Heterogeneous Cellular Response of Primary and Metastatic Human Gastric Adenocarcinoma Cell Lines to Magnoflorine and Its Additive Interaction with Docetaxel

Gastric cancer is the most common cancer and remains the leading cause of cancer death worldwide. In this study, the anticancer action of magnoflorine isolated via counter-current chromatography from the methanolic extract of Berberis vulgaris root against gastric cancer in models of primary ACC-201 and AGS and metastatic MKN-74 and NCI-N87 cell lines was analyzed. Cell viability and proliferation were tested through the use of MTT and BrdU tests, respectively. Cell cycle progression and apoptosis were evaluated using flow cytometry. The interaction of magnoflorine and docetaxel has been examined through isobolographic analysis. Moreover, potential toxicity was verified in zebrafish in an in vivo model. Gastric cancer cell lines revealed different responses to magnoflorine treatment with regard to viability/proliferation, apoptosis induction and cell cycle inhibition without any undesirable changes in the development of larval zebrafish at the tested concentrations. What is more, magnoflorine in combination with docetaxel produced an additive pharmacological interaction in all studied gastric cancer cell lines, which may suggest a complementary mechanism of action of both compounds. Taken together, these findings provide a foundation for the possibility of magnoflorine as a potential therapeutic approach for gastric cancer and merits further investigation, which may pave the way for clinical uses of magnoflorine.

Short-term risk prediction after major lower limb amputation: PERCEIVE study

BACKGROUND

The accuracy with which healthcare professionals (HCPs) and risk prediction tools predict outcomes after major lower limb amputation (MLLA) is uncertain. The aim of this study was to evaluate the accuracy of predicting short-term (30 days after MLLA) mortality, morbidity, and revisional surgery.

METHODS

The PERCEIVE (PrEdiction of Risk and Communication of outcomE following major lower limb amputation: a collaboratIVE) study was launched on 1 October 2020. It was an international multicentre study, including adults undergoing MLLA for complications of peripheral arterial disease and/or diabetes. Preoperative predictions of 30-day mortality, morbidity, and MLLA revision by surgeons and anaesthetists were recorded. Probabilities from relevant risk prediction tools were calculated. Evaluation of accuracy included measures of discrimination, calibration, and overall performance.

RESULTS

Some 537 patients were included. HCPs had acceptable discrimination in predicting mortality (931 predictions; C-statistic 0.758) and MLLA revision (565 predictions; C-statistic 0.756), but were poor at predicting morbidity (980 predictions; C-statistic 0.616). They overpredicted the risk of all outcomes. All except three risk prediction tools had worse discrimination than HCPs for predicting mortality (C-statistics 0.789, 0.774, and 0.773); two of these significantly overestimated the risk compared with HCPs. SORT version 2 (the only tool incorporating HCP predictions) demonstrated better calibration and overall performance (Brier score 0.082) than HCPs. Tools predicting morbidity and MLLA revision had poor discrimination (C-statistics 0.520 and 0.679).

CONCLUSION

Clinicians predicted mortality and MLLA revision well, but predicted morbidity poorly. They overestimated the risk of mortality, morbidity, and MLLA revision. Most short-term risk prediction tools had poorer discrimination or calibration than HCPs. The best method of predicting mortality was a statistical tool that incorporated HCP estimation.

Association of SARC-F Score and Rockwood Clinical Frailty Scale with CT-Derived Muscle Mass in Patients with Aortic Aneurysms

OBJECTIVES

Patients with aortic aneurysms (AA) are often co-morbid and susceptible to frailty. Low core muscle mass has been used as a surrogate marker of sarcopenia and indicator of frailty. This study aimed to assess association between core muscle mass with sarcopenia screening tool SARC-F and Clinical Frailty Scale (CFS) in patients with AA.

METHODS

Prospective audit of patients in pre-operative aortic clinic between 01/07/2019-31/01/2020 including frailty assessment using Rockwood CFS and sarcopenia screening using SARC-F questionnaire. Psoas and sartorius muscle area were measured on pre-operative CT scans and adjusted for height. Association was assessed using Spearman's rank correlation coefficient.

RESULTS

Of 84 patients assessed, median age was 75 years [72,82], 84.5% were men, 65.5% were multimorbid and 63.1% had polypharmacy. Nineteen percent were identified as frail (CFS score >3) and 6.1% positively screened for sarcopenia (SARC-F score 4 or more). Median psoas area (PMA) at L3 was 5.6cm2/m2 [4.8,6.6] and L4 was 7.4cm2/m2 [6.3,8.6]. Median sartorius area (SMA) was 1.8 cm2/m2 [1.5,2.2]. CFS demonstrated weak but statistically significant negative correlation with height-adjusted PMA at L3 (r=-0.25, p=0.034) but not at L4 (r=-0.23, p=0.051) or with SMA (r=-0.22, p=0.065). No association was observed between SARC-F score and PMA or SMA (L3 PMA r=-0.015, p=0.9; L4 PMA r=-0.0014, p= 0.99; SMA r=-0.051, p=0.67).

CONCLUSION

CFS showed higher association with CT-derived muscle mass than SARC-F. Comprehensive pre-operative risk-stratification tools which incorporate frailty assessment and body composition analysis may assist in decision making for surgery and allow opportunity for pre-habilitation.

Clinical Outcomes after Oat Beta-Glucans Dietary Treatment in Gastritis Patients

The prevalence of gastritis in humans is constantly growing and a prediction of an increase in this health problem is observed in many countries. For this reason, effective dietary therapies are sought that can alleviate the course of this disease. The objective of this study was to determine the effect of chemically pure oat beta-glucan preparations with different molar masses, low or high, used for 30 days in patients with histologically diagnosed chronic gastritis. The study enrolled 48 people of both genders of different ages recruited from 129 patients with a gastritis diagnosis. Before and after the therapy, hematological, biochemical, immunological and redox balance parameters were determined in the blood and the number of lactic acid bacteria and SCFA concentrations in the feces. Our results demonstrated a beneficial effect of oat beta-glucans with high molar mass in chronic gastritis in humans, resulting in reduced mucosal damage and healthy changes in SCFA fecal concentration and peripheral blood serum glutathione metabolism and antioxidant defense parameters. This fraction of a highly purified oat beta-glucan is safe for humans. Its action is effective after 30 days of use, which sheds new light on the nutritional treatment of chronic gastritis.

The inhibitory effect of combination treatment with leptin and cannabinoid CB1 receptor agonist on food intake and body weight gain is mediated by serotonin 1B and 2C receptors

Previous studies reported that the co-injection of leptin and cannabinoid CB1 receptor antagonists reduces food intake and body weight in rats, and this effect is more profound than that induced by these compounds individually. Additionally, serotonin mediates the effects of numerous anorectic drugs. To investigate whether serotonin interacts with leptin and endocannabinoids to affect food intake and body weight, we administered 5-hydroxytryptamine(HT)1B and 5-hydroxytryptamine(HT)2C serotonin receptor antagonists (3 mg/kg GR 127935 and 0.5 mg/kg SB 242084, respectively) to male Wistar rats treated simultaneously with leptin (100 μg/kg) and the CB1 receptor inverse agonist AM 251 (1 mg/kg) for 3 days. In accordance with previous findings, the co-injection of leptin and AM 251, but not the individual injection of each drug, resulted in a significant decrease in food intake and body weight gain. Blockade of the 5-HT1B and 5-HT2C receptors completely abolished the leptin- and AM 251-induced anorectic and body-weight-reducing effects. These results suggest that serotonin mediates the leptin- and AM 251-dependent regulation of feeding behavior in rats via the 5-HT1B and 5-HT2C receptors.

Synthesis, characterization, and pharmacological evaluation of novel azolo- and azinothiazinones containing 2,4-dihydroxyphenyl substituent as anticancer agents

ABSTRACT

We reported the synthesis and characterization of a series of azolo- and azino[1,3]thiazinones containing the 2,4-dihydroxyphenyl substituent. The compounds were prepared by a new one-step reaction of aryl-modified sulfinylbis[(2,4-dihydroxyphenyl)methanethione]s and the corresponding aminoazolo(azino)carboxamides. Their chemical structures were confirmed by IR, NMR: 1H, 13C, HSQC, and EI-MS spectral data. The compounds inhibited proliferation and viability of lung cancer A549, colon cancer HT-29, and glioma C6 cells in a structure- and concentration-dependent manner. The activity of some analogues was below 10 μmol dm-3 (IC50). Glioma C6 cells were the most sensitive to tested compounds. Generally, the derivatives were not toxic for the skin fibroblast HSF culture. Moreover, some of them exerted a protective effect on the treated normal cells. Evaluation of compound properties in silico showed that they possess significant drug-like characteristics and most of them display a low toxicity.

GRAPHICAL ABSTRACT

The influence od melatonin receptors antagonists, luzindole and 4-phenyl-2-propionamidotetralin (4-P-PDOT), on melatonin-dependent vasopressin and adrenocorticotropic hormone (ACTH) release from the rat hypothalamo-hypophysial system. In vitro and in vivo studies

Melatonin exerts its biological role acting via G protein-coupled membrane receptors - MT1 and MT2, as well as through cytoplasmic and/or nuclear receptors. Melatonin has previously been shown to change vasopressin (AVP) and adrenocorticotropic hormone (ACTH) secretion dependently on its concentration. To determine whether the response of vasopressinergic neurones to different concentrations of melatonin is mediated through the membrane MT1 and/or MT2 receptors, the influence of luzindole - an antagonist of both MT1 and MT2 receptors, and 4-phenyl-2-propionamidotetralin (4-P-PDOT) - a selective MT2 receptor antagonist, on melatonin-dependent AVP release from the rat hypothalamo-neurohypophysial (H-NH) system was studied in vitro (melatonin at the concentrations of 10(-9), 10(-7) and 10(-3) M) and in vivo (melatonin at the concentrations of 10(-9) and 10(-7) M). Moreover, the second goal of this study was to find out whether melatonin receptors MT1 and/or MT2 are involved in the regulation of ACTH and corticosterone secretion into the blood. We have demonstrated that melatonin, at the concentrations of 10(-9) and 10(-7) M, significantly inhibited AVP secretion from isolated rat H-NH explants when antagonists solvent (i.e. 0.1% DMSO) was present in the medium. Neither luzindole, nor 4-P-PDOT, applied without melatonin, did influence AVP release in vitro. Luzindole applied together with melatonin (10(-7) M and 10(-9) M) significantly suppressed melatonin-dependent effect, while 4-PPDOT did not eliminate the inhibitory influence of 10(-7) M and 10(-9) M melatonin on AVP secretion from isolated rat H-NH explants. Melatonin at a concentration of 10(-3) M significantly increased AVP release when the H-NH explants were incubated in the medium containing luzindole or 4-P-PDOT. Under present experimental in vivo conditions, infused intracerebroventricularly (i.c.v.) melatonin, at a concentration close to its physiological level in the blood, significantly diminished AVP secretion into the blood, however, at higher concentration (10(-7) M) it remained inactive in this process. Moreover, melatonin at both concentrations of 10(-9) M and 10(-7) M, was able to inhibit AVP secretion into the blood (and increase its neurohypophysial content) when animals were previously i.c.v. injected with 4-P-PDOT, but not with luzindole. Blood plasma concentration of ACTH was diminished significantly by 10(-7) M melatonin in DMSO-infused, but not in luzindole- or 4-P-PDOT-injected rats, however, it remained inactive in modifying the corticosterone blood plasma concentrations in any of the studied subgroups. The present study demonstrates that subtype MT1 membrane receptor may contribute to the inhibitory effect of physiological concentration of melatonin on functional regulation of vasopressinergic neurones in the rat. However, for the stimulatory effect of pharmacological dose of the hormone on AVP secretion in vitro, mechanisms different from membrane MT1/MT2 receptors are involved. The present experiment do not determines whether MT1 and/or MT2 receptors affect the function of the rat pituitary-adrenal cortex axis.

Chlorpyrifos and cypermethrin induce apoptosis in human neuroblastoma cell line SH-SY5Y

Our previous in vivo studies showed that chlorpyrifos (CPF) and cypermethrin (CM) in a mixture dermally administered, strongly inhibited cholinesterase activity in plasma and the brain and were very toxic to the rat central nervous system. In this work, the mechanisms of neurotoxicity have not been elucidated. We used human undifferentiated SH-SY5Y cells to study mechanisms of pesticide-induced neuronal cell death. It was found that chlorpyrifos (CPF) and its mixture with cypermethrin (CPF+CM) induced cell death of SH-SY5Y cells in a dose- and time-dependent manner, as shown by MTT assays. Pesticide-induced SH-SY5Y cell death was characterized by concentration-dependent down-regulation of Bcl-2 and Bcl-xL as well as an increase in the caspase 3 activation. Pan-caspase inhibitor Q-VD-OPh produced a slight but significant reversal effect of pesticide-induced toxicity indicating that the major caspase pathways are not integral to CPF- and CPF+CM-induced cell death. Furthermore, signal transduction inhibitors PD98059, SL-327, SB202190, SP600125 and mecamylamine failed to attenuate pesticides effect. Atropine exhibited minimal ability to reverse toxicity. Finally, it was shown that inhibition of TNF-α by pomalidomide attenuated CPF-/CPF+CM-induced apoptosis. Overall, our data suggest that FAS/TNF signalling pathways may participate in CPF and CPF+CM toxicity.

Neuroprotective activity of 2-amino-1,3,4-thiadiazole derivative 4BrABT--an in vitro study

4BrABT (2-(4-Bromophenylamino)-5-(2,4-dihydroxyphenyl)-1,3,4-thiadiazole) is a compound known for its interesting in vitro anticancer profile. 4BrABT inhibited proliferation and motility of several cancer cell lines in concentrations which were not toxic to normal cells. A major problem associated with cancer chemotherapy, but also caused by environmental factors such as pesticides, is neurotoxicity. Therefore, the aim of the presented study was an in vitro evaluation of the neuroprotective activity of this compound. 4BrABT activity (1-100 μM) was tested in cultures of mouse neurons, rat astrocytes and rat oligodendrocytes. A possible protective action of the compound in different neurodegenerative models, as serum deprivation (SD), excitotoxicity (presence of 500 μM glutamate in culture medium), as well as cisplatin toxicity (astroglia--50 μM and oligodendroglia--100 μM) was investigated. Cell viability in the tested cultures was assessed with the use of LDH and MTT methods. Moreover, 4BrABT ability to prevent the cisplatin-induced apoptosis in astrocyte and oligodendrocyte cultures was analysed after Hoechst 33342 fluorostaining. The obtained results indicate that 4BrABT was not toxic to neurons, astrocytes and oligodendrocytes. Moreover, a decrease in the neuronal LDH level was observed, which may suggest the ability of 4BrABT to act as a trophic agent. Furthermore, the protective action of the studied compound was shown in neuronal cultures exposed to neurotoxic conditions (presence of glutamate and trophic stress) and in cisplatin-treated astrocytes and oligodendrocytes. The expression of anticancer and neuroprotective activity raises hopes for the potential use of 4BrABT as a safe anticancer drug, or neuroprotective agent in chemotherapy-associated neurotoxicity.

2-Amino-1,3,4-thiadiazole derivative (FABT) inhibits the extracellular signal-regulated kinase pathway and induces cell cycle arrest in human non-small lung carcinoma cells

The anticancer potential of 2-amino-1,3,4-thiadiazole compounds has been documented by in vitro and in vivo studies. In our previous research, we described the synthesis as well as the antiproliferative and neuroprotective activities of 2-(4-fluorophenyloamino)-5-(2,4-dihydroxyphenyl)-1,3,4-thiadiazole (FABT). The aim of the present study was to investigate the molecular mechanisms involved in FABT-induced growth inhibition in A549 lung carcinoma cells. Western blotting analysis revealed that FABT inhibited the activation of the extracellular signal-regulated kinase 1/2 (ERK1/2) pathway, and Real-time PCR analysis showed no changes in the expression of P44ERK1 and CREB1 genes. Furthermore, FABT induced cell cycle arrest in the GO/G1 phase and enhanced p27/Kip1 expression. Our results suggest that FABT acts by inhibiting ERK1/2 pathway and cell cycle progression through G1 into S phase in A549 cells. Further studies are needed to completely explain the molecular mechanisms of anticancer action of this 2-aminothiadiazole derivative.

Alpha-ketoglutarate (AKG) inhibits proliferation of colon adenocarcinoma cells in normoxic conditions

BACKGROUND AND OBJECTIVE

Alpha-ketoglutarate (AKG), a key intermediate in Krebs cycle, is an important biological compound involved in the formation of amino acids, nitrogen transport, and oxidation reactions. AKG is already commercially available as a dietary supplement and its supplementation with glutamine, arginine, or ornithine alpha-ketoglutarate has been recently considered to improve anticancer immune functions. It is well documented that AKG treatment of Hep3B hepatoma cells in hypoxia induced HIF-alpha (hypoxia-inducible factor) degradation and reduced vascular endothelial growth factor (VEGF) synthesis. Moreover, AKG showed potent antitumor effects in murine tumor xenograft model, inhibiting tumor growth, angiogenesis, and VEGF gene expression. However, the mechanisms of its anticancer activity in normoxia have not been examined so far.

RESULTS

Here, we report that in normoxia, AKG inhibited proliferation of colon adenocarcinoma cell lines: Caco-2, HT-29, and LS-180, representing different stages of colon carcinogenesis. Furthermore, AKG influenced the cell cycle, enhancing the expression of the inhibitors of cyclin-dependent kinases p21 Waf1/Cip1 and p27 Kip1. Moreover, expression of cyclin D1, required in G1/S transmission, was decreased, which accompanied with the significant increase in cell number in G1 phase. AKG affected also one the key cell cycle regulator, Rb, and reduced its activation status.

CONCLUSION

In this study for the first time, the antiproliferative activity of AKG on colon adenocarcinoma Caco-2, HT-29, and LS-180 cells in normoxic conditions was revealed. Taking into consideration an anticancer activity both in hypoxic and normoxic conditions, AKG may be considered as a new potent chemopreventive agent.

Vasopressin release from the rat hypothalamo-neurohypophysial system: effects of gonadotrophin-releasing hormone (GnRH), its analogues and melatonin

The influence of gonadotrophin-releasing hormone (GnRH) and its analogues (i.e., agonist and antagonist) on vasopressin (VP) release from the rat hypothalamo-neurohypophysial (H-N) system was studied both in vitro and in vivo. Additionally, it was determined whether the possible response of vasopressinergic neurones to these peptides could be modified by melatonin through a cAMP-dependent mechanism. In this study we demonstrate, for the first time, that the highly selective GnRH agonist (i.e., [Des-Gly(10),D-His(Bzl)(6),Pro-NHEt(9)]-LHRH; histrelin) stimulates the release of VP from the rat H-N system, while native GnRH and its antagonist remain inactive in modifying this process in vitro. Melatonin significantly inhibited basal and histrelin-induced release of VP in vitro, but displayed no significant influence on VP secretion when GnRH or its antagonist were present in a medium. Melatonin fully suppressed forskolin-stimulated VP release from the rat H-N system. On the other hand, addition of forskolin to a medium containing both histrelin and melatonin did not further alter the inhibitory influence of melatonin on the histrelin-dependent release of VP in vitro. After intracerebroventricular (i.c.v.) infusion of native GnRH or its agonist, blood plasma VP concentration was significantly higher than in control animals, which was accompanied by decreased content of the hormone in the neurohypophysis. Intravenous (i.v.) injection of melatonin did not change, in any subgroup, blood plasma VP concentration, when compared to the vehicle-injected rats. However, the neurohypophysial levels of the hormone were significantly higher after melatonin injection in control, GnRH- and histrelin-infused animals. Our present results suggest that activation of the GnRH receptor in the hypothalamus is involved in stimulation of VP secretion from the rat H-N system. We have also shown that melatonin, at a concentration close to its physiological level in the blood, significantly reduces the in vitro response of vasopressinergic neurones to a GnRH agonist - histrelin; this effect of melatonin could be mediated through intracellular processes that involve, among others, the cAMP-dependent mechanism.

[Collagen type III biosynthesis by cultured pubocervical fascia fibroblasts surrounding mono and multifilament polypropylene mesh after estrogens and tamoxifen treatment]

AIM

Surgical procedures using synthetic implants are currently considered as the most efficient therapy for stress urinary incontinence (SUI) and pelvic organ prolapse (POP). Insertion of the tape or mesh causes enhanced collagen synthesis that largely affects the biomechanical property of the implant. This process is significantly modulated by estrogens and improper wound healing and treatment failure may result in hypoestrogenism. The aim of the study was to assess the rate of collagen type II synthesis by pubocervical fascia fibroblasts cultured with polypropylene meshes in the presence of estrogens and tamoxifen.

MATERIAL AND METHODS

Fibroblasts were obtained from pubo-cervical fascia sampled from a 52-year-old premenopausal woman who underwent surgical treatment for SUI and cultured with monofilament or multifilament polypropylene meshes in the presence of 17B-estradiol, estriol, daidzein or tamoxifen. The cultures were run for 216 hr and the media were replaced every 72hr N-terminal propeptide of type III procollagen (PIIINP) was used as a marker of collagen type III synthesis. Its concentration in the media was measured by radioimmunoassay Pubocervical fascia fibroblast cultured with monofilament or multifilament meshes are capable of collagen type III synthesis. Following treatment with estradiol or tamoxifen, the highest PIIINP concentrations were observed after 72 hr whereas in case of estriol, daidzein or no treatment after 144hr of culture, regardless of the type of mesh used.

RESULTS

Only in cultures containing monofilament mesh and stimulated with estriol the high rate of collagen type III synthesis persisted until the end of the experiment. Paradoxically the highest total production of PIIINP was observed in culture treated with tamoxifen, both for multifilament and monofilament meshes.

CONCLUSION

The rate of collagen type III synthesis by pubocervical fascia fibroblast cultured with polypropylene meshes is subjected to modulation by estrogens and antiestrogens.

Betulin elicits anti-cancer effects in tumour primary cultures and cell lines in vitro

Betulin is a pentacyclic triterpene found in many plant species, among others, in white birch bark. The aim of the study was in vitro characterization of the anticancer activity of betulin in a range of human tumour cell lines (neuroblastoma, rhabdomyosarcoma-medulloblastoma, glioma, thyroid, breast, lung and colon carcinoma, leukaemia and multiple myeloma), and in primary tumour cultures isolated from patients (ovarian carcinoma, cervical carcinoma and glioblastoma multiforme). In this study, we demonstrated a remarkable anti-proliferative effect of betulin in all tested tumour cell cultures. Neuroblastoma (SK-N-AS) and colon carcinoma (HT-29) were the most sensitive to the anti-proliferative effect of betulin. Furthermore, betulin altered tumour cells morphology, decreased their motility and induced apoptotic cell death. These findings demonstrate the anti-cancer potential of betulin and suggest that they may be applied as an adjunctive measure in cancer treatment.

Evaluation of the antiproliferative activity of 2-(monohalogenophenylamino)-5-(2,4-dihydroxyphenyl)-1,3,4-thiadiazoles

Two 2-(monohalogenophenylamino)-5-(2,4-dihydroxyphenyl)-1,3,4-thiadiazoles were synthesized by reaction of sulfinyl bis(2,4-dihydroxythiobenzoyl) with 4-substituted 3-thiosemicarbazides and evaluated for their antiproliferative activity in tumor cells and for cytotoxicity in normal cells. Both derivatives in micromolar concentrations elicited a prominent antiproliferative effect in tumor cells derived from cancers of the nervous system (rhabdomyosarcoma/medulloblastoma, glioma) and peripheral cancers, including breast adenocarcinoma and lung carcinoma. The anticancer effect was attributed to decreased DNA synthesis and was not connected with apoptosis induction. Both compounds were not toxic to normal human skin fibroblasts.

Oxytocin release from the rat neurohypophysis into the blood: effects of tachykinin NK-1 and NK-2 receptors agonists and antagonists

The aim of the present study was to investigate the effect of peptide NK-1 and NK-2 receptors agonists and antagonists (and their natural ligands, i.e., substance P and neurokinin A) on the oxytocin (OT) secretion from the rat neurohypophysis into the blood. Intracerebroventricular (icv) injection of substance P (SP) or highly selective NK-1 receptor agonist--[(Sar(9),Met(O2)(11))-Substance P]-- significantly stimulated the OT secretion from the rat neurohypophysis into the general circulation. After icv injection of the NK-1 receptor antagonist--[(Tyr(6),D-Phe(7),D-His(9))-Substance P (6-11)]--the blood plasma OT concentration was significantly lower, when compared to vehicle-injected animals. On the other hand, the icv administered neurokinin A (NKA) and the NK-2 receptor agonist--[(beta-Ala(8))-Neurokinin A (4-10)]--were essentially inactive in modifying OT secretion. However, such injection of the NK-2 receptor antagonist--[(Tyr(5),D-Trp(6,8,9),Lys-NH2(10))-Neurokinin A (4-10)]--was found to diminish the blood plasma hormone concentration, when compared to vehicle-injected animals. The neurohypophysial content of OT was decreased in NKA-treated rats, but neither the NK-2 receptor agonist nor antagonist were able to affect the OT output from the rat posterior pituitary. The hypothalamic levels of OT were not modified by any of the studied peptides. The present data strongly indicate a major role for the tachykinin NK-1 receptor in SP- and/or NKA-dependent regulation of OT secretion from the rat neurohypophysis into the blood.

Effect of melatonin on the vasopressin secretion as influenced by tachykinin NK-1 receptor agonist and antagonist: in vivo and in vitro studies

The aim of the present study was to investigate the influence of melatonin on vasopressin (AVP) release from the rat hypothalamo-neurohypophysial (H-NH) system, both in vivo and in vitro, possibly modified by the peptide NK-1 and/or NK-2 receptor agonists and antagonists. Highly selective NK-1 receptor agonist, i.e., [Sar(9),Met(O(2))(11)]-Substance P, has been shown to enhance the AVP release from isolated rat H-NH system in vitro, while the NK-1 receptor antagonist--(Tyr(6),DPhe(7),D-His(9))-Substance P (6-11) as well as the NK-2 receptor selective agonist--(beta-Ala(8))-Neurokinin A (4-10) and antagonist--(Tyr(5),D-Trp(6,8,9),Lys-NH(2)(10))-Neurokinin A (4-10) were essentially inactive in modifying AVP secretion. Melatonin inhibited basal release of AVP but was not able to reduce significantly the in vitro response of vasopressinergic neurones to NK-1 receptor agonist. After intracerebroventricular (icv) administration, substance P (SP), neurokinin A (NKA) and the NK-1 receptor agonist (all at the concentration of 10(-7) M/L) significantly enhanced plasma AVP concentration. Such stimulatory effect of the latter peptide on AVP output from the eurohypophysis was reduced by an intravenous (iv) injection of melatonin, which itself (at a concentration of 5 ng/ml) caused a significant decrease in AVP release 10 min after injection. The inhibitory influence of melatonin on the AVP secretion was absent in rats injected icv with both tachykinin receptors antagonists, the NK-2 receptor agonist or NKA. The present data indicate a distinct role for NK-1 receptor in NKA/SP-mediated regulation of AVP release from the rat H-NH system. They have also shown that, under present experimental conditions, the stimulatory effect of NK-1 receptor activation on AVP secretion into the blood is sensitive to inhibitory influence of melatonin.

Role of tachykinin receptors and melatonin in oxitocin secretion from isolated rat hypothalmo-neurohypophysial system

Present investigations were undertaken to study the influence of peptide NK-1 and NK-2 receptor agonists and antagonists as well as substance P and neurokinin A (the natural ligands for these tachykinin receptors) on oxytocin (OT) release from isolated rat hypothalamo-neurohypophysial (H-N) system as well as to determine whether the tachykinin NK-1 and/or NK-2 receptors contribute to the response of oxytocinergic neurons to melatonin. The results show, for the first time, that highly selective NK-1 receptor agonist, i.e., [Sar(9),Met(O(2))(11)]-Substance P, enhances while the NK-1 receptor antagonist (Tyr(6),D-Phe(7),D-His(9))-Substance P (6-11) - sendide - diminishes significantly OT secretion; the latter peptide was also found to antagonize the substance P-induced hormone release from isolated rat H-N system, when used at the concentration of 10(-7) M/L. Melatonin significantly inhibited basal and substance P-stimulated OT secretion. Neurokinin A and the NK-2 receptor selective agonist (beta-Ala(8))-Neurokinin A (4-10) as well as the NK-2 receptor antagonist (Tyr(5),D-Trp(6,8,9),Lys-NH(2)(10))-Neurokinin A (4-10) were essentially inactive in modifying OT release from the rat H-N system in vitro. The present data indicate a distinct role for tachykinin NK-1 (rather than NK-2) receptor in tachykinin-mediated regulation of OT secretion from the rat H-N system. Under present experimental conditions, however, a role of respective tachykinin receptors in the response of oxytocinergic neurons to melatonin has not been found.

Pancreatic islets isolation using different protocols with in situ flushing and intraductal collagenase injection

Human islet transplantation seems to be a very promising clinical procedure for patients with type I diabetes mellitus. The aim of our study was to investigate the influence of in situ intravascular flushing with University of Wisconsin (UW) solution and intraductal collagenase injection at the time of pancreas procurement on the isolated islets and exocrine tissue injury. Our experiments indicated that in situ perfusion with the UW solution has a beneficial effect on pancreatic islets and intraductal distention results in an increase in the concentration of pancreatic enzymes released into the cold preservation solution during ischemic conditions. Cold ischemia reduced islet yield, but pancreas perfusion with the UW solution showed better ischemic tolerance of isolated islets during glucose static incubation. We conclude that intravascular pancreas flushing has a crucial effect on recovery and yield of pancreatic islets and protects against exocrine tissue injury.

Pancreatic islets isolation using different protocols with in situ flushing and intraductal collagenase injection

Human islet transplantation seems to be a very promising clinical procedure for patients with type I diabetes mellitus. The aim of our study was to investigate the influence of in situ intravascular flushing with University of Wisconsin (UW) solution and intraductal collagenase injection at the time of pancreas procurement on the isolated islets and exocrine tissue injury. Our experiments indicated that in situ perfusion with the UW solution has a beneficial effect on pancreatic islets and intraductal distention results in an increase in the concentration of pancreatic enzymes released into the cold preservation solution during ischemic conditions. Cold ischemia reduced islet yield, but pancreas perfusion with the UW solution showed better ischemic tolerance of isolated islets during glucose static incubation. We conclude that intravascular pancreas flushing has a crucial effect on recovery and yield of pancreatic islets and protects against exocrine tissue injury.

Neurokinin A and the neurohypophysial response to melatonin: in vitro studies

The aim of this study was to investigate a possible role of neurokinin A (a member of a family of peptides known as tachykinins) in the pineal-neurohypophysial interrelationship. The effect of neurokinin A (NKA) alone or in the presence of pineal hormone - melatonin on basal and K(+)-stimulated vasopressin and oxytocin secretion from the hypothalamo-neurohypophysial system was studied in vitro. The present results show that NKA stimulated basal vasopressin and oxytocin release from the isolated hypothalamo-neurohypophysial system, when used at the concentration of 10(-7) M/L. Melatonin diminished basal release of the neurohypophysial hormones; it also significantly inhibited the NKA-stimulated secretion of vasopressin and oxytocin. Lower concentrations of NKA did not affect the neurohypophysial hormones basal release, however, when melatonin was added to the medium enriched with NKA at the concentration of 10(-9) M/L, the vasopressin secretion from the hypothalamo-neurohypophysial explants was decreased significantly. The K(+)-evoked release of neurohypophysial hormones was not further modified by either NKA or melatonin. The present results confirm previous reports as to the inhibitory effect of melatonin on both vasopressin and oxytocin secretion from the hypothalamo-neurohypophysial complex in vitro. However, under present experimental conditions, the contribution of NKA in the mechanisms of pineal-neurohypophysial interrelationships has not been demonstrated.

The hypothalamo-neurohypophysial response to melatonin

The present paper reviews the findings accumulated on the role of pineal gland and its hormone - melatonin - in regulation of the hypothalamo-neurohypophysial system activity. Effects of modified photoperiod, pinealectomy or treatment with melatonin on the vasopressin and oxytocin biosynthesis and/or secretion have been described. Taken together, the in vivo and in vitro data suggest that the effect of melatonin on the vasopressin and oxytocin secretion depends on this pineal hormone concentration and experimental conditions.

Melatonin and the synthesis of vasopressin in pinealectomized male rats

The pineal hormone, melatonin, is known to modify, under different experimental conditions, neurohypophysial hormone secretion in the rat. The aim of this study was to investigate the effect of melatonin on the vasopressin biosynthesis rate in the hypothalamus of either pinealectomized or sham-operated rats, using the colchicine method. To estimate whether colchicine affects the function of the neurohypophysis in these animals, the neurohypophysial and plasma vasopressin levels were also measured. The vasopressin synthesis rate was increased after pineal removal, when compared with sham-operated animals, and melatonin strongly inhibited the rise in the hormone synthesis due to pinealectomy. After pineal removal plasma vasopressin concentration was significantly elevated, and melatonin attenuated this effect. On the contrary, the neurohypophysial vasopressin content was significantly decreased after pinealectomy, but it was not further modified by melatonin.Thus, melatonin suppresses the synthesis and secretion of vasopressin in pinealectomized rats. The present results confirm our previous reports as to the inhibitory impact of the pineal on both vasopressin synthesis and release and suggest that melatonin may mediate the effect of the pineal gland on vasopressinergic neuron activity.

Melatonin and the synthesis of vasopressin in pinealectomized male rats

The pineal hormone, melatonin, is known to modify, under different experimental conditions, neurohypophysial hormone secretion in the rat. The aim of this study was to investigate the effect of melatonin on the vasopressin biosynthesis rate in the hypothalamus of either pinealectomized or sham-operated rats, using the colchicine method. To estimate whether colchicine affects the function of the neurohypophysis in these animals, the neurohypophysial and plasma vasopressin levels were also measured. The vasopressin synthesis rate was increased after pineal removal, when compared with sham-operated animals, and melatonin strongly inhibited the rise in the hormone synthesis due to pinealectomy. After pineal removal plasma vasopressin concentration was significantly elevated, and melatonin attenuated this effect. On the contrary, the neurohypophysial vasopressin content was significantly decreased after pinealectomy, but it was not further modified by melatonin.Thus, melatonin suppresses the synthesis and secretion of vasopressin in pinealectomized rats. The present results confirm our previous reports as to the inhibitory impact of the pineal on both vasopressin synthesis and release and suggest that melatonin may mediate the effect of the pineal gland on vasopressinergic neuron activity.

Lidocaine as a protective agent during pancreas cold ischemia

Pancreatic islet transplantation in humans is a promising alternative for substitutive insulin therapy of IDDM (Insulin Dependent Diabetes Mellitus). Storage of harvested organs is a one of the most important factors, which influence efficacy of islet isolation process. In this sense, appropriate pancreas storage is the main point the successful pancreatic islet isolation. The purpose of the present study was to find out whether lidocaine, a well known membrane stabilizer and PLA2 (phospholipase A2) inhibitor could be applied in pancreas preservation for protection of endo- and exocrine pancreatic tissue from cells damage which occurs during and after storage. For this purpose, the effects of lidocaine on 1) viability and 2) endocrine function of pancreatic islets, isolated from pancreases exposed to cold ischemia, were investigated in this study. Our study showed hat lidocaine, injected intraductally before pancreas harvesting, improves efficacy of islet isolation. We found that the yields of islets in the groups treated with lidocaine were significantly higher when compared with controls. Glucose challenge test performed on these islets indicated that after the treatment with lidocaine, islets were more sensitive to glucose stimulation when compared with control islets, although the metabolic activity estimated by MTT test was comparable in both groups. In summary, donor pretreatment with lidocaine seems to be the safe method of protection of preserved pancreases from cell damage, caused by membranes destruction during cold ischemia.

Luteinizing hormone-releasing hormone and oxytocin response to hyperosmotic stimulation: in vitro study

It was shown previously that luteinizing hormone-releasing hormone (LHRH) affects the neurohypophysial oxytocin release in water-deprived rats. However, the detailed mechanisms by which LHRH modifies the oxytocin response to hyperosmotic stimulation have not been explained so far. Using the isolated hypothalamo-neurohypophysial explants obtained from euhydrated rats, the effect of LHRH on the oxytocin secretion was studied under conditions of direct osmotic (i.e., Na(+)- evoked) as well as nonosmotic (i.e., K(+)-evoked) stimulation. Additionally, the oxytocin response to LHRH was investigated using the explants obtained from animals drinking 2% saline for eight days (systemic, i. e., both direct and indirect, osmotic stimulation). LHRH significantly enhanced Na(+)- and K(+)-evoked oxytocin release from explants taken from rats drinking tap water, indicating that LHRH could affect the Na(+)/K(+)-dependent depolarization of perikarya of oxytocin neurones. In contrast, LHRH significantly diminished the K(+)-stimulated hormone release when the neurohypophysial complex was obtained from previously salt-loaded rats, suggesting that peripheral osmotic stimulation somehow modifies the sensitivity of oxytocinergic neurones to LHRH (possible mechanisms are discussed). It is concluded that LHRH may participate in the regulation of oxytocin secretion via both direct and indirect impact on magnocellular oxytocinergic neurones depending on the current functional status of the hypothalamo-neurohypophysial complex.

The effect of melatonin on vasopressin release under stress conditions in pinealectomized male rats

The findings here reported showed that the response of vasopressinergic neurons to immobilization stress is augmented by melatonin. The effectiveness of melatonin in functional modification of these neurons' activity under conditions of stress changes after pineal removal.

The pineal and oxytocin synthesis

The aim of this study was to investigate the effect of pineal removal on oxytocin synthesis in the hypothalamus using the colchicine method. To this end, rats were injected intracerebroventricularly (i.c.v.) with colchicine solution (5 microg/5 microl) or normal saline and decapitated 20 h later. The animals were either pinealectomized or sham-operated two or eight weeks before i.c.v. injection. The oxytocin content in the hypothalamus was significantly higher in colchicine-treated rats whereas no significant differences were seen in the neurohypophysial hormone level between saline- or colchicine-injected animals. Thus, colchicine inhibited the hormonal transport but probably did not affect the function of the neurohypophysis. Two weeks after pinealectomy neither the oxytocin synthesis rate nor its neurohypophysial content were significantly different from control values. The oxytocin synthesis rate was increased markedly eight weeks after pineal removal. At that time, the neurohypophysial oxytocin content was reduced suggesting the increased secretion of the hormone. It is concluded that the pineal has an inhibitory impact on both oxytocin synthesis and release.

Melatonin affects the oxytocin and prolactin responses to stress in male rats

Since the pineal-neurohypophysial interactions are now well established and oxytocin secretion is known to be a component of the neuroendocrine response to the majority of stressful stimuli, the present experiments were undertaken to estimate whether melatonin modifies the response of oxytocinergic neurons to the immobilization stress. Oxytocin (OT) content in the hypothalamus and neurohypophysis as well as plasma level of OT, prolactin (PRL) and adrenocorticotropin (ACTH) were studied after melatonin treatment in sham-operated or pinealectomized male rats. In sham-operated rats, melatonin diminished the hypothalamic OT content as well as plasma OT and PRL concentrations, but was without effect on neurohypophysial OT and plasma ACTH levels in otherwise not treated rats. In both wehicle- or melatonin-treated rats, food and water deprivation did not affect the OT, PRL and ACTH secretion. Under stress conditions, however, pituitary OT storage was diminished in vehicle-treated rats and melatonin augmented this response of OT to stress. Melatonin also diminished the PRL and ACTH secretion into the blood in stressed rats. In pinealectomized animals neither hypothalamo-neurohypophysial OT content nor plasma OT, PRL or ACTH concentrations were modified by melatonin treatment in animals otherwise not treated or in those deprived of food and water for 24 hrs. However, melatonin increased the pituitary oxytocin content as well as plasma OT and ACTH concentrations in immobilized animals. Plasma PRL concentration was diminished after melatonin treatment in stressed rats. The results suggest that the response of oxytocinergic neurons to immobilization stress is augmented by melatonin. The effect of melatonin on the OT, PRL and ACTH secretion is modified by pinealectomy.

The effect of melatonin on suckling-induced oxytocin and prolactin release in the rat

There is growing evidence that melatonin (MEL) inhibits oxytocin (OT) release when used in a low dose, while higher doses stimulate the release of the hormone in the rat. In the present study we investigated the effect of exogenous MEL, administered intracerebroventricularly (ICV), on suckling-induced OT and prolactin (PRL) release in the urethane-anesthetized rat. Lactating rats suckled by 8-12 pups were studied on days 8-12 of postpartum, and lactating pups-deprived rats on the same days of postpartum served as a control. Plasma OT and PRL levels as well as hypothalamic and neurohypophyseal OT contents were measured by RIA. Suckling stimulated the secretion of both OT and PRL. The ICV injection of 1 ng/ml MEL produced a significant inhibition of suckling-induced OT as well as PRL secretion. Melatonin in doses of 100 ng/ml or 10 micrograms/ml did not modify the OT release but significantly inhibited PRL release brought about by suckling; 10 pg/ml of MEL was not effective in this regard. Thus, exogenous MEL seems to inhibit suckling-induced OT as well as PRL secretion when applied at doses regarded to be in the range of the physiological level; when applied in higher doses, it was shown not to influence the release of OT following physiological stimulation such as suckling.

Neurohypophyseal vasopressin in the Syrian hamster: response to short photoperiod, pinealectomy, melatonin treatment, or osmotic stimulation

In the present study, the effect of photoperiod on vasopressin content in the pituitary neurointermediate lobe (NIL), as well as the ability of pinealectomy to prevent and melatonin to mimic the short photoperiod-induced changes in NIL vasopressin were studied in male Syrian hamsters. The ability of melatonin to modify the hyperosmotically stimulated vasopressin release was also determined. Exposure to short photoperiod (SD) for 4 or 10 weeks increased vasopressin content in the hamster NIL. In long photoperiod (LD)-exposed hamsters, pinealectomy induced a decrease in NIL vasopressin content, whereas no effect of melatonin injections on vasopressin storage in the NIL was detected. In SD-exposed animals, pineal removal failed to alter vasopressin content in the NIL. Hypertonic saline administration led to the expected decrease in vasopressin content in the NIL both in vehicle- and melatonin-treated animals. The hyperosmotically stimulated release of vasopressin was not modified by previous treatment with melatonin. The data from the present study show that, in male Syrian hamsters, exposure of animals to SD increases the vasopressin content in the posterior pituitary, but these changes appear not to be mediated by SD-induced changes in melatonin secretion. Furthermore, the exposure of animals to SD prevents the pinealectomy-induced changes in NIL vasopressin content. Melatonin does not modify the hyperosmotically stimulated vasopressin release in the male Syrian hamster.

Effect of pinealectomy and melatonin on vasopressin-potentiated passive avoidance in rats

The pineal indoleamine, melatonin, and the hypothalamic neuropeptide, vasopressin, facilitate passive avoidance behaviour in rats. The similarity of the effects suggest that interaction might occur between the two substances. Therefore, the effect of intraperitoneally applied vasopressin and/or melatonin on one-trial learning passive avoidance behaviour was studied in pinealectomized rats. Intraperitoneal treatment with 500 ng vasopressin 1 hr before the retention test increased passive avoidance latency of sham-operated rats. In pinealectomized rats, an identical amount of vasopressin was ineffective. In sham-operated rats, melatonin blocked the effect of vasopressin. It is concluded that vasopressin needs a regulated pineal function for developing effects in passive avoidance behaviour.

Oxytocin and prolactin release after hypertonic saline administration in melatonin-treated male Syrian hamsters

The aim of the present investigations was to examine the effects of melatonin (Mel) on oxytocin (OT) release under conditions of osmotic stimulation, brought about by hypertonic saline administration, as well as to determine whether osmotically stimulated OT release in Mel-treated Syrian hamster is associated with alterations in the release of prolactin (PRL) and in norepinephrine (NE) and dopamine (DA) content in the hypothalamus. In both Mel- and vehicle-treated hamsters, injection of hypertonic saline was followed by a significant decrease in OT content in the pituitary neurointermediate lobe (NIL) and elevation of plasma OT and PRL levels. Melatonin injections had no significant affect on NIL OT content in either isotonic- or hypertonic-saline treated animals. Pretreatment with Mel did not alter plasma OT or PRL levels in isotonic saline-injected animals. However, Mel facilitated the release of OT, but prevented the release of PRL after hypertonic saline administration. Melatonin treatment reduced hypothalamic NE content (but not that of DA) in isotonic-saline treated animals. After osmotic stimulation, hypothalamic content of NE and DA was significantly lower in Mel-treated than in vehicle-treated animals. Data from the present study suggest that the osmotically-stimulated release of OT and PRL seems to be related to the activation of noradrenergic rather than dopaminergic transmission. Both dopaminergic and noradrenergic transmission may be, however, involved in mediating the effects of Mel on the osmotically-activated OT and PRL release.

The effects of short photoperiod, pinealectomy, and melatonin treatment on oxytocin synthesis and release in the male syrian hamster

The pineal gland has been shown to affect plasma oxytocin (OT) levels, but the mechanism of this action is not apparent. In the present study, the ability of the photoperiod to affect plasma OT levels, neurointermediate lobe (NIL) OT content, and hypothalamic OT mRNA levels was studied in male Syrian hamsters. In addition, the ability of pinealectomy to prevent and melatonin (MEL) to mimic the short photoperiod-induced changes were also determined. Exposure to short days (SD) led to the expected decrease in testes weight and plasma PRL levels, but plasma OT levels were unchanged. However, NIL OT content was increased in the SD-exposed animals. Hypothalamic OT mRNA levels were not significantly altered by SD exposure. Pinealectomy blocked the effects of SD on testes weight, whereas afternoon MEL injections mimicked the effects of SD. In long day (LD)-exposed hamsters, pinealectomy induced a decrease in NIL OT content without altering hypothalamic OT mRNA levels. In SD-exposed animals, NIL OT content was not affected by pinealectomy. Melatonin injections had no significant effect on NIL OT content or hypothalamic OT mRNA levels. The data from the present study suggest that exposure of male Syrian hamsters to short photoperiods influences some aspects of OT synthesis and/or transport to produce its increased accumulation in the NIL, but does not affect OT release. These changes are apparently not the result of SD-induced changes in MEL secretion, but conceivably could be related to the previously documented effects of SD on hypothalamic catecholamine turnover.

Melatonin inhibits oxytocin and vasopressin release from the neurointermediate lobe of the hamster pituitary

The aim of this investigation was to study whether melatonin affects the release of oxytocin and vasopressin by the pituitary neurointermediate lobe of the Syrian hamster in vitro. The effect of melatonin was studied on the unstimulated (pre- and post-K+ -stimulated) release of oxytocin and vasopressin and on the response to K+ stimulation. Melatonin significantly inhibited unstimulated release of these hormones in all concentrations (10(-11) M, 10(-9) M and 10(-7) M) studied. K+ -stimulated release of oxytocin and vasopressin was significantly decreased by the 10(-9) M dose of melatonin. It is concluded that melatonin is active in modifying the release of these peptides in the Syrian hamster neurointermediate lobe, as it has been previously demonstrated in the rat hypothalamus.

Photoperiod effects on neurohypophyseal and tuberoinfundibular dopamine metabolism in the male hamster

Exposure of golden hamsters to a short photoperiod (< 12.5 h light/day) leads to suppression of gonadal function secondary to reduced gonadotropin and PRL secretion. PRL secretion is decreased despite a reduction of tuberoinfundibular dopaminergic activity. In the present study, the ability of photoperiod to affect tuberohypophyseal dopamine (DA) turnover was evaluated in long day (LD; 16 h of light, 8 h of darkness) and short day (SD; 8 h of light, 16 h of darkness) male hamsters. Exposure to SD led to decreases in testicular weight within 10 weeks and decreases in plasma PRL levels within 1 week. DA turnover in the neurointermediate lobe of the pituitary, as estimated by measuring the depletion of DA 60 min after tyrosine hydroxylase inhibition with alpha-methyl-p-tyrosine (250 mg/kg), was significantly elevated 1 and 4 weeks after transfer to SD, but returned by 10 weeks to the levels seen in LD animals. After 14 days of SD exposure an enhanced lactotroph sensitivity to DA was demonstrated and may also have contributed to suppression of PRL levels. Similarly to the findings of previous studies, DA turnover in the median eminence was depressed in animals housed in SD. The DA content of the anterior pituitary was not significantly affected by photoperiod. The data from this study suggest that decreases in PRL secretion associated with the transfer of hamsters from LD to SD conditions are at least in part caused by an increase in DA turnover by neurohypophyseal neurons. However, the involvement of other PRL-inhibiting or -stimulating factors in mediating the effects of photoperiod on PRL secretion cannot be ruled out.

The effect of haemorrhage and melatonin on neurohypophysial vasopressin and oxytocin content in pinealectomized male rats

The effect of haemorrhage and melatonin on the vasopressin and oxytocin storage in the neurohypophysis of pinealectomized male rats was determined. Sham operated or pinealectomized rats as well as rats pinealectomized and injected with melatonin (100 micrograms/100 g b. w., once daily over 8 days) or with melatonin vehicle (2.2% ethanol in 0.9% NaCl) were subsequently subjected to haemorrhage. Pinealectomy was followed by known decrease of both vasopressin and oxytocin content in the neurohypophysis as compared to sham operated rats. Similarly, haemorrhage decreased the neurohypophysial vasopressin and oxytocin storage in both sham operated and pinealectomized animals. Melatonin, injected to pinealectomized animals, did not modify the diminution of neurohypophysial vasopressin and oxytocin content caused by bleeding. The results demonstrate that in pinealectomized rats melatonin does not affect the rate of the response of vasopressinergic and oxytocinergic neurones to bleeding.