Erich Wünsch

Analysis of the Motor Effects Of 13-Norleucine Motilin on the Rabbit, Guinea Pig, Rat, and Human Alimentary Tract in Vitro

Motor effects of 13-norleucine motilin (13-Nle-M), a synthetic analog of motilin and biologically equivalent to the natural polypeptide, on the rabbit, guinea pig, rat, and human alimentary tract were investigated in vitro. Whereas guinea pig and rat preparations proved refractory to 13-Nle-M action, muscle strips of the stomach and upper small intestine from rabbits and man were highly sensitive to 13-Nle-M, contractile responses being elicited with concentrations of less than 2 times 10-minus 9 M. Although circular muscle from rabbit colon responded to 13-Nle-M, Taenia coli preparations were unaffected by the polypeptide; in man, the reverse was observed. Gallbladder, uterine, and vascular smooth muscle were unresponsive to 13-Nle-M. Pharmacological analysis revealed that the effects of 13-Nle-M on the gastrointestinal muscle are not mediated via nervous pathways: ganglion blockade by hexamethonium, blockade of axonal conduction by tetrodotoxin, or anticholinergic action by atropine failed to affect 13-Nle-M actions. It was therefore concluded that 13-Nle-M caused contractions by stimulating receptors on or in the muscle cell. By use of the antihistaminic pheniramine, histamine receptors could be differentiated from the site of 13-Nle-M action. As the contractile response to 13-Nle-M was abolished by the Ca++ antagonistic compound verapamil, a role for 13-Nle-M in the transport of Ca++ to the cytosol of intestinal smooth muscle might be considered.

Influence of enkephalin on K+-evoked efflux of putative neurotransmitters in rat brain

SummaryIn rat brain slices preincubated with various radiolabelled putative neurotransmitters, methionine-enkephalin diminished the potassium-evoked release of dopamine and acetylcholine. The effect was antagonised by naloxone. The potassium-induced efflux of three other neurotransmitters, histamine, 5-hydroxytryptamine and γ-aminobutyric acid, were unaffected by methionine-enkephalin. A probable physiological function for the endogenous ligands in specifically affecting the catecholaminergic and cholinergic transmission is suggested.

Intrathecal somatostatin in terminally ill patients. A report of two cases

&NA; Intrathecal morphine has been shown to be reliable in producing analgesia in patients with intractable cancer pain [5,8,9,11,13]. Recently, we have demonstrated that intrathecal somatostatin is as effective in the treatment of cancer pain as intrathecal morphine [3]. This report presents 2 cases in whom analgesia could be maintained for 60 and 25 days, respectively, under continuous intrathecal infusion of somatostatin by means of infusion devices.

Effect of the Peptide PHI-27 on Prolactin Release in vitro

The present study demonstrates that PHI, a peptide belonging to the glucagon-secretin group and thus structurally similar to VIP, can release prolactin from dispersed rat anterior pituitary cells and also causes release of prolactin from hemipituitaries. PHI-like immunoreactivity has previously been demonstrated in a hypothalamic system with nerve endings in the median eminence, and, taken together, these findings suggest that PHI may represent a physiologic prolactin-releasing factor.

Enkephalin regulates the levels of cyclic nucleotides in neuroblastoma × glioma hybrid cells

NARCOTICS do not normally occur in vivo. “Opiate receptors” must therefore have evolved to recognise endogenous ligands, which are mimicked by the opiates1. Indeed such compounds have been isolated2–5 and their structure elucidated as that of the two pentapeptides leucine and methionine-enkephalin6. Neuroblastoma × glioma hybrid cells 108CC15 display many properties characteristic of neurones7. In these cells morphine and other narcotics8–10 prevent the increase in the level of cyclic AMP that is caused by prostaglandin E1(PGE1)11. The opiates also increase the level of cyclic GMP in the hybrid cells12. On long term incubation with morphine, the hybrid cells show phenomena which can be interpreted as biochemical correlates of morphine tolerance, dependenceand withdrawal9,13. Here we report that leucine-enkephalin (leu-enk) has effects like those of opiates on the hybrid cells.

Evidence for a cyclic AMP system highly sensitive to secretin in gastric glands isolated from the rat fundus and antrum

The effects of secretin and vasointestinal peptide (VIP) on the production of cyclic AMP have been studied in gastric glands isolated by means of EDTA from rat fundic and antral mucosa. (1) In gastric fundus, secretin and VIP caused a time- and temperature-dependent stimulation of cyclic AMP production that was maximal when the test agents were incubated for 60 min at 20 degrees C in the presence of 0.5 mM 3-isobutyl-1-methylxanthine as a phosphodiesterase inhibitor. The dose-response curve was monophasic for both peptides, the production of cyclic AMP being sensitive to 10(-10) M secretin and to 5 . 10(-8) M VIP. Half-maximal stimulation was obtained with 2.9 10(-9) M secretin or 2 . 10(-7) M VIP and the maximal stimulation represented a 21-fold and a 19-fold increase above control for secretin and VIP, respectively. Histamine also stimulated cyclic AMP production, with a Km of about 5 . 10(-4) M. No additive effect on cyclic AMP production was oberved when secretin and VIP were simultaneously added at maximally active concentrations, while an additive effect was observed when secretin and histamine were added together. (2) In gastric antrum, the characteristics of the secretin- and VIP-stimulated cyclic AMP production were similar to those observed in gastric fundus. Histamine nevertheless failed to stimulate the formation of cyclic AMP in antral mucosa. (3) These data demonstrate the existence of a cyclic AMP system highly sensitive to secretin in gastric glands isolated from the rat fundus and antrum and suggest that VIP operates through this system. (4) It is proposed that the pepsinogen- and/or mucous-secreting cells are implicated in the regulation of cyclic AMP production by secretin in gastric glands of the rat.

Enkephalin evokes biochemical correlates of opiate tolerance and dependence in neuroblastoma X glioma hybrid cells

Since opiates are not normally occurring in animals, opiate receptors must be made to recognize endogenous agents that resemble opiates [ 11. Some of these compounds have been isolated [2-51 and characterized as two pcntapeptides named leucineand methionineenkephalin [6], for which structural similarity to opiates has been suggested [7,8]. The endogenous ligands of the opiate receptors compete with opiates for the same receptors [2,4] and cause analgesia if applied properly [9]. In the presence of prostaglandin El (PGE1) the neuroblastoma-glioma hybrid cells 108CCl5 [ 1 l] increase their intracellular concentration of adenosine 3’S’-cyclic monophosphate (cyclic AMP) [ 121. This increase is inhibited by acetylcholine [ 131, noradrepalin [ 141, morphine [ 15171 and enkephalin [ lo] . Besides these short-term actions of opiates on the hybrid cells, also long-term effects were observed which could be correlated with morphine tolerance, dependence and withdrawal phenomena: Hybrid cells that had been preincubated with morphine for many hours showed an increased response to PGEl [ 18,191. In the present communication we report that also enkephalins can cause such long-term effects. In addition we present evidence that the enkephalins are inactivated by incubation with the hybrid cells.

Effects of Vasoactive Intestinal Peptide on Resting and Pentagastrin-Stimulated Lower Esophageal Sphincter Pressure

Vasoactive intestinal peptide (VIP) administered as an intravenous infusion at different doses (0.8, 1.6, and 3.2 micrograms per kg per hr, respectively) inhibited dose-dependently the response of the lower esophageal sphincter to an intravenous injection of pentagastrin (0.6 microgram per kg) in 4 healthy volunteers. Inhibition ranged from about 20% (not significant) with the low dose to about 55% (P less than 0.05) with the high dose. On the other hand, the VIP doses employed did not substantially decrease basal lower esophageal sphincter pressure. Calculated on the basis of plasma levels of the respective peptides, the inhibitory effect of VIP was about one-third of that of secretin. Even at the smallest dose of VIP, plasma levels of radioimmunoassayable VIP (20 to 100 pmoles per liter) markedly exceeded those encountered normally (1 to 19 pmoles per liter). So, the data presented do not support the suggestion that normally circulating VIP essentially contributes to the physiological regulation of the lower esophageal sphincter pressure; they do not exclude, however, such a role for locally released VIP.

Secretin receptor activity in rat gastric glands. Binding studies, cAMP generation and pharmacology

We measured 125I-secretin binding to memebranes prepared from rat fundic glands and compared the abilities of natural and synthetic secretin (SN) analogs to inhibit 125I-secretin binding and to activate the cAMP generating system in glandular and subcellular preparations from the fundus and antrum. The natural peptides structurally related to porcine secretin (pSN) included: chicken secretin (cSN), vasoactive intestinal peptide (VIP), porcine peptide with N-terminal histidine and C-terminal isoleucine amide (PHI), helodermin, growth hormone releasing factors isolated from the rat hypothalamus (rhGRF-43, rhGRF-29) or from a human pancreatic tumour (hpGRF-40). These peptides inhibited the binding of 125I-secretin to rat fundic membranes: pSN>cSN>PHI, VIP and activated the cAMP generating system in fundic glands, according to the following order of potency; pSN>cSN>PHI, VIP>rhGRF-29>rhGRF-43. Porcine peptide with N-terminal tyrosine and C-terminal tyrosine (PYY), GIP, SOM and hpGRF-40 were inactive. Structural requirements for secretin receptor activity were evaluated with four synthetic secretin analogs corresponding to porcine secretin substituted at the N-terminal end by sequence portion of VIP, GIP, GLU and SOM: Ala4-Val5-SN(VIP-SN); Tyr1-Ala2-Glu3-SN (GIP-SN); Gln3-SN (GLU-SN) and Phe1-Phe1-Trp3-Lys4-SN (SOM-SN). The relative potencies of the analogs in fundic and antral preparations were: pSN>VIP-SN>VIP, GIP-SN>GLU-SN>SOM-SN for 125I-secretin displacement and cAMP production (glandular cAMP generation and adenylate cyclase activation). We conclude that secretin receptors in rat fundic and antral mucosae are pharmacologically identical and are preferentially localized in antral glands. The 1–8 N-terminal and 9–27 C-terminal parts of secretin sequence are of importance in determining secretin receptor interaction and activation in the rat gastric mucosae.

Secretin binding sites coupled with adenylate cyclase in rat fundic membranes

Specific binding sites for secretin have been identified in rat fundic membranes, using 125I-secretin. The binding was saturable, reversible, time and temperature dependent. Optimal pH for binding was around 7-7.5. Scatchard plots were compatible with the existence of 2 classes of receptors; the first class with a high affinity for secretin (apparent Kd of 4 x 10(-10) M) and a low binding capacity (150 fmol per mg membrane protein, i.e., 4,500 high affinity sites/cell) and a class of receptors with a lower affinity (Kd of 3 x 10(-9) M) and a higher binding capacity (580 fmol per mg membrane protein i.e., 17,400 sites/cell). Glucagon, gastric inhibitory polypeptide and somatostatin had no-effect on secretin binding. In contrast, VIP inhibited 125I-secretin binding and stimulated adenylate cyclase activity, in both cases at a 200-times lower potency than secretin (ID50 and Ka = 2 x 10(-7) M VIP). The properties of these secretin receptors strongly support the concept that secretin acts as a regulatory peptide on the rat gastric epithelium.