The subcellular distribution of peptides immunoreactive for the amino-terminal of pro-cholecystokinin in rat brain

Antiserum 1942 raised against the synthetic peptide V-9-M is specific for the amino-terminus of pro-cholecystokinin (pro-CCK). It detects three major peptides in whole rat brain extracts with molecular weights of about 13 000 (peak 1), 8000 (peak 2) and 2700 (peak 3), of which the major one is peak 3. Rat brain was found to contain large quantities of these V-9-M-like peptides. Subcellular fractionation of whole rat brain was performed to determine what cellular component was enriched in these peptides. The molecular weight of the V-9-M-like and CCK-8-like peptides enriched in various subcellular fractions has been determined by Sephadex G-50 chromatography. Primary subcellular fractionation experiments indicated a significant enrichment of V-9-M-like peptides in the mitochondrial pellet (P2), a lesser amount in the microsomal pellet (P3), and a slight enrichment in the soluble fraction (S3). Further purification of the P2 fraction demonstrated an increase of V-9-M-like immunoreactivity in purified synaptosomes. With the exception of the enrichment in the soluble fraction, V-9-M-like peptides follow a similar distribution to that of CCK-8-like peptides. Sephadex chromatography of P2 and P3 fractions indicates that the major form of V-9-M present is the peak 3 (2700) form. This V-9-M-like peptide may represent an intermediate in the processing of CCK, and its presence in synaptosomes may indicate that the proteolytic cleavage of pro-CCK into CCK 58 and peak 3 takes place in synaptic vesicles.     

Effect of V-9-M, a peptide fragment derived from procholecystokinin, on memory processes in the rat

It has been reported that a nonapeptide (Val-Pro-Val-Glu-Ala-Val-Asp-Pro-Met) called V-9-M is produced from procholecystokinin in the brain. Since this peptide is particularly abundant in the hippocampus, septum, and amygdala. V-9-M may be involved in memory processes. The present study was attempted to observe the effect of V-9-M on memory processes of rat performing a one-trial passive avoidance task and a platform jumping active avoidance task. The results indicate that injection of V-9-M into the lateral ventricle of the rat prevents experimental amnesia induced by electroconvulsive shock in passive avoidance testing, and that this effect is not significantly affected by cholecystokinin-8 antagonists. V-9-M also causes a long-lasting enhancement of memory in the active avoidance task. These results suggest that V-9-M may participate in the facilitation of memory.     

The depolarization-induced release of cholecystokinin C-terminal octapeptide (CCK-8) from rat synaptosomes and brain slices

Studies on the subcellular distribution of immunoreactive cholecystokinin (CCK) in homogenates of rat cerebral cortex showed that approximately 95% was associated with particulate fractions, including presynaptic terminals (synaptosomes). Chromatography of extracts of tissue and medium from incubated synaptosomes revealed that this material was almost exclusively in the form of COOH-terminal octapeptide (CCK-8), very little CCK-33 being present. There was a wide range of CCK-8 concentrations in synaptosomes from different brain regions (cortex > striatum ? hypothalamus > brain stem). Cerebral cortex synaptosomes were incubated in vitro and showed a complex pattern of CCK-8 release with varying concentrations of tissue: amounts in the medium rose rapidly with increasing synaptosome concentrations, then fell to a plateau at higher tissue values. A mechanism for the rapid disposal of extracellular CCK-8 was associated with synaptosomal fractions. Depolarization-induced (high K⁺) release of CCK-8 was observed with cortex and corpus striatum synaptosomes. A rapid and reversible enhancement of CCK-8 release from cortex slices was observed in response to elevated K⁺. Veratrine also released CCK-8 from cortex slices, although this was not reversible. Stimulus-induced release of CCK-8 from synaptosomes and slices required extracellular Ca²⁺. The storage, release and degradation of CCK-8 by nerve-endings suggest a synaptic function for this peptide.     

Cholecystokinin octapeptide: Vesicular localization and calcium dependent release from rat brain in vitro

Sub-cellular fractionation tissue from rat hypothalamus and cerebral cortex in sucrose gradients indicated a concentration of cholecystokinin-like peptides in synaptosomal fractions. Lysis of synaptosomes yielded a vesicle rich fraction which was further enriched in cholecystokinin-like peptides, particularly the octapeptide (CCK-8). In vitro release experiments carried out using rat cerebral cortex tissue slices showed a calcium dependent release of cholecystokinin (primarily as CCK-8). The demonstration of a vesicular localization and calcium evoked release of cholecystokinin is consistent with a role for cholecystokinin as a neurotransmitter/neuromodulator in the CNS.     

Differential changes in calcitonin, somatostatin and gastrin/cholecystokinin-like immunoreactivities in rat thyroid parafollicular cells during ontogeny

Immunocytochemical quantitative studies on the development of rat thyroid calcitonin (C) cells have been performed. In neonatal rat pups up to day 6 nearly 90% of all calcitonin cells are also somatostatin immunoreactive and 45% of these cells also show immunoreactivity to a C-terminal gastrin/cholecystokinin antiserum (CCK-4-like immunoreactivity). Already at day 8 the frequency of somatostatin immunoreactive calcitonin cells has dropped to 25%, whereas half of the calcitonin cells still display CCK-4-like immunoreactivity. In adult rats, less than 1% of the calcitonin cells are somatostatin immunoreactive, whereas 90% of the calcitonin cells display CCK-4-like immunoreactivity. These data show that between day 6-8 a pronounced change in the peptide repertoire of rat thyroid C cells occur and that these cells, prior to this time, mainly contain calcitonin and somatostatin immunoreactivity and after this time mainly contain calcitonin and CCK-4-like immunoreactivity. The time course of the change in the C cell peptides is similar to that observed with changes in transitory peptides of neonatal rat pancreas and duodenum, suggesting that possible hormonal mechanisms during this period act to change the peptide repertoire of several endocrine cell types simultaneously. It is possible that many of the transitory peptides exert actions in the developing individual that are necessary for growth and differentiation. Interestingly, many of these transitory peptides reappear in tumours, where theoretically they could exert similar actions.     

Differential changes in calcitonin,somatostatin and gastrin/cholecystokinin-like immunoreactivities in rat thyroid parafollicular cells during ontogeny

Summary Immunocytochemical quantitative studies on the development of rat thyroid calcitonin (C) cells have been performed. In neonatal rat pups up to day 6 nearly 90% of all calcitonin cells are also somatostatin immunoreactive and 45% of these cells also show immunoreactivity to a C-terminal gastrin/cholecystokinin antiserum (CCK-4-like immunoreactivity). Already at day 8 the frequency of somatostatin immunoreactive calcitonin cells has dropped to 25%, whereas half of the calcitonin cells still display CCK-4-like immunoreactivity. In adult rats, less than 1% of the calcitonin cells are somatostatin immunoreactive, whereas 90% of the calcitonin cells display CCK-4-like immunoreactivity. These data show that between day 6–8 a pronounced change in the peptide repertoire of rat thyroid C cells occur and that these cells, prior to this time, mainly contain calcitonin and somatostatin immunoreactivity and after this time mainly contain calcitonin and CCK-4-like immunoreactivity. The time course of the change in the C cell peptides is similar to that observed with changes in transitory peptides of neonatal rat pancreas and duodenum, suggesting that possible hormonal mechanisms during this period act to change the peptide repertoire of several endocrine cell types simultaneously. It is possible that many of the transitory peptides exert actions in the developing individual that are necessary for growth and differentiation. interestingly, many of these transitory peptides reappear in tumours, where theoretically they could exert similar actions.     

Neuropharmacological properties of V-9-M, a putative neuropeptide derived from procholecystokinin, in the rat

It has been suggested that a nonapeptide called V-9-M (Val-Pro-Val-Glu-Ala-Val-Asp-Pro-Met) is produced by the processing of procholecystokinin. However, its physiological and pharmacological activities are not known. In the present study, synthetic V-9-M amide was injected into the lateral ventricle of the rat and its effects on general activities were observed. V-9-M caused a marked sedation; it suppressed spontaneous activity and hypermotility induced by thyrotropin-releasing hormone, methamphetamine, and apomorphine. Hypomotility induced by small doses of apomorphine was also decreased further. V-9-M caused hypothermia and prolonged the duration of pentobarbital-induced sleep, and it decreased locomotion in an open-field situation. However, V-9-M did not affect appetite in fasted rats.     

Stimulus-specific inhibition of insulin release from rat pancreas by both rat and porcine galanin.

The effect of the neuropeptide galanin on insulin and somatostatin secretion in the rat was studied under various conditions. In the perfused rat pancreas, insulin secretion stimulated by arginine, but not cholecystokinin-8 (CCK-8) or acetylcholine (ACh) was inhibited by both rat and porcine galanin, whereas ACh-stimulated somatostatin release was inhibited by rat but not porcine galanin. Neither arginine nor CCK-8 significantly altered somatostatin secretion and galanin was without effect under those conditions. Gastric inhibitory polypeptide-stimulated insulin release from cultured mixtures of purified rat beta- and non-beta-cells was inhibited by rat and porcine galanin in a concentration-dependent and equipotent manner. The results suggest that the inhibitory effect of galanin on insulin and somatostatin secretion may be stimulus-specific and species-specific.     

Differential bile-pancreatic secretory effects of CCK-58 and CCK-8

In this work, we 1) synthesized rat CCK-58, 2) determined the amounts and forms of rat CCK in whole blood after stimulation of its release by casein, 3) determined the potency of CCK-8 and CCK-58 peptides to displace labeled CCK-8 from CCK(A) and CCK(B) receptors transfected into Chinese hamster ovary (CHO) cells, and 4) examined the biological actions of CCK-8 and rat CCK-58 in an anesthetized rat model. CCK-58 was the only detected endocrine form of CCK in rat blood. Synthetic rat CCK-58 was less potent than CCK-8 for displacing the label from CCK(A) and CCK(B) receptors in transfected CHO cells. However, rat CCK-58 was more potent than CCK-8 for stimulation of pancreatic protein secretion in the anesthetized rat. In addition, CCK-58 but not CCK-8 stimulated fluid secretion in this anesthetized rat model. These data suggest that regions outside the COOH terminus of rat CCK-58 influence the expression of CCK biological activity. The presence of only CCK-58 in the circulation and the fact that its biological activity differs from CCK-8 suggests that CCK-58 deserves scrutiny in other physiological models of CCK activity.     

Immunoreactive cholecystokinin in human and rat plasma: correlation of pancreatic secretion in response to CCK

Immunoreactive cholecystokinin (CCK) levels in human and rat plasma are described using a radioimmunoassay specific for the biologically active sulfated end of CCK. This assay detected significant changes in plasma cholecystokinin levels during intrajejunal administration of amino acids and intravenous infusions of CCK-8 which were followed by increased pancreatic secretion. In humans, the concentration (pg/ml) of plasma cholecystokinin increased from 10.8 to 18.9 following intrajejunal amino acid instillation and from 15.4 to 31.1 during CCK infusion, while pancreatic trypsin secretion increased more than 15 fold. Ingestion of a test meal also caused a rapid and significant elevation (P less than 0.05) in both plasma CCK (14.5-21.7 pg/ml) and gastrin (50-160 pg/ml) levels. In the rat, an injection of 46 ng of CCK-8 produced a 300% increase in immunoreactive plasma CCK levels (2 min) and caused peak pancreatic protein secretion within 5 min; 4 fold lower doses (11.5 ng) elevated plasma CCK by 38% and pancreatic protein secretion to a small but significant extent. The ability of this assay to detect various forms of sulfated CCK in human plasma was also determined. Following gel chromatography on Sephadex G-50, at least three different immunoreactive peaks were found in plasma from fasted subjects and after intrajejunal amino acid stimulation. While the lower molecular weight CCK peptides (CCK-8 and CCK-12) were detected in plasma from both fasted and stimulated subjects, the larger form (CCK-33) was only present in measurable concentrations after amino acid infusion. The simultaneous measurement of increased plasma CCK levels and pancreatic secretion and the changes in the distribution of CCK peptides following amino acid infusion provides strong support that this assay detects physiologically relevant changes in biologically active CCK peptides.     

Characterization of interactions between CCK-33 and CCK receptors in isolated dispersed pancreatic acini.

In isolated dispersed pancreatic acini, we have characterized the interactions between cholecystokinin (CCK) and CCK receptors by simultaneously measuring CCK-33 immunoreactivity and CCK bioactivity. Incubation of acinar cells with CCK-33 at cell density of 0.2-0.3 mg acinar protein per ml resulted in stimulation of amylase release concomitant with significant and time-dependent decrease of the immunoreactive CCK. With L-364,718 (0.1 microM), a specific CCK receptor antagonist, immunoreactive CCK levels in the media were not significantly altered during incubation; however, CCK-stimulated amylase release was almost completely abolished (94% inhibition). Vasoactive intestinal peptide (1 nM) significantly potentiated CCK stimulated amylase release without affecting immunoreactive CCK in the media. Insulin (167 nM) did not affect the CCK stimulated amylase release or immunoreactive CCK in the media. Incubation of acinar cells with CCK-33 at 4 degrees C did not affect the levels of immunoreactive CCK; however, a significant change in levels of immunoreactive CCK were found at 37 degrees C at 90 min. Incubation of cell free medium with CCK-33 in the presence or absence of secreted enzymes revealed no changes in CCK immunoreactivity in the medium at 90 min. Addition of bacitracin in the incubation media did not affect the CCK immunoreactivity or bioactivity. These findings indicate that in isolated rat pancreatic acini, CCK-33 stimulates amylase release through a receptor that is specifically blocked by L-364,718. Specificity of the interactions of CCK-33 with acinar cells in the media appears to be receptor-mediated and time- and temperature-dependent.     

In vivo and in vitro effects of cholecystokinin octapeptide on the release of growth hormone in rats

The effect of cholecystokinin octapeptide (CCK-8) on the release of growth hormone (GH) in rats was studied in vivo and in vitro. Intravenous injection of 5 micrograms/100 g BW of CCK-8 resulted in significant increase in the plasma GH level after 10 and 20 min. CCK-8 at concentrations of 10(-11)M to 10(-7)M also caused dose-dependent stimulation of GH release from dispersed cells of rat anterior pituitary. On the other hand, somatostatin (SRIF) inhibited GH release from dispersed cells of rat anterior pituitary in a dose-related manner at concentrations of 10(-7)M to 10(-9)M. Release of GH from the cells was increased by addition of K+ at high concentration (50 mM) in a Ca++-dependent manner. Addition of 10(-3)M verapamil to the incubation medium inhibited CCK-8-induced GH release from the cells. Addition of SRIF (10(-7)M) to the incubation medium inhibited GH release from the cells induced by CCK-8 or high K+ (50 mM). These results indicate that CCK-8 acts directly on the anterior pituitary cells to stimulate GH release and that calcium ion is involved in the mechanism of this effect.     

Effects of Cholecystokinin Peptides and GV 150013, a Selective CholecystokininB Receptor Antagonist, on Electrically Evoked Endogenous GABA Release from Rat Cortical Slices

The effects of cholecystokinin (CCK) agonists and antagonists on spontaneous and electrically evoked endogenous GABA release from rat cerebral cortex slices were evaluated. Neither the nonselective and CCK(B)-selective receptor agonists CCK-8S (3-1,000 nM) and CCK-4 (3-1,000 nM), respectively, nor the selective CCK(B) and CCK(A) receptor antagonists GV 150013 (3-30 nM) and L-364,718 (10-100 nM), respectively, significantly affected spontaneous GABA release. CCK-8S (1-1,000 nM) and CCK-4 (1-1,000 nM) increased the electrically (5 and 10 Hz)-evoked GABA release. On the contrary, GV 150013 (10 and 30 nM) significantly decreased the electrically evoked GABA release only when the slices were stimulated at the higher 10 Hz frequency. The CCK-8S- and CCK-4-induced increases in electrically evoked GABA release were counteracted by GV 150013, but not by L-364,718. Furthermore, GV 150013 at 3 nM shifted to the right the CCK-4 concentration-response curve, whereas at the higher 10 nM concentration it dramatically flattened the curve. Finally, in cortical slices obtained from rats chronically treated with GV 150013, the concentration-response curve of CCK-4 was shifted to the left and the peak effect of the peptide was significantly higher than that observed in naive animals. These results suggest that CCK increases electrically evoked, but not spontaneous, endogenous GABA release from rat cortical slices, possibly by activating local CCK(B) receptors. In addition, chronic treatment with the novel CCK(B) receptor antagonist GV 150013 leads to an enhanced responsiveness of cortical slices to CCK-4 application.     

Evidence that Somatostatin Enhances Endogenous Acetylcholine Release in the Rat Hippocampus

The present experiments show that somatostatin (SS)-like immunoreactive material is present in the hippocampus and that its release can be increased by K+ stimulation of rat hippocampal slices, suggesting that SS-like peptides may be of significance to neurotransmission in the hippocampus. Exogenous SS-28 and SS-14 enhanced the K(+)-evoked release of endogenous acetylcholine (ACh) from rat hippocampal slices, whereas amino-terminal fragments of SS-28 did not. The increased ACh release in the presence of either peptide appeared to be mediated by an interaction with SS receptors because cyclo-SS, a putative SS antagonist, abolished the effects of both SS-28 and SS-14. In addition, the increase in ACh release induced by SS-14 or SS-28 was antagonized by the calcium channel antagonists omega-conotoxin GVIA, nifedipine, and cinnarizine, implicating voltage-sensitive calcium channels in this effect. Moreover, the effect was sensitive to tetrodotoxin, suggesting an indirect action of the peptides at a site distal to cholinergic nerve terminals. Cysteamine, which has been reported to deplete SS content and to increase SS release in brain, augmented the basal and evoked release of ACh from hippocampal slices, without affecting SS-like content and release. Finally, neuropeptide Y, which is colocalized with SS in many neurons of the hippocampal formation, did not alter ACh release, nor did it facilitate the SS-induced increase. The results suggest that in the rat hippocampus, both SS-28 and SS-14 interact with SS receptors to regulate ACh release indirectly by a mechanism that involves alterations of calcium influx during depolarization.     

Relative bioactivities of cholecystokinins-8 and -33 on rat pancreatic acini

The relative potencies of cholecystokinin (CCK-33) and its carboxyl terminal octapeptide (CCK-8) for stimulation of amylase release from rat pancreatic acini was measured. Porcine CCK-33 and synthetic CCK-8 were initially subjected to high pressure liquid chromatography to assess purity. Concentrations of each peptide were determined by amino acid analysis. The relative immunoreactivities of CCK-33 and CCK-8 were compared using an antibody that recognizes the common carboxyl terminus of these forms. This antibody bound CCK-8 and CCK-33 with nearly equal affinity. The relative potencies of CCK-33 and CCK-8 were then measured by comparing their abilities to stimulate amylase release from isolated rat pancreatic acini. Statistical analysis of the relative potencies of the two hormones indicated that CCK-8 was 36% more potent than CCK-33 in this assay system. These data suggest that differences in biological activities between large and small forms of CCK are not as great as previously reported.     

Effect of sodium valproate on the secretion of proopiomelanocortin derived peptides from cultured rat anterior pituitary cells

We examined effects of sodium valproate, a gamma amino butyric acid (GABA)-transaminase inhibitor, on the secretion of immunoreactive (IR)-ACTH and IR-beta-endorphin/LPH from cultured rat anterior pituitary cells to determine whether sodium valproate has a direct action on the secretion of ACTH and its related peptides from the cultured rat anterior pituitary gland. During the 3 h incubation, the basal secretion of IR-ACTH and IR-beta-endorphin/LPH decreased to 50.8% and 58.3%, respectively, of the control concentration after adding 10(-7) M sodium valproate into the incubation media and to 67.7% and 69.3%, respectively, of the control levels with 10(-8) M sodium valproate. However, sodium valproate at a concentration of 10(-6) M or 10(-9) M did not affect the basal concentration of IR-ACTH and IR-beta-endorphin/LPH. Sodium valproate at a concentration of 10(-7) M significantly attenuated the stimulated release of IR-ACTH and IR-beta-endorphin/LPH by 10(-9) or 10(-10) M of ovine corticotrophin releasing factor. These results indicate that sodium valproate could directly effect rat anterior pituitary cells to suppress both basal and stimulated release of proopiomelanocortin derived peptides and this supports the hypothesis that sodium valproate has a direct effect at the pituitary corticotroph in reducing plasma ACTH.     

N-Carboxyacyl analogues of CCK with a substituted Gly: Interaction with pancreatic and gallbladder CCK receptors

It has been reported that certain N-carboxyacyl analogues of CCK-8 and of CCK-7 with a substituted Gly in position 3 or 4 of the peptide possess higher potencies at stimulating pancreatic enzyme secretion than at stimulating gallbladder contraction, suggesting that these analogues are able to differentiate subtypes of CCK_A receptors. However, no studies examined directly the interaction of these peptides with the CCK receptors in both tissues. In the present study, CCK-8 and various N-carboxyacyl analogues of CCK-7 and of CCK-8 were prepared by solid phase synthesis using Fmoc chemistry and were purified by HPLC; molecular weight and sufficient sulfation were determined by mass spectrometry. [¹²⁵I]Bolton-Hunter(BH)-CCK-8 binding to sections of the guinea pig pancreas and gallbladder was determined under identical conditions; amylase release from pancreatic acini and contraction of gallbladder muscle strips were measured in vitro. Each peptide stimulated amylase release (EC₅₀):

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). The same relative potencies were found for stimulation of gallbladder contraction, and for the inhibition of [¹²⁵I]BH-CCK-8 binding to pancreas and gallbladder sections. These data demonstrate that the CCK_A receptors in the pancreas and on gallbladder smooth muscle possess similar affinities for the various N-carboxyacyl analogues of CCK-7 and CCK-8 with a substituted Gly and provide further evidence that the CCK_A receptors in gallbladder and pancreas cannot be distinguished pharmacologically.     

Effect of natriuretic peptides on in vitro stimulated adrenocorticotropic hormone release and pro-opiomelanocortin mRNA expression by the fetal rat pituitary gland in late gestation

OBJECTIVE AND METHODS: We investigated the effects of individual natriuretic peptides (atrial natriuretic peptide, ANP; brain natriuretic peptide, BNP, and C-type natriuretic peptide, CNP) on rat corticotropin-releasing factor stimulated adrenocorticotropic hormone (ACTH) secretion by the pituitary gland of 21-day-old rat fetuses in vitro and on pro-opiomelanocortin gene expression using in situ hybridization. RESULTS: Graded concentrations of ANP, BNP, or CNP (10(-10), 10(-9), and 10(-8) mol/l) induced a log dose dependent inhibition of ACTH secretion induced by rat corticotropin-releasing factor (10(-10) mol/l). These natriuretic peptides showed equipotent effects on a molar basis. Moreover, ANP, BNP, or CNP at 10(-10) mol/l reduced significantly the pituitary pro-opiomelanocortin mRNA expression. In addition, the immunoreactive ANP, BNP, and CNP cells were localized in the anterior lobe, but not in the intermediate lobe of the fetal pituitary gland. CONCLUSIONS: These data suggest that the fetal pituitary gland may be both a source and a target for natriuretic peptides that might control ACTH synthesis and release via an endocrine and/or paracrine mechanism. The natriuretic peptides could participate, as well as glucocorticoids, in the control of the corticotropin-stimulating activity of the fetal rat in late gestation.     

24-hour variation in content and release of hypothalamic neuropeptides in the rat

The tissue content of up to eight neuropeptides, viz bombesin (BOM), cholecystokinin (CCK-8), neurotensin (NT), neuropeptide Y (NPY), peptide histidine isoleucine amide (PHI), somatostatin (SRIF), substance P (SP) and vasoactive intestinal polypeptide (VIP), in rat hypothalami removed at various times of the day, was measured using specific radioimmunoassays. There was significant variation in the content of BOM, CCK-8, NT, PHI, SP and VIP across a 24-h period. The levels of BOM, CCK-8 and NT were lowest around the onset of darkness (1900 h) and rose throughout the night to reach a peak around the time of lights on. Hypothalamic content of all eight peptides fell between 0700 h and 1300 h by an average of 45 +/- 4%. Basal release of these peptides, as well as that in the presence of 48 mM potassium (K+), was measured from hypothalami removed between 0700 and 1900 h and incubated in vitro in a CSF-like medium. Basal secretion of NT significantly increased, whilst that of CCK-8 significantly decreased over the same period. There was no significant change in the basal release of the other neuropeptides. The release in the presence of 48 mM K+ of SP decreased significantly during the day, whilst that of VIP significantly increased. There was also a significant change in the stimulated release of BOM, levels falling during the morning and rising again at 1900 h. 48 mM K+ caused a significant increase in the release of SRIF and SP at all times tested. Whilst 48 mM K+ induced a significantly higher release of CCK-8 and NT in the morning, this stimulus was ineffective in the evening. The contrary was true in the case of BOM, NPY and VIP, where a significant stimulation was induced only at 1900 h. The possible implications of these findings are discussed.     

Peptides in rat brain immunoreactive for the amino terminus of cholecystokinin 33: distribution and chromatography

Antisera directed against the amino-terminus of porcine CCK 33 detects related immunoreactivity in rat brain extracts, the distribution of which follows that of CCK 8. Sephadex chromatography indicates that several immunoreactive peptides are present with a molecular weight range of 2600-3500. These peptides are likely to be CCK 39 or CCK 33 and the amino terminal segments of CCK 39/33 without the CCK 8 sequence. The presence of CCK 39/33 and its amino-terminal fragments without CCK 22 and its amino-terminal fragments confirms the absence of CCK 22 in the rat brain. This cleavage at CCK 22 is one of the major differences between the processing of CCK in rat brain and gut and may reflect differences in their physiological roles.