Release of catecholamines follows suckling or electrical stimulation of mammary nerve in lactating rats

The hypothesis that catecholamines may be released by mammary gland stimulation during lactation was tested by measuring, with an HPLC electrochemical method, plasma epinephrine (E) and norepinephrine (NE) concentrations during suckling in conscious rats and during electrical stimulation (pulses: 1 msec duration, 10/sec at 5-30 V) of the central end of a cut abdominal mammary nerve in urethane-anesthetized rats. Plasma E and NE concentrations were significantly elevated in two different strains of rats (Wistar and Holtzman) within 5 min of suckling. The concentration of E and NE did not change in control unsuckled rats during the same time period. As a complementary indication of sympathetic activation, it was observed that piloerection occurred during suckling. Plasma E levels (but not NE levels) increased significantly within 30 sec of a 2-min period of nerve stimulation in lactating rats on either day 7 or day 21 of lactation, as well as in nonlactating rats. The effect was significantly greater in nonlactating rats. The levels of E and NE were not altered after sham stimulation, whereas adrenalectomy abolished the rise in plasma E after mammary nerve stimulation. Blockade of the rise in plasma E also occurred after rapid injection of 100 microliters milk intraductally into each of two thoracic mammary glands, 15 sec before the onset of mammary nerve stimulation. These results show that E and NE can be released in response to suckling, and that activation of ductal mechanoreceptors may inhibit such release. These mechanisms may operate to regulate the rate of milk removal during suckling in the rat.     

Release of oxytocin and vasopressin by intracerebroventricular vasoactive intestinal polypeptide

Vasoactive intestinal polypeptide (VIP)ergic nerves innervate both the neurohypophysis and the hypothalamus. To test the hypothesis that VIP is a releasing factor for neurohypophyseal hormones, rats were given intracerebroventricular (icv) infusions of VIP in doses varying from 0.3 pmol/kg.min to 3 nmol/kg.min for 5 min (0.001-10 micrograms/rat). Serial blood samples were drawn from the vena cava for measurement of oxytocin (OT), vasopressin (AVP), and VIP by RIA. After the VIP infusions mean plasma OT and AVP levels rose in a dose-dependent manner; the rise was significant for both hormones at the dose of 300 pmol/kg.min. Peak levels after infusion of 3 nmol/kg.min were greater for OT than AVP [96.1 +/- 14.7 vs. 33.9 +/- 9 microU/ml (mean +/- SE); n = 6]. In addition, the concentration of plasma OT increased more promptly than that of AVP. Plasma OT was significantly raised over control values at 5 min, whereas plasma AVP was not increased until 15 min after the VIP infusion began. The concentration of VIP in peripheral plasma rose somewhat after icv infusions (maximum, 300 pmol/liter 30 min after 10 micrograms/rat), but the rise was only 5% of that observed after systemic infusions of equimolar doses of VIP (maximum, 6000 pmol/liter 5 min after 10 micrograms/rat). Peak plasma OT levels after administration of 3 nmol/kg.min VIP were significantly higher after icv than after systemic infusion of the same dose of VIP reported previously. Intravenous injection of 0.5 ml VIP antiserum with a binding capacity of VIP of 2.3 micrograms/ml before the icv administration of VIP (1 microgram/rat) did not prevent the VIP-induced rise in plasma OT and AVP. These observations suggest a central site of action for VIP in OT and AVP release, probably in the hypothalamus. The results are in harmony with the hypothesis that endogenous VIP is a physiological regulator of OT and AVP release in rats.     

Lack of release of vasoactive intestinal polypeptide and calcitonin gene-related peptide during electrical stimulation of enteric nerves in streptozotocin-diabetic rats

The simultaneous release of endogenous acetylcholine, serotonin, vasoactive intestinal polypeptide, substance P, and calcitonin gene-related peptide was measured during electrical field stimulation of isolated preparations of rat ileum from control and 8-wk streptozotocin-treated diabetic rats. Electrical field stimulation of the control rat ileum caused a significant increase in the release of all the above substances from the enteric nerves. The electrically evoked, but not the basal, release of these substances was inhibited by tetrodotoxin. In the diabetic rat ileum, however, there was no increase in the release of vasoactive intestinal polypeptide and calcitonin gene-related peptide during electrical stimulation, whereas endogenous release of acetylcholine, serotonin, and substance P was unaffected by the diabetic state. This was surprising in view of the increased fluorescence intensity and tissue content of vasoactive intestinal polypeptide-like immunoreactivity in the same tissue reported previously. The lack of increase in evoked release of vasoactive intestinal polypeptide in the diabetic preparations might be due to an impaired mechanism of release at the terminal site or to defective axonal transport of the peptide, whereas in the case of calcitonin gene-related peptide, it might be the result of the low level of the peptide present in the enteric nerve fibers of the diabetic rat ileum. The differential effect of diabetes on enteric nerves is discussed.     

Prenatal alcohol exposure and pineal response to isoproterenol, vasoactive intestinal polypeptide, and desmethvlimipramine

Abstract: Pineals from neonatal rats born to alcohol-fed mothers had lower unstimulated serotonin-N-acetyltransferase activity (NAT) and responded less to isoproterenol, vasoactive intestinal polypeptide, or desmethylimipramine challenge than did pineals from pups born to normal or pair-fed mothers. Group differences disappeared after the first week of life. Reduced NAT activity is coincident with elevated glucocorticoids in these pups. In contrast to these effects of chronic in utero ethanol exposure, acute ethanol addition to normal adult pineals in organ culture enhanced ISO but not VIP stimulation of NAT activity. The results suggest that the neonatal pineal is more affected by ethanol-induced activation of the adrenocortical axis during gestation than by the direct effect of ethanol on membrane fluidity.     

Density of substance P, vasoactive intestinal polypeptide and somatostatin-containing nerve fibers in the ageing small intestine of the rats

Immunoelectron microscopic investigations were carried out to study the substance P, vasoactive intestinal polypeptide (VIP) and somatostatin immunoreactive nerve elements in the wall of the small intestine. In young and old animals a large number of immunoreactive nerve fibers were found in all layers of the small intestine. They were observed closely to the epithelial cells, to the blood vessel basement membrane and to the smooth muscle cells and in some cases they were observed in a synapse with other unlabelled nerve fibers. On the other hand, in the senile animals very few immunoreactive nerve fibers were observed, calculated for a 100 micron2 tissue area. In the senile animals the overall number of nerve fibers was decreased in comparison to the young and old animals and most of them were in degeneration. This change could be the cause of the changes in the senescence-related epithelial transport processes and furthermore, of the modifications of the overall intestinal motility of the gastrointestinal tract, resulting in the age-dependent transit rates.     

Intracerebroventricular injection of cholecystokinin octapeptide elevates plasma prolactin levels through stimulation of vasoactive intestinal polypeptide

We investigated the effect of cholecystokinin octapeptide (CCK-8) on plasma PRL levels in freely moving male rats. Intravenous injection of CCK-8 did not affect basal plasma PRL levels in doses up to 5000 ng/rat; however, plasma PRL increased significantly after intracerebroventricular (icv) injection of the peptide at a dose of 40 ng/rat. Proglumide (0.2 mg/kg, iv) and benzotript (0.2 mg/kg, iv), specific CCK receptor antagonists, blocked the icv CCK-8-induced increase in plasma PRL levels. There was no apparent effect of icv CCK-8 on the enhancement of PRL release by haloperidol (0.2 mg/kg, iv), sulpiride (0.1 mg/kg, iv), domperidone (0.1 mg/kg, iv), or RO22-1319 (0.1 mg/kg, iv). However, the apomorphine-induced inhibition of PRL secretion was significantly antagonized by icv CCK-8. Furthermore, icv CCK-8 increased plasma PRL levels in rats depleted of dopamine by pretreatment with reserpine and alpha-methyl-p-tyrosine. Finally, the elevation in plasma PRL levels produced by icv CCK-8 was substantially antagonized by vasoactive intestinal polypeptide antiserum (1:3; 10 microliter/rat, icv). These results suggest that CCK-8 increases plasma PRL through an interaction with a central CCK receptor, which stimulates the activity of vasoactive intestinal polypeptide, a putative PRL-releasing factor.     

Circulating levels of vasoactive intestinal polypeptide in liver disease.

In animals, the effects of vasoactive intestinal polypeptide (VIP) include peripheral vasodilation, hyperdynamic circulation, hyperglycemia, and hyperventilation. Because these phenomena are noted in patients with cirrhosis, it has been postulated that VIP might be escaping hepatic inactivation and entering the systemic circulatory system and contributing to these abnormalities. The major purpose of this study is to establish whether or not VIP levels are elevated in patients with cirrhosis. Additional goals are to determine if VIP levels are elevated in acute liver disease and in chronic illnesses with secondary liver involvement. The data demonstrate that patients with cirrhosis and those with acute liver disease or chronic illnesses with secondary hepatic involvement have a wide range of VIP levels with mean values significantly above that of normal individuals and patients with chronic illness and no liver involvement.     

Osmoregulation in rats with long-term enhanced cerebrospinal fluid levels of vasopressin or vasoactive intestinal polypeptide

The cerebrospinal fluid level of arginine vasopressin (AVP) or vasoactive intestinal polypeptide (VIP) was enhanced chronically by implantation of a device for controlled drug delivery in the lateral ventricle of the rat. Urine production, water consumption, urine osmolality as well as urinary AVP excretion were then measured for a period of 26 days. During this period the rats were studied under normal hydration and under conditions of osmotic stress induced by water deprivation (2 days) and the drinking of 2% (w/v) NaCl (6 days), in order to see whether the capacity of central systems to react adequately to osmotic stimuli was affected by high central peptide levels. Immediately after the central AVP treatment was started, a temporary increase was found in urinary AVP levels which was not accompanied by a change in any of the other parameters but which decreased again to control levels within 10 days. After this burst of AVP excretion, AVP-treated rats showed a tendency during periods of normal hydration for a lower urine osmolality, combined with a higher water intake and urine production without changes in urinary AVP excretion. Since there was no clear-cut correlation between urinary AVP excretion and body water turnover, this could still indicate a slowly acquired and slight inhibition of pituitary AVP release by long-term centrally administered AVP. However, the capacity of these rats to respond to osmotic stimuli was not different from the controls. In the VIP-treated rats a slight but significant reduction in urine production was found in all three periods of normal hydration.(ABSTRACT TRUNCATED AT 250 WORDS)     

Rhythmic secretion of prolactin in rats: action of oxytocin coordinated by vasoactive intestinal polypeptide of suprachiasmatic nucleus origin

Prolactin (PRL) is secreted from lactotrophs of the anterior pituitary gland of rats in a unique pattern in response to uterine cervical stimulation (CS) during mating. Surges of PRL secretion occur in response to relief from hypothalamic dopaminergic inhibition and stimulation by hypothalamic releasing neurohormones. In this study, we characterized the role of oxytocin (OT) in this system and the involvement of vasoactive intestinal polypeptide (VIP) from the suprachiasmatic nucleus (SCN) in controlling OT and PRL secretion of CS rats. The effect of OT on PRL secretion was demonstrated in cultured lactotrophs showing simultaneous enhanced secretion rate and increased intracellular Ca(2+). Neurosecretory OT cells of the hypothalamic paraventricular nucleus that express VIP receptors were identified by using immunocytochemical techniques in combination with the retrogradely transported neuronal tracer Fluoro-Gold (iv injected). OT measurements of serial blood samples obtained from ovariectomized (OVX) CS rats displayed a prominent increase at the time of the afternoon PRL peak. The injection of VIP antisense oligonucleotides into the SCN abolished the afternoon increase of OT and PRL in CS-OVX animals. These findings suggest that VIP from the SCN contributes to the regulation of OT and PRL secretion in CS rats. We propose that in CS rats the regulatory mechanism(s) for PRL secretion comprise coordinated action of neuroendocrine dopaminergic and OT cells, both governed by the daily rhythm of VIP-ergic output from the SCN. This hypothesis is illustrated with a mathematical model.     

Effects of tactile and electrical stimuli upon release of vasoactive intestinal polypeptide in the mammalian penis

Plasma levels of vasoactive intestinal polypeptide (VIP) in the corpora cavernosa penis and dorsal penile veins greatly exceeded those measured in the limb or caudal veins during anaesthesia in various mammals (Bennett's wallaby, Barbary sheep, cheetah, puma, sooty mangabey, pigtail macaque and chimpanzee). Tactile stimulation of the penis immediately before or during collection of blood samples resulted in an increase. In the wallaby, VIP levels (mean +/- S.E.M.) in blood samples collected from the flaccid penis in the absence of tactile stimulation were very low (0.6 +/- 0.5 pmol/l). A 36-fold increase in VIP occurred after manual extension of the flaccid penis (24.8 +/- 3.2 pmol/l) or during manually stimulated erections (25.1 +/- 1.7 pmol/l). Electrical stimulation of erection produced no significant increase in VIP levels (2.3 +/- 0.9 pmol/l) unless accompanied by tactile stimulation (17.5 +/- 1.4 pmol/l). These studies provide the first demonstration that sensory feedback from the penis plays an important role in regulating vasoactive intestinal polypeptidergic activity. Since VIP is a potent vasodilator its release due to tactile stimuli during copulation may play a role in the maintenance of penile erection.     

The effects of secretin on prolactin, estradiol, vasoactive intestinal polypeptide, and somatostatin levels in women

The effect of graded doses of intravenous secretin (0.5, 1.0, and 2.0 CU.kg-1.h-1) on serum prolactin and estradiol levels, as well as plasma vasoactive intestinal polypeptide and somatostatin levels was studied in 6 normally cycling and healthy women, and compared with the hormone levels obtained by a control infusion with physiologic saline (0.15 mol/l). A significant decrease in serum prolactin concentrations was found with increasing doses of secretin at steady-state levels of plasma secretin (+30 to +60 min). A significant negative correlation (p less than 0.007, r = -0.2764) existed between serum prolactin and plasma secretin concentrations at steady-state conditions. No effect of graded doses of secretin was observed on serum estradiol levels and plasma concentrations of vasoactive intestinal polypeptide and somatostatin. The results suggest a dose-related inhibitory effect of secretin on prolactin release in women.     

Effects of gastrin on circulating levels of somatostatin, pancreatic polypeptide, and vasoactive intestinal peptide in dogs

The effect of synthetic human gastrin I, infused at two doses, on the concentrations of somatostatin, pancreatic polypeptide, and vasoactive intestinal peptide in portal and systemic blood was studied in six anesthetized dogs. Intragastric pH was maintained at 5.5, and acid output was measured by intragastric titration. Significant increases in somatostatin and pancreatic polypeptide concentrations in portal blood were found with the lower dose of gastrin (0.5 microgram/kg . h) infused for 40 min. When gastrin was infused at 1.5 microgram/kg . h for 100 min, both portal and systemic blood concentrations of somatostatin and pancreatic polypeptide rose significantly. Cimetidine (300 mg, as an iv bolus), given 40 min after the beginning of the second infusion, did not affect gastrin-stimulated release of somatostatin and pancreatic polypeptide, whereas acid output was completely abolished. Vasoactive intestinal peptide concentrations did not change with the infusion of either dose of gastrin. This daily shows that gastrin releases somatostatin and pancreatic polypeptide in a dose-dependent fashion, and since this release was not acid mediated, it appears likely to be a direct action of gastrin.     

Increases in plasma insulin levels in response to electrical stimulation of the dorsal motor nucleus of the vagus nerve

In order to investigate the physiological counterpart of the anatomical finding showing that the dorsal motor nucleus of the vagus nerve (DMX) is a source of efferent vagal fibers innervating the pancreas, unilateral electrical stimulation using monopolar electrodes (50 microA, 30 Hz, 0.2 msec) at a glycemia of 150 mg/100 ml was performed in normal anesthetized rats. DMX stimulation resulted in rapid (within 1 min) rise in plasma insulin levels (greater than or equal to 200%). Stimulation of the nucleus of tractus solitarius, anatomically connected to DMX, also produced a 50% increase in insulinemia. The effect of DMX stimulation was almost completely abolished by atropine pretreatment or acute bilateral subdiaphragmatic vagotomy. The effect of DMX stimulation was not potentiated by the alpha-adrenergic blocker (infusion of phentolamine) indicating that no inhibitory fiber was recruited during DMX stimulation. It is concluded that DMX is connected to the endocrine pancreas exclusively via vagal fibers and has a role in neurally mediated insulin release.     

Plasma concentration of vasoactive intestinal polypeptide during prolonged physical exercise, calorie supply deficiency, and sleep deprivation

Twenty-four military cadets went through a 5-day period of heavy physical exercise (35% of max O2 uptake), severe calorie supply deficiency (about 36,000 kJ/24 h), and sleep deprivation (2 h of sleep as a total during 5 days). Some cadets compensated for the caloric deficiency, whereas others partly compensated for the sleep deprivation. Fasting and meal- and glucose-induced changes in the plasma concentration of vasoactive intestinal polypeptide (VIP) were measured on separate days during the course and 8 h after the course was finished (day 6). Fasting plasma concentration of VIP increased two- to five-fold during the course, with the highest increase on day 2. The calorie-compensated subjects showed a smaller increase than those who did not receive any calorie or sleep compensation. Intake of a meal or glucose solution lowered the VIP concentration in plasma within 30-60 min to the concentrations found in the control experiments performed several weeks after the course. The results indicate a role of VIP as 'a polypeptide of substrate need'.     

Effects of hexamethonium and atropine on the basal levels of immunoreactive vasoactive intestinal polypeptide in dogs

The basal levels of immunoreactive vasoactive intestinal polypeptide (IR-VIP) in veins of the gastrointestinal tract and the effect of hexamethonium and atropine on basal levels of IR-VIP were examined in anesthetized dogs. The basal mean plasma IR-VIP levels in the pancreaticoduodenal vein, the mesenteric vein of the jejunum, the mesenteric vein of the ileum and the right colonic vein, but not the left gastroepiploic vein, were significantly higher than those in the femoral vein. These basal levels of IR-VIP were decreased by atropine, but not by hexamethonium. Thus, the main source of basal VIP in the portal vein is probably the duodenum (and pancreas) and the small and large intestine, and the basal levels of VIP are under the control of muscarinic receptors, in canine gastrointestinal tract.     

Lack of plasma prolactin response to intravenously injected vasoactive intestinal polypeptide in patients with prolactin-secreting adenoma

Although bromocriptine administration produces reduction in size of prolactinomas, its effect upon non-functional pituitary adenomas is still uncertain. Nine patients with macroadenomas, 2 of them with prolactinomas and 7 with non-functional tumours, received bromocriptine prior to transsphenoidal surgery. Size reduction of tumour mass was assessed by computerized tomography and by visual field examination before and following bromocriptine treatment. There were no signs of size diminution or pathological changes in the non-functional adenomas treated pharmacologically during 15 to 360 days. Both patients with prolactinomas had radiological evidence of size reduction and morphological changes on microscopic examination. These 2 patients had tumours with prolactin granules (immunocytochemistry) and adenoma cells showed reduced cytoplasmatic, nuclear and nucleolar areas. Neither vascular damage, cell necrosis, nor infarction was observed by electron microscopy. Patients with non-functional tumours as determined by immunocytochemistry and hormone production did not benefit from bromocriptine. The suggestion that bromocriptine can be used as primary treatment for non-functional pituitary tumours is not supported by the present study. Conversely, in cases of macroprolactinoma, bromocriptine is a useful pre-operative adjunct when surgery is planned and for those patients in whom a surgical cure is considered difficult owing to the tumour size.     

Administration of antisera to vasoactive intestinal polypeptide and peptide histidine isoleucine attenuates ether-induced prolactin secretion in rats

The effect of immunoneutralization of endogenous vasoactive intestinal polypeptide (VIP) and peptide histidine isoleucine (PHI)-like peptides by administration of specific and potent antisera to the respective peptides on ether stress-induced prolactin (PRL) release was examined in male rats bearing an indwelling atrial catheter. Forty-five minutes after an injection of 1 ml of either normal rabbit serum (NRS), anti-VIP serum (AVS), anti-PHI serum (APS) or AVS plus APS, the rat was placed for 1 min in a beaker containing an ether-impregnated cotton ball. Ether exposure caused a prompt and significant increase in plasma PRL in all of the animal groups tested. Pretreatment with either antisera did not affect basal plasma PRL levels, whereas plasma PRL rises after ether exposure were significantly lower in rats pretreated with AVS, APS or AVS plus APS than those with NRS. These results suggest that hypothalamic VIP and PHI-like peptides may be involved, at least in part, in the mechanism by which ether stress stimulates PRL secretion in rats.     

Twenty-four-hour secretory pattern of vasoactive intestinal polypeptide in the elderly

A chronobiological study was carried out in 8 elderly male subjects (74-85 years) to evaluate the 24-hour vasoactive intestinal polypeptide (VIP) secretory pattern. Eight young adult males (21-32 years) made up the control group. Blood samples were drawn from each subject every 2 h during the day and hourly during the night for a 24-hour period. Mean 24-hour VIP values in elderly (21.1 +/- 0.3 pg/ml) and young adults (19.1 +/- 0.3 pg/ml) did not differ statistically, but daytime VIP values observed in elderly subjects (21.4 +/- 0.5 pg/ml) were higher (p less than 0.05) than those recorded in young adults (17.5 +/- 0.5 pg/ml). The young adults showed significant (p less than 0.05) circadian VIP fluctuations with highest values during the nighttime, while the elderly subjects did not. An age-related decreased activity of the peripheral neuronal VIP-ergic network is hypothesized.     

Ultrastructural localisation of substance P, vasoactive intestinal polypeptide, somatostatin and neuropeptide Y immunoreactivity in perivascular nerve plexuses of the gut

Substance P, vasoactive intestinal polypeptide, somatostatin and neuropeptide Y-like immunoreactivity was studied by immunocytochemistry in the wall of the blood vessels of the small intestine of the cat, rat and guinea-pig. Immunoreactive nerve fibres were localized by means of the peroxidase-antiperoxidase (PAP) procedure, by use of antisera raised against these peptides. These neuropeptide-containing nerve fibres were widespread in association with the blood vessels and especially with the dense network of perivascular nerves supplying arterioles. At the ultrastructural level, immunoreactive nerve fibres were found very close to the basement membrane of the capillary walls. No immunoreactive nerve fibres were found in the wall of the veins. The anatomical findings of the present study are consistent with the proposal that several neuropeptides could function as neurotransmitters or neuromodulators in the control of blood flow in the small intestine.     

Cerebrospinal fluid levels of acetylcholinesterase, monoamines and oxytocin during labour, parturition, vaginocervical stimulation, lamb separation and suckling in sheep

Acetylcholinesterase (AChE) activity, and concentrations of monoamines, monoamine metabolites and oxytocin (OT) were measured in the cerebrospinal fluid (CSF) of sheep during late pregnancy, labour, parturition, vaginocervical stimulation, lamb separation and suckling. Concentrations of AChE, 4-hydroxy-3 methoxyphenylethan-1,2-diol (MHPG) and OT were significantly elevated during labour and parturition. OT levels were also significantly raised in cycling ewes given vaginocervical stimulation. Separation of the ewes from their lambs (0.5-2 h) caused significant increases in AChE and MHPG, but not in OT. During suckling, following reunion of the ewes and lambs, concentrations of AChE and OT were significantly raised. The dopamine metabolites 3,4-dihydroxyphenylacetic acid and homovanillic acid were significantly lower in CSF during late pregnancy than during parturition and post-partum. Intravenous injections of OT which produced high circulating levels of this hormone in plasma produced significant, but very small, increases in concentrations of OT in the CSF. Our results show that in the sheep, labour, parturition, suckling and vaginocervical stimulation provoke a release of OT in the brain similar to that in the peripheral circulation. Changes in CSF levels of AChE and MHPG during labour, parturition and lamb separation, but not during vaginocervical stimulation, may be related to stress or hypertension.