immunoreactivity in major arteries of postmortem adult human circles of Willis. Calcitonin gene-related peptide-, NPY-, and VIP-LI exhibited a variety of varicose and nonvaricose single axons, and small and large perivascular nerve bundles. Although the density of innervation within each vascular segment was highly variable, the pattern of innervation for each neuropeptide observed was consistent throughout the circle of Willis. With the use of human and rat circles of Willis as positive control preparations, the lack of CGRP-LI, NPY-LI, and VIP-LI in vessel segments taken from five cases of intracranial arteriovenous malformations (AVMs) is also reported. It is concluded that adult human circles of Willis exhibit CGRP-LI, NPY-LI, and VIP-LI perivascular nerves. In addition, intracranial AVMs do not possess these peptide-containing nerves that, in animals, normally mediate neurogenic control in the cerebrovasculature. It is hypothesized that this lack of innervation, and hence neurotrophic influence, may contribute to the development of AVMs.

Selective antagonism by PPADS at P2X-purinoceptors in rabbit isolated blood vessels

1. Pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS), a P2-purinoceptor antagonist, was investigated for its ability to antagonize: (1) P2X-purinoceptor-mediated contractions of the rabbit central ear artery and saphenous artery evoked by either alpha,beta-methylene ATP (alpha,beta-MeATP) or electrical field stimulation (EFS); (2) P2Y-purinoceptor-mediated relaxations of the rabbit mesenteric artery; (3) endothelium-dependent and endothelium-independent, P2Y-purinoceptor-mediated relaxations of the rabbit aorta. 2. alpha,beta-MeATP (0.1-100 microM) caused concentration-dependent contractions of the rabbit ear and saphenous arteries. The negative log[alpha,beta-MeATP] that produced a contraction equivalent to the EC25 for noradrenaline (ear artery) or histamine (saphenous artery) in the absence of PPADS was 6.60 +/- 0.18 (9) and 6.18 +/- 0.17 (9) in the ear artery and saphenous artery, respectively. These effects of exogenous alpha,beta-MeATP were concentration-dependently inhibited by PPADS (1-30 microM). In the ear artery, the negative log[alpha,beta-MeATP] producing a contractile response equivalent to the EC25 of noradrenaline, in the presence of PPADS at 1, 3 and 10 microM was 6.16 +/- 0.18 (8), 5.90 +/- 0.18 (8) and 4.72 +/- 0.36 (8), respectively (P < 0.01). In the saphenous artery, the negative log[alpha,beta-MeATP] values equivalent to the EC25 for histamine in the presence of PPADS at concentrations of 1, 3, 10 and 30 microM were 5.90 +/- 0.19 (8), 5.73 +/- 0.16 (8), 4.99 +/- 0.14 (8) and 4.51 +/- 0.13 (8), respectively (P < 0.01). 3. PPADS at a concentration of 1 microM had no effect on contractions of the ear artery evoked by EFS (4-64 Hz; 1 microM phentolamine present). At higher concentrations (3-30 MicroM) it caused concentration dependent inhibition of neurogenic contractions. In the saphenous artery, PPADS (1-30 MicroM) concentration-dependently inhibited contractions evoked by EFS at frequencies of 4, 8 and 16 Hz. Contractions evoked by EFS at frequencies of 32 and 64 Hz were significantly inhibited by PPADS only at concentrations of 10 and 30 MicroM.4. PPADS (30 MicroM) had no effect on relaxations to 2-methylthio ATP (3 nM-3 MicroM) in rabbit mesenteric artery and to ATP (1 MicroM-I mM) in rabbit aorta (with endothelium intact or removed). In addition,PPADS (30 MicroM) had no significant influence on the contractile potency of noradrenaline and histamine in rabbit ear and saphenous artery, respectively.5. In conclusion, these results support the evidence that PPADS is a selective antagonist of P2X-purinoceptor-mediated responses.

On radiation damage to normal tissues and its treatment. II. Anti-inflammatory drugs

In addition to transiently inhibiting cell cycle progression and sterilizing those cells capable of proliferation, irradiation disturbs the homeostasis effected by endogenous mediators of intercellular communication (humoral component of tissue response to radiation). Changes in the mediator levels may modulate radiation effects either by assisting a return to normality (e.g., through a rise in H-type cell lineage-specific growth factors) or by aggravating the damage. The latter mode is illustrated with reports on changes in eicosanoid levels after irradiation and on results of empirical treatment of radiation injuries with anti-inflammatory drugs. Prodromal, acute and chronic effects of radiation are accompanied by excessive production of eicosanoids (prostaglandins, prostacyclin, thromboxanes and leukotrienes). These endogenous mediators of inflammatory reactions may be responsible for the vasodilatation, vasoconstriction, increased microvascular permeability, thrombosis and chemotaxis observed after radiation exposure. Glucocorticoids inhibit eicosanoid synthesis primarily by interfering with phospholipase A2 whilst non-steroidal anti-inflammatory drugs prevent prostaglandin/thromboxane synthesis by inhibiting cyclooxygenase. When administered after irradiation on empirical grounds, drugs belonging to both groups tend to attenuate a range of prodromal, acute and chronic effects of radiation in man and animals. Taken together, these two sets of observations are highly suggestive of a contribution of humoral factors to the adverse responses of normal tissues and organs to radiation. A full account of radiation damage should therefore consist of complementary descriptions of cellular and humoral events. Further studies on anti-inflammatory drug treatment of radiation damage to normal organs are justified and desirable.

Changes in purinergic responses of the rabbit isolated central ear artery after chronic electrical stimulation in vivo

1. The effect of chronic (4-16 days) electrical stimulation (5 Hz, 0.3 ms, 4-10 V) of the great auricular nerve in vivo on sympathetic cotransmission in the rabbit isolated central ear artery was examined. 2. Chronic stimulation had no significant effect on frequency-dependent (4-60 Hz) neurogenic contractions or contractile responses induced by exogenous noradrenaline (0.1-300 microM). 3. In contrast, contractions induced by exogenous alpha, beta-methylene ATP (10.0 microM) were significantly decreased in preparations from 16-day stimulated animals in comparison with sham-operated, 4-day and 8-day chronically stimulated animal groups. 4. It is concluded that chronic electrical stimulation of nerves supplying the ear artery may lead to the selective alteration of postjunctional P2x-purinoceptor mechanisms, while the effects mediated by post-junctional alpha 1-adrenoceptors remain unchanged.

X-irradiation attenuates relaxant responses in the rabbit ear artery

1. The relaxant actions of acetylcholine, substance P and calcitonin gene-related peptide, and the levels of neuropeptide Y and calcitonin gene-related peptide were assessed in the rabbit central ear artery 1, 4 and 6 weeks after a single dose of 45 Gy X-irradiation, a dose similar to that used clinically in intraoperative radiotherapy. 2. Relaxant responses induced by acetylcholine and substance P (both endothelium-dependent) and calcitonin gene-related peptide (endothelium-independent) were reduced, and endogenous neuropeptide Y and calcitonin gene-related peptide levels were unaffected after X-irradiation. 3. The mechanism(s) by which a single dose of 45 Gy X-irradiation may selectively damage relaxant, but not direct, contractile responses of the smooth muscle (as we have shown previously) of the rabbit central ear artery are discussed.

BAY u3405, a potent and selective thromboxane A2 receptor antagonist on airway smooth muscle in vitro

1. BAY u3405 (3(R)-[[(4-fluorophenyl) sulphonyl]amino]-1,2,3,4- tetrahydro-9H-carbazole-9-propanoic acid) has been evaluated on airway smooth muscle, from a number of species including man, for its thromboxane A2 (TXA2) antagonist activity. 2. BAY u3405 was a potent, and competitive, antagonist of the TXA2-mimetic U46619-induced contractions of human, guinea-pig, rat and ferret airway smooth muscle with pA2 values between 8.0 and 8.9 and with no inherent contractile activity (10(-9)-10(-4) M). 3. The TXA2 antagonist activity of BAY u3405 was stereoselective. Its (S)-enantiomer, BAY u3406, was approximately 50 fold less effective against U46619 on guinea-pig and human airway smooth muscle. 4. BAY u3405 also competitively antagonized contractions of guinea-pig airway smooth muscle induced by prostaglandin D2 (PGD2) or its metabolite 9 alpha, 11 beta-PGF2. On human and ferret airway smooth muscle it abolished contractions induced by PGD2, PGF2 alpha and 16,16-dimethyl-PGE2. 5. A high concentration (10(-6) M) of BAY u3405 had no effect on the contraction, or relaxation, of airway smooth muscle induced by a range of other agonists, nor did BAY u3405 have any effect on other prostanoid receptor types (DP, EP2, FP or IP). 6. BAY u3405, in contrast to some other TXA2 antagonists, is a potent and selective antagonist on a wide range of airways including human. This high affinity, and the oral activity of the compound described elsewhere, suggest it may be an appropriate tool to investigate the role of prostanoids in airway diseases such as asthma.

Changes in sympathetic and endothelium-mediated responses in the rabbit central ear artery after acrylamide treatment

The effect of acrylamide intoxication on the innervation and local control of the rabbit central ear artery was investigated. There was no difference in the noradrenaline, neuropeptide Y and calcitonin gene-related peptide tissue content between control and experimental animals. There was, however, a slight reduction in catecholamine histofluorescence. Although the contractile efficiency of the rabbit central ear artery as measured by responses to potassium chloride was unchanged, nerve-mediated contractile responses were significantly attenuated in acrylamide-treated animals. Contractile responses induced by exogenous alpha,beta-methylene ATP were markedly increased after acrylamide treatment, in contrast to contractions induced by exogenous noradrenaline which were attenuated at maximal concentrations. Modulatory effects of nerve-mediated contractile responses by neuropeptide Y were unaffected by acrylamide intoxication. It therefore appears that acrylamide intoxication damages sympathetic cotransmission, perhaps with preferential action on the purinergic component. Endothelium-dependent relaxant responses to acetylcholine and substance P were attenuated in acrylamide-treated animals, whereas relaxant responses mediated by calcitonin gene-related peptide (endothelium independent) were unaffected. The question of whether the damage to the endothelial cell action is a primary effect, or a secondary consequence of sympathetic nerve damage, is discussed.