Antagonist effects of seglitide (MK 678) at somatostatin receptors in guinea-pig isolated right atria

Cortisol as a Target for Treating Mental Disorders: A Promising Avenue for Therapy

Cortisol, commonly known as the "stress hormone," plays a critical role in the body's response to stress. Elevated cortisol levels have been associated with various mental disorders, including anxiety, depression, and post-traumatic stress disorder. Consequently, researchers have explored cortisol modulation as a promising avenue for treating these conditions. However, the availability of research on cortisol as a therapeutic option for mental disorders is limited, and existing studies employ diverse methodologies and outcome measures. This review article aimed to provide insights into different treatment approaches, both pharmacological and non-pharmacological, which can effectively modulate cortisol levels. Pharmacological interventions involve the use of substances, such as somatostatin analogs, dopamine agonists, corticotropin-releasing hormone antagonists, and cortisol synthesis inhibitors. Additionally, non-pharmacological techniques, including cognitivebehavioral therapy, herbs and supplements, transcranial magnetic stimulation, lifestyle changes, and surgery, have been investigated to reduce cortisol levels. The emerging evidence suggests that cortisol modulation could be a promising treatment option for mental disorders. However, more research is needed to fully understand the effectiveness and safety of these therapies.

Characterization of somatostatin receptor subtypes

Somatostatin regulates endocrine and exocrine secretion, possesses antiproliferative properties and acts as a neurotransmitter/neuromodulator in the central nervous system. These effects are mediated by G protein-coupled receptors, of which at least five types have been cloned (sstr1-5). In radioligand-binding studies we have compared the binding properties of sstr1-5 with their activities as somatostatin receptors. All receptors identified so far bind somatostatin-14 and somatostatin-28 with high affinity. The similarities in receptor sequence and in the binding profiles of short synthetic somatostastin analogues such as octreotide, MK 678 or RC 160 for sstr1-5 indicate the existence of two classes of receptors sstr1/sstr4 with virtually no or very low affinity and sstr2/sstr3/sstr5 with intermediate to high affinity for the short somatostatin analogues. All five receptors mediate inhibition of adenylyl cyclase; this inhibition is sensitive to pertussis toxin. In vitro and in vivo studies suggest the importance of sstr2 and/or sstr5 in the inhibition of growth hormone release. The sstr2 receptor is apparently the predominant subtype expressed in somatostatin receptor-positive tumours. Evidence exists for the importance of sstr5 receptors in insulin secretion and sstr1 receptors in oncology. Somatostatin receptor-selective agonists and antagonists will help to explore new therapeutic opportunities in oncology as well as in endocrine and gastrointestinal disorders and those of the central nervous system.

Hemodynamic effects of intravenous somatostatin administered in the postoperative period

OBJECTIVE

To evaluate the hemodynamic effects of intravenous somatostatin administration in patients during the early postoperative period.

DESIGN

Prospective, case-controlled trial.

SETTING

Postanesthesia care unit.

PATIENTS

Ten postoperative, noncirrhotic, American Society of Anesthesiologists physical status II patients, after resection of nonsecretory (i.e., non-neuroendocrine) tumors. No patient received any vasoactive medication perioperatively.

INTERVENTIONS

Three hours after the end of surgery, normal saline or somatostatin was intravenously administered in two phases: a) in phase 1, patients received a 20-mL bolus of normal saline within 1 min, followed by a continuous infusion of 20 mL of normal saline for the next 30 mins. Patients were left undisturbed for the subsequent 30 mins. b) in phase 2, patients received somatostatin (3.5 micrograms/kg, 20-mL bolus) over 1 min, followed by a continuous infusion of somatostatin (3.5 micrograms/kg/hr) for 72 hrs.

MEASUREMENTS AND MAIN RESULTS

Anesthesia was managed according to a prospectively designed protocol. Patients' hemodynamic profiles and pressure waveforms were recorded immediately before the bolus injections of normal saline and somatostatin, and at every minute thereafter for 30 mins. Bolus doses of somatostatin produced a transient, nonsignificant decrease in heart rate, along with short-lived increases in systolic arterial pressure, diastolic arterial pressure, systolic pulmonary arterial pressure, diastolic pulmonary arterial pressure, and central venous pressure.

CONCLUSION

Bolus intravenous somatostatin administered postoperatively after tumor resection in patients produced transient cardiovascular changes that were not sustained during a subsequent continuous infusion.

A somatostatin receptor inhibits noradrenaline release from chick sympathetic neurons through pertussis toxin-sensitive mechanisms: comparison with the action of alpha 2-adrenoceptors

The effects of somatostatin and analogues were investigated in cultures of chick sympathetic neurons. Electrically evoked tritium overflow from cultures labelled with [3H]noradrenaline was reduced by somatostatin-14 in a concentration-dependent manner, with half maximal effects at 0.3 nM and a maximum of 45% inhibition. Somatostatin-28 was equipotent to somatostatin-14 (half maximal concentration at 0.5 nM), and seglitide was less potent, the effects being half maximal at 4.2 nM. The inhibitory action of somatostatin-14 on stimulation-evoked overflow desensitized within minutes at 100 nM, but not at 10 nM, and was abolished by a pretreatment of neurons with pertussis toxin. All somatostatin analogues reduced voltage-activated Ca2+ currents recorded in the whole-cell configuration of the patch-clamp technique, with somatostatin-14 being equipotent to somatostatin-28, but more potent than seglitide. However, the inhibition of Ca2+ currents occurred at concentrations more than ten-fold higher than those required for the reduction of stimulation evoked 3H overflow. The action of somatostatin upon Ca2+ currents was also abolished by pertussis toxin and desensitized within minutes. In preceding experiments, alpha 2-adrenoceptor activation had been found to reduce transmitter release and Ca2+ currents of chick sympathetic neurons through a pertussis toxin-sensitive mechanism. In the present study, the alpha 2-adrenergic agonist UK 14,304 completely occluded the inhibition of Ca2+ currents and of electrically evoked overflow by somatostatin-14. Neither UK 14,304 nor somatostatin affected the resting membrane potential or voltage-dependent K+ currents. These results demonstrate that chick sympathetic neurons possess SRIF1 type somatostatin receptors which control transmitter release. This effect is mediated by pertussis toxin-sensitive GTP binding proteins and apparently involves an inhibition of voltage-activated Ca2+ channels, but not a modulation of K+ channels. Since alpha 2-adrenergic agonists share all of these actions and occlude the effects of somatostatin, alpha 2-adrenoceptors and SRIF1 receptors seem to regulate sympathetic transmitter release via common signalling mechanisms.

Further evidence from functional studies for somatostatin receptor heterogeneity in guinea-pig isolated ileum, vas deferens and right atrium

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.

Pharmacological identity between somatostatin SS-2 binding sites and SSTR-1 receptors

Somatostatin (SRIF) SS-2 binding sites were originally defined in rat brain cerebral cortex membranes using [125I]Tyr11-SRIF-14 in the presence of 120 mM NaCl. These sites were characterized by their high affinity for SRIF-14 and SRIF-28, but very low affinity for cyclic peptides such as octreotide (SMS 201-995) and seglitide (MK 678). The characteristics of SS-2 sites are reminiscent of 125I]CGP 23996-labelled sites in rat brain which have been termed SRIF-2 sites. In the present study, the pharmacological profile of SS-2 sites was determined in radioligand binding studies performed in rat cortex membranes using [125I]SRIF-14 in the presence of 120 mM NaCl and compared to that of human SSTR-1 receptors expressed in human embryonic kidney (HEK 293) cells, using [125I]SRIF-14. The rank orders of affinity of a variety of SRIF analogues and synthetic peptides for SS-2 binding sites and recombinant human SSTR-1 receptors were very similar and correlated highly significantly (r = 0.99). However, SS-2 binding correlated also with binding to recombinant SSTR-4 receptors (r = 0.91). Autoradiographic studies were performed using the radioligand [125I]CGP 23996 which has been claimed to label selectively SRIF-2 binding sites and compared with the distribution of SSTR-1 receptor mRNA determined using in situ hybridization in rat brain. Although some overlap was observed between the distribution of SSTR-1 mRNA and [125I]CGP 23996 binding sites, the latter were clearly more widespread, suggesting this ligand to label SSTR-1 and other sites. In addition, inhibition of forskolin-stimulated adenylate cyclase was investigated in HEK 293 cells transfected with human SSTR-1 receptors; a variety of SRIF analogues and short synthetic peptides behaved as agonists at adenylate cyclase and displayed a rank order of potency highly similar to that observed for these compounds at SS-2 binding sites. Seglitide acted as an antagonist at SSTR-1 receptor mediated inhibition of adenylate cyclase activity with a pKB of 4.42. It is concluded that the pharmacological profile of SS-2 binding sites resembles most closely that of SSTR-1 receptors (although similarities with SSTR-4 receptors were observed), that [125I]CGP 23996 labels presumably several SRIF receptors in rat brain, and that SSTR-1 receptors are negatively and efficiently coupled to adenylate cyclase activity.

Classification and nomenclature of somatostatin receptors

There is considerable controversy about the classification and nomenclature of somatostatin receptors. To date, five distinct receptor genes have been cloned and named chronologically according to their respective publication dates, but two were unfortunately given the same appellation (SSTR4). Consensually, a nomenclature for the recombinant receptors has been agreed according to IUPHAR guidelines (sst1, sst2, sst3, sst4, and sst5). However, a more informative classification is to be preferred for the future, employing all classification criteria in an integrated scheme. It is already apparent that the five recombinant receptors fall into two classes or groups, on the basis of not only structure but also pharmacological characteristics. One class (already referred to by some as SRIF1) appears to comprise sst2, sst3 and sst5 receptor subtypes. The other class (SRIF2) appears to comprise the other two recombinant receptor subtypes (sst1 and sst4). This promising approach is discussed but it is acknowledged that much more data from endogenous receptors in whole tissues are needed before further recommendations on somatostatin receptor nomenclature can be made.

Molecular pharmacology of somatostatin receptors

The neuropeptide somatostatin (SRIF) is widely expressed in the brain and in the periphery in two main forms, SRIF-14 and SRIF-28. Similarly, the presence of SRIF receptors throughout the whole body has been reported. SRIF produces a variety of effects including modulation of hormone release (e.g. GH, glucagon, insulin), of neurotransmitter release (e.g. acetylcholine, dopamine, 5-HT), and its own release is modulated by many neurotransmitters. SRIF affects cognitive and behavioural processes, the endocrine system, the gastrointestinal tract and the cardiovascular system and also has tumor growth inhibiting effects. Initially, two classes of SRIF receptors have been proposed on the basis of biochemical and functional studies. However, the recent cloning of five putative SRIF receptor subtypes which belong to the G-protein coupled receptor superfamily suggests that SRIF mediates its various effects via a whole family of receptors. Here we review, in this new context, the molecular pharmacology of the SRIF receptor subtypes present in the brain and in the periphery, and address the question of nomenclature of SRIF receptors.

Mediation by SRIF1 receptors of the contractile action of somatostatin in rat isolated distal colon; studies using some novel SRIF analogues

1. The motor effects of somatostatin-14 (SRIF), and several SRIF peptide analogues were investigated on the rat isolated distal colon. The objective of these studies was to characterize the receptor mediating the contractile action of SRIF by comparing the relative agonist potencies of a range of SRIF analogues. 2. SRIF (1 nM-1 microM) produced concentration-dependent contractions with an EC50 value of approximately 10 nM. Contractile responses induced by SRIF were insensitive to atropine (1 microM) or naloxone (1 microM) but abolished by tetrodotoxin (1 microM). Somatostatin-28 (SRIF28), also induced concentration-dependent contractions and was equipotent with SRIF. Phosphoramidon (1 microM) and amastatin (10 microM) did not increase the potency of either SRIF or SRIF28. 3. The SRIF peptide analogues, octreotide, SRIF25, seglitide, angiopeptin and CGP23996 (1 nM-1 microM) produced contractile responses in the rat distal colon, each having similar potency and maximal activity relative to SRIF. The SSTR2 receptor-selective hexapeptide, BIM23027 (0.1 nM-1 microM), and the SRIF stereoisomer, D-Trp8-SRIF (0.1 nM-1 microM), were the most potent agonists examined being approximately 12 and 7 times more potent than SRIF, respectively. In contrast, the SSTR5 receptor-selective analogue, L362,855, was approximately 120 times weaker than SRIF, whilst the SSTR3 receptor-selective analogue, BIM23056, was inactive at concentrations up to 3 microM. 4. The putative SRIF receptor antagonist, (cyclo(7-aminoheptanoyl Phe-D-Trp-Lys-Thr[Bzl]))(CPP) (1 microM), had no agonist activity and had no effect on contractions induced by SRIF. 5. The contractile actions of BIM23027 and seglitide were subject to pronounced desensitization. Desensitization of preparations by BIM23027 (0.3 JIM) abolished the contractile action of SRIF andSRIF28 but had no effect on contractions produced by acetylcholine (0.1 nM-I1M), suggesting thatBIM23027, SRIF and SRIF28 act via a common receptor mechanism.6. In conclusion, the rat isolated distal colon contracts in response to SRIF and a number of SRIF analogues. Seglitide and octreotide exhibited similar potency and maximal activity relative to SRIF,suggesting that in the rat colon the receptor mediating contraction belongs to the SRIF,-receptor group,of which the recombinant SSTR2, SSTR3 and SSTR5 receptors appear to be subtypes. The high potency of BIM23027, the weak agonist activity of L362,855 and the lack of activity exhibited by BIM23056suggests that the SRIF receptor mediating contraction in the rat distal colon is similar to there combinant SSTR2 receptor.

Characterization of somatostatin receptors in guinea-pig isolated ileum, vas deferens and right atrium

1. Somatostatin14 (SS14) inhibits neurogenically mediated contractile responses in guinea-pig ileum and vas deferens and exerts a direct negative inotropic action in guinea-pig spontaneously beating right atrium. In this study, the receptors mediating these inhibitory effects have been characterized by comparing the potencies of several cyclic somatostatin analogues. 2. In the guinea-pig ileum, SS14, somatostatin28 (SS28), somatostatin25 (SS25) and several smaller cyclic somatostatin analogues including octreotide, angiopeptin and CGP 23996, inhibited neurogenically mediated contractile responses, each being of similar potency. 3. In contrast, in the guinea-pig vas deferens and right atrium, SS28 was about 30 times more potent than SS14. However, although angiopeptin was nearly as potent as SS14 as an agonist in the vas deferens, in guinea-pig atrium angiopeptin had low intrinsic activity and antagonized the negative inotropic action of both SS14 and SS28 (pKB values of 7.4 and 7.2, respectively). CGP 23996 was 2-7 times weaker than SS14 in guinea-pig vas deferens and atria. 4. Phosphoramidon (1 microM) and amastatin (10 microM) did not influence the potency of SS14 or SS28 in either the guinea-pig ileum or right atrium. In the guinea-pig vas deferens, phosphoramidon and amastatin did not affect the potency of SS28, but enhanced the potency of SS14 about 5 fold. Despite the presence of phosphoramidon and amastatin, SS28 was still more potent than SS14 in the vas deferens. 5. The putative somatostatin receptor blocking drug, cyclo(7-aminoheptanoyl Phe-D-Trp-Lys-Thr[Brl]) (CPP; 1 microM), did not antagonize the effects of either SS14 or SS28 in ileum, vas deferens or atrial preparations. 6. Somatostatin14 did not modify the contractile action of carbachol or alpha,beta-methylene ATP in the ileum and vas deferens respectively, suggesting that the site of the inhibitory effects on neurogenically mediated contractile responses in both preparations was pre-junctional. Consistent with this conclusion was the observation that the inhibitory effect of SS14 was markedly and inversely related to the external Ca2+concentration. The inhibitory effect of SS14 in guinea-pig atrium was only partly dependent on the external Ca2+ concentration.7. The somatostatin receptors mediating the inhibitory effect of SS14 in the ileum and vas deferens can be distinguished by the differential relative potencies of SS14 and SS28. In the former, SS14 and SS28 have similar potency whilst in the latter SS28 is much more potent. In this respect, the somatostatin receptor mediating negative inotropy in the guinea-pig right atrium appears similar to that identified in the vas deferens.8. We suggest that the somatostatin receptor mediating inhibition of neurogenic contraction in the ileum is similar to the recently cloned SSTR2 receptor. In contrast, the somatostatin receptor mediating negative inotropy in the atrium and inhibition of neurotransmission in the vas deferens appears similar to the SSTR4 receptor which recognises SS28 with higher affinity than SS14.