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Background/Objectives : A balanced nutritious diet is vital during pregnancy for both the mother and the baby. The aims of this longitudinal study were to (1) determine any differences in macro- and micronutrient intakes in a group of UK women during pregnancy (and in the post-partum period) who were overweight or obese (BMI mean (SD) 31.1 (2.9)) at antenatal booking appointment compared with women who were within the ideal BMI range (BMI mean (SD) 22.1 (1.9)) and (2) determine the proportion of women who met the Harmonized Average Requirements (H-AR) during pregnancy. Methods : Forty-two participants attended four clinic visits: three during pregnancy, one in each trimester (V1, V2, and V3), and one 12 weeks post-partum (V4). Dietary intake was assessed by 24 h diet recall and analysed using DietPlan6. Results : There were no differences in energy and macronutrient intakes between overweight/obese and lean women. During pregnancy, the overweight/obese women consumed a mean (SD) of 3238 (941) sodium (mg per day), which was approximately 10% higher compared to 2934 (732) sodium (mg per day) in the lean group ( p = 0.015). Dietary and supplemental intakes of the sodium to potassium ratio was 21% higher in overweight/obese women compared to the lean women, p = 0.0031 (mean (SD) of 1.17 (0.35) versus 0.93 (0.28), respectively). Virtually all women did not meet the H-AR for niacin, folate, and vitamin D through dietary intake alone. Conclusions : The 'eat better and not more' message during pregnancy is supported.

Arachidonic acid (AA) and docosahexaenoic acid (DHA) are important for neurological development. The aim was to determine the distribution and relative enrichment of AA and DHA among lipoprotein fractions prior to pregnancy, throughout gestation and in the post-partum period. Our hypothesis was that in pregnancy, in contrast to the non-pregnant state, AA and DHA are carried in highest concentration in the very low density lipoprotein (VLDL) fraction secondary to increased gestational liver triglyceride secretion. Two independent prospective, observational cohort studies carried out in Glasgow were combined; one early in pregnancy and one later in pregnancy with post-partum follow up. Across the pregnancy timeline plasma lipoproteins were isolated using sequential ultracentrifugation and lipoprotein fatty acids were extracted and analysed by gas chromatography. High density lipoprotein (HDL) had the highest concentration of AA and DHA compared to other lipoproteins. HDL became progressively enriched in the proportion of triglycerides at 16 weeks of gestation, which peaked at 35 weeks and returned to baseline at 13 weeks postpartum. HDL DHA per HDL-cholesterol and HDL DHA per apoA-I became progressively enriched at 16 weeks of gestation, peaked at 25 weeks and returned to baseline at 13 weeks postpartum, whereas HDL AA (per HDL-C or HDL-apoA-I) did not differ. DHA is carried primarily in HDL rather than VLDL. HDL has anti-oxidant properties that might afford DHA protection against oxidation., (Copyright © 2020. Published by Elsevier Ltd.)

Context: Maternal body mass index (BMI) is associated with increased birth weight but does not explain all the variance in fetal adiposity., Objective: To assess the contribution of maternal body fat distribution to offspring birth weight and adiposity., Design: Longitudinal study throughout gestation and at delivery., Setting: Women recruited at 12 weeks of gestation and followed up at 26 and 36 weeks. Cord blood was collected at delivery., Patients: Pregnant women (n = 45) with BMI 18.0 to 46.3 kg/m2 and healthy pregnancy outcome., Methods: Maternal first trimester abdominal subcutaneous and visceral adipose tissue thickness (SAT and VAT) was assessed by ultrasound., Main Outcome Measures: Maternal body fat distribution, maternal and cord plasma glucose and lipid concentrations, placental weight, birth weight, and fetal adiposity assessed by cord blood leptin., Results: VAT was the only anthropometric measure independently associated with birth weight centile (r2 adjusted 15.8%, P = .002). BMI was associated with trimester 2 and trimesters 1 through 3 area under the curve (AUC) glucose and insulin resistance (Homeostatic Model Assessment). SAT alone predicted trimester 2 lipoprotein lipase (LPL) mass (a marker of adipocyte insulin sensitivity) (11.3%, P = .017). VAT was associated with fetal triglyceride (9.3%, P = .047). Placental weight was the only independent predictor of fetal adiposity (48%, P < .001). Maternal trimester 2 and AUC LPL were inversely associated with fetal adiposity (r = -0.69, P = .001 and r = -0.58, P = .006, respectively)., Conclusions: Maternal VAT provides additional information to BMI for prediction of birth weight. VAT may be a marker of reduced SAT expansion and increased availability of maternal fatty acids for placental transport., (© Endocrine Society 2019. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Delayed gastric emptying symptoms are often reported after chemotherapy. This study aims to characterise the effects of chemotherapy on gastric neuro-muscular function. Patients undergoing elective surgery for oesophago-gastric cancer were recruited. Acetylcholinesterase, nNOS, ghrelin receptor and motilin expressions were studied in gastric sections from patients receiving no chemotherapy (n = 3) or oesophageal (n = 2) or gastric (n = 2) chemotherapy. A scoring system quantified staining intensity (0-3; no staining to strong). Stomach sections were separately suspended in tissue baths for electrical field stimulation (EFS) and exposure to erythromycin or carbachol; three patients had no chemotherapy; four completed cisplatin-based chemotherapy within 6 weeks prior to surgery. AChE expression was markedly decreased after chemotherapy (scores 2.3 ± 0.7, 0.5 ± 0.2 and 0 ± 0 in non-chemotherapy, oesophageal- and gastric-chemotherapy groups (p < 0.03 each) respectively. Ghrelin receptor and motilin expression tended to increase (ghrelin: 0.7 ± 0.4 vs 2.0 ± 0.4 and 1.2 ± 0.2 respectively; p = 0.04 and p = 0.2; motilin: 0.7 ± 0.5 vs 2.2 ± 0.5 and 2.0 ± 0.7; p = 0.06 and p = 0.16). Maximal contraction to carbachol was 3.7 ± 0.7 g and 1.9 ± 0.8 g (longitudinal muscle) and 3.4 ± 0.4 g and 1.6 ± 0.6 (circular) in non-chemotherapy and chemotherapy tissues respectively (p < 0.05 each). There were loss of AChE and reduction in contractility to carbachol. The tendency for ghrelin receptors to increase suggests an attempt to upregulate compensating systems. Our study offers a mechanism by which chemotherapy markedly alters neuro-muscular gastric function.

The release of calcitonin gene-related peptide (CGRP) plays a key role gastrointestinal tract homeostasis. We aimed to investigate mechanisms that mediate CGRP release from the rat colon in vitro. Colon segments were stimulated and the amount of CGRP released was measured using an enzyme immunoassay. Capsaicin and low pH induced significant increases in CGRP release which was shown to be mediated by TRPV1 activation as demonstrated with the TRPV1 antagonists CTPC and capsazepine. The mast cell degranulator, compound 48/80 significantly increased CGRP release an effect that was blocked in the presence of the mast cell stabilizer, ketotifen and the selective Gi inhibitor benzalkonium chloride. The addition of a mixture of inflammatory mediators containing pro-inflammatory cytokines, 5HT, bradykinin and PGE2 showed no effect at neutral pH but at low pH a significant additive effect was observed. We conclude that CGRP release in the rat distal colon occurs in response to mast cell degranulation, inflammatory mediators, low pH and capsaicin and describe a role for TRPV1 receptors in mediating the response.

Optimisation of a series of benzazepine sulfonamide hit compounds identified from high throughput screening led to the discovery of a new series of tractable, potent motilin receptor agonists.

There is an urgent clinical need for a safe, efficacious stimulant of gastric emptying; current therapies include erythromycin (an antibiotic with additional properties which preclude chronic use) and metoclopramide (a 5-hydroxytryptamine type 4 receptor agonist and an antagonist at brain D2 receptors, associated with movement disorders). To move away from the complex motilide structure of erythromycin, a small molecule motilin receptor agonist, GSK962040, was identified and characterized. The compound was evaluated using recombinant human receptors, rabbit and human isolated stomach preparations known to respond to motilin and in vivo, by measuring its ability to increase defecation in conscious rabbits. At the human motilin receptor, the pEC50 (the negative logarithm to base 10 of the EC50 value, the concentration of agonist that produces 50% of the maximal response) values for GSK962040 and erythromycin as agonists were, respectively, 7.9 and 7.3; GSK962040 had no significant activity at a range of other receptors (including ghrelin), ion channels and enzymes. In rabbit gastric antrum, GSK962040 300 nmol L(-1)-10 micromol L(-1) caused a prolonged facilitation of the amplitude of cholinergically mediated contractions, to a maximum of 248 +/- 47% at 3 micromol L(-1). In human-isolated stomach, GSK962040 10 micromol L(-1), erythromycin 10 micromol L(-1) and [Nle13]-motilin 100 nmol L(-1), each caused muscle contraction of similar amplitude. In conscious rabbits, intravenous doses of 5 mg kg(-1) GSK962040 or 10 mg kg(-1) erythromycin significantly increased faecal output over a 2-h period. Together, these data show that GSK962040, a non-motilide structure, selectively activates the motilin receptor. Simplification of the structural requirements to activate this receptor greatly facilitates the design of potentially new medicines for gastroparesis.

P2Y receptors have been reported to modulate gastrointestinal functions. The newest family member is the nucleotide-sugar receptor P2Y14. P2ry14 mRNA was detected throughout the rat gut, with the highest level being in the forestomach. We investigated the role of the receptor in stomach motility using cognate agonists and knockout (KO) mice. In rat isolated forestomach, 100 microM UDP-glucose and 100 muM UDP-galactose both increased the baseline muscle tension (BMT) by 6.2+/-0.6 and 1.6+/-0.6 mN (P<0.05, n=3-4), respectively, and the amplitude of contractions during electrical field stimulation (EFS) by 3.7+/-1.7 and 4.3+/-2.5 mN (P<0.05, n=3-4), respectively. In forestomach from wild-type (WT) mice, 100 microM UDP-glucose increased the BMT by 1.0+/-0.1 mN (P<0.05, n=6) but this effect was lost in the KO mice (change of -0.1+/-0.1 mN, n=6). The 100 microM UDP-glucose also increased the contraction amplitude during EFS in this tissue from the WT animals (0.9+/-0.4 mN, P < 0.05, n=6) but not from the KO mice (0.0+/-0.2 mN, n=6). In vivo, UDP-glucose at 2,000 mg/kg ip reduced gastric emptying in rats by 49.7% (P<0.05, n=4-6) and in WT and KO mice by 56.1 and 66.2%, respectively (P<0.05, n=7-10) vs. saline-treated control animals. There was no significant difference in gastric emptying between WT and KO animals receiving either saline or d-glucose. These results demonstrate a novel function of the P2Y14 receptor associated with contractility in the rodent stomach that does not lead to altered gastric emptying after receptor deletion and an ability of UDP-glucose to delay gastric emptying without involving the P2Y14 receptor.

N-(3-fluorophenyl)-1-[(4-([(3S)-3-methyl-1-piperazinyl]methyl)phenyl)acetyl]-4-piperidinamine 12 (GSK962040) is a novel small molecule motilin receptor agonist. It possesses excellent activity at the recombinant human motilin receptor and also at the native rabbit motilin receptor where its agonist activity results in potentiation of the amplitude of neuronal-mediated contractions of isolated gastric antrum tissue. Compound 12 also possesses highly promising pharmacokinetic profiles in both rat and dog, and these results, in combination with further profiling in human native tissue and an in vivo model of gastrointestinal transit in the rabbit, have led to its selection as a candidate for further development.

High-throughput screening resulted in the identification of a series of novel motilin receptor agonists with relatively low molecular weights. The series originated from an array of biphenyl derivatives designed to target 7-transmembrane (7-TM) receptors. Further investigation of the structure-activity relationship within the series resulted in the identification of compound (22) as a potent and selective agonist at the motilin receptor.

Optimisation of urea (5), identified from high throughput screening and subsequent array chemistry, has resulted in the identification of pyridine carboxamide (33) which is a potent motilin receptor agonist possessing favourable physicochemical and ADME profiles. Compound (33) has demonstrated prokinetic-like activity both in vitro and in vivo in the rabbit and therefore represents a promising novel small molecule motilin receptor agonist for further evaluation as a gastroprokinetic agent.

Acetylcholinesterase (AChE) inhibitors stimulate gastrointestinal (GI) motility and are potential treatments of conditions associated with inadequate GI motility. The ability of itopride to facilitate neuronally (predominantly cholinergic) mediated contractions of rat isolated stomach, evoked by electrical field stimulation (EFS), has been compared with other cholinesterase inhibitors and with tegaserod, a clinically effective prokinetic and non-selective 5-HT(4) receptor agonist which also facilitates GI cholinergic function. Neostigmine greatly increased EFS-evoked contractions over a narrow concentration range (0.01-1 microM; 754+/-337% facilitation at 1 microM); higher concentrations (1, 3 microM) also increased muscle tension. Donepezil increased EFS-evoked contractions gradually over the full range of concentrations (0.01-10 microM; maximum increase 516+/-20% at 10 microM). Itopride increased the contractions even more gradually, rising to 188+/-84% at 10 microM. The butyrylcholinesterase inhibitor iso-OMPA 0.01-10 microM also increased EFS-evoked contractions, to a maximum of 36+/-5.0% at 10 microM, similar to that caused by tegaserod (35+/-5.2% increase at 1 microM). The effects of tegaserod, but not itopride were inhibited by the 5-HT(4) receptor antagonist SB-204070A 0.3 microM. In rat isolated colon, neostigmine was again the most efficacious, causing a defined maximum increase in EFS-evoked contractions (343+/-82% at 10 microM), without changing muscle tension. Maximum increases caused by donepezil and itopride were, respectively, 57.6+/-20 and 43+/-15% at 10 microM. These data indicate that the abilities of different AChE inhibitors to increase GI cholinergic activity differ markedly. Understanding the reasons is essential if AChE inhibitors are to be optimally developed as GI prokinetics.

5-Hydroxytryptamine (5-HT4) receptor agonists increase gastrointestinal (GI) motility by enhancing enteric acetylcholine release which is then metabolized by acetylcholinesterase (AChE) to inactive metabolites. As both AChE inhibitors and, more usually, 5-HT4 receptor agonists are used to increase GI motility, an understanding of how these two different types of drugs might interact becomes of great importance. Our aim was to investigate the hypothesis that the effect of AChE inhibition will synergise with the ability of 5-HT4 receptor agonism to increase cholinergic activity, leading to an effect greater than that evoked by each action alone. We tested the activity of the 5-HT4 receptor agonist, prucalopride (10 nmol L(-1)-30 micromol L(-1)) and an AChE inhibitor, neostigmine (1 nmol L(-1)-10 micromol L(-1)) on cholinergically mediated contractions elicited by electrical field stimulation of human isolated colon circular muscle and rat isolated forestomach longitudinal strips. The experiments with human colon were performed in the presence of an inhibitor of nitric oxide synthase (N(omega)-nitro-l-arginine methyl ester, 300 micromol L(-1)). Prucalopride and neostigmine both enhanced cholinergic contractions in both tissues. The effect of prucalopride was inhibited in both tissues by SB-204070, a 5-HT4 receptor antagonist. In the presence of a minimum effective concentration of neostigmine (30 nmol L(-1)) and a submaximum concentration of prucalopride (3 micromol L(-1)) the enhancement of contractions was greater than either compound alone in both tissues. These data demonstrate that the combination of prucalopride and neostigmine potentiate cholinergic contractions more than their arithmetic sum of their individual values. The results suggest that a synergy between 5-HT4 receptor agonism and AChE inhibition could be established pharmacologically which could be utilized as a novel prokinetic approach to functional GI disorders.

Background and Purpose: Lubiprostone (Amitiza), a possible ClC-2 channel opener derived from prostaglandin E(1) and indicated for the treatment of constipation, increases chloride ion transport and fluid secretion into the intestinal lumen. As lubiprostone may also directly modulate gastrointestinal motility, we investigated its actions and the possible involvement of prostaglandin EP receptor activation on rat and human isolated gastrointestinal preparations., Experimental Approach: Rat and human isolated preparations were mounted in tissue baths for isometric recording. The effects of lubiprostone on muscle tension and on electrically stimulated, neuronal contractions were investigated in the absence and presence of EP receptor antagonists., Key Results: In rat and human stomach longitudinal muscle, lubiprostone induced a contraction (pEC(50) of 7.0+/-0.0, n=4 and 6.4+/-0.2, n=3, respectively), which was inhibited by pretreatment with the EP(1) receptor antagonist, EP(1)A 300 nM (pEC(50) reduced to 6.2+/-0.2, n=6), but not by the EP(3) or EP(4) receptor antagonists (L-798106 and GW627368X, respectively, 1 microM, P>0.05). Lubiprostone also reduced electrically stimulated, neuronal contractions in rat and human colon circular muscle preparations (pIC(50) of 8.9+/-0.4, n=7 and 8.7+/-0.9, n=6, respectively), an effect mediated pre-junctionally. This effect was reduced by the EP(4) receptor antagonist (pIC(50) of 6.7+/-1.1, n=7 and 7.7+/-0.4, n=6, respectively) but not by EP(1) or EP(3) receptor antagonists., Conclusions and Implications: In rats and humans, lubiprostone contracts stomach longitudinal muscle and inhibits neuronally mediated contractions of colon circular muscle. Experiments are now needed to determine if this additional activity of lubiprostone contributes to its clinical efficacy and/or side-effect profile.

Background and Purpose: Motilin or 5-HT4 receptor agonists stimulate gastrointestinal motility. Differences in activity are suggested but direct comparisons are few. A method was devised to directly compare the gastric prokinetic activities of motilin, the motilin receptor agonist, erythromycin, and the 5-HT4 receptor agonist, tegaserod., Experimental Approach: Gastric prokinetic-like activity was assessed by measuring the ability to facilitate cholinergically-mediated contractions evoked by electrical field stimulation (EFS) in rabbit isolated stomach. Comparisons were made between potency, maximal activity and duration of responses., Key Results: Rabbit motilin (r.motilin) 0.003-0.3 microM, [Nle13]motilin 0.003-0.3 microM, erythromycin 0.3-10 microM and tegaserod 0.1-10 microM caused concentration - dependent potentiation of EFS-evoked contractions. The potency ranking was r.motilin = [Nle13]motilin > tegaserod > erythromycin. The Emax ranking was r.motilin = [Nle13]motilin = erythromycin > tegaserod. Responses to r.motilin and [Nle13]motilin faded rapidly (t1/2 9 and 11 min, respectively) whereas those to erythromycin and tegaserod were maintained longer (t1/2 24 and 28 min). The difference did not appear to be due to peptide degradation. A second application of [Nle13]motilin was excitatory after 60 min contact and fade of the initial response (responses to 0.03 and 0.1 microM [Nle13]motilin were not different from those caused by the first application)., Conclusions and Implications: Prokinetic-like activities of the 5-HT4 agonist tegaserod and the motilin receptor agonists were compared by measuring changes in cholinergically-mediated contractions. This novel approach highlighted important differences between classes (greater Emax of motilin, compared with tegaserod) and for the first time, within each class (short t1/2 for motilin, compared with erythromycin).

Previous studies have demonstrated mixed inhibitory and facilitatory effects of 5-hydroxytryptamine-4 (5-HT(4)) receptor agonists on electrical field stimulation (EFS)-induced responses in human isolated colon. Here we report three types of responses to EFS in human isolated colon circular muscle: monophasic cholinergic contraction during EFS, biphasic response (nitrergic relaxation during EFS followed by cholinergic contraction after termination of EFS) and triphasic response (cholinergic contraction followed by nitrergic relaxation during EFS and a tachykininergic contraction after EFS). The effects of two 5-HT(4) receptor agonists, prucalopride and tegaserod were then investigated on monophasic responses only. Each compound inhibited contractions during EFS in a concentration-dependent manner. In the presence of N(omega)-nitro-l-arginine methyl ester (l-NAME) however, prucalopride and tegaserod enhanced the contractions in a concentration-dependent manner. In strips where the tone was elevated with substance-P and treated with scopolamine, EFS-induced relaxations were enhanced by the two agonists. The above observed effects by the two agonists were abolished by 5-HT(4) receptor antagonist SB-204070. The two agonists did not alter the tone raised by substance-P in the presence of scopolamine and l-NAME and did not affect carbachol-induced contractions in the presence of tetrodotoxin. These results suggest that in the circular muscle of human colon, 5-HT(4) receptor agonists simultaneously facilitate the activity of neurones which release the inhibitory and excitatory neurotransmitters, nitric oxide and acetylcholine respectively.

Calcitonin gene-related peptide (CGRP), a potent vasodilator, has been implicated in the pathogenesis of migraine. Its release from adult rat trigeminal neurons in culture was shown to be markedly increased by the activation of adenylate cyclase with forskolin. Modulation of this secretion was investigated by a number of agents with known inhibitory effects on cAMP generation mediated via receptor coupling to G(i/o) proteins. Significantly, forskolin-stimulated CGRP release could be closely correlated with the phosphorylation of the protein kinase A (PKA) substrate cyclic AMP response element-binding protein (CREB). Forskolin-stimulated CGRP release could be potently and effectively inhibited by the adenosine A(1) receptor-selective agonist GR79236X (pIC(50) = 7.7 +/- 0.1, maximal inhibition 65 +/- 2.5% at 300 nM), whereas the A(2A) (CGS21680) and the A(3) (2-chloro-N(6)-(3-iodobenzyl)-adenosine-5'-N-methyluronamide) receptor-selective agonists were without effect. GR79236X-mediated inhibition was abolished by the A(1) receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine. Immunocytochemical studies and Western analysis revealed the presence of adenosine A(1) receptors on trigeminal neurons. However, despite the additional detection of 5-hydroxytryptamine (5-HT)(1B) receptors on these cells, the clinically effective antimigraine 5-HT(1B/1D) agonist sumatriptan did not inhibit forskolin-stimulated CGRP release nor did it show any effect on the concomitant CREB phosphorylation. In contrast, the mu-opioid agonist fentanyl elicited a 74 +/- 4% reduction in CGRP levels. Forskolin-stimulated CGRP release and CREB phosphorylation could be mimicked by incubation of the cells with chlorophenylthio-cAMP and blocked by pretreatment with the PKA inhibitor myrPKI(14-22). Taken together, the present data confirm the PKA-dependence of forskolin-stimulated CGRP release and suggest that A(1) adenosine agonists may warrant further investigation in models of migraine and neurogenic inflammation.

Constrained analogues 5-7 of the potent and subtype selective somatostatin mimetic 1 were prepared by incorporating conformational constraints into the nine-membered heterocyclic scaffold. Each constrained peptidomimetic showed an altered activity profile relative to lead compound 1, with compound 7 exhibiting a 25-fold and 2-fold binding enhancement against somatostatin receptor subtypes sst4 and sst5, respectively.

A series of trisubstituted hydantoins has been prepared by a versatile solid phase route employing primary alcohols, amines and amino acids as the monomeric building blocks. Several compounds showed submicromolar affinity in binding assays at recombinant human somatostatin receptors.

1. The mouse somatostatin (SRIF) sst2 receptor exists in two splice variants, sst2(a) and sst2(b), which differ in their intracellular carboxy-termini only. The murine sst2(b) receptor was reported to be less prone to agonist-induced desensitization as compared with the sst2(a) receptor. To determine whether a sst2(b) splice variant with similar functional characteristics exists in the rat, we have isolated a cDNA fragment from rat gastric mucosa encoding a sst2(b) receptor and expressed the full-length protein in CHO-K1 cells for functional characterization. 2. This study provides the first evidence for the occurrence in the rat of the sst2(b) receptor, which has a 15 amino acid carboxy-terminus differing in composition to the 38 amino acid C-terminus of the rat sst2(a) receptor. 3. In CHO-K1 cells expressing rat recombinant sst2(a) or sst2(b) receptors, SRIF caused concentration-dependent increases in extracellular acidification rates (EAR) with pEC50 values of 9.0 and 9.9, respectively. Pre-treatment with pertussis toxin (Ptx) caused a rightward displacement of the SRIF concentration-effect curves with pEC50 values of 8.3 (sst2(a) and 8.4 (sst2(b)). 4. SRIF (3 pM-3 nM) also caused concentration-dependent inhibition of forskolin-stimulated cyclic AMP formation in CHO-sst2(a) cells (pIC50 10.5) and CHO-sst2(b) cells (pIC50 10.4). The degree of inhibition was less with higher concentrations of SRIF resulting in bell-shaped concentration-effect curves. Following pre-treatment with Ptx, the inhibitory effect of SRIF was abolished and SRIF caused only increases in cyclic AMP formation. 5. Both the SRIF-induced increases in EAR and inhibition of cyclic AMP formation were susceptible to agonist-induced desensitization, but this was less apparent following pre-treatment with Ptx. 6. This demonstrates that the operational characteristics of the recombinant rat sst2(a) and sst2(b) receptors are broadly similar. Both isoforms couple to Ptx-sensitive as well as -insensitive G proteins and are equally prone to agonist-induced desensitization.

1. Somatostatin (SRIF) causes a concentration-dependent inhibition of neurotransmission in guinea-pig ileum and vas deferens as well as negative inotropy in guinea-pig isolated right atrium. The SRIF receptors mediating these effects have now been further characterized by use of the peptides BIM-23027, BIM-23056 and L-362855, reported as selective for the recombinant SRIF receptor types, sst2, sst3 and sst5, respectively. 2. BIM-23027 was a highly potent agonist at causing an inhibition of neurotransmission in the guinea-pig ileum (EC50 value 1.9 nM), being about 3 times more potent than SRIF (EC50 value 6.8 nM). In contrast, in both guinea-pig vas deferens and right atrial preparations, BIM-23027 was a relatively weak agonist being at least 30-100 times weaker than SRIF. In guinea-pig atria, BIM-23027 (3 microM) antagonized the negative inotropic action of SRIF28 (apparent pKB = 5.9 +/- 0.1) but had no effect on the negative inotropic action of cyclohexyladenosine. 3. The inhibitory effect of BIM-23027 in the guinea-pig ileum was readily desensitized. Prior exposure to BIM-23027 (0.3 microM) markedly attenuated the inhibitory effect of SRIF but had no effect on the inhibitory action of clonidine suggesting that BIM-23027 and SRIF act via a common receptor mechanism. 4. L-362855 caused a concentration-dependent inhibition of neurotransmission in both the guinea-pig ileum and vas deferens as well as causing negative inotropy in the guinea-pig atrium but was at least 30-100 times weaker than SRIF. In guinea-pig isolated atria, L-362855 (3 microM) did not antagonize the negative inotropic action of SRIF28. 5. BIM-23056 in concentrations up to 1 microM was inactive as an agonist in guinea-pig isolated ileum, vas deferens and atrium and did not antagonize the inhibitory actions of SRIF in any of these preparations.6. The results from this study support our previous contention that the sst2 receptor type mediates inhibition of neurotransmission by SRIF in the guinea-pig ileum. The SRIF receptor type mediating inhibition of neurotransmission in the guinea-pig vas deferens appears different, but similar, to that mediating negative inotropy in the atrium. However the characteristics of these latter receptors appear different from that of the recombinant sst2, sst3 and sst5 receptors for SRIF described for rat and man.