Action of FMRFamide-like peptides on porcine gastrointestinal motility in vitro.

Mechanical activity was recorded in circular and longitudinal smooth muscle preparations isolated from extensive regions of the porcine gastrointestinal tract in response to the FMRFamide-like neuropeptides F8Famide and A18Famide. In all preparations, the peptides were about equipotent in producing phasic contractions or enhancing spontaneous activity. The most prominent responses were observed in jejunal longitudinal strips which were on the average 91% (+/- 4% SEM, n = 15; 10(-6) M) of the histamine (10(-5) M) responses. The peptide-induced phasic activity was completely abolished by nifedipine but was unaffected by tetrodotoxin, atropine, phentolamine, yohimbine, phenoxybenzamine, propranolol, methysergide, cimetidine, indomethacin, levallorphane or naloxone. Both peptides enhanced acetylcholine-induced contractions. However, bovine ileum and guinea-pig taenia coli was not affected by these peptides. The results indicate that F8F- and A18F-amide contract porcine gastrointestinal smooth muscle by acting directly via non-opioid receptors on L-type calcium channels. In addition an increase of the sensitivity to cholinergic stimulation occurs.

Effects of gastrin-releasing peptide (GRP) on the mechanical activity of the human ileocaecal region in vitro.

Mechanical activity was recorded in muscle preparations isolated from the human ileocaecal region. Gastrin-releasing peptide (GRP, 10(-9)-10(-7) mol L-1) produced two types of response in the different muscle layers. Longitudinally cut strips showed a concentration-dependent increase in the rhythmic activity, whereas the circularly orientated layers generally reacted with a small decrease in tone. These effects could not be influenced by blockade of adrenergic or cholinergic receptors or nerve blockade with tetrodotoxin (TTX). Application of pentagastrin did not mimic the action of GRP. These findings suggest a direct action of GRP on smooth muscle via distinct receptors which have already been demonstrated to exist in human gastrointestinal tract. The opposite effects on circular and longitudinal strips might indicate a modulatory role of GRP in the control of ileocolonic transit.

Electrical and chemical control of smooth muscle activity of rabbit corpus cavernosum in vitro.

OBJECTIVES: This study sought to further elucidate the regulation of cavernous smooth muscle tone and to characterize mechanisms of cavernous activation and relaxation. METHODS: In isolated strips of rabbit corpus cavernosum, extracellular electrical and mechanical activity were recorded simultaneously before and after pharmacologic stimulation. RESULTS: Spontaneous mechanical activity was characterized by fast phasic contractions (frequency 6 to 30 min-1) associated with fluctuations of the extracellular electrical signals. Phasic activity was increased by blockade of potassium channels or by moderate activation of L-type calcium channels. Faster spikelike fluctuations occurred in the electrical activity, indicating the existence of spike discharges. All mechanical and electrical fluctuations were completely abolished by blockade of L-type calcium channels with nifedipine. CONCLUSIONS: Our results indicate that cavernous smooth muscle tone is regulated by both phasic and tonic activation mechanisms caused by the opening of L-type calcium channels and calcium influx through chemically controlled calcium influx/release.

Electrophysiological methods in smooth-muscle physiology. Corpus cavernosum in vitro.

The variety of the electrophysiological and mechanical properties of smooth muscle is abundant. In different organs they have different properties and also the orientation of the muscle layers can play a prominent role. Additionally, great species differences exist and some types of animal studies can be completely irrelevant for human physiology. The classic method for electrophysiologic studies of smooth muscle activity is the use of impaled glass microelectrodes. Also extracellular electrodes can be used but due to the method applied, only measurements of the changes in the true membrane potential can be obtained. Another approach is the so-called sucrose gap method which allows, in principle, access to the real membrane potential; due to methodological problems it is now rarely used. With corporal tissue, electrical measurements can be obtained with extracellular electrodes and, concomitantly, also measurements of the mechanical activity are possible. Spontaneous mechanical activity of isolated strips of rabbit corpus cavernosum is characterized by phasic contractions with a frequency of 6-30 min-1, accompanied by the extracellularly measured fluctuations of the membrane potential. Stimulation of the tissue with tetraethylammonium chloride (10 mmol/l) and noradrenaline (10(-5) mol/l) produced strong tonically appearing contractions, which were characterized by a relative electrical silence. Additional application of the nitric oxide donor 3-morpholino-syndominin (SIN-1, 5 X 10(-5) mol/l) relaxed the tissue and revealed phasic mechanical activity with associated electrical activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Regional differentiation of gastric and of pyloric smooth muscle in the pig: mechanical responses to acetylcholine, histamine, substance P, noradrenaline and adrenaline.

1. Mechanical activity was recorded in isolated muscle preparations from the circular and longitudinal layers of different regions of porcine stomach and from the pyloric ring. 2. In all gastric strips acetylcholine (10(-7)-10(-4) mol l-1), histamine (10(-7)-10(-5) mol l-1) and substance P (10(-9)-10(-7) mol l-1) elicited contractions. 3. In fundic strips the catecholamines, noradrenaline and adrenaline (10(-8)-10(-5) mol l-1), produced inhibitory responses at lower concentrations and excitatory responses at high concentrations. After blockade of beta-adrenoceptors by propranolol, a pure excitatory response remained which could be inhibited by alpha-adrenoceptor blockade with phentolamine. No responses were observed in corpus and antrum. 4. Strong contractions were induced by these catecholamines in circular muscle strips of the pyloric ring, in contrast to previous findings reported for human and canine preparations. The contractile response of strips from the inner layer of the pyloric ring corresponded to an average shortening of 25-30% of resting length, at a concentration of 10(-5) mol l-1 of noradrenaline or adrenaline. The responses of preparations from the outer layer of the pyloric ring were similar to those of the inner layer but generally weaker. The excitatory responses to the catecholamines were totally suppressed by 10(-5) mol l-1 phentolamine or prazosin but remained unaltered after pretreatment with 10(-5) mol l-1 propranolol or 10(-6) mol l-1 yohimbine, which indicates that they are mediated by alpha 1-adrenoceptors. 5. Application of substance P (10(-7) mol l-1) in the pyloric preparations caused a contraction as strong as that induced by noradrenaline or adrenaline. However, histamine, which is known to induce strong contractions in canine pylorus, had--as in human pylorus--no effect on porcine pylorus at concentrations up to 10(-5) mol l-1.

Responses of porcine gastric and duodenal smooth muscle to VIP.

1. Mechanical activity was recorded in isolated muscle preparations from circular and longitudinal layers of gastric fundus, corpus and antrum and from the duodenum of pigs, using conventional organ bath technique. Rectangular current pulses were applied to the muscle strips for electrical field stimulation (EFS). 2. Fundic and circular corpus preparations developed a marked spontaneous tonic activity. Vasoactive intestinal polypeptide (VIP, 10(-9)-10(-7) mol l-1) inhibited this spontaneous activity. This inhibitory effect was not affected by application of tetrodotoxin (TTX) showing its myogenic nature. 3. Pretreatment of fundic and circular corpus preparations with VIP reduced the excitatory responses to substance P, bombesin, serotonin and histamine, but it had no effect on the acetylcholine (ACh)-induced tonic and phasic activity. 4. Longitudinal duodenal preparations showed purely phasic activity which was almost insensitive to VIP. In circular duodenal preparations particularly strong spontaneous tonic contractions were observed which could be inhibited by VIP. 5. Circular duodenal preparations excised 3-5 cm postpyloric had a spontaneous tone which could reach up to 80% of the maximum contractions induced by 10(-4) mol l-1 ACh. These preparations were chosen for further pharmacological studies and for experiments with EFS. VIP was the most powerful substance for the inhibition of spontaneous tone, followed by serotonin, PGE2 and bradykinin. This type of preparation exhibited particularly strong inhibitory effects to EFS; even single stimuli could induce near maximum relaxation. The inhibition induced by EFS was unaffected by treatment with ATP, guanethidine, atropine, methysergide and apamin. TTX completely abolished the EFS-induced relaxation, showing its neurogenic nature. 6. Porcine circular duodenum is a good model for studying the transmitter system of the non-adrenergic, non-cholinergic (NANC) innervation. The results are consistent with the assumption that VIP is the transmitter in this system, although the very slow time-course of the VIP-induced inhibition in comparison with the EFS-induced inhibition is not consistent with this notion.

Effect of vasoactive intestinal peptide (VIP) on the mechanical activity and [3H] acetylcholine release in guinea-pig gastric muscle.

Muscle strips, 30 x 3 mm, were cut out in circular direction from the fundus region of the stomach. Mechanical activity was recorded by means of mechanoelectrical force transducers. Vasoactive intestinal peptide (VIP) at concentrations of 10(-9) to 10(-7) M caused a dose-dependent relaxation of muscle strips which was insensitive to tetrodotoxin. Field electrical stimulation (10 Hz, 1 ms, supramaximal voltage) produced contractions, which were blocked by atropine. VIP (10(-9) to 10(-7) M) dose-dependently decreased the amplitude of the electrically-induced contractions. VIP dose-dependently reduced the electrically-stimulated [3H] acetylcholine release. It is suggested that at least two different mechanisms are involved in the VIP-induced relaxation of the gastric muscle: a direct action on the smooth muscle and an indirect action mediated through cholinergic innervation.

Diameter and wall thickness recording of canine pylorus with implantable miniature ultrasonic transducers.

Outer diameter and thickness of the muscular wall of canine pylorus were measured simultaneously by determining the distance between pairs of implanted ultrasonic transducers, evaluating the sonic transit time with a digital sonometer. For the study of the motility in the gastroduodenal transit zone, the ultrasonically determined pyloric responses were compared with signals from conventional strain-gauge transducers sutured to the neighboring duodenum and gastric antrum. After stimulation of the gastrointestinal motility by an intravenous bolus injection of cholecystokinin octapeptide, pyloric contractions with a frequency of 5.2 min-1 could be recorded for some minutes; those contractions were independent of the more rapid antral and duodenal motility. Together with the observed tonic constriction of the pyloric ring, which could be inhibited by intravenous injection of adrenaline, an autonomous role of the gastroduodenal junction as a true sphincter is supported.

Bombesin--the most stimulating peptide of human gastric smooth muscle.

The mechanical activity of isolated muscle strips from different regions of 33 human stomachs was measured under auxotonic conditions. After application of bombesin (stepwise increases in organ bath concentrations 10(-9) to 10(-6) mol/l) the following in vitro effects were observed in human gastric muscle: (1) Bombesin stimulated both circular and longitudinal preparations from all regions of the human stomach and circular duodenum. (2) The quality of the responses to bombesin application was dependent on the general myogenic characteristics of the preparations of the different stomach regions. The contraction pattern changed at high bombesin concentrations in the organ bath to slower fluctuations. (3) Bombesin resulted in a maximal tonic response in the pyloric region preparations. An increase in tone was usually observed in the inner pyloric preparations, being typical for the region. (4) The effects of bombesin on the human stomach were stronger than the effects of many other regulatory peptides and of the reaction to acetylcholine. (5) The bombesin-induced effects were unaltered by pretreatment with atropine or TTX. (6) The response to bombesin frequently lasted for hours after washing before reassuming the original state.

Myogenic basis of motility in the pyloric region of human and canine stomachs.

In vitro gastric motility was investigated in 48 human and 16 canine stomachs by measuring the mechanical activity of isolated muscle strips under auxotonic conditions. For a precise regional differentiation, we recorded the mechanical activity of longitudinal and circular strips from fundus, corpus and antrum, as well as from circular preparations of the inner and outer layer of the pyloric sphincter and from the duodenum. The analysis showed that the anatomical division of the stomach into three distinct regions resulted physiologically in different patterns of contraction in vitro for each region. The fundus exhibited purely tonic spontaneous activity and a tonic contraction pattern after application of acetylcholine whereas the activity in the circular antrum was purely phasic. A combination of tonic and phasic contractions was found in the corpus and longitudinal antrum. A major difference in the basic spontaneous activity pattern was evident between man and dog. A gradient of intrinsic frequency in the stomach from proximal to distal was seen in the dog but not in man. A physiologically distinct area exists in the pyloric region of both species adjacent to the antrum and duodenum. The pyloric ring has its own spontaneous activity (minute-rhythm), reacts to the application of acetylcholine with relatively weak contractions and, unique to the dog, was delineated by histamine-induced maximal contractions. The results provide evidence that the pyloric ring is a distinct organ with specific functional characteristics in its cellular-myogenic structure.

Phasic and tonic contraction processes in the gastrointestinal tract.

The contraction mechanisms of GI smooth muscle can be differentiated with the aid of blockers of the voltage-controlled calcium channel (e.g. nifedipine). On the one hand, nifedipine-sensitive processes produce predominantly phasic-rhythmical contractions which can merge to sustained tonic activation, called 'tetanic tone', and which are combined with spike discharges and calcium influx. On the other hand, nifedipine-resistant and electrically silent processes produce a 'specific tone'. The cooperation of both processes in one and the same cell leads to a great diversity of patterns of smooth muscle activity. 'Specific tone' dominates in regions with reservoir function and contributes significantly to the contractions of GI sphincters, with great differences between sphincter types, the various species, and, in man, also between individuals.

Contractile action of gastrin-releasing peptide on isolated preparations of human gastroduodenal muscle.

Mechanical activity was recorded in muscle preparations isolated from different regions of the human stomach (circular and longitudinal strips from fundus, corpus and antrum) and duodenum. Application of gastrin-releasing peptide (GRP, 10(-9) to 10(-7) mol/l) caused a concentration-dependent increase in the activity in all stomach strips, the height and the pattern of contraction was similar to the acetylcholine (ACh) responses (10(-7) to 10(-5) mol/l). Longitudinally cut duodenal strips were also excitable by GRP. Circularly cut duodenal strips, however, showed no responses to GRP. Both layers were excitable by ACh. The most prominent effect of GRP on longitudinal duodenal strips near the jejunum was a tonically appearing activation, which could reach up to 180% of the maximum ACh-induced activation.

Continuous recording of blood vessel diameter in vitro during perfusion with regulated pressure patterns.

A system is described for continuously measuring blood vessel diameter during perfusion with constant pressure or with fluctuating pressure of preselected patterns. An electromechanical modulator controls the inflow of the perfusion solution, keeping the actual pressure in the blood vessel at a preselected value via a feed-back circuit. The outer diameter of the vessel can be simultaneously and continuously recorded at several chosen positions with the aid of a multichannel video angiometer. The whole set-up is suitable for small vessels of a diameter reaching down to 0.5 mm.

Comparison of the inhibitory effects of nifedipine, nitroglycerin, and nitroprusside sodium on different types of activation in canine coronary arteries, with comparative studies in human coronary arteries.

The mechanical activity of helical strips from canine coronary arteries was recorded. Vessels from normal hearts and from hearts with a collateral circulation after experimental occlusion were investigated. Two types of activation were studied: (a) activation induced by noradrenaline, 10(-5) M, after blockade of beta-adrenoceptors with propranolol (NA activation) and (b) activation induced by application of tetraethylammonium (TEA), 10(-2) M, after blockade of endogenous prostaglandin synthesis by indomethacin, 2 X 10(-6) M (TEA activation). TEA activation was more sensitive to nifedipine (ED50, 2 X 10(-8) M) than to nitroglycerin (ED50, 10(-7) M) or nitroprusside sodium (ED50, 3 X 10(-7) M). NA activation, on the other hand, was more sensitive to nitroglycerin (ED50, 10(-8) M) or nitroprusside sodium (ED50, 2 X 10(-8) M) than to nifedipine (ED50, 6 X 10(-8) M). In comparative studies with human coronary arteries excised postmortem, spontaneous rhythmic activity was often observed. This phasic activity was, as in TEA activation of canine coronary arteries, more sensitive to fedipine than to nitroglycerin. The differences between human and canine coronary smooth muscle are discussed.

Mechanical activity of isolated canine coronary arteries after coronary occlusion.

Collateral vessels from dogs showed good mechanical responses, with well-developed inhibitory responses, for example to noradrenaline. Endogenous inhibitory processes, which resulted in a low spontaneous basal tone, were also well-developed in most tissues. However, signs of hyperactivity were observed in some cases - and this might be the most interesting result. This hyperactivity was characterized by a strong phasic spontaneous activity. This might be an abnormality associated with the rapid proliferation of smooth muscle cells in collateral vessels. It is quite possible that such states of hyperactivity may play a role in human pathology, Producing coronary spasm and leading to angina or infarction, perhaps even in hearts with well developed collaterals.