Characterization of the contractile serotonergic receptor in guinea pig trachea with agonists and antagonists.

5-Hydroxytryptamine (5-HT)2 receptors can be partially characterized by their sensitivity to ketanserin blockade and increase in phosphoinositide turnover upon stimulation. Previously, the contraction of guinea pig trachea to 5-HT was shown to be antagonized by the 5-HT2 receptor antagonists ketanserin and LY53857. However, 5-HT did not dramatically increase phosphoinositide turnover in guinea pig trachea, suggesting that the contractile receptor may be different from the classically defined 5-HT2 receptor. The present in vitro studies better characterize this receptor, using diverse serotonergic agonists and antagonists to profile in more detail the contractile serotonergic receptor in guinea pig trachea. With regard to agonists, the 5-HT2 receptor agonists DOI and alpha-methyl-5-HT contracted guinea pig trachea with greater potency than quipazine, 5-methoxytryptamine, 5-carboxamidotryptamine, 8-hydroxy-2-(di-N-propylamino)tetralin and 2-methyl-5-HT. Sumatriptan and 1-(3-chlorophenyl)-piperazine (10 nM-100 microM) were inactive as agonists. A strong correlation between agonist potency (EC50) and reported 5-HT receptor binding affinities was found for both the 5-HT1C (r = 0.890) and 5-HT2 (r = 0.831) receptor. Ketanserin, spiperone, ritanserin, LY53857, 1-napthylpiperazine, 1-(3-chlorophenyl)-piperazine, rauwolscine, ICS 205-930, cyanopindolol and sumatriptan all blocked 5-HT-induced contractions in guinea pig trachea. As occurred with agonist potencies, strong correlations were found between reported 5-HT1C (r = 0.814) and 5-HT2 (r = 0.912) receptor binding affinities in brain membranes and apparent dissociation constants (KB) for the 10 antagonists of 5-HT induced contraction in guinea pig trachea.(ABSTRACT TRUNCATED AT 250 WORDS)     

Species differences in the localization and number of CNS beta adrenergic receptors: rat versus guinea pig

The localization and number of beta adrenergic receptors were directly compared in the brains of rats and guinea pigs. The time course of association and saturability of [125I]cyanopindolol (CYP) binding to slide-mounted tissue sections was similar in rats (Kd = 17 pM) and guinea pigs (Kd = 20 pM). The beta-1 and beta-2 receptor subtypes were examined through the use of highly selective unlabeled receptor antagonists, ICI 118,551 (50 nM) and ICI 89,406 (70 nM). Dramatic species differences between rats and guinea pigs were observed in the neuroanatomical regional localization of the beta adrenergic receptor subtypes. For example, in the thalamus prominent beta-1 and beta-2 receptor populations were identified in the rat; however, the entire thalamus of the guinea pig had few, if any, beta adrenergic receptors of either subtype. Hippocampal area CA1 had high levels of beta-2 adrenergic receptors in both rats and guinea pigs but was accompanied by a widespread distribution of beta-2 adrenergic receptors only in rats. Quantitative autoradiographic analyses of 25 selected neuroanatomical regions 1) confirmed the qualitative differences in CNS beta adrenergic receptor localization, 2) determined that guinea pigs had significantly lower levels of beta adrenergic receptors than rats and 3) indicated a differential pattern of receptor subtypes between the two species. Knowledge of species differences in receptor patterns may be useful in designing effective experiments as well as in exploring the relationships between receptor and innervation patterns. Collectively, these data suggest caution be used in extrapolation of the relationships of neurotransmitters and receptors from studies of a single species.     

Effects of putative thromboxane receptor agonists and antagonists on rat small intestinal ion transport

Effects of a thromboxane mimic, U46619, on electrolyte transport were examined in vitro using stripped segments of rat ileal mucosa mounted in Ussing chambers. Addition of U46619 to the serosal bathing solution elicited a transient increase in short-circuit current (Isc) and decrease in transepithelial conductance (Gt). The increase in Isc was accompanied by a transient increase in Cl- secretion and decrease in Na+ absorption. In the steady-state, Isc was not increased whereas Gt remained decreased and Na+ and Cl- absorption were inhibited. Removal of Cl- or pretreatment with serosal and mucosal indomethacin (1 microM) or the thromboxane receptor antagonist, SK&F 88046, added to the serosal bathing solution, inhibited the increase in Isc stimulated by U46619 (apparent KB approximately 8 nM). The effects of U46619 on both Isc and Gt are qualitatively similar to those resulting from stimulation with leukotriene D4. However, the changes in Isc with leukotriene D4 (10 microM) are antagonized by SK&F 88046 only at high concentrations (1-10 microM). In addition, the secretagogues prostaglandin F2 alpha, lys-bradykinin, serotonin and histamine, produce qualitatively similar changes in Isc to those seen with U46619 without altering Gt. With the exception of prostaglandin F2 alpha, the effects of these secretagogues are not inhibited by SK&F 88046 (10 microM). These results indicate that U46619 acts at a thromboxane receptor to stimulate intestinal Cl- secretion and inhibit Na+ and Cl- absorption. These changes are inhibited selectively by the thromboxane receptor antagonist, SK&F 88046.     

Effects of histamine H2 receptor agonists and antagonists on the isolated guinea pig gallbladder

Histamine H2 receptor-mediated responses were examined on cholecystokinin-octapeptide (CCK-8)-precontracted guinea pig gallbladder in vitro, testing histamine and a series of specific histamine H2 receptor agonists and antagonists. Among the antagonists tested, zolantidine and compound SKF 92857 were previously shown to antagonize H2 receptor-mediated responses in the heart, but not in the stomach. Histamine, in the presence of the H2 receptor antagonist mepyramine (10 microM), and the H2 receptor agonists dimaprit, impromidine and amthamine, inhibited CCK-8 (3 nM)-induced contractions in a concentration-dependent fashion, with the following rank orders of potency: impromidine > amthamine > histamine > dimaprit (pD2 values were 6.73 +/- 0.04, 5.44 +/- 0.07, 4.64 +/- 0.04 and 3.71 +/- 0.05, respectively). The maximal relaxation produced by dimaprit was significantly lower than that produced by histamine, as well as by impromidine and amthamine, which behaved as full agonists. All the H2 receptor antagonists examined were able to inhibit amthamine-induced relaxation. Famotidine (pA2 = 7.09 +/- 0.26), zolantidine (pA2 = 6.54 +/- 0.11), compound SKF 92857 (pA2 = 6.58 +/- 0.13) and aminopotentidine (pA2 = 6.86 +/- 0.06) competitively antagonised the amthamine-induced effect, while iodoaminopotentidine produced surmountable antagonism only at low concentrations (1 microM, pA2 = 6.83 +/- 0.21). Finally, the slowly-dissociable antagonist loxtidine caused a non-parallel displacement to the right of the concentration--response curve to amthamine (pKB = 7.55 +/- 0.24), with a significant depression of the maximal response to the agonist, even at the lowest effective concentration (0.3 microM). In conclusion, histamine H2 receptors in guinea pig gallbladder resemble those of the heart, as regards their sensitivity to zolantidine and compound SKF 92857, which, by contrast, were unable to antagonize histamine effects at gastric H2 receptors in different experimental models.     

Tachykinin receptor antagonists inhibit hyperpnea-induced bronchoconstriction in guinea pigs.

We tested the hypothesis that hyperpnea-induced bronchoconstriction (HIB) and hyperpnea-induced bronchovascular hyperpermeability (HIBVH) are mediated through stimulation of NK-1 and NK-2 receptors in guinea pigs. We first established the efficacy and selectivity of (+/-) CP-96,345 (3 mg/kg i.v.) and of SR-48,968 (300 micrograms/kg i.v.) as NK-1 and NK-2 antagonists, respectively. (+/-) CP-96,345 substantially attenuated bronchoconstriction and systemic vascular leak caused by administration of Sar9,Met(O2)11-Substance P (a specific NK-1 agonist), but had no effect upon bronchoconstriction induced by selective NK-2 stimulation with Nle10-Neurokinin A[4-10]. Conversely, SR-48,968 antagonized the bronchoconstrictor response to Nle10-NKA[4-10], right-shifting the dose-response curve by 2 log units, but had no effect on Sar9, Met(O2)11-SP-induced bronchoconstriction. Anesthetized, tracheostomized, opened-chest male Hartley guinea pigs were pretreated with (+/-) CP-96,345 (3 mg/kg i.v.), SR-48,968 (300 micrograms/kg i.v.), or their respective vehicles, and Evans blue dye (30 mg/kg i.v.) to label circulating albumin. 10 min isocapnic dry gas hyperpnea (12 ml/kg, 150 breaths/min) provoked HIB and HIBVH in vehicle-treated animals. (+/-) CP-96,345 reduced the magnitude of HIB by one-half (peak posthyperpnea RL 7.8 +/- 1.9 [SE] times prehyperpnea baseline versus 16.1 +/- 2.6, vehicle-treated; P < or = 0.0001, ANOVA); SR-48,968 blocked HIB more completely (peak posthyperpnea RL 5.1 +/- 1.7 [SE] times prehyperpnea baseline versus 19.3 +/- 2.8, vehicle-treated; P < 0.0001, ANOVA). Neither drug reduced HIBVH. We conclude that dry gas hyperpnea causes bronchoconstriction in guinea pigs through activation of tachykinin receptors. The differential effects of neurokinin receptor blockade on HIB and HIBVH demonstrate that hyperpnea-induced airflow obstruction is not primarily a consequence of hyperpnea-induced bronchovascular leak.     

Histamine receptors in isolated guinea pig duodenal muscle: H3 receptors inhibit cholinergic neurotransmission.

A series of histamine H3 receptor agonists and the H3 receptor antagonist thioperamide were tested in the isolated guinea pig duodenum, to investigate the role of this new receptor subtype in the intestinal contractility. At the same time the selectivity of the different compounds for the various histamine receptor subtypes was investigated. In the presence of famotidine (10(-6) M) and thioperamide (10(-5) M), histamine, N alpha-methylhistamine (NMH) and (R)-alpha-methylhistamine (alpha-MH) exerted a concentration-dependent contractile effect through activation of H1 receptors; the ratio of potency was histamine = NMH greater than alpha-MH (this last compound was approximately 500 times less potent). In the presence of pyrilamine (10(-6) M) and thioperamide (10(-5) M), histamine, dimaprit and impromidine caused a slight contractile effect, showing a high degree of tachyphylaxis; this effect was abolished by tetrodotoxin (10(-6) M) and by famotidine (10(-6) M). alpha-MH was ineffective up to 10(-4) M. The H2 receptor agonists dimaprit (10(-4) to 10(-3) M) and impromidine (10(-6) to 10(-5) M) caused a relaxant effect on the contraction elicited by acetylcholine (ACh), BaCl2 and electrical stimulation. This effect, which was unaffected by famotidine, was not mimicked by alpha-MH and not reversed by thioperamide (10(-5) M). In the presence of pyrilamine (109-6) M) and famotidine (10(-6) M), histamine, NMH and alpha-MH inhibited the twitch responses to electrical stimulation, with EC50 values of 1.17 x 10(-7), 6.76 x 10(-8) and 2.45 x 10(-8) M, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Bradykinin receptors in rat uterine smooth muscle: studies using radiolabeled ligand binding

Direct binding of 125I-Tyr8-bradykinin to a microsomal fraction prepared from rat uterine smooth muscle, showed an apparent dissociation constant (KD) at 29 degrees C of 5.0 X 10(-10) M calculated from kinetic studies and 6.6 X 10(-10) M from Scatchard plot analysis. The binding of 125I-Tyr8-bradykinin was reversible and saturable, and demonstrated high specificity for Tyr8-bradykinin, bradykinin and Lys-bradykinin, but was not displaced by unrelated peptides angiotensin I, angiotensin II, Arg8-vasopressin and oxytocin. The binding sites were copurified by differential centrifugation and on a discontinuous sucrose density gradient with 5'-nucleotidase activity, a plasma membrane marker enzyme. Prolonged intravenous infusion of bradykinin (5 nmol/h for 2 days) induced a 20% decrease in the number of bradykinin binding sites without a change in the equilibrium dissociation constant. The present results demonstrate that receptors mediating the effect of bradykinin on rat uterine smooth muscle are situated on plasma membranes and the regulation of the receptors is in part under the control of endogenous bradykinin levels.     

Endothelins: functional and autoradiographic studies in guinea pig trachea

The presence of binding sites for [125I]endothelin-1 and the contractile activities of endothelins (ETs) and sarafotoxin S6b and the endothelin fragment ET(16-21) were investigated in guinea pig trachea. ETs and sarafotoxin S6b (0.1-100 nM) induced potent contractile responses in guinea pig trachea with EC50 values ranging from 1.57 to 12.97 nM. Epithelium removal increased the potencies of ET-1, ET-2 and S6b, but not that of ET-3, and maximal responses to ET-1 and ET-2 were also increased. Effects of epithelium removal were partially mimicked by phosphoramidon (10 microM), an enkephalinase inhibitor, suggesting that enkephalinase (EC.3.4.24.11.) is able to degrade ET-1 and ET-2. ET-3-induced contractions were not affected by phosphoramidon. Autoradiographic studies suggested the presence of at least two specific binding sites for [125]ET-1 in guinea pig airway smooth muscle. The correlation between Kd and EC50 values suggests that the binding sites identified in the airway smooth muscle represent functional receptors for ETs. ET(16-21) and ET(16-21)-NH2 were less potent agonists than the ETs in guinea pig trachea and 10 microM ET(16-21) was unable to inhibit [125I]ET-1 binding in guinea pig airway smooth muscle. Therefore, these results suggest that the C-terminal hexapeptide of ET-1 cannot be used to classify ET receptors in guinea pig trachea.     

Evidence for postjunctional release of ATP evoked by stimulation of muscarinic receptors in ileal longitudinal muscles of guinea pig.

The origin of the ATP release evoked by muscarinic agonists and veratridine from longitudinal muscles of the guinea pig was assessed with muscarinic antagonists. Acetylcholine (ACh) (1 microM) and bethanechol (10 microM) produced an immediate and marked ATP release, which was almost completely blocked by atropine (0.3 microM) and by the M3 muscarinic antagonist 4-diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP) (1 microM); release was only slightly affected by tetrodotoxin (0.6 microM). The bethanechol-evoked release of ATP was partly, but not significantly, inhibited by pirenzepine, a M1 muscarinic antagonist. Veratridine, an ACh releaser, also elicited a delayed ATP release, in a concentration-related manner. This ATP release was greatly antagonized by atropine and by Ca++ removal from the medium, implying mediation by endogenous ACh released after depolarization. In contrast, electrically evoked ACh release was enhanced by atropine and 4-DAMP. Bethanechol, unlike veratridine, failed to elicit measurable ACh release from the tissue. The contraction evoked by bethanechol was notably inhibited by atropine and 4-DAMP, but not by pirenzepine and AFDX-116, a M2 muscarinic antagonist, at a concentration of 0.3 microM. These findings suggest strongly that ATP is postjunctionally released from the ileal smooth muscles after stimulation of postsynaptic muscarinic receptors, presumably M3 receptors.     

中药对豚鼠胆囊肌条运动影响的实验研究

目的观察乌梅、芫花、巴豆对豚鼠胆囊肌条运动的影响. 方法用 8个灌流肌槽同时记录实验动物胆囊肌条的自发收缩活动. 结果①低浓度的乌梅对胆囊肌条的收缩活动具有抑制作用( P< 0.01,t=3.918),而高浓度的乌梅对胆囊肌条张力的影响则呈现先降低后增高的双向性反应 (P< 0.05,t=2.297).普萘洛尔、吲哚美辛、雷尼替丁、六烃季胺、 L-NNA均末阻断乌梅对肌条的作用 (P >0.05).②芫花和巴豆均可增高离体胆囊肌条的张力 (P< 0.01,t=16; t=11.79)、加快收缩频率 (P< 0.01,t=5.47; t=4.00)、减小收缩波平均振幅 (P< 0.01,t=12.37; t=10.5).③酚妥拉明、苯海拉明、吲哚美辛可部分阻断芫花和巴豆对胆囊肌条的作用.另外,六烃季胺可部分阻断巴豆的作用. 结论①乌梅对豚鼠胆囊肌条的作用可能是直接作用于平滑肌.②芫花和巴豆对胆囊肌条的作用与肾上腺能α受体、组胺 H1受体、前列腺素合成酶有关.而巴豆还与胆碱能 N受体有关.     

Action of adenosine in estrogen-primed nonpregnant guinea pig myometrium: characterization of the smooth muscle receptor and coupling to phosphoinositide metabolism.

The smooth muscle of guinea pig uterus is contracted by adenosine in a manner consistent with the presence of a purine nucleoside receptor of the P1-A1 subtype that is uncoupled from adenylate cyclase. Here we investigate the signal transduction mechanism responsible for adenosine's ability to contract uterine smooth muscle. The A1 adenosine receptor antagonist [3H]-8-cyclopentyl-1.3- dipropyl xanthine ([3H]CPX) bound reversibly to a large number (172 +/- 25 fmol/mg of protein) of receptors in myometrial smooth muscle membranes from estrogen-primed virgin guinea pigs with an affinity (KD = 1.77 +/- 0.21 nM) similar to that expected of [3H]CPX binding to both central and peripheral A1 receptors. In the absence of the stable GTP analog, guanosine-5'-O-[3-thiotriphosphate], agonist competition of [3H]CPX binding resulted in a biphasic curve that was best fit assuming the presence of equal populations of two affinity states of the receptor. Addition of guanosine-5'-O-[3-thiotriphosphate] (10 microM) resulted in a monophasic competition curve of low affinity suggesting coupling of this A1 receptor to effector via a GTP binding protein. In [3H]myo-inositol labeled strips of myometrial smooth muscle, the adenosine agonist R-phenylisopropyl adenosine (R-PIA) stimulated the rapid formation of inositol-1,4,5-trisphosphate (InsP3) that was antagonized by addition of the nucleoside receptor antagonist 8-sulfophenyl theophylline. Prostaglandin stimulation of myometrial strips also increased InsP3 formation. Furthermore, R-PIA stimulated the disappearance of inositol phosphate (InsP) in a fashion consistent with agonist stimulation of an inositol phosphatase activity.(ABSTRACT TRUNCATED AT 250 WORDS)     

Human vascular vasopressin receptors: analysis with selective vasopressin receptor antagonists

The vascular activity of arginine vasopressin (AVP) and selective AVP receptor antagonists was investigated in isolated arterial ring segments from human superior mesenteric arteries. AVP elicited a potent and concentration-dependent contraction in human mesenteric arterial rings with an EC50 value of 2.01 X 10(-9) M. The presence or absence of the vascular endothelium did not affect significantly AVP-induced contraction. AVP induced slight, although significant, tachyphylaxis in human mesenteric arteries. The selective vascular (V1) receptor antagonist [d(CH2)5 1Tyr(Me)2]AVP (SK&F 100273) shifted the concentration-response curves for AVP-induced vascular contraction to the right in a parallel manner (KB = 2.23 X 10(-9) M). A mixed V1/V2 receptor antagonist, [d(CH2)5 1D-Tyr(Et)2Val4desGly9]AVP (SK&F 101926), was also a potent antagonist of AVP-mediated vascular contraction; however, inhibition was marked by a nonparallel shift of the concentration-response curves with depression of maximum contraction. Furthermore, a relatively renal (V2) selective receptor antagonist [d(CH2)5 1D-Ile2Val4]AVP (SK&F 101485) was approximately 100-fold less potent at inhibiting AVP-induced vascular contraction (KB = 1.37 X 10(-7) M). These studies illustrate for the first time the in vitro effects of selective vasopressin receptor antagonists in isolated human blood vessels. Studies of other blood vessels and the design of therapeutically useful antagonists should proceed with the hypothesis that the vasopressin receptors mediating vascular contraction in human mesenteric arteries are of the V1 subtype.     

Characterization of beta-1 and beta-2 adrenoceptors in guinea pig atrium: functional and receptor binding studies

The selective beta-2 adrenoceptor agonist procaterol produced positive inotropic and chronotropic responses over a concentration range of 1 nM to 0.1 mM in spontaneously beating right atria and in three of seven electrically driven left atria. The pD2 values (right atria, 7.30; left atria, 7.18) were midway between its known affinities at beta-1 and beta-2 adrenoceptors and are evidence that positive inotropic and chronotropic responses involve a minor beta-2 adrenoceptor component. The pKB values for procaterol against (-)-isoproterenol in the right atria (5.59) and left atria (5.29) were consistent with its affinity for beta-1 adrenoceptors and suggest that these are responsible primarily for positive inotropic and chronotropic responses. Receptor binding studies in right atrial homogenates showed that [125I]cyanopindolol binding was saturable (KD = 36.2 pM, maximal density of binding sites = 49.2 fmol mg-1 protein) and stereoselective with respect to the isomers of propranolol. Competition binding curves for the beta-1 adrenoceptor antagonist CGP 20712A and beta-2 selective antagonist ICI 118,551 against [125I]cyanopindolol binding were resolved into two components using iterative curve fitting techniques. Binding sites with the characteristics of beta-1 and beta-2 adrenoceptors were present in the proportions of approximately 75 to 25%. These studies indicate either that the beta-1 adrenoceptor is coupled more efficiently to the positive inotropic and chronotropic response than the beta-2 adrenoceptor or that a proportion of the beta-2 adrenoceptors subserve other functions.     

Differences in pulmonary and cardiovascular beta receptors in the guinea pig and rabbit.

An in vivo preparation, in which a body plethysmograph was incorporated, was useful in monitoring the cardiopulmonary effects of pharmacological agents in the guinea pig and rabbit. Isoproterenol, given 30 seconds prior to histamine challenge, reproducibly blocked histamine-induced dynamic compliance decreases and increased heart in the artificially ventilated guinea pig. These effects were used to separate the activity of beta adrenergic blockers on airway and heart muscle. Dose-response data were obtained and ED50 values for pulmonary and cardiovascular blockade were compared. Relative potencies and cardioselectivity ratios for dichloroisoproterenol, practolol, dl-propranolol and d-propranolol were determined. Both practolol and dichloroisoproterenol were cardioselective; dl-propranolol was found to be the most potent. When a similar protocol was tried in the rabbit, isorpoterenol failed to antagonize either histamine or methacholine-induced airway constriction. This finding was supported in subsequent in vitro tests. Isoproterenol and epinephrine were ineffective in blocking methacholine-induced tracheal chain contractions and epinephrine did not significantly enhance adenylate cyclase activity. Our observations suggest rabbit airway smooth muscle is insensitive to beta adrenergic stimulants.     

Evidence for leukotriene D4 receptors in guinea pig left atria.

The effects of peptidoleukotrienes (LTs) on electrically driven guinea pig left atria (GPLA) were investigated. LTD4 produced a positive inotropic response; however, rapid desensitization required the construction of noncumulative dose-response curves to naive tissues. The maximal inotropic response to LTD4 was 24 +/- 3% of isoproterenol and the EC50 = 267 +/- 77 nM. The functional response was corroborated by the demonstration of specific and rapid [3H]LTD4 binding to GPLA membranes with low affinity (Kd = 212 +/- 80.2 nM), in a saturable (Bmax = 20 +/- 1.1 pmol/mg protein) manner. In tissues pretreated with acivicin, which inhibits conversion of LTC4 to LTD4, the response to LTC4, but not LTD4, was abolished. Selectivity towards LTD4 was demonstrated by the inability of propranolol, prazosin, atropine, pyrilamine, capsaicin or indomethacin (all tested at 1 microM) to alter the functional response to LTD4. Similarly, none of the tested compounds (100 microMs) was inhibitory in the binding assay. Structurally diverse LTD4 antagonists SKF102922 (pKb = 6.42) and ICI 198.615 (pKb = 8.74) were able to inhibit the functional response as well as [3H]LTD4 binding to GPLA membranes. The calcium channel antagonist, verapamil, inhibited the functional response but did not alter [3H]LTD4 binding. These data support the existence of specific LTD4 receptors in GPLA which evoke a modest, rapidly desensitized, increase in the force of myocardial contraction.     

Effect of endothelin-1 on guinea pig gallbladder smooth muscle in vitro.

The purpose of this study was to investigate the pharmacological activity of endothelin-1 (ET-1) on guinea pig gallbladder smooth muscle. Guinea pig gallbladder muscle strips were mounted in 10-ml siliconized organ baths containing Krebs' solution. After 1 hr of equilibration, ET-1 was added cumulatively. ET-1 induced slow-developing and long-duration contractile responses. The EC50 was approximately 10 nM. ET-1 was 5 times less potent than cholecystokinin (EC50, 2 nM), but 20 and 40 times more potent than carbachol (EC50, 200 nM) and histamine (EC50, 400 nM), respectively. The concentration-response curve to ET-1 was not affected by tetrodotoxin (0.1 microM) or by the muscarinic antagonist, atropine (10 microM). The neuronal N-type calcium channel blocker, omega-conotoxin (0.1 microM), had no significant effect on the ET-1 concentration-response curve. In contrast, the contractile effect to ET-1 was reduced markedly by removal of extracellular calcium or by the voltage-dependent calcium channel blockers nicardipine and diltiazem. Substitution of strontium (an inhibitor of intracellular calcium release) for Ca++ significantly reduced the response to ET-1. The cyclooxygenase inhibitor indomethacin had no significant effect on the contractile activity of ET-1. These finding suggest that ET-1 is a potent contractile stimulant of guinea pig gallbladder and that it acts directly on the smooth muscle. The activity depends on extracellular Ca++, suggesting involvement of Ca++ influx via the voltage-dependent Ca++ channel and on intracellular calcium.     

Recurrent genital infection in the guinea pig: differences between herpes simplex types 1 and 2.

Recurrence rates of genital infections are significantly higher for herpes simplex virus (HSV) type 2 than HSV type 1. Reasons for this difference are not known. In this report, multiple strains of HSV-1 and HSV-2 were evaluated in the guinea-pig model. HSV-2 strains showed significantly higher genital lesion recurrence than HSV-1, including HSV-1 McKrae strain which is highly recurrent in ocular infections. HSV-2 strains were also associated with more frequent asymptomatic vaginal virus shedding. Further study showed that HSV-1 strains replicated as well as HSV-2 in both the genital tract and the nervous system during acute infection. In addition, no difference was detected between HSV-1 and HSV-2 in nervous system latency. Thus, a number of possible explanations for the observed difference in genital herpes recurrence rates were examined and excluded.     

Effect of newly developed tachykinin agonist and antagonists on the guinea pig isolated gallbladder.

The present study was undertaken to assess the activity of the neurokinin-2 (NK2) tachykinin receptor-selective antagonists MEN 10,376, L 659,877 and R 396 along with the NK2 receptor-selective ligand, MDL 28,564 on the isolated guinea pig gallbladder. None of the antagonists tested inhibited the response to the peptide CCK-8, although they competitively antagonized the contractile effect produced by NKA in the above tissue. The following rank order of potency was observed: MEN 10,376 (pKB = 6.77) greater than L 659,877 (pKB = 6.29) greater than R396 (pKB = 5.26). MEN 10,376 also antagonized the response to the NK3-selective agonist [MePhe7].NkB (10 microM), showing that the agonist activity of this peptide is due to NK2 receptor stimulation. On the other hand, MDL 28,564 had an agonist effect in the isolated gallbladder, its maximal effect approaching 58% of that to NKA. The results obtained using the above NK2 receptor-selective drugs in the guinea pig gallbladder was similar to that observed in other mammalian tissues bearing the NK2A receptor subtype, such as the endothelium-denuded rabbit pulmonary artery, the guinea pig bronchus and the circular muscle of the human colon and ileum. Therefore, we conclude that in the isolated guinea pig gallbladder tachykinins exert their contractile effect by activating NK2 receptors, which seem to belong to the NK2A receptor subtype.     

Respiration and glucose oxidation in human and guinea pig leukocytes: comparative studies

A comparison has been made of the metabolic shifts in human and guinea pig leukocytes when they phagocytize. Respiration of guinea pig polymorphonuclear leukocytes (PMN) and the increment during phagocytosis were each about 2(1/2)-fold that of human PMN. This was also true of the direct oxidation of glucose-6-P (hexose monophosphate shunt). Enzymes potentially responsible for these phenomena have been compared in each species. Cyanide-insensitive NADH oxidase and NADPH oxidase were measured and only the formed exhibited adequate activity to account for the respiratory stimulus durintg phagocytosis. The hydrogen peroxide formed by this enzyme stimulates the hexose monophosphate shunt by oxidizing glutathione which upon reduction by an NADPH-linked glutathione reductase provides NADP to drive the hexose monophosphate shunt. Other linkages between respiratory stimulation and that of the hexose monophosphate shunt also pertain in the guinea pig.     

Pharmacological characterization of potent, long-acting thromboxane receptor antagonists, SQ 33,261 and SQ 33,552.

SQ 33,261 ([1S-[1 alpha,2 alpha(Z),3 alpha,4 alpha]]-6-[3-[[2- [(phenylamino)carbonyl]hydrazono]methyl]-7-oxabicyclo[2.2.1]hept-2 - yl]-4-hexenoic acid) and SQ 33,552 ([1S-[1 alpha,2 alpha(Z),3 alpha,4 alpha]]-6-[3-[[[[(4- chlorophenyl)amino]carbonyl]hydrazono]methyl]-7- oxabicyclo[2.2.1]hept-2-yl]-4-hexenoic acid) are potent thromboxane (Tx) A2 receptor antagonists. They inhibited platelet aggregation in platelet-rich plasma induced by the TxA2 mimetic, U-46,619 (10 microM), with IC50 values of 200 and 70 nM, respectively. Neither compound inhibited ADP (20 microM)-induced platelet aggregation (IC50 greater than 1000 microM). SQ 33,261 and SQ 33,552 competitively antagonized U-46,619-induced contraction of rat aortic strips with respective pA2 values of 9.0 and 10.1 and KB values of 1.2 and 0.1 nM. They also competitively antagonized U-46,619-induced contraction of guinea pig tracheal strips with pA2 values of 8.9 and 9.9 and KB values of 1.9 and 0.4 nM, respectively. SQ 33,261 and SQ 33,552 (p.o.) were potent inhibitors of U-46,619 (2 mg/kg i.v.)-induced death in mice with ID50 values of 8 and 1 micrograms/kg, respectively. SQ 33,261 and SQ 33,552 (0.2 mg/kg p.o.), also had long duration of action in this assay with 50% survival times of 7 and 15 hr, respectively. SQ 33,261 at 0.01 and 1.0 mg/kg i.v., inhibited arachidonic acid-induced bronchoconstriction and reversed arachidonic acid-induced hypertension to a hypotensive response. SQ 33,552 inhibited TxA2 synthase at high concentrations (IC50 = 307 microM), whereas SQ 33,261 was inactive. Neither compound inhibited cyclooxygenase or caused an elevation of platelet cyclic AMP levels.(ABSTRACT TRUNCATED AT 250 WORDS)