The influence of cadmium (CdCl2) on the canine plasma levels of gastrin,cholecystokinin (CCK), and pancreatic polypeptide (PP)

The influence of cadmium on basal and stimulated plasma levels of gastrin, cholecystokinin (CCK), and pancreatic polypeptide (PP) was investigated in conscious dogs using three doses of cadmium (0.15, 0.5, and 0.75 mg Cd/kg-h). Levels of gastrointestinal (GI) hormones were stimulated with bombesin (BBS), a peptide known to stimulate GI hormone release. Plasma cadmium was measured employing atomic absorption spectrophotometry and GI hormone levels were measured with specific radioimmunoassays (RIA). Basal plasma levels of hormones (pg/mL) in the dogs were in the range (mean ± SE): 38±5 to 44±6 for gastrin, 80±25 to 107±17, for CCK and 120±5 to 142±5 for PP; these levels did not change with cadmium. Significant increases above basal levels in all three hormones were found with infusions of BBS and with BBS plus cadmium. Gastrin levels remained steady during Cd and saline after BBS; however, CCK and PP levels dropped to values that were 68 and 73% less than their stimulated peak levels. With reinfusion of BBS, gastrin, CCK, and PP were significantly elevated above basal; however, the peak values for CCK and PP, but not gastrin, were less than those found during the first BBS infusion. The data suggest that in response to bombesin, cadmium has little or no effect on the release of gastrin, but that is exerts a latent effect on the release of both CCK and PP.     

Effect of immunoneutralisation of cholecystokinin on bombesin-stimulated pancreatic enzyme secretion in the rat

Infusion of bombesin stimulates plasma cholecystokinin (CCK) and pancreatic enzyme secretion in various species, including the rat. This study was undertaken in two groups of four conscious rats with a cannulated pancreatic duct to determine the role of endogenously released CCK in mediating the effect of bombesin on pancreatic enzyme secretion. Infusion of 2 ml CCK antiserum or normal rabbit serum for 40 min was followed 10 min later by infusion of 18 pmol/kg bombesin for 30 min and after an interval of 90 min by infusion of 24 pmol/kg CCK for 30 min. After administration of control rabbit serum, pancreatic protein secretion increased by 3.2 +/- 1.0 mg/30 min during bombesin and 4.0 +/- 1.5 mg/30 min during CCK, while the plasma CCK increments were 1.7 +/- 0.5 pM and 7.0 +/- 0.9 pM for the bombesin and CCK infusions, respectively. Immunoneutralisation with the CCK antiserum did not significantly affect bombesin-stimulated pancreatic protein secretion (3.6 +/- 1.3 mg/30 min), but almost abolished the pancreatic protein response to CCK (0.5 +/- 0.2 mg/30 min). It is therefore concluded that CCK is not an important mediator of the stimulatory effect of bombesin on the pancreas in the rat.     

Factors regulating amylase secretion from chicken pancreatic acini in vitro

In mammals, cholecystokinin regulates pancreatic exocrine secretion under physiological conditions. We have shown, however, that cholecystokinin at physiological concentrations does not induce pancreatic amylase secretion in birds. Therefore, we investigated the effects of various neurotransmitters and gut hormones on the pancreatic amylase secretory response in isolated chicken pancreatic acini. Acetylcholine (half-maximal stimulation at 800 nM) and vasoactive intestinal polypeptide (half-maximal stimulation at 40 pM) produced a concentration-dependent increase in amylase secretion at physiological concentrations. The combination of acetylcholine and vasoactive intestinal polypeptide produced an additive response in amylase secretion. Sodium nitroprusside, a spontaneous nitric oxide releaser, and bombesin, induced amylase secretion at concentrations greater than 10 nM and 100 nM, respectively. Gastrin and secretin increased amylase secretion at pharmacological concentrations (10 to 100 nM). Our findings suggest that neural regulation is important for pancreatic enzyme secretion in birds and the contribution of gut hormones seems to be physiologically unimportant.     

Differential stimulation of pancreatic-polypeptide and gastrin secretion by bombesin in man

Bombesin, besides many other actions on the mammalian gastroentero-pancreatic tract, strongly stimulates the release of pancreatic-polypeptide (PP) in dogs. In 8 healthy human volunteers (5 males, 3 females), the PP response during bombesin infusion was low (25.7 ± 6.3 peak vs. 5.0 ± 2.0 basal pmol/1) compared to the effect of a protein meal (144.1 ± 13.4 pmol/1) or to the gastrin response to the same dose of the amphibian polypeptide (140.0 ± 23.6 pmol/1 eq SHG 17 I). The response pattern of PP and gastrin was different as PP concentrations peaked 10 min after cessation of bombesin infusion (32.0 ± 4.9 pmol/1) when gastrin concentrations already were down to one third of the maximal response. Atropine inhibited the PP response to bombesin but did not abolish it completely. It is concluded that in man, the total effect of bombesin on PP secretion is minor compared both to the effect of the peptide on gastrin secretion in man and to the effect of bombesin in dogs. It is suggested that bombesin might have a dual, inhibitory-stimulatory, effect on PP secretion in man.     

Regulatory peptides in the gastrointestinal tract of Alligator mississipiensis

Summary The gastrointestinal tract of the alligator Alligator mississipiensis has been investigated for the presence of immunoreactivity to fourteen regulatory peptides all known to occur in the mammalian gut system.Mucosal endocrine cells reacting specifically with the antisera to neurotensin, C-terminal gastrin, somatostatin, bombesin, secretin, pancreatic glucagon and enteroglucagon were detectable, the distribution of these cells being, in general, similar to the mammalian pattern. Peripheral nerve cell bodies and nerve fibres were detected with the antisera to vasoactive intestinal polypeptide, substance P, bombesin and somatostatin again with a distribution similar to that seen in mammals.No immunoreactivity was observed with the available antisera to glicentin, motilin, gastric inhibitory polypeptide, gastrin 34, cholecystokinin 9–20 and met-enkephalin.     

铃蟾肽(Bombesin)对离体灌流大鼠胃的胃泌素、生长抑素、胰升糖素及胃酸释放的影响

本研究用离体大鼠胃灌流技术来观察铃蟾肽对胃-肠激素及胃酸分泌的影响。2×10~(?)mol/L铃蟾肽以0.3ml/min速度作动脉内输注,可刺激胃酸的分泌,自2.50±0.05×10~(-1)增至5.50±1.50×10~(-1)mEq/min,但与外源性五肽胃泌素无协同作用。铃蟾肽引起两次性的门脉中胃泌索及生长抑素的释放,但抑制胰升糖素释放。这三种激素的基础释放率分别为:胃泌素62±8pg,生长抑素5.9±1.1ng,胰升糖素0.40±0.03ng/min;2×10~(-8)mol/L铃蟾肽以0.3ml/min作动脉内输注,胃泌素及生长抑素的峰值分别为1,000±20pg及12.2±2.0ng/min,胰升糖素的最低值为0.17±0.05ng/min,三种激素的反应均与铃蟾肽的浓度成正比。在胃腔流出液中也可测到上述三种激素,但量要少得多。     

Cholinergic inhibition of meal stimulated plasma neurotensin like immunoreactivity in man

Meal stimulated plasma neurotensin like immunoreactivity (NTLI) was compared during saline or atropine infusion in six volunteers over six hours. Plasma gastrin and pancreatic polypeptide were also measured to compare the timing of their release to that of NTLI. Like plasma gastrin and PP, plasma NTLI rose rapidly following the meal, rising from 27±7 pmol/1 to a peak of 45±8 pmol/1 at 20 minutes (p < 0.05). Also, like that of pancreatic polypeptide, the release of NTLI was biphasic. Sixty minutes after the meal, plasma NTLI had returned to basal values, followed by a rise to a prolonged peak of 64±10 pmol/1 between 90–180 minutes (p < 0.05) returning once more to basal values by 240 minutes. Following atropine, basal plasma NTLI fell from 22±4 pmol/1 to 11±2 pmol/1 (p < 0.05), but rose to basal levels 30–60 minutes after the meal, where it remained unaltered for the remainder of the study. We conclude that both basal and meal stimulated plasma NTLI are inhibited by cholinergic blockade. Further, the similar temporal relationship between plasma NTLI and pancreatic polypeptide in the late phase of the meal response, suggests that a component of NTLI may mediate part of the intestinal phase of pancreatic polypeptide release.     

Somatostatin,prostaglandin E2 and atropine inhibition of the gastric actions of bombesin in the dog

Bombesin, acetylcholine, prostaglandins and somatostatin are all thought to be involved in the regulation of gastrin release and gastric secretion. We have studied the effects of low doses of atropine, 16-16(Me)₂-prostaglandin E₂ (PGE₂) and somatostatin-14 on bombesin-stimulated gastrin release and gastric acid and pepsin secretion in conscious fistula dogs. For reference, synthetic gastrin G-17 was studied with and without somatostatin. Bombesin, in a dose-related manner, increased serum gastrin, which in turn stimulated gastric acid and pepsin secretion in a serum gastrin, concentration-dependent manner. Somatostatin inhibited gastrin release by bombesin as well as the secretory stimulation by G-17; the combination of sequential effects resulted in a marked inhibition of bombesin-stimulated gastric acid and pepsin secretion. PGE₂ also strongly inhibited gastrin release and acid and pepsin secretion. Atropine had no significant effect on gastrin release, but greatly inhibited gastric secretion. Thus somatostatin and PGE₂ inhibited at two sites, gastrin release and gastrin effects, while atropine affected only the latter.     

Effect of pancreatic enzyme supplementation on postprandial plasma cholecystokinin secretion in patients with pancreatic insufficiency

To test the hypothesis, based on studies in healthy man and dog, that patients with impaired digestion due to severe pancreatic insufficiency have impaired postprandial cholecystokinin (CCK) secretion that can be improved by the addition of pancreatic enzymes, we have studied plasma CCK responses to a test meal with and without addition of pancreatic enzymes in 10 patients with pancreatic insufficiency and steatorrhea, in 8 patients with chronic pancreatitis without steatorrhea, and in 6 healthy subjects. The patients with steatorrhea had a significantly (P less than 0.001) lower integrated plasma CCK response to the meal (177 +/- 23 pM.150 min) than the healthy subjects (468 +/- 41 pM.150 min), while patients with chronic pancreatitis without steatorrhea had an intermediate integrated postprandial CCK secretion (327 +/- 101 pM.150 min). Addition of pancreatic enzymes to the meal significantly augmented the integrated CCK response in both the patients with steatorrhea to 483 +/- 72 pM.150 min (P less than 0.01) and in those without steatorrhea to 480 +/- 85 pM.150 min (P less than 0.05). These values were not significantly different from those in the healthy subjects (521 +/- 86 pM.150 min). Integrated CCK secretion in the three groups during bombesin infusion was similar (patients with steatorrhea 134 +/- 23 pM.20 min, patients without steatorrhea 131 +/- 33 pM.20 min, and healthy subjects 146 +/- 28 pM.20 min), indicating a normal capacity to secrete CCK in response to a humoral stimulus. These data are in agreement with the suggestions from previous studies that digestion of nutrients by pancreatic enzymes plays an important role in the regulation of plasma CCK secretion after feeding.     

Effect of atropine on plasma gastrin and somatostatin concentrations during sham feeding in man

The purpose of these studies was to measure circulating gastrin and somatostatin concentrations during sham feeding in humans and to evaluate the effect of two doses of intravenous atropine on circulating concentrations of these peptides. Gastric acid and bicarbonate secretion and pulse rate were also measured. Sham feeding increased plasma gastrin concentrations by approximately 15 pg/ml but had no effect on plasma somatostatin-like immunoreactivity (SLI). A small dose of atropine (5 micrograms/kg) augmented plasma gastrin concentrations during sham feeding significantly (P less than 0.01), but did not affect plasma SLI. Atropine also significantly inhibited gastric acid secretion and gastric bicarbonate secretion (by 62% and 52%, respectively), but pulse rate was not affected. A larger dose of atropine (15 micrograms/kg intravenously) suppressed plasma gastrin concentrations significantly compared to the smaller 5 micrograms/kg atropine dose (P less than 0.02), so that plasma gastrin concentrations when 15 micrograms/kg atropine was given were not significantly different from those during the control study. 15 micrograms/kg atropine reduced gastric acid and bicarbonate secretion by 81% and 66%, respectively, and also increased pulse rate by 15 min-1. These studies indicate that small doses of atropine enhance vagally mediated gastrin release in humans, probably by blocking a cholinergic inhibitory pathway for gastrin release. Although the nature of this cholinergic inhibitory mechanism is unclear, we found no evidence to incriminate somatostatin. Our finding that the larger dose of atropine reduced serum gastrin concentrations compared with the smaller dose suggests that certain vagal-cholinergic pathways may facilitate gastrin release.     

Neurohormonal regulation of secretion from isolated rat stomach ECL cells: a critical reappraisal

ECL cells are endocrine/paracrine cells in the oxyntic mucosa. They produce, store and secrete histamine and chromogranin A-derived peptides such as pancreastatin. The regulation of ECL-cell secretion has been studied by several groups using purified ECL cells, isolated from rat stomachs. Reports from different laboratories often disagree. The purpose of the present study was to re-evaluate the discrepancies by studying histamine (or pancreastatin) secretion from standardized preparations of pure, well-functioning ECL cells. Cells from rat oxyntic mucosa were dispersed by pronase digestion, purified by repeated counter-flow elutriation and subjected to density gradient centrifugation. The final preparation consisted of more than 90% ECL cells (verified by histamine and/or histidine decarboxylase immunocytochemistry). They were maintained in primary culture for 48 h before they were exposed to candidate stimulants and inhibitors for 30 min after which the medium was collected for determination of mobilized histamine (or pancreastatin). Gastrin-17 and sulphated cholecystokinin octapeptide (CCK-8s) raised histamine secretion 4-fold, the EC(50) for both peptides being around 100 pM. The neuropeptide pituitary adenylate cyclase activating peptide (PACAP-27) (5-fold increase) and the related neuropeptides vasoactive intestinal peptide (VIP) and peptide histidine isoleucine (PHI) (3-fold increase) mobilized histamine with similar potency (EC(50) ranging from 80 to 140 pM). Adrenaline, isoprenaline and terbutaline stimulated secretion by activating a beta2 receptor subtype, while acetylcholine and carbachol were without effect. Secretion experiments were invariably run in parallel with a gastrin standard curve. Somatostatin, prostaglandin E2 (PGE2) and the PGE1 congener misoprostol inhibited PACAP- and gastrin-stimulated secretion by more than 90%, with IC(50) values ranging from 90-720 (somatostatin) to 40-200 (misoprostol) pM. The neuropeptide galanin inhibited secretion by 60-70% with a potency similar to that of somatostatin. Proposed inhibitors such as peptide YY, neuropeptide Y and the cytokines interleukin 1-beta and tumor necrosis factor alpha induced at best a moderate inhibition of gastrin- or PACAP-stimulated secretion at high concentrations, while calcitonin gene-related peptide, pancreatic polypeptide and histamine itself were without effect. Inhibition of gastrin- or PACAP-stimulated secretion was routinely compared to a somatostatin standard curve. In conclusion, gastrin, PACAP, VIP/PHI and adrenaline stimulated secretion. Somatostatin and PGE2 were powerful inhibitors of both gastrin- and PACAP-stimulated secretion; although equally potent, galanin was less effective than somatostatin and PGE2.     

Gastrin secretion by ovine antral mucosa in vitro

The effect on gastrin and somatostatin release in sheep of stimulatory and inhibitory peptides and pharmacological agents was investigated using an in vitro preparation of ovine antral mucosa. Carbachol stimulated gastrin release in a dose-dependent manner but had no effect on somatostatin release. As atropine blocked the effect of carbachol, cholinergic agonists appear to stimulate gastrin secretion directly through muscarinic receptors on the G-cell and not by inhibition of somatostatin secretion. Both vasoactive-intestinal peptide (VIP) and gastric-inhibitory peptide (GIP) increased somatostatin release but did not inhibit basal gastrin secretion, although VIP was effective in reducing the gastrin response to Gastrin-releasing peptide (GRP). Porcine and human GRP were stimulatory to gastrin secretion in high doses but bombesin was without effect. The relative insensitivity to GRP (not of ovine origin) previously reported from intact sheep may be caused either by a high basal release of somatostatin or by the ovine GRP receptor or peptide differing from those of other mammalian species.     

Neural, hormonal, and paracrine regulation of gastrin and acid secretion.

Physiological stimuli from inside and outside the stomach coverage on gastric effector neurons that are the primary regulators of acid secretion. The effector neurons comprise cholinergic neurons and two types of non-cholinergic neurons: bombesin/GRP and VIP neurons. The neurons act directly on target cells or indirectly by regulating release of the hormone, gastrin, the stimulatory paracrine amine, histamine, and the inhibitory paracrine peptide, somatostatin. In the antrum, cholinergic and bombesin/GRP neurons activated by intraluminal proteins stimulate gastrin secretion directly and, in the case of cholinergic neurons, indirectly by eliminating the inhibitory influence of somatostatin (disinhibition). In turn, gastrin acts on adjacent somatostatin cells to restore the secretion of somatostatin. The dual paracrine circuit activated by antral neurons determines the magnitude of gastrin secretion. Low-level distention of the antrum activates, preferentially, VIP neurons that stimulate somatostatin secretion and thus inhibit gastrin secretion. Higher levels of distention activate predominantly cholinergic neurons that suppress antral somatostatin secretion and thus stimulate gastrin secretion. In the fundus, cholinergic neurons activated by distention or proteins stimulate acid secretion directly and indirectly by eliminating the inhibitory influence of somatostatin. The same stimuli activate bombesin/GRP and VIP neurons that stimulate somatostatin secretion and thus attenuate acid secretion. In addition, gastrin and fundic somatostatin influence acid secretion directly and indirectly by regulating histamine release. Acid in the lumen stimulates somatostatin secretion, which attenuates acid secretion in the fundus and gastrin secretion in the antrum.     

The effect of atropine on bombesin and gastrin releasing peptide stimulated gastrin, pancreatic polypeptide and neurotensin release in man

The effects of 1-h infusions of bombesin and gastrin releasing peptide (GRP) at 50 pmol/kg per h and neurotensin at 100 pmol/kg per h on gastrin, pancreatic polypeptide (PP) and neurotensin release in man were determined following either saline or atropine infusion (20 micrograms/kg). Bombesin produced a rise in plasma neurotensin from 32 +/- 6 to 61 +/- 19 pmol/l and of PP from 26 +/- 8 to 36 +/- 7 pmol/l. There was a further rise of plasma PP to 50 +/- 13 pmol/l after cessation of the infusion. GRP had no significant effect on plasma neurotensin, but compared to bombesin, produced a significantly greater rise in plasma PP from 34 +/- 6 to 66 +/- 19 pmol/l during infusion. There was no post-infusional increase. At this dose, GRP was as effective as bombesin in releasing gastrin, although unlike bombesin its effect was enhanced by atropine. Neurotensin produced a rise in plasma PP from 17 +/- 4 to 38 +/- 8 pmol/l. Atropine blocked the release of PP during GRP and neurotensin infusion. Atropine had no effect on neurotensin or PP release during bombesin infusion, but did block the rise in plasma PP following bombesin infusion. We conclude that, in contrast to meal-stimulated neurotensin release, bombesin-stimulated neurotensin release is cholinergic independent. Despite structural homology, bombesin and GRP at the dose used are dissimilar in man in their actions and sensitivity to cholinergic blockade.     

Human pancreatic polypeptide has a marked diurnal rhythm that is affected by ageing and is associated with the gastric TFF2 circadian rhythm

Normal circadian variations in vasoactive intestinal polypeptide, somatostatin, cholecystokinin and pancreatic polypeptide were measured to determine if these alter with aging and to identify gastrointestinal regulatory hormones that might control the dramatic diurnal variation in the gastric cytoprotective trefoil protein TFF2. Plasma pancreatic polypeptide concentrations showed a marked diurnal rhythm (p < 0.0001). Basal and postprandial pancreatic polypeptide concentrations increased with age (p < 0.01). The timing of the diurnal rhythm was consistent with pancreatic polypeptide inhibiting TFF2 secretion and there was a negative association between pancreatic polypeptide and TFF2 concentrations (p < 0.002). The much higher pancreatic polypeptide concentrations in older people will induce increased satiety that may contribute to 'anorexia of ageing'. These results identify potential therapies for treatment of gastric mucosal morbidity and age-associated loss of appetite.     

The effect of gastrin-releasing peptide on the endocrine pancreas

The 27-amino acid peptide gastrin releasing peptide (GRP-(1–27)) was infused at 4 dose levels (0.01, 0.1, 1.0, and 10 nM) into the arterial line of the isolated perfused porcine pancreas. Infusions were performed at 3 different perfusate glucose levels (3.5, 5.0, and 8.0 mM) and at two levels of amino acids (5 and 15 mM). GRP-(1–27) stimulated insulin and pancreatic polypeptide secretion and inhibited somatostatin secretion in a dose-dependent manner. Glucagon secretion was unaffected by infusion of GRP under all circumstances. The effect of GRP-(1–27) on insulin secretion was enhanced with increasing perfusate glucose levels, whereas the effects upon somatostatin and pancreatic polypeptide secretion were independent of perfusate glucose levels. The responses to GRP were unaffected by elevation of the concentration of amino acids in the perfusate. The effects of GRP were unaffected by atropine at 10⁻⁶ M. The localization of GRP within the porcine pancreas, its release during electrical stimulation of the vagus nerve, and its potent effects upon pancreatic endocrine secretion make it conceiveable that the peptide participates in parasympathetic regulation of pancreatic endocrine secretion.     

Effect of bombesin-stimulated gastrin on gastric acid secretion in man

The effect of bombesin on gastrin release and gastric acid secretion was investigated in 10 healthy volunteers. Bombesin (0.6 μg · Kg^?1 · hr^?1) produced a significantly higher $\text{(}\text{p}\text{<}\text{0.001)}$ increase in plasma gastrin levels (86.7 11.1 pmo/1 than after a protein meal (39.6 ± 5.6 pmol1/1). The gastric acid secretory response to bombesin (12.1 ± 2.9 mEq · hr^?1) was however significantly lower $\text{(}\text{p}\text{<}\text{0.005)}$ than the maximal response produced by pentagostrin (20.9 ± 3.5 mEq · hr^?1) at the dose of 6 μg · Kg^?1. Atropine did not modify gastrin release induced by bombesin but significantly reduced gastric acid secretion $\text{(}\text{p}\text{<}\text{0.01)}$. From the data presented it may be hypothesized that less biologically active forms of gastrin and/or other peptides inhibiting the gastrin effect upon gastric acid secretion may be released by bombesin.     

Effect of nicotine on basal and bombesin stimulated canine plasma levels of gastrin, cholecystokinin and pancreatic polypeptide

The influence of nicotine on the basal and bombesin (BBS) stimulated plasma levels of gastrin, cholecystokinin (CCK) and pancreatic polypeptide (PP) was investigated in conscious dogs. Plasma levels of nicotine and gastrointestinal (GI) hormones were measured by employing gas liquid chromatography and specific radioimmunoassay (RIA). The basal levels of gastrin, CCK and PP were found to be in pg/ml (pmol/l) (mean +/- S.E.), 28 +/- 5 (13 +/- 3), 252 +/- 32 (66 +/- 8) and 347 +/- 136 (83 +/- 32), respectively and these values remained unchanged with nicotine. Significant increases in levels of gastrin, CCK and PP were, however, found with infusions of BBS alone or with BBS in combination with nicotine. Gastrin levels were higher whereas CCK and PP levels were lower with BBS alone than with BBS plus nicotine. The peak values for CCK and PP, but not gastrin, were less during second BBS infusion. These results indicate that nicotine, in presence of bombesin, has an inhibitory effect on the release of gastrin and a stimulatory effect on the release of PP and CCK.     

Meal-induced increase in plasma gastrin immunoreactivity in the rhesus monkey (Macaca mulatta)

The hormonal response to food intake in rodents, dogs, and humans involves gastrin and cholecystokinin, structurally related peptides present in plasma, gut, and brain. In order to determine the time course of plasma gastrin response in a nonhuman primate, six overnight-fasted adult male rhesus monkeys were offered a meal of bananas (11g) and peanut butter (1 Tbsp) or a fresh water bottle in a crossover design. All animals completely consumed the meal within 10 min. Compared to non-fed control levels, plasma gastrin was significantly elevated (52 ± 11 pM vs. 32 ± 9 pM, means ± S. E. M.) from 10 to 45 min post-ingestion, but returned to near basal fasted level by 120 min. Levels of gastrin in tissue samples (n = 2) were highest in the antrum of the stomach, with decreasing amounts measured in the upper and lower duodenum, respectively. The results demonstrate that the plasma concentration and response to a meal of rhesus monkey gastrin are similar to those of other mammalian species. However, the high concentrations of gastrin found in duodenum are thus far unique to Macaca mulatta and humans.     

Immunohistochemical investigations of neuropeptides in the brain,corpora cardiaca,and corpora allata of an adult lepidopteran insect,Manduca sexta (L)

In the brain of adult specimens of the tobacco hornworm moth, Manduca sexta (L), cells immunoreactive for several kinds of neuropeptides were localized by means of the PAP procedure, by use of antisera raised against mammalian hormones or hormonal peptides. In contrast, no such neurosecretory cells were found in the corpora cardiaca and corpora allata (CC/CA); in the CC/CA, however, immunoreactive nerve fibres were observed, reaching these organs from the brain. The neurosecretory cells found in the brain were immunoreactive with at least one of the following mammalian antisera, namely those raised against the insulin B-chain, somatostatin, glucagon C-terminal, glucagon N-terminal, pancreatic polypeptide (PP), secretin, vasoactive intestinal polypeptide (VIP), glucose-dependent insulinotropic peptide (GIP), gastrin C-terminus, enkephalin, alpha- and beta-endorphin, Substance P, and calcitonin. No cells were immunoreactive with antisera specific for detecting neurons containing the insulin A-chain, nerve growth factor, epidermal growth factor, insulin connecting peptide (C-peptide), polypeptide YY (PYY), gastrin mid-portion (sequence 6-13), cholecystokinin (CCK) mid-portion (sequences 9-20 and 9-25), neurotensin C-terminus, bombesin, motilin, ACTH, or serotonin. All the neuropeptide-immunoreactive cells observed emitted nerve fibers passing through the brain to the CC and in some cases also to the CA. In CC these immunoreactive nerve fibers tended to accumulate near the aorta. It was speculated that neuropeptides are released into the circulating haemolymph and act as neurohormones.