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).

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.

Experimental hypothyroidism increases content of collagen and glycosaminoglycans in the heart.

The connective tissue matrix of the heart remains under regulatory influence of the thyroid hormones. Some conflicting data describe the connective tissue changes in subjects with thyroid gland disorders. The aim of the study was to assess the changes of the connective tissue accumulation in the heart of rats in the state of hypothyroidism and to answer the question whether TSH is involved in mechanism of the observed phenomena.

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.

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.

Effects of glucagon-like peptide-1 (7-36) amide on neurohypophysial hormone secretion induced by acute hyperosmotic challenge.

This study was designed to investigate possible effects of glucagon-like peptide-1 (7-36) amide on the vasopressin and oxytocin release induced by acute peripheral or central osmotic stimulation. In the first series of experiments, rats were injected intraperitoneally with the isotonic (0.15 M) or hypertonic (1.

Mechanisms involved in glucagon-like peptide-1 (7-36) amide action on the rat hypothalamo-neurohypophysial system.

Glucagon-like peptide-1 (7-36) amide (tGLP-1) has been shown to modify the secretory function of the rat hypothalamo-neurohypophysial complex (HNC). However, mechanisms underlying this action are still unclear. Using explants containing the HNC obtained from euhydrated rats, possible interactions of tGLP-1 with angiotensin II (Ang II), forskolin-induced cAMP synthesis or calcium ions were investigated.

Effects of tGLP-1 on feeding behaviour and neurohypophysial function under chronic osmotic stimulation.

Effects of repeated daily intracerebroventricular injections of 1 microg of glucagon-like peptide-1 (7-36) amide (tGLP-1) on feeding and drinking behaviour, as well as neurohypophysial hormone secretion, was investigated in rats drinking tap water or 2% saline for 6 days. In euhydrated rats, tGLP-1 decreased moderately food and water consumption without a marked reduction of body weight. In salt-loaded rats, tGLP-1 considerably inhibited saline intake.

Melatonin inhibits the substance P-induced secretion of vasopressin and oxytocin from the rat hypothalamo-neurohypophysial system: in vitro studies.

The aim of the present investigations was to study the influence of substance P (a member of a family of peptides known as tachykinins) on basal and K(+)-evoked vasopressin (AVP) and oxytocin (OT) release from rat hypothalamo-neurohypophysial system in vitro as well as to determine whether this effect of substance P is sensitive to melatonin. The present results show that substance P stimulates basal AVP and OT release from isolated hypothalamo-neurohypophysial system, when used at the concentrations of 10(-6) and 10(-7)M/l. At the concentration of 10(-9)M/l, however, substance P was found to stimulate the in vitro secretion of AVP, but not that of OT.

tGLP-1 action on the isolated hypothalamo-neurohypophysial system under glutamate receptor blockade.

The isolated rat hypothalamo-neurohypophysial system was used to investigate possible mechanisms of glucagon-like peptide-1 (7-36) amide (tGLP-1) effects on the vasopressin/oxytocin (AVP/OXY) release. The non-selective inhibition of synaptic transmission as brought about by excess of MgSO(4) in the incubation medium completely abolished the tGLP-1-induced AVP release and attenuated OXY secretion. The non-specific blockade of excitatory amino acid receptors with kynurenic acid (KA) completely suppressed the tGLP-1-induced AVP but not OXY release.

Effects of glucagon-like peptide-1(7-36) amide on neurohypophysial and cardiovascular functions under hypo- or normotensive hypovolaemia in the rat.

To date, glucagon-like peptide 1(7-36) amide (tGLP-1) has been found to affect the neurohypophysial and cardiovascular functions in normotensive and normovolaemic rats. The aim of the present study was to investigate possible effects of tGLP-1 on the mean arterial blood pressure and the release of vasopressin and oxytocin under conditions of blood volume depletion in the rat. In the first series of experiments, the animals were injected i.

tGLP-1 and release of vasopressin and oxytocin from the isolated rat hypothalamo-neurohypophysial system: effects of a tGLP-1 receptor agonist and antagonist.

To date, glucagon-like peptide-1 (7-36) amide (tGLP-1) has been found to enhance the vasopressin and oxytocin secretion in vivo but not in vitro (i.e., when the isolated neurointermediate lobe of the pituitary was used for experiments).

Effects of centrally or systemically injected glucagon-like peptide-1 (7-36) amide on release of neurohypophysial hormones and blood pressure in the rat.

The present study was designed to compare the effects of glucagon-like peptide-1 (7-36) amide (GLP-1) injected centrally or systemically in a dose range of 10-10000 ng on the vasopressin and oxytocin release as well as the blood pressure in the rat. The urethane-anaesthetised Wistar male and female rats were fitted with venous as well as arterial catheters and, in the second study, additionally with the intracerebroventricular cannula. The arterial blood pressure was monitored throughout the experiment.

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 influence of vasopressin or oxytocin on thyroid-stimulating hormone and thyroid hormones' concentrations in blood plasma of euthyroid rats.

The effects of arginine vasopressin (AVP) and oxytocin (OT) upon thyroid-stimulating hormone (TSH), free thyroxine (FT4) and free triiodothyronine (FT3) release were studied in euthyroid rats. Intracerebroventricular (i.c.

Effects of methylphenidate on oxytocin and vasopressin levels in pinealectomized rats during light-dark cycle.

Although previous reports have shown that methylphenidate (MPH), in addition to its known behavioral effect, can influence the hypothalamo-pituitary-adrenal axis by increasing the plasma ACTH, the pineal gland seems to be involved in neuroendocrinological processes too, e.g., in hypothalamic synthesis and release of oxytocin (OXY) and vasopressin (AVP).

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.

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.

Thyrotropin-releasing hormone (TRH) inhibits vasopressin and oxytocin release from rat hypothalamo-neurohypophysial explants in vitro.

Incubation of hypothalamo-neurohypophysial explants in Locke's solution containing 28 nM/L thyrotropin-releasing hormone (TRH) resulted in an inhibition of vasopressin and oxytocin secretion during depolarization due to excess potassium. These data suggest the involvement of TRH in the regulatory mechanisms of vasopressin and oxytocin release; the inhibitory effect of TRH cannot be excluded.

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.

Luliberin inhibits the release of Oxytocin from hypothalamo-neurohypophysial system in dehydrated but not in euhydrated or haemorrhaged rats.

Rats euhydrated, dehydrated for two days or haemorrhaged were given intracerebroventricularly (i.c.v.

Thyrotropin-releasing hormone (TRH) modifies oxytocin release from the hypothalamo-neurohypophysial system in salt-loaded rats.

Rats drinking ad libitum tap water or hypertonic (i.e. 2%) sodium chloride solution were given intracerebroventricularly (i.

Insulin-like immunoreactivity (IRI) in the rat hypothalamo-neurohypophysial system: effect of dehydration and haemorrhage.

Hypothalamic IRI was not affected in haemorrhaged rats, but diminished considerably in the dehydrated ones. In the neurohypohysis, IRI was distinctly higher both in dehydrated and haemorrhaged rats, i.e.

Thyrotropin-releasing hormone (TRH) inhibits vasopressin release from hypothalamo-neurohypophysial system of rats drinking hypertonic saline.

Rats drinking ad libitum tap water or hypertonic (i.e. 2%) sodium chloride solution were given intracerebroventricularly (i.

Hypothalamic and neurohypophysial vasopressin and oxytocin content as influenced by haemorrhage in melatonin-treated male rats.

The effect of haemorrhage (1 ml per 100 g b. w.) on the vasopressin and oxytocin storage in the hypothalamus and neurohypophysis of melatonin-treated male rats was determined.