Effect of substance P and eledoisin on K+ efflux, amylase release and cyclic nucleotide levels in slices of rat parotid gland.

The undecapeptides, substance P and eledoisin, caused a rapid, concentration-dependent increase in K+ efflux and amylase release from parotid tissue slices. The effects were not blocked by beta-adrenergic, alpha-adrenergic, or cholinergic antagonists. Incubation buffer calcium was required for stimulation of K efflux and amylase release. The action of the undecapepides was independent of any effects on parotid cyclic AMP or cyclic GMP levels. Since the actions of the undecapeptides were Ca2+ dependent and no effects on cyclic nucleotide levels were discerned it was concluded that Ca2+ plays a primary role in agonist regulation of K+ efflux from the parotid.

Potassium release from submandibular salivary gland in vitro.

Rat submandibular gland slices, incubated in continuously-gassed Krebs-Ringer bicarbonate buffer, were shown to release K+ in response to alpha-adrenergic and muscarinic cholinergic stimulation. The system employed the specific alpha-, beta-adrenergic and cholinergic receptor-blocking agents phentolamine, propranolol and atropine, respectively, in combination with the agonists L-epinephrine and carbamylcholine both of which required the presence of Ca2+ for their effect. The introduction of Ca2+ into the cell via the ionophore A23187, with all neurotransmitter receptors blocked, resulted in K+ release. Ouabain also allowed extensive K+ release which was in addition to, and hence independent of, that elicited by epinephrine and carbamylcholine. Ethacrynic acid, a potent inhibitor of salivary secretion in vivo, had no influence on K+ movement. K+ was released by both physalaemin and an eledoisin-related peptide independently of normal neurotransmitter receptors. The activity of the eledoisin-related peptide did not require the presence of extracellular Ca2+. The implication of cyclic GMP at some stage of K+ release was suggested by experiments with a phosphodiesterase inhibitor. The results support an hypothesis where the initial stimulus at either alpha-adrenergic or muscarinic cholinergic receptors causes an immediate permeability change such that Ca2+ enters the cells resulting in K+ release. The loss of K+ is quickly countered by the ouabain-sensitive (Na+ + K+) ATPase which would be activated by the lowered intracellular K+ levels.

Differing actions of convulsant and nonconvulsant barbiturates: an electrophysiological study in the isolated spinal cord of the rat.

The effects of various pairs of convulsant and nonconvulsant barbiturates on mono- and polysynaptic activity were studied in the isolated spinal cord of the immature rat, using extracellular recording. The convulsant barbiturates, 5-ethyl-5-(3-methylbut-2'-enyl) barbituric acid (3M2B), 5-ethyl-5-(1,3-dimethylbut-1'-enyl) barbituric acid (1,3M1B) and (+)-5-(1,3-dimethylbutyl)-5-ethyl barbituric acid [(+) DMBB] all increased the monosynaptic reflex at concentrations between 5 and 50 microM with no change in polysynaptic activity. When the concentration was raised to between 100 and 300 microM, however, the convulsants all reduced the monosynaptic reflex, thus producing a biphasic dose-response relationship. The nonconvulsant barbiturates phenobarbital, 5-ethyl-5-(3-methylbut-1'-enyl) barbituric acid (3M1B), amylobarbital (3MB) and (-)-5-(1,3-dimethylbutyl)-5-ethyl barbituric acid [(-)DMBB] produced only a decrease in mono- and polysynaptic reflexes. At concentrations which enhanced the monosynaptic reflex, the responses of motoneurones to glycine and eledoisin-related peptide (an analogue of substance P) were reduced by (+)DMBB, while 1,3M1B and 3M2B had no significant effects upon any of the neurotransmitters tested. At concentrations which depressed the monosynaptic reflex, the convulsants all reduced the response to glycine whereas the nonconvulsant barbiturates all increased the response to GABA. With the exception of phenobarbital, both convulsant and nonconvulsant barbiturates produced a direct depolarisation of the presynaptic terminal membrane, with only the convulsants producing a depolarisation of the membrane of the motoneurone. Using another convulsant barbiturate, 5-(2-cyclohexylideneethyl)-5-ethyl barbituric acid (CHEB), this direct depolarising action was found to be calcium-dependent.

Strychnine-like action of the convulsant barbiturate, CHEB.

The effect of 5-(2-cyclohexylideneethyl)-5-ethyl barbituric acid (CHEB) on the isolated spinal cord of the immature rat was examined using extracellular recording. At concentrations less than 20 microM CHEB increased the monosynaptic reflex (MSR) but depressed the reflex at greater concentrations (30-100 microM). At concentrations which enhanced the monosynaptic reflex, CHEB reduced the responses of motoneurones to glycine and to a lesser extent to those of L-glutamate. In the presence of strychnine (5 microM), which enhanced both mono- and polysynaptic reflexes, CHEB produced only slight enhancement of the monosynaptic reflex. At concentrations of 30-100 microM the responses to gamma-aminobutyric acid (GABA), glycine, L-glutamate and eledoisin-related peptide (ERP a substance P and analogue) were all reduced. At these concentrations CHEB directly depolarised the motoneurone membrane. Increases in [Mg2+]0, which reduced spontaneous activity, blocked the enhancement, by CHEB, of the monosynaptic reflex. The actions of CHEB in small doses may be due therefore to its ability to block the action of glycine and thus block tonic inhibition.

Substance P, injected intrathecally, antagonizes the spinal antinociceptive effect of morphine, baclofen and noradrenaline.

The effect of substance P on the antinociceptive effect of morphine, baclofen and noradrenaline in the spinal cord was examined in the tail-flick and hot plate tests, after intrathecal administration. Substance P (5-20 micrograms) produced a dose-related antagonism of the effect of all three agents, which persisted for the entire time-course of the antinociceptive effect in each case. The rank order of potency of substance P and related peptides in antagonizing the antinociceptive effect of morphine, was substance P greater than physalaemin greater than eledoisin greater than eledoisin-related peptide. A similar order of potency was observed against noradrenaline, except that physalaemin appeared to be the most potent. The intrathecal administration of these peptides did not alter reaction latencies in the tail-flick test when baseline values were 2-3 sec, but produced a significant decrease in latency (hyperalgesia) when baseline values were 6-8 sec. There was a slight increase in reaction latency in the hot plate test. The specificity of the antagonism was examined by determining the effect of phentolamine on the antinociceptive effect of morphine and baclofen. Although phentolamine (30 micrograms) produced comparable hyperalgesia to substance P, it did not significantly alter the antinociceptive effect of morphine or baclofen. These results suggest that alterations in the function of substance P in the spinal cord may contribute to the spinal antinociceptive effects of morphine, baclofen and noradrenaline. The effects of substance P on nociception in the spinal cord appear to be mediated by substance P type receptors.

Effects of glutamate, substance P and eledoisin-related peptide on solitary tract neurones involved in respiration and respiratory reflexes.

Recent studies have implicated glutamate and substance P in synaptic transmission in the nuclei tractus solitarii and in central regulation of cardiorespiratory functions. Consequently, in chloralose-anaesthetized cats that were artificially ventilated, we examined the effects of the microiontophoretic application of both chemicals (and the substance P homologue, eledoisin-related peptide) on single neurones of the nuclei tractus solitarii implicated in the control of respiration and respiratory tract reflexes. These neurones were functionally identified as either respiratory neurones or presumed reflex interneurones, and showed functional properties comparable to those previously documented for each of these two types. The iontophoretic application of glutamate produced an excitation of rapid onset in 23 or 25 reflex interneurones tested, but the respiratory neurones showed a differential sensitivity: one type (n = 32) was "glutamate-sensitive" and showed rapid excitation with glutamate applications of less than 30 nA, the other type of respiratory neurone (n = 26) was termed "glutamate-insensitive" since it either showed excitation only with applications of 60 nA or more or showed no response even with currents up to 94 nA. Each neurone studied was clearly of one type or the other. Glutamate could increase the number of spikes per rhythmic burst and the burst duration of respiratory neurones, it facilitated evoked activity in the reflex interneurones and in those respiratory neurones having a superior laryngeal nerve or vagus nerve afferent input, and the magnitude of the excitatory responses to glutamate varied directly with the amount of ejecting current. Substance P and eledoisin-related peptide also had excitatory effects on respiratory neurones and reflex interneurones, but compared with glutamate-induced effects the excitation was slower in onset and more prolonged in after-discharge. Both rhythmic and evoked activity could be facilitated, and the magnitude of the effect varied directly with the magnitude of the ejecting current. In showing that both glutamate and substance P (and its analogue, eledoisin-related peptide) have excitatory effects on the activity of respiratory neurones and reflex interneurones, this study provides evidence suggesting that these neurones have receptors for these neural chemicals, supportive of a role for each chemical in the regulation of respiration and respiratory tract reflexes.

NK-1 receptor mediation of neurogenic plasma extravasation in rat skin.

1. Plasma extravasation was induced by electrical nerve stimulation and by perfusion of tachykinins over a vacuum-induced blister base on rat footpad. 2. Stimulation of the sciatic nerve (18 V, 15 Hz, 0.5 ms) for 20 min produced a significant increase in the protein content of the perfusate. The response in capsaicin pretreated rats was only 4% of the control response. This indicates that the electrically-induced plasma extravasation response was mediated by capsaicin-sensitive sensory fibres. 3. Exogenous perfusion of the mammalian tachykinins substance P, neurokinin A and neurokinin B and the non-mammalian tachykinins physalaemin, kassinin and eledoisin was used to determine the tachykinin receptor type mediating the plasma extravasation response. Dose-response curves of the tachykinins (10(-9) M-10(-4) M) gave a rank order of potency of substance P = physalaemin greater than eledoisin greater than or equal to kassinin greater than neurokinin B = neurokinin A. 4. In addition, specific agonists of neurokinin receptors were perfused. Perfusion of [Glp6, D-Pro9] SP6-11 and [Glp6, L-Pro9]SP6-11 demonstrated that the L-Pro isomer was much more potent than the D-Pro isomer. 5. The rank order of potency and the greater potency of [Glp6, L-Pro9]SP6-11 over its D-isomer indicate an NK-1 neurokinin receptor mediates plasma extravasation in rat footpad skin.

The effects of chronic section of dorsal roots on the responsiveness of motoneurones to 5-hydroxytryptamine and a substance P analogue.

1 Experiments were performed on rats 14-21 days after unilateral dorsal root section in order to determine if the effects on motoneurone excitability of a substance P analogue, 5-hydroxytryptamine (5-HT) and noradrenaline were altered by section of primary afferents. 2 The effects of iontophoretic applications of these agents on motoneurone excitability were quantified by measuring the change in amplitude of the short latency field potentials evoked antidromically, by ventral root stimulation. 3 Iontophoretic application of the substance P analogue (eledoisin-related peptide, ERP) always produced an increase in the amplitude of the field potential. These increases in amplitude were 25.9% larger on the sides of the cords with sectioned dorsal roots. This was not statistically significant difference (P greater than 0.05). 4 Section of dorsal roots did not alter responses to noradrenaline. 5 Responses to 5-HT were significantly larger following section of dorsal roots. There is very little evidence for the release of 5-HT by primary afferents and denervation supersensitivity is an improbable explanation. It is possible that descending 5-HT systems directly excite motoneurones and indirectly inhibit primary afferent transmission. Dorsal root section would alter the balance between these actions of 5-HT in favour of an excitatory effect.

Contractile effects of substance P and other tachykinins on the mouse isolated distal colon.

1. Substance P (SP), physalaemin, eledoisin and kassinin induced concentration-related contractions of the longitudinal muscle of the mouse distal colon. The responses were not antagonized by atropine (1.5 x 10(-7) M), mepyramine (2.5 x 10(-7) M), methysergide (5 x 10(-7) M), timolol (10(-6) M), phentolamine (10(-6) M) or naloxone (4 x 10(-7) M). They were enhanced by tetrodotoxin (TTX, 1.5 x 10(-7) M). These observations indicate that the contractile responses to the tachykinins result from a direct activation of smooth muscle cells. 2. The contractile activity provoked by SP and physalaemin was inhibited by nifedipine (a Ca2+-entry blocker) and was abolished in Ca2+-free EGTA solution. Such data suggest that the myogenic effects of SP and physalaemin are mainly dependent on their ability to promote Ca2+ influx. 3. Eledoisin and kassinin evoked a contractile response in the absence of external Ca2+ and their myogenic activity was, to some extent, resistant to the inhibitory effect of nifedipine. This may indicate that an additional process, probably the release of an intracellularly bound Ca2+ store, participates in the mechanism by which eledoisin and kassinin contract the mouse distal colon. 4. After desensitization of the mouse distal colon to SP, the contractile activity provoked by SP or physalaemin was totally abolished whilst the responses evoked by eledoisin and kassinin were barely affected. These observations and other experimental findings indirectly support the assumption that the mouse distal colon could possess different tachykinin-binding sites.

A comparison of the effects of three substance P antagonists on tachykinin-stimulated [3H]-acetylcholine release in the guinea-pig ileum.

The potencies of three tachykinin antagonists [D-Pro4,D-Trp7,9,10]SP(4-11), [D-Arg1,D-Pro2,D-Trp7,9,Leu11]SP(1-11) and [D-Arg1,D-Trp7,9,Leu11]SP(1-11) (spantide) against eledoisin were examined in the guinea-pig ileum myenteric plexus, where a continuous superfusion system was employed to examine evoked release of [3H]-acetylcholine [( 3H]-ACh]); effects on mechanical activity of the preparations were also measured. Eledoisin was chosen as the standard tachykinin agonist since the rank order of potency observed in evoking release was eledoisin, kassinin, substance P, physalaemin; on this basis is may be presumed that an 'SP-E' type receptor was involved in the release process. The two undecapeptide antagonists both significantly reduced the response to eledoisin (10 nM) as assessed by both [3H]-ACh release and mechanical activity which under these conditions was largely dependent on ACh release, and the response levels could be restored by increasing the concentration of eledoisin to 100 nM. The pA2 values for the two antagonists were estimated as 5.3 for [D-Arg1,D-Pro2,D-Trp7,9,Leu11]SP(1-11) and 5.2 for [D-Arg1,D-Trp7,9,Leu11]SP(1-11). [D-Pro4,D-Trp7,9,10]SP(4-11) was markedly less potent with a pA2 value of less than 4.8. All three antagonists possessed considerable inherent stimulatory activity as measured both by [3H]-ACh release and mechanical activity, [D-Pro4,D-Trp7,9,10]SP(4-11) being the most active in this respect, a 10 microM concentration producing 50% of the response seen with 10 nM eledoisin. These findings are discussed both in relation to tachykinin receptor classifications and limitations in the use of such antagonists in the study of the role of tachykinins in neurotransmission.

The actions of some vasoactive polypeptides and their antagonists on the anococcygeus muscle.

1 The action of three polypeptides, bradykinin, substance P and eledoisin known to inhibit vascular smooth muscle has been examined on the anococcygeus muscle of the rat, cat and rabbit.2 In the atonic rat muscle, bradykinin and substance P had little or no effect on tone but eledoisin produced a sustained dose-related contraction which could be abolished by phentolamine (1 muM) and is, therefore, probably an indirect sympathomimetic effect. On the motor response to field stimulation of adrenergic nerves, bradykinin had no effect whereas both substance P and eledoisin reduced this response. The mechanism of action was further analysed with eledoisin by examining its effect on the response to noradrenaline. Eledoisin did not alter the dose-response curve to noradrenaline and its inhibitory action is likely, therefore, to be presynaptic.3 In the rat anococcygeus muscle in which the tone was raised by guanethidine or carbachol, bradykinin and substance P reduced this tone whereas eledoisin continued to exert a motor action. Compared with substance P the inhibitory effect of bradykinin appeared at lower concentrations (threshold 0.01 mug/ml), developed more rapidly and the size of the response was greater.4 The effect of bradykinin on the tonically contracted cat and rabbit anococcygeus muscles was examined in addition to that of the rat. In all three species bradykinin caused inhibition and the magnitude of the response was equal to the maximum effect of inhibitory nerve stimulation. None of the peptides affected the inhibitory response to nerve stimulation itself.5 The effects of three substances, hesperitin, khellin and apiin, reported in other tissues to antagonize the action of bradykinin were examined both on the inhibitory response to bradykinin and to field stimulation. None of them was able to inhibit either response, although they reduced tone when given by themselves. During these experiments it was found that ethanol antagonized the inhibitory response to field stimulation.6 The possibility that bradykinin or some related peptide might play a part in the inhibitory response to nerve stimulation in the anococcygeus is discussed.

Pharmacological characterization of a substance P antagonist, [D-Arg1,D-Pro2,D-Trp7,9,Leu11]-substance P.

The substance P antagonist [D-Arg1,D-Pro2,D-Trp7,9,Leu11]-substance P produced parallel log dose-response curve shifts to both substance P and eledoisin on five in vitro smooth muscle preparations. The slope values of Arunlakshana-Schild plots were not significantly different from unity suggesting that it acts as a simple competitive antagonist on all five preparations with an association constant (Ka) in the range of 0.3-1.5 X 10(6)M-1. The Ka value of the antagonist was always slightly greater when tested against eledoisin than against substance P; however, this difference appears too small to suggest that these two agonists are acting on different receptor sub-types.

Contractile responses to substance P and related peptides of the isolated muscularis mucosae of the guinea-pig oesophagus.

The site of action of substance P and related tachykinins with respect to isotonic contractions was examined on the isolated muscularis mucosae attached to the submucous plexus of the guinea-pig oesophagus. Substance P (greater than 30 nM) produced a concentration-dependent contraction of the muscularis mucosae (EC50 1.9 +/- 0.5 microM, n = 10). The contractions were rapid in onset (2 min or less), sustained, reversible by washing and the preparation did not show tachyphylaxis. Eledoisin and physalaemin produced similar sustained contraction of the muscularis mucosae. The order of sensitivity was eledoisin greater than substance P greater than physalaemin. Contractions induced by 1 microM of each tachykinin were not significantly modified by incubation of the tissue with substance P or eledoisin (10 microM for 30 min). The contractile responses to tachykinins were unaffected by tetrodotoxin (0.3 microM), atropine (0.3 microM), phentolamine (1 microM), chlorpheniramine (1 microM), methysergide (1 microM), baclofen (100 microM) and verapamil (10 microM), but were abolished by the incubation of the tissue with calcium-free, EGTA (0.1 mM)-containing Tyrode solution. A substance P antagonist, [D-Pro2, D-Trp7,9]-substance P (greater than 0.1 microM), produced a transient contraction of the muscularis mucosae and the smooth muscle regained its original tone within 6 to 10 min. Contractions to the tachykinins were now inhibited by the antagonist (0.1-10 microM) in a concentration-dependent manner, the order of sensitivity being physalaemin greater than substance P = eledoisin. The cholinergically mediated electrically (0.1 Hz, 0.5 ms, supramaximal voltage)-induced twitch contractions of the muscularis mucosae were not significantly modified by substance P (0.01-0.3 microM). 7 The present results indicate that substance P and related tachykinins contract the isolated muscularis mucosae of the guinea-pig oesophagus by a direct action on the smooth muscle, probably by stimulating SP-E receptors.

Hyperalgesia produced by intrathecal substance P and related peptides: desensitization and cross desensitization.

The hyperalgesic effect of intrathecally administered substance P (SP), physalaemin, eledoisin and eledoisin-related peptide (ERP) was investigated in the rat tail flick test. Hyperalgesia produced by SP (2.5-15 micrograms, 1.9-11 nmol) was maximal 10-20 min after injection, lasted 30 min and was dose-related. The effect was mimicked by all of the peptides examined. The rank order of potency was physalaemin greater than SP greater than eledoisin greater than ERP. Desensitization to the hyperalgesic effect of SP was produced by three repeated intrathecal injections. Rats desensitized to SP no longer responded to physalaemin or ERP, indicating cross-desensitization. Phentolamine continued to produce hyperalgesia following such desensitization. The demonstration of a hyperalgesic effect for SP provides further support for a role for SP in nociceptive transmission. The receptor mediating this effect appears to be a SP-P subtype. Cross-desensitization between peptides suggests an action on the same receptor.

Facilitation by tachykinins of neurotransmission in guinea-pig pulmonary parasympathetic nerves.

1. The effect of tachykinins on cholinergic neurotransmission was studied in an innervated tracheal tube preparation isolated from guinea-pigs anaesthetized with urethane. The tracheal tube was bathed in Krebs-Henseleit solution containing 5 microM indomethacin. 2. Neurokinin A (NKA), eledoisin (El) and substance P (SP) caused concentration-dependent increases in intraluminal pressure (ILP), with an order of potency NKA greater than El much greater than SP. 3. Low concentrations of tachykinins, that had little effect on ILP, caused an increase in the contractions elicited by stimulation of the preganglionic vagal nerve fibres and by postganglionic (transmural) stimulation. The order of potency was NKA greater than or equal to El greater than SP. Contractions induced by exogenous acetylcholine (ACh) were not increased by the tachykinins. 4. The magnitude of the tachykinin-induced augmentation of responses to nerve stimulation was inversely related to stimulation voltage and frequency. 5. These results suggest that tachykinins act on NK2 receptors, both on the trachealis muscle and on postganglionic pulmonary parasympathetic nerve terminals. Activation of the neuronal receptors may increase the probability of transmitter release from the nerve terminals.

Classification of tachykinin receptors in muscularis mucosae of opossum oesophagus.

1. Muscularis mucosae of the distal oesophagus of the opossum contracts in response to substance P and to a variety of tachykinins. To delineate the nature of the receptors present in this tissue, we evaluated contractile responses to substance P, neurokinin A, neurokinin B, eledoisin and analogues believed to be highly selective for NK-1, NK-2 and NK-3 receptors. In addition, the effects of prolonged exposure to each of these agents (10(-6) M or 10(-5) M) on contractile responses to substance P and to itself were evaluated. Similarly effects of prolonged exposure to the various tachykinins and their analogues on the field-stimulated responses of this muscle were studied. 2. All naturally occurring tachykinins were full agonists and differed in potency (comparing ED50 values) by less than ten fold. In nearly all cases there was cross tachyphylaxis between substance P and the other tachykinins and each reduced tonic responses to field stimulation, a response previously shown to be mediated by a substance P like agent. Eledoisin failed to cause tachyphylaxis under the conditions of these experiments. 3. When highly selective tachykinin analogues were used, only that believed to activate NK-1 receptors was a full agonist. [beta-Ala4,Sar9,MetO2(11)]SP(4-11) was also only slightly less potent than substance P. In contrast, an agonist selective for NK-2 (NK-A) receptors, [Nle10]NKA(4-10), and one selective for NK-3 (NK-B) receptors, [beta-Asp4, MePhe7]NKB(4-10) were unable to produce a response equal to 50% of the maximum even at 10(-5) M. However, all three selective tachykinin analogues reduced responses to substance P but not to carbachol. They usually reduced both phasic and tonic responses to field stimulation. 4. We conclude, based on this and earlier study, that the tachykinin receptors of opossum oesophagus muscularis mucosae recognize all naturally occurring tachykinins but may represent only NK-1 receptors. The ability of analogues selective for other types of tachykinin receptors to reduce responses to substance P raises the possibility that their selectivity depends in part on diminished efficacy rather than totally on diminished affinity at some classes of receptor.

The action of eledoisin on the peristaltic reflex of guinea-pig isolated ileum.

1. Low concentrations of eledoisin, acting from the serosal surface of the guinea-pig isolated ileum, had no effect on the peristaltic reflex, whereas in high concentrations it depressed or sometimes abolished this reflex.2. Eledoisin stimulated the peristaltic activity of the guinea-pig ileum subjected to continuously raised intraluminal pressure. This stimulatory effect could be produced regularly when the interval between additions of eledoisin was at least 20 min. When added at shorter intervals, tachyphylaxis to eledoisin developed, but its ability to promote peristaltic activity was restored by the addition of an anticholinesterase to the bath fluid. During tachyphylaxis to eledoisin, nicotine and dimethylphenylpiperazinium were unable to restore peristalsis.3. When the peristaltic reflex had been abolished by ganglion-blocking agents, morphine and morphine-like substances, or adrenaline, eledoisin restored the reflex. Eledoisin was much more effective in overcoming the blocking effect of hexamethonium, tetraethylammonium and azamethonium than that of nicotine or dimethylphenylpiperazinium.4. Eledoisin did not antagonize the inhibitory effects of atropine, hyoscine and hyoscine butylbromide.5. It is suggested that the stimulant effect of eledoisin may be due to a direct action on the smooth muscle and a release of acetylcholine from postganglionic nerve endings, but an effect on the intestinal ganglion cells cannot be excluded.

The action of ranatensin, a new polypeptide from amphibian skin, on the blood pressure of experimental animals.

1. The blood pressure response to ranatensin, an undecapeptide from the skin of the frog, Rana pipiens, has been studied in various experimental animals.2. Ranatensin raised blood pressure in the dog and rabbit. The response was not altered by atropine, phentolamine, propranolol or hexamethonium, suggesting a direct peripheral vasoconstrictor action. In both animals ranatensin was about one-tenth as potent as angiotensin. Tachyphylaxis to ranatensin did occur, but there was no cross-tachyphylaxis with angiotensin, bradykinin, or noradrenaline.3. The peptide lowered blood pressure in the monkey, being as potent as eledoisin. The response was not altered by atropine, phentolamine, propranolol, tripelennamine, tetraethylammonium, bretylium, or methysergide. This again suggests a direct peripheral action on vascular smooth muscle. There was no tachyphylaxis to the depressor action, nor was there cross-tachyphylaxis with angiotensin, eledoisin, bradykinin, or noradrenaline.4. Ranatensin did not alter the blood pressure in cats and had a variable action in the guinea-pig with a rapid onset of tachyphylaxis.5. Ranatensin has a variable effect on the blood pressure in the rat that is related to the basal level of blood pressure. When the blood pressure is high, the response to the peptide is hypotension. Ranatensin raises blood pressure in the rat when the basal blood pressure is low. The pressor response to ranatensin appears to be due, in part, to the release of noradrenaline from peripheral sympathetic nerve endings.6. The composite action of ranatensin on blood pressure of various experimental animals is unlike that of any other peptide. Its hypertensive action in the dog or rabbit, together with a potent hypotensive action in the monkey, readily distinguishes it from all other vasoactive peptides.

The action of bombesin on the systemic arterial blood pressure of some experimental animals.

1. The changes in blood pressure in response to parenteral administration of bombesin, the active tetradecapeptide of the skin of the European discoglossid frogs Bombina bombina and Bombina variegata variegata have been investigated in some experimental animals.2. In most species, the polypeptide elicited hypertension which was usually gradual in onset and slow to disappear. Blood pressure increases rarely exceeded 40-50 mmHg. At the beginning of an experiment some dose-response relationship could often be observed, but later tachyphylaxis developed. During an intravenous infusion of bombesin the rise in blood pressure could sometimes be maintained at a steady level as long as the infusion was continued, but at other times, the rise of pressure slowly subsided with continued administration of the polypeptide. In the rat and the chicken hypertension elicited by high doses of bombesin was often followed by secondary hypotension.3. Bombesin-induced hypertension was apparently not affected by pretreatment with either alpha- or beta-adrenergic blocking agents. Similarly secondary hypotension was not abolished by atropine. Thus, the effect of bombesin on vascular smooth muscle seems to be predominantly a direct one.4. Angiotensin was usually more potent than bombesin, and its effect on blood pressure was more rapid and of shorter duration. Tachyphylaxis to angiotensin was lacking or moderate.5. In sharp contrast to the other species, the monkey responded to bombesin with frank hypotension, which was usually proportional to the dose. In the monkey the hypotensive effect of bombesin was equal to, or greater than that of eledoisin or physalaemin and bombesin-induced hypotension was of longer duration than that of the other polypeptides. Tachyphylaxis was moderate for low and adequately spaced doses of the polypeptide, but prompt and intense for high doses. Long-lasting hypotension was obtained by intravenous infusion of bombesin, but repeated infusions caused tachyphylaxis. Bombesin-induced hypotension was not affected by pretreatment with atropine.6. Bombesin may be easily distinguished from all other known peptides active on vascular and extravascular smooth muscle by its effects on blood pressure. This does not apply to bombesin-like peptides, such as alytesin and ranatensin.

The action of substance P on contraction, inositol phospholipids and adenylate cyclase in rat small intestine.

The actions of substance P and eledoisin on contraction, [3H]inositol 1-phosphate and cAMP formation in the rat ileum have been compared. Eledoisin was considerably more potent than substance P on both contraction and [3H]inositol 1-phosphate production. Neither peptide altered the cAMP levels in the tissue. These results are discussed in relation to the substance P receptor sub-type present in the rat ileum, and its second messenger.