In vitro hypoxia differentially affects constriction and relaxation responses of isolated pulmonary arteries from broiler and leghorn chickens.

Under normoxic conditions in vitro, isolated pulmonary arteries from broilers exhibit reduced endothelium-dependent relaxation responses when compared with Leghorns. In vivo, hypoxia increases the susceptibility of broiler chickens to pulmonary hypertension syndrome (PHS), whereas Leghorns are considered resistant to PHS. Because L-arginine supplementation decreases the incidence of PHS in vivo and improves the relaxation responses of broiler isolated pulmonary arteries in vitro, we hypothesized that in vitro hypoxia would further reduce the relaxation responses of broilers to endothelium-derived nitric oxide (EDNO)-dependent vasodilators and that L-arginine supplementation would alleviate this impairment. As a test of this hypothesis, pulmonary arteries from broiler and Leghorn chickens were isolated and exposed to normoxia or hypoxia in the presence or absence of L-arginine while their constriction and relaxation responses to vasoactive compounds were recorded. In broilers, hypoxia did not affect the constriction responses of isolated pulmonary arteries but decreased EDNO-dependent acetylcholine-induced relaxation responses. In contrast, in Leghorns hypoxia increased endothelin-1-induced vasoconstriction responses and reduced the EDNO-dependent relaxation responses only to the lowest concentration of acetylcholine used. L-Arginine supplementation augmented the relaxation responses to acetylcholine in broilers and Leghorns under normoxia but failed to augment them under hypoxia. Relaxation responses to the NO donor, sodium nitroprusside, were not affected by hypoxia in Leghorns but were increased by hypoxia in broilers. These results suggest that the increased incidence of PHS in broiler chickens reared under hypoxia may be associated with a hypoxia-induced reduction in the synthesis or activity of EDNO in the pulmonary circulation.

Pulmonary artery vasoactivity in broiler and Leghorn chickens: an age profile.

Vascular function plays a preponderant role in the pulmonary changes that occur with maturation, during birth, and in the development of pulmonary hypertension. This study was designed to characterize the changes in vasoactivity occurring in broiler and Leghorn chickens from late embryonic life to 5 wk of age. Pulmonary arteries were isolated from 19- and 20-d-old embryos, hatchlings, and 1-, 2-, 3-, 4- and 5-wk-old chickens of both lines and subjected to KCl (45.4 mM)- and endothelin-1 (10(-7.5) M)-induced vasoconstrictions followed by acetylcholine (ACh; 10(-5), 10(-6) and 10(-7) M)- and papaverine (10(-4) M)-induced vasodilations. Vasoconstrictions were greatest at hatch and rapidly declined thereafter, whereas vasodilations were greatest in 20-d-old embryos except with 10(-7) M ACh. Broilers grew faster than Leghorns and had lower vasodilation responses to all concentrations of ACh at 2 and 5 wk of age. Broilers also had greater right-to-total ventricular weight ratios at 5 wk of age, whereas ratios were greater in Leghorn embryos at 20 d of incubation and at hatch. Thus, for a brief period before hatch there is a significant increase in pulmonary endothelium-dependent vasodilation capacity in the chicken embryo, which may aid in the transition from chorioallantoic to pulmonary respiration. The absence of differences in vasodilator capacity between broilers and Leghorns before hatch suggests that the differences in pulmonary artery relaxation capacity and pulmonary hypertension observed after hatch in broilers are not necessarily acquired during incubation but may be related to rapid growth of the broiler chicken.

Pulmonary artery endothelium-dependent vasodilation is impaired in a chicken model of pulmonary hypertension.

Among chicken strains, broilers are prone to pulmonary hypertension, whereas Leghorns are not. Relaxations to endothelium-dependent (ACh, A23187) and endothelium-independent [sodium nitroprusside (SNP), papaverine (PPV)] vasodilators were compared in preconstricted pulmonary artery (PA) rings from these chicken strains. ACh (10(-7), 10(-6), and 10(-5) M)- and A23187 (10(-6) and 10(-5.5) M)-induced relaxations were smaller (P < 0.05) in broilers than Leghorns. N(G)-nitro-L-arginine methyl ester (10(-3.5) M) caused similar reductions in ACh-induced relaxations in both strains. L-Arginine (10(-4) M) enhanced ACh-induced relaxations more in broilers than Leghorns. Relaxations to 10(-10)-10(-6) M SNP did not differ between strains, but were greater (P < 0.05) in broilers than Leghorns at higher concentrations (10(-5) and 10(-4) M). PPV (10(-4) M)- and SNP (10(-4) M)-induced maximal relaxations were greater in broilers than in Leghorns (176.2 +/- 14.7 vs. 120.9 +/- 14.7% and 201.3 +/- 7.8 vs. 171.2 +/- 10.7%, respectively, P < 0.05). Broiler PA rings appear to have increased intrinsic tone and reduced endothelium-derived nitric oxide activity, both of which may contribute to the susceptibility of broiler chickens to pulmonary hypertension.

Videotaped training in alcohol counseling for obstetric care practitioners: a randomized controlled trial.

OBJECTIVE: To determine the feasibility of videotaped training for obstetric care practitioners in motivational interviewing skills that could be used in brief patient consultations on problem drinking. METHODS: Thirty health care practitioners participated in a clinical trial using a 20-minute videotape to instruct them in motivational interviewing. Participants engaged in a pretest roleplay with an actress playing a drinking pregnant woman. Those randomly assigned to the experimental condition watched the motivational interviewing videotape. Control condition participants watched a 20-minute docudrama of a pregnant problem drinker. Both groups then engaged in a post-test roleplay similar to the pretest. Behavioral ratings of the roleplays and participant evaluations of the motivational interviewing video constituted the outcome measures. RESULTS: Participant evaluations indicated that the training video was clear in explaining and demonstrating the principles and skills of motivational interviewing. Change in behavioral ratings from pretest to post-test showed significant differences in motivational interviewing skills between the experimental and control groups. Obstetric care practitioners who viewed the training video were rated as showing greater empathy, minimizing patient defensiveness, and supporting women's beliefs in their ability to change. CONCLUSION: Obstetric care practitioners can improve their alcohol intervention skills through the use of a 20-minute videotaped instruction in motivational interviewing. Clinicians who improve their skills in motivational interviewing can intervene more effectively with their drinking pregnant patients. Using motivational interviewing with this population holds promise for helping prevent alcohol-related health problems.

Behavioral Self-Control Program for Windows: results of a controlled clinical trial.

Forty nonalcoholic heavy drinkers were randomly assigned to receive a computer-based version of behavioral self-control training either immediately after pretreatment assessment or after a 10-week waiting period. Results at each of 3 follow-ups strongly support the study hypotheses. Participants in the immediate treatment group significantly reduced their drinking relative to their pretreatment levels and relative to those in the delayed treatment condition at the initial follow-up, 10 weeks after the pretreatment assessment. The delayed group did not change their drinking behaviors during this period of time. However, they significantly reduced their drinking by the second follow-up conducted after they received training. At the 12-month follow-up, participants maintained the gains they had achieved during treatment. There were no interactions involving participant ethnicity or gender. Although use of other drugs was not specifically addressed, such use did not increase, and there was some evidence of a decline.

The direct vascular relaxing action of betaxolol, carteolol and timolol in porcine long posterior ciliary artery.

The vascular relaxing properties of three beta adrenoceptor antagonists, betaxolol, carteolol and timolol, currently used in the treatment of glaucoma, were characterized, compared and contrasted in the porcine long posterior ciliary artery. Isolated arterial ring segments precontracted with increased extracellular KCl (plus 40 mM) or the thromboxane analog, U-46619 (3 x 10(-7) M), were relaxed in a concentration-dependent fashion by betaxolol, carteolol, timolol or nitroprusside. In vessel segments depolarized with increased extracellular KCl, EC50 values indicated that the intrinsic relaxant sensitivity to betaxolol was equal to that of nitroprusside, six-fold greater than that of carteolol, and ten-fold greater than that of timolol. Similarly, the maximum relaxation occurring at equimolar concentrations (10(-4) M) for the beta adrenoceptor antagonists was betaxolol > carteolol = timolol. Qualitatively similar results were noted in ring segments of the rabbit external iliac artery precontracted with increased extracellular KCl (plus 30 mM). Under conditions in which specific receptor-linked events are absent and voltage-gated Ca++ entry is maximized, the Ca++ concentration response relationship in porcine long posterior ciliary artery was shifted to the right in an apparent competitive manner by betaxolol, reflecting a 5.6-fold reduction in the sensitivity to Ca++. Conversely, nitroprusside reduced the Ca++ sensitivity three-fold in a noncompetitive fashion; not only shifting the Ca++ concentration response relationship to the right, but also depressing the maximum by 57%. Porcine long posterior ciliary arterial segments precontracted to a similar degree with U-46619, in which voltage-gated Ca++ entry is only one component of many specific cell signalling transduction mechanisms contributing to the precontraction, exhibited a sensitivity to betaxolol that was six-fold less than to nitroprusside, but two-fold greater than to timolol and 20-fold greater than to carteolol. These results are consistent with an obvious direct vascular relaxing capacity for beta adrenoceptor antagonists that primarily represents a capacity for inhibiting voltage-gated Ca++ entry in vascular smooth muscle. Additionally, the differential potencies of these three beta adrenoceptor antagonists characterized in this study suggests that this property is much more likely to contribute to any potentially beneficial effects of betaxolol than carteolol or timolol.

Calcium entry, mobilization, and extrusion in postcapillary venular endothelium exposed to bradykinin.

The effect of bradykinin (BK) on cytosolic calcium in coronary venular endothelial cells (CVEC) was studied using the intracellular calcium indicator indo 1. At normal extracellular calcium levels, CVEC responded to BK at concentrations as low as 0.1 pM; maximum cytosolic calcium spikes occurred at 10 nM. In calcium-free medium, poststimulation cytosolic calcium concentration returned to levels below prestimulation values, implying that BK modulates calcium extrusion mechanisms that are normally masked by calcium influx into the cell. To test this hypothesis, we depleted internal stores of calcium using two approaches: preconditioning or blockade of the endoplasmic reticulum calcium pump with the sesquiterpene lactone, thapsigargin. Depletion by preconditioning consisted of two prior doses of BK followed by a third stimulus of the agonist. Under these conditions, the final dose of BK caused a fall, rather than rise, in cytosolic calcium. Thapsigargin blocked the endoplasmic reticulum calcium pump, leading to a steady-state rise in intracellular calcium concentration. Subsequent exposure of these cells to BK also led to a fall in cytosolic calcium. The preconditioning and thapsigargin studies are consistent with a modulation of calcium extrusion processes by BK in CVEC. The signals responsible for this modulation are unknown.

Pharmacological characteristics of NP-252, a new dihydropyridine slow Ca2+ channel blocker, in isolated rabbit vascular smooth muscle and guinea pig myocardium: vascular selectivity.

NP-252, a new dihydropyridine derivative, and nifedipine non-competitively inhibited contractile responses to KCl and responses to Ca2+ in Ca(2+)-free medium containing KCl in rabbit aorta and renal, mesenteric, coronary and basilar arteries, mesenteric veins and vena cava. The effects of NP-252 in these smaller arteries and veins were much greater than those in aorta. However, a similar differential selectivity was not seen with nifedipine. In aorta, only NP-252 reduced total La3+ resistant 45Ca binding. However, the increases in bound 45Ca at La3+ resistant sites and 45Ca unidirectional influx due to KCl were inhibited by both NP-252 and nifedipine. The displacement of [3H]nitrendipine binding to rabbit aorta was monophasic for both NP-252 and nifedipine. In guinea-pig papillary muscles, NP-252 (greater than 10(-7) M) slightly decreased action potential duration, developed tension and slow action potentials. The cardiac effects of NP-252 were much less prominent than those of nifedipine. These results indicate that NP-252 inhibits voltage-operated Ca2+ channels in small arteries and veins much more effectively than those in aorta, and this tissue selectivity is more apparent for NP-252 than nifedipine.

Characteristics of the vasorelaxing action of (3E)-4-ethyl-2-hydroximino-5-nitro-3-hexamide FK409, a new vasodilator isolated from microbial sources, in isolated rabbit arteries.

We examined the vasoinhibitory effect of (3E)-4-ethyl-2-hydroximino-5-nitro-3-hexamide FK409, a new vasodilator, on contractile responses in isolated rabbit arteries. FK409 (10(-8)-10(-5) M) inhibited contractile responses to norepinephrine (NE), histamine (His), and 5-hydroxytryptamine (5-HT) in rabbit aorta. The pattern of inhibition by FK409 was not competitive. The inhibitory effect of FK409 on the 5-HT response was much greater than that of nitroglycerin (NG). A high concentration of FK409 (10(-5) M) was necessary to inhibit the response to KCl (10-70 mM). The effect of combined treatment with FK409 (10(-5) M) and a subthreshold concentration of nifedipine (10(-9) M) on the KCl response was much greater than a single treatment with either agent. In addition, 3 x 10(-6) M D600, but not FK409 (10(-6) or 10(-5) M), inhibited the increase in the rate of 45Ca influx stimulated by a 40-mM KCl substituted solution. In a Ca2(+)-free medium containing EGTA and nifedipine, FK409 (10(-9)-10(-5) M) inhibited phasic responses to NE, His, and 5-HT, and subsequent sustained responses owing to addition of Ca2+. The response to caffeine in rabbit iliac arteries incubated in Ca2(+)-free medium was also inhibited by FK409 (10(-6) and 10(-5) M). In rabbit aorta precontracted with NE (10(-5) M) and partially inhibited by prior exposure to NG (10(-5) M), the relaxing effect of FK409 was slightly attenuated. Pretreatment of tissues with FK409 (10(-6) M) inhibited the relaxing action of NG much more than prior NG inhibited the relaxing action of FK409. Methylene blue (10(-5) M), but not hemoglobin (10(-6) M), inhibited the relaxing action of FK409, whereas M&B 22,948 (3 x 10(-4) M) potentiated it. FK409 caused a relaxation of precontracted aorta without endothelium that was inhibited by methylene blue. In rabbit aorta precontracted with NE, FK409 (10(-6) M) increased cyclic GMP but not cyclic AMP content. FK409 (10(-5) M) had no effect on the NE-mediated increase in tissue inositol monophosphate (IP). These results suggest that FK409 inhibits the responses attributed to both intracellular Ca2+ release and Ca2+ influx through receptor-operated channels. The inhibitory effect of FK409 on both the KCl contractile response and KCl-stimulated 45Ca influx appears to be different from that of nifedipine or D600. Furthermore, the inhibitory action of FK409 may be partially mediated by cyclic GMP.

Characterization of the vasoinhibitory actions of KT2-230, a new benzothiazepine vasodilator derivative on isolated rabbit vascular smooth muscles: an alpha-adrenergic- and serotonergic-receptor antagonist.

1. Pharmacological properties of KT2-230 (benzothiazepine derivative), a newly synthesized vasorelaxing agent, were studied. 2. In the anesthetized dogs, KT2-230 increased the femoral and vertebral blood flow without effect on systemic blood pressure. 3. In rabbit aorta, KT2-230, methysergide and phentolamine inhibited contractile responses to 5-hydroxytryptamine. 4. The response to norepinephrine was also inhibited by KT2-230 and phentolamine. Responses to histamine were not affected by KT2-230. 5. Responses to KCl and Ca2+ in K+ depolarized aorta in Ca2(+)-free medium were inhibited by a high concentration of KT2-230. 6. In rabbit iliac artery, KT2-230 inhibited the response to caffeine in Ca2(+)-free medium. 7. KT2-230 decreased total La3(+)-resistant Ca2(+)-binding at high affinity sites. 8. These results indicate that KT2-230 inhibits alpha 1-adrenoceptors and 5-HT-receptors and at high concentrations it inhibits slow Ca2(+)-channels. KT2-230 may inhibit the Ca2(+) release from caffeine- and agonist-sensitive Ca2+ stores.

KT-362 related effects on intracellular calcium release and associated clinical potential: arrhythmias, myocardial ischemia, and hypertension.

The following discourse addresses the pharmacologic profile of KT-362, its clinical potential as an anti-arrhythmic agent with associated hypotensive effects, as well as its additional related potential in myocardial ischemia and related sequellae, and the specific cellular actions that may be responsible for these potential therapeutic effects. Although these include specific actions on both sodium and calcium entry, the focus is on the relevance of independent effects on calcium release. KT-362 relaxes arterial smooth muscle, concomitantly reducing the total peripheral resistance and mean arterial blood pressure. Vascular relaxing actions are attributed primarily to inhibitory effects on calcium release and secondarily to inhibitory effects on calcium entry via both potential-gated and receptor-linked channels. The "intracellular calcium antagonist" properties are correlated with a decrease in the production of the major second messenger, inositol 1,4,5-trisphosphate, which is responsible for calcium release and a concurrent ryanodine-like action that further decreases the amount of calcium released. Ventricular arrhythmias associated with coronary occlusion, cardiac glycosides, catecholamines, and chloroform are prevented by KT-362. General antiarrhythmic properties are associated with a use-dependent block of the "fast" sodium channel, primarily in the activated state, with ancillary effects on the "slow" calcium current. More selective effects on arrhythmias specifically associated with delayed after-depolarizations are attributed to effects on calcium release. In myocardial ischemia, KT-362 primarily reduces myocardial oxygen consumption rather than increases oxygen supply. The former is accomplished by depressing myocardial contractility and reducing afterload, while the latter is associated with a limited effect on coronary collateral blood flow. The negative inotropic effect is fundamentally related to its effects on calcium release, with additional contributions from its effects on calcium entry. Thus, the one intrinsic property of KT-362 that consistently emerges as significant and relevant in cardiovascular disease is the capacity to diminish calcium release.

Behavioral treatment of alcohol and drug abuse. What do we know and where shall we go?

Over the last 20 years there has been a substantial increase in the use of alcohol and drugs in industrialized nations and a concomitant shift in the emphasis of treatment for alcohol and drugs. Rather than seeking treatment for alcohol alone or a single class of drug, many individuals are seeking treatment for alcohol and/or a number of drugs. While theoreticians have been exploring the similarities in the addictive behaviors, clinical researchers are only just beginning to do so. Unfortunately, most treatment research has focused almost exclusively on alcohol abusers or drug abusers, with little research conducted to date with alcohol and drug abusers. Behavioral interventions developed for alcohol abuse are now being tested with drug abusers, and vice versa. The purpose of this chapter is fourfold: (1) to briefly discuss the similarities in the assessment of alcohol and drug abuse; (2) to describe behavioral interventions that have been supported by research and briefly review this treatment outcome research; (3) to discuss the theoretical similarities in behavioral interventions for alcohol and drug abuse; and (4) to make recommendations for future advancements in treatment and research.

Differential inhibitory effects of nitroglycerin on contractile responses to the alpha-adrenoceptor agonists, methoxamine and clonidine, in rabbit aorta.

The vasoinhibitory action of nitroglycerin was examined on contractile responses to methoxamine and clonidine in isolated rabbit aorta. Nitroglycerin at 10(-5) M, but not 10(-6)-10(-8) M, shifted the concentration response curve for methoxamine to the right. Nitroglycerin (10(-8)-10(-5) M), however, noncompetitively inhibited responses to clonidine in a concentration dependent manner. Nitroglycerin (10(-5) M) had no effect on responses to potassium (10-70 mM), but slightly inhibited responses to Ca2+ (0.1-5 mM) in a Ca2+-free medium containing potassium. Nifedipine (10(-6) and 10(-5) M), however, almost abolished responses to both potassium and Ca2+ but had no effect on responses to either methoxamine or clonidine. Agonist-antagonist interactions using prazosin and yohimbine revealed that responses to both methoxamine and clonidine were due to activation of alpha 1-adrenoceptors. Results with phenoxybenzamine suggested that the aorta has more receptor reserve for methoxamine than for clonidine. Furthermore, in tissues pretreated with phenoxybenzamine, nitroglycerin (10(-5) M) inhibited the maximal contractile response to methoxamine (3 x 10(-4) M). The maximal response to clonidine in tissues pretreated with phenoxybenzamine was not affected by nitroglycerin (10(-8) M). Nitroglycerin (10(-9)-10(-4) M) had greater inhibitory effect on residual responses to clonidine (10(-5) M) than that to methoxamine (10(-5) M) in a Ca2+-free medium containing EGTA. The contractile responses to Ca2+ (2 mM) in a Ca2+-free medium containing EGTA, nifedipine, and either methoxamine (5 x 10(-7) M) or clonidine (3 x 10(-7) M) were inhibited by nitroglycerin (10(-9) - 10(-5) M). The effect of nitroglycerin was greater on responses in the presence of clonidine than methoxamine.(ABSTRACT TRUNCATED AT 250 WORDS)

Receptor-mediated Ca++ entry in blood vessels.

The importance of receptor-mediated Ca++ entry (RMCa++E) relative to Ca++ release and potential-dependent Ca++ entry (PDCa++E) in agonist-induced responses in rabbit aorta and renal artery was quantitatively delineated by utilizing a solution without added Ca++ containing low ethyleneglycol bis(beta-aminoethylether)-N,N'-tetraacetic acid (EGTA) plus D600 to inhibit PDCa++E. Adding an approximate ED80 concentration of norepinephrine (NE; 3 x 10(-7) M), histamine (Hist; 3 x 10(-6) M), or serotonin (5HT; 3 x 10(-6) M) to this solution results in a transient increase in developed force that is attributed to release of a limited cellular pool of Ca++. (NE greater than Hist much greater than 5HT). When the concentrations are approximately equipotent (NE, 3 x 10(-7) M; Hist, 3 x 10(-5) M; 5HT, 10(-5) M) the Ca++ release component increases for Hist and 5HT such that NE = Hist greater than 5HT. Subsequent addition of Ca++ results in an increase in developed force that is sustained and represents RMCa++E. In aorta, RMCa++E can account for 91% of the total NE-induced developed force; for an equipotent concentration of Hist, 71%; and for an equipotent concentration of 5HT, only 37%. This capacity for stimulating RMCa++E is inversely related to the sensitivity of these agonists to the PDCa++E blocker, D600 (5HT much greater than Hist greater than NE). Chronic Mg++ potentiates control responses to NE in normal Ca++, but depresses the sensitivity to Ca++ in the RMCa++E concentration response relationship. The sustained response associated with RMCa++E is only minimally relaxed or inhibited by Mg++ (acute) and is completely inhibited or slowly and completely relaxed by La . In renal artery, a similar approximate ED80 concentration of NE (3 x 10(-6) M) results in a NE-induced transient response attributed to Ca++ release that is 60% less than that seen in aorta, whereas the RMCa++E component in renal artery accounts for 78% of the total response (only 10% less than in aorta). Thus, it appears that there are pharmacologically distinct Ca++ channels in some blood vessels that are differentially activated in a selective and potential-independent manner as a result of specific agonist-receptor interactions.

The potentiation of norepinephrine-induced contraction of rabbit aorta by Mg2+ deletion in a Ca2+-free medium.

Residual responses to norepinephrine (NE) in an Mg2+-, Ca2+-free medium with low EGTA (0.1 mM) for 15 min were potentiated following preincubation of rabbit aortas in Mg2+-free medium for 60 min. Responses to Ca2+ in a Ca2+-free medium with nifedipine and NE were not affected under a similar Mg2+-free condition. Nifedipine, theophylline, dibutyryl cAMP, 8-bromo-cGMP, methylene blue, La3+ or vanadate did not affect the residual response or the potentiation. However, high EGTA (1 mM) inhibited both the residual response and the potentiation. The residual response to NE was not potentiated following incubation in Mg2+-, Ca2+-free medium for 60 min. These results suggest that, in the rabbit aorta, Mg2+ deletion from the medium selectively potentiates the residual response to NE in a Ca2+-free medium without any effect on the response due to Ca2+-influx through receptor-operated channels. This potentiation does not appear to be related to either the levels of cAMP and cGMP or the activity of an Mg2+-dependent, Ca2+-ATPase.

Functional importance of alpha adrenoceptor-mediated, D600-insensitive Ca++ entry in rabbit aorta.

Specific receptor-linked Ca++ entry (RLCa++E) was studied separately from Ca++ release and potential-dependent Ca++ entry (PDCa++E) in rabbit aorta after incubation in a Ca++-free solution containing ethylene glycol bis(beta-aminoethyl ether)-N,N'-tetraacetic acid to bind trace levels of Ca++ and including methoxyverapamil (D600) (10(-5) M) to inhibit PDCa++E. Adding norepinephrine (NE) under these conditions resulted in a transient response which was attributed to Ca++ release from a limited cellular store. Subsequent addition of Ca++ results in a sustained contraction that was dependent upon the concentration of agonist and Ca++. This maintained response which by definition was insensitive to D600 was attributed to RLCa++E, was extensively relaxed or inhibited by nitroprusside or nitroglycerin and was partially relaxed by KCl or tetraethylammonium. Contractions due to RLCa++E alone equaled or exceeded the peak tension attained solely as a result of Ca++ release. At higher NE concentrations (greater than 10(-7) M), RLCa++E provided sufficient Ca++ to attain and sustain maximal levels of developed tension without requiring any additional Ca++ from either PDCa++E or Ca++ release. This high flux capacity of these receptor-linked Ca++ channels may partially account for the relative insensitivity of contractile responses to these higher concentrations of NE to D600. The relative contribution of PDCa++E to the elevation of myoplasmic Ca++ and concurrent sensitivity to D600 was increased at lower concentrations of NE because the degree of Ca++ release and RLCa++E were relatively small. Additionally, it appears that RLCA++E may be attenuated by concomitant membrane depolarization.

The mode of vasoinhibitory action of a pyridazione derivative (MCI-154), a new cardiotonic agent, on contractile responses induced by alpha-adrenoceptor agonists and 45Ca influx in isolated vascular smooth muscles.

The vasoinhibitory effects of MCI-154 (MCI), a new pyridazione derivative, on contractile responses to alpha 1- and alpha 2-adrenoceptor agonists were examined in isolated rabbit aorta. MCI (10(-8)-10(-5) M) inhibited the maximum contractile responses to clonidine and BHT-920 (BHT) in a concentration-dependent manner, but only inhibited responses to lower concentrations of methoxamine. In aortas pretreated with phenoxybenzamine however, MCI (10(-5) M) readily inhibited responses to methoxamine. MCI (10(-5) M) had no significant effect on responses to potassium or added Ca2+ in a Ca2+ free, K+-depolarizing medium. In aortas incubated in a Ca2+-free medium with EGTA, the addition of methoxamine (10(-5) M), clonidine (10(-5) M) or BHT (3 X 10(-4) M) induced a phasic contraction. The inhibitory effect of MCI (10(-9)-10(-5) M) on these phasic responses was much greater for clonidine or BHT than for methoxamine. In rabbit iliac artery caffeine (10 mM) induced a rapid phasic contraction in a Ca2+-free medium, which was inhibited by MCI (10(-7)-10(-5) M) in a concentration-dependent manner. In aortas incubated in a Ca2+-free medium with low EGTA and nifedipine (10(-6) M) in the presence of alpha-adrenoceptor agonists (methoxamine, clonidine or BHT), the addition of Ca2+ (2 mM) induced a tonic contraction. MCI (10(-8)-10(-5) M) inhibited these Ca2+-dependent, agonists-mediated responses in a concentration-dependent manner. MCI had no effect on unstimulated La3+ resistant Ca2+ binding or methoxamine-induced Ca2+ influx.(ABSTRACT TRUNCATED AT 250 WORDS)

Endothelium-dependent relaxations in rabbit aorta are depressed in artificial buffered solutions.

Contractile and relaxant responses of rabbit aortae in artificial buffered (Tris and N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid) solutions were compared with those in bicarbonate-buffered solution. EC50 values for responses to KCl in aortae equilibrated in Tris and N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid were slightly less than those in bicarbonate; maximum contractions did not differ. There were no significant differences in contractile responses to prostaglandin Fa alpha or histamine in the three buffered solutions. In aortae precontracted with prostaglandin F2 alpha, both acetylcholine and the calcium ionophore, A23187, elicited much less relaxation in artificial buffered solutions than in bicarbonate-buffered solutions. Maximum relaxations to nitroprusside or D600 did not differ among the three solutions. Relaxant responses to isoproterenol were also depressed in artificial buffered solutions. Endothelial damage eliminated relaxant responses to acetylcholine and A23187, as well as the difference in responsiveness to KCl and isoproterenol noted in artificial buffered compared with bicarbonate-buffered solutions. Within the same solution, endothelial damage alone did not alter the responsiveness to KCl or histamine. Total and La -resistant Ca++ binding was similar in all three buffered solutions. Thus, contractile responses are not depressed in Tris- or N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid-buffered solutions, whereas endothelium-dependent relaxations are attenuated in similar solutions. Overall, the results imply that, in artificial buffered solutions, the production and/or release of an endothelium derived relaxing factor is attenuated or that its action on aortic smooth muscle is, in some manner, functionally antagonized.

Effects of nicorandil on receptor-mediated Ca2+ release and Ca2+ entry in vascular smooth muscle.

In a solution containing La3+, or one without Ca2+ (Ca2+-free) and containing 1.0 mM ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA), norepinephrine (NE)-induced transient contractions in rabbit aorta attributed to Ca2+ release are depressed 31 and 38%, respectively, by an approximate ED60 relaxing concentration of nicorandil (SG-75). In addition, after 15 min in a Ca2+-free, low-EGTA (0.01 mM) solution, plus D600 to eliminate any potential-dependent Ca2+ entry, NE elicits a similar phasic response that is attenuated 34% by SG-75. Apparently, this is primarily due to inhibition of Ca2+ release rather than to stimulation of rebinding, uptake, and/or extrusion of Ca2+ following release. For, when tissues initially exposed to a Ca2+-free, low-EGTA plus D600 solution with or without SG-75 and NE are then rinsed with the same solution for 20 min to remove SG-75 and/or NE and again exposed to NE there is only a small residual maintained response in tissues not exposed to SG-75. However, in tissues that have been exposed to SG-75 prior to NE, a measurable phasic response is elicited that is approximately 50% of control NE responses. When Ca2+ is added to a Ca2+-free, low-EGTA plus D600 solution after NE-induced Ca2+ release, a rapid and significant increase in tension ensues that is well maintained and is proposed to represent specific alpha-adrenoceptor-mediated Ca2+ entry. This NE-mediated, D600-insensitive Ca2+ entry is readily inhibited or relaxed by SG-75.(ABSTRACT TRUNCATED AT 250 WORDS)