Whole body autoradiography of CCK-8 in rats

Organization of vagal afferents in pylorus: mechanoreceptors arrayed for high sensitivity and fine spatial resolution?

The pylorus is innervated by vagal mechanoreceptors that project to gastrointestinal smooth muscle, but the distributions and specializations of vagal endings in the sphincter have not been fully characterized. To evaluate their organization, the neural tracer dextran biotin was injected into the nodose ganglia of rats. Following tracer transport, animals were perfused, and their pylori and antra were prepared as whole mounts. Specimens were processed to permanently label the tracer, and subsets were counterstained with Cuprolinic blue or immunostained for c-Kit. Intramuscular arrays (IMAs) in the circular muscle comprised the principal vagal afferent innervation of the sphincter. These pyloric ring IMAs were densely distributed and evidenced a variety of structural specializations. Morphometric comparisons between the arbors innervating the pylorus and a corresponding sample of IMAs in the adjacent antral circular muscle highlighted that sphincter IMAs branched profusely, forming more than twice as many branches as did antral IMAs (means of 405 vs. 165, respectively), and condensed their numerous neurites into compact receptive fields (∼48% of the area of antral IMAs) deep in the circular muscle (∼6μm above the submucosa). Separate arbors of IMAs in the sphincter interdigitated and overlapped to form a 360° band of mechanoreceptors encircling the pyloric canal. The annulus of vagal IMA arbors, putative stretch receptors tightly intercalated in the sphincter ring and situated near the lumen of the pyloric canal, creates an architecture with the potential to generate gut reflexes on the basis of pyloric sensory maps of high sensitivity and fine spatial resolution.

Cholecystokinin octapeptide induces hypothermia and improves outcomes in a rat model of cardiopulmonary resuscitation

OBJECTIVES

To investigate the effects of cholecystokinin octapeptide on thermoregulation, postresuscitation myocardial function, neurologic outcome, and duration of survival in a rat model of cardiopulmonary resuscitation.

DESIGN

: Prospective, randomized, placebo-controlled experimental study.

SETTING

University-affiliated animal research laboratory.

SUBJECTS

Ten male Sprague-Dawley rats.

INTERVENTIONS

Ventricular fibrillation was induced and untreated for 6 mins. Defibrillation was attempted after 8 mins of cardiopulmonary resuscitation. Animal temperature was adjusted to 37.0 °C with the aid of a heating lamp. At 30 mins after resuscitation, animals were randomized to receive an intravenous injection of either cholecystokinin octapeptide (200 μg/kg in 0.3 mL saline) or vehicle placebo (0.3 mL saline). The ambient temperature settings and that of the distance of the heating lamp from the animal remained the same in both groups throughout the entire experiment.

MEASUREMENTS AND MAIN RESULTS

Body temperature, hemodynamic measurements, and postresuscitation myocardial function, including cardiac output, left ventricular ejection fraction, and myocardial performance index, were measured together with neurologic deficit scores and duration of survival.

RESULTS

After injection of cholecystokinin octapeptide, blood temperature decreased progressively from 37.0 °C to 34.8 °C 5 hrs after resuscitation and returned to 37.0 °C at 9 hrs after injection. In the control group, blood temperature was sustained at 37.0 °C ± 0.2 °C during the same period of observation. Myocardial and neurologic function and duration of survival were significantly better in the cholecystokinin octapeptide-treated animals when compared to the control group.

CONCLUSIONS

: In a rat model of cardiopulmonary resuscitation, cholecystokinin octapeptide induced mild hypothermia, attenuated postresuscitation myocardial dysfunction, and improved neurologic outcome and duration of survival.

Effect of intraperitoneal and intravenous administration of cholecystokinin-8 and apolipoprotein AIV on intestinal lymphatic CCK-8 and apo AIV concentration

CCK and apolipoprotein AIV (apo AIV) are gastrointestinal satiety signals whose synthesis and secretion by the gut are stimulated by fat absorption. Intraperitoneally administered CCK-8 is more potent in suppressing food intake than a similar dose administered intravenously, but the reason for this disparity is unclear. In contrast, both intravenous and intraperitoneally administered apo AIV are equally as potent in inhibiting food intake. When we compared the lymphatic concentration of CCK-8 and apo AIV, we found that neither intraperitoneally nor intravenously administered CCK-8 or apo AIV altered lymphatic flow rate. Interestingly, intraperitoneal administration of CCK-8 produced a significantly higher lymphatic concentration at 15 min than did intravenous administration. Intraperitoneal injection of apo AIV also yielded a higher lymphatic concentration at 30 min than did intravenous administration. Intraperitoneal administration of CCK-8 and apo AIV also resulted in a much longer period of elevated CCK-8 and apo AIV peptide concentration in lymph than intravenous administration. Furthermore, enzymatic activity of dipeptidyl peptidase IV (DPPIV) and aminopeptidase was higher in plasma than in lymph during fasting, and so, satiation peptides, such as CCK-8 and apo AIV in the lymph, are protected from degradation by the significantly lower DPPIV and aminopeptidase activity levels in lymph than in plasma. Therefore, the higher potency of intraperitoneally administered CCK-8 compared with intravenously administered CCK-8 in inhibiting food intake may be explained by both its higher concentration in lymph and the prolonged duration of its presence in the lamina propria.

Tonic and phasic pyloric activity in response to CCK-octapeptide

BACKGROUND

The purpose of this study was to determine whether a high-resolution solid-state catheter system could detect regional pressure changes within the antrum and pylorus in response to CCK-octapeptide.

METHODS

Subjects received a 30 min infusion of CCK-octapeptide at either 0.02 or 0.06 microg kg(-1) h(-1).

RESULTS

Five males and two females were studied. Mean antral pressure during phase I MMC increased from 5.3 +/- 2.1 to 9.9 +/- 2.4 mmHg (P = 0.028) after infusion. At the pylorus, only the 0.06 microg kg(-1) h(-1) dose increased tonic pressure (8.8 +/- 1.4 to 17.6 +/- 2.0 mmHg; P = 0.01) as compared with the 0.02 microg kg(-1) h(-1) dose (4.7 +/- 0.7 to 7.3 +/- 0.4 mmHg; P = NS). The peak pressure of pyloric phasic pressure waves was 153 +/- 28.4 mmHg and their frequency was 4.9 +/- 1.1 contractions min(-1).

CONCLUSIONS

CCK-octapeptide elicits both tonic and phasic activity of the pyloric sphincter. The contractile response to a dose of 0.06 mug kg(-1) h(-1) is greater than the response to 0.02 mug kg(-1) h(-1).

Hepatic uptake of cholecystokinin octapeptide by organic anion-transporting polypeptides OATP4 and OATP8 of rat and human liver

BACKGROUND & AIMS

Cholecystokinin (CCK) is a major gastrointestinal peptide hormone that is released postprandially from the small intestine and exerts marked effects on gallbladder and gastrointestinal motility. The smaller isoforms CCK-8 and CCK-4 are rapidly taken up into hepatocytes, metabolized, and excreted into bile. Our aim was to identify and characterize the hepatocellular CCK-8 uptake system.

METHODS

CCK-8 uptake was measured in Xenopus laevis oocytes expressing the organic anion-transporting polypeptides of rat liver (Oatp1, Oatp2, Oatp3, or Oatp4) and of human liver (OATP-A, OATP-B, OATP-C, or OATP8) and in primary cultured rat hepatocytes.

RESULTS

Rat Oatp4 and human OATP8 efficiently mediated CCK-8 uptake in oocytes, with Michaelis constant (Km) values of 14.9 +/- 2.9 micromol/L and 11.1 +/- 2.9 micromol/L, respectively. CCK-8 uptake by hepatocytes was also saturable, with a Km of 6.7 +/- 2.1 micromol/L. The Km value in rat hepatocytes is consistent with Oatp4-mediated transport.

CONCLUSIONS

CCK-8 is selectively transported by rat Oatp4 and human OATP8, both of which are exclusively expressed at the basolateral membrane of hepatocytes. These 2 transporters are the first and probably the predominant hepatic uptake systems for CCK-8 and may be critical for the rapid clearance of this hormone from the circulation.

Cholecystokinin and thermoregulation--a minireview

Thermoregulatory effects of cholecystokinin (CCK) peptides are reviewed with special emphasis on two types of responses, that is hypothermia or hyperthermia. In rodents exposed to cold a dose-dependent hypothermia has been observed on peripheral injection of CCK probably acting on CCKA receptors. Central microinjection of CCK in rats induced a thermogenic response that could be attenuated by CCKB receptor antagonists, but some authors observed a hypothermia. It is suggested that neuronal CCK may have a specific role in the development of hyperthermia, and endogenous CCK-ergic mechanisms could contribute to the mediation of fever. Possible connections between thermoregulatory and other autonomic functional changes induced by CCK are discussed.

C-fos protein expression in the nucleus of the solitary tract correlates with cholecystokinin dose injected and food intake in rats

C-fos protein expression was investigated in the nucleus of the solitary tract (NTS) in response to increasing cholecystokinin (CCK) doses and food intake in rats by counting the number of c-fos protein positive cells in the NTS. C-fos protein expression in the NTS dose-dependently increased in response to CCK, the lowest effective dose being 0.1 microg/kg. The ED(50) for c-fos protein expression in the NTS in response to CCK was calculated to be 0.5 to 1.8 microg/kg, depending on the anatomical level of the NTS investigated. Food intake increased c-fos protein expression in the NTS, the maximum number of c-fos protein positive cells being reached at 90 min after the start of food intake. Regression analysis identified a positive correlation between c-fos protein expression and the amount of food intake. Our data indicate that subpopulations of the NTS that are activated by CCK or food intake are involved into the short-term regulation of food intake and the neural control of feeding by the caudal brainstem.

Gastrin/cholecystokinin type B receptors in the kidney: molecular, pharmacological, functional characterization, and localization

BACKGROUND

Gastrin/cholecystokinin type B receptors (CCKBRs) can be found on parietal cells and smooth muscle cells and are the predominant brain CCK receptors. Recent cloning studies indicate that this is receptor type might also be expressed in the kidney.

MATERIALS AND METHODS

We used Northern blot analysis in guinea pig. kidney and reverse transcriptase polymerase chain reaction (RT-PCR) in several murine kidney cells lines to evaluate this organ for the expression of the CCKBRs. The receptor was pharmacologically characterized by displacement experiments using [125I]-BH-CCKs and various agonists and antagonists. Polyclonal antibodies vs. the CCKBRs were raised in chicken, and immunohistochemistry on tissue sections was used to localize the receptor within the organ. The effect of gastrin on renal cell growth was measured using proximal tubulus (MCT) cells, which were cultured with gastrin (10-9 M) for 24-72 h. Cell counts and [3H]-thymidine incorporation experiments were performed.

RESULTS

CCKBR transcripts can be detected in kidney RNA (tubules > glomeruli > interstitium). RT-PCR revealed CCKBR transcripts in proximal tubules (MCT cells) and in mesangium (MMC). The medullary thick ascending limb of Henle's loop and several control tissues such as liver and muscle were negative. Displacement experiments using [125I]-BH-CCK and various agonists and antagonists identified binding sites with typical CCKBR pharmacology. CCKBRs were localized in the proximal tubulus, distal collecting ducts and mesangium cells. Treatment of rested MCT cells with gastrin 17-1 induced cell proliferation and [3H]-thymidine incorporation by at least 40% compared with normal growth (P < 0.05).

CONCLUSION

These results show for the first time that CCKBRs are present in selected areas of the kidney, and strongly confirm our previous observation that this organ expresses binding sites for [125I]-gastrin. Furthermore, gastrin might act as a growth factor in the kidney.

Sulfated cholecystokinin (26-33) induces mild taste aversion conditioning in rats when administered by three different routes

We investigated the ability of sulfated cholecystokinin (26-33) (CCK-8) and cholecystokinin (30-33) (CCK-4) to induce taste aversion or avoidance conditioning (TAC) in a one-bottle testing paradigm after either intravenous (i.v.), intracerebroventricular (i.c.v.), or intraperitoneal (i.p.) administration. Significant TAC was induced by i.p. administration of CCK-8 at 0.1 but not at 0.025, 0.5, or 1.0 micromol/kg; the TAC was not robust and, in this case, not even dose related. I.p. administration of CCK-4 at 0.05, 0.1, 0.5, or 1.0 micromol/kg did not induce TAC, replicating other studies from our lab. Mild but significant TAC was also induced by i.v. administration of CCK-8 (at 0.025 and 1.0 but not 0.1 or 0.5 micromol/kg) but not by i.v. administration of CCK-4 (at 0.05, 0.1, 0.5, or 1.0 micromol/kg). Finally, mild but significant TAC was induced by i.c.v. (i.e., lateral ventricular) administration of CCK-8 (at 0.0015 but not at 0.015 micromol/brain) but not by i.c.v. administration of CCK-4 (at 0.005 or 0.010 micromol/brain). Because CCK-4 failed to induce TAC, CCK-8 apparently induced TAC via all three routes by an action at a CCK(a), not CCK(B), receptor mechanism. Because i.c.v. or i.v. administrations of CCK-8 were not more efficacious than i.p. administration, the taste avoidance induced by i.p. administration of CCK-8 was not so mild simply because it failed to reach a critical central locus adequately or because it failed to be delivered at a critical speed (i.e., via i.v. injections). We demonstrate that CCK-8 can induce mild TAC at either peripheral or central sites and suggest that these effects of CCK-8 may be independent and may be a sign of salience but not necessarily of toxicosis.

Effect of L364.718 during suckling on the sensitivity to the hypophagic effect of cholecystokinin in adult rats

1. In the present study it was investigated whether drugs acting at the cholecystokinin (CCK)-A receptor given to rat pups may result in long-lasting changes in body weight or regulation of food intake controlled by CCK. 2. From day 3 to day 10 of life, male and female Wistar rat pups were treated with the CCK-A receptor antagonist L-364.718 and the CCK-A + B agonist CCK-8S. 3. In adult rats, treated with L364.718 during suckling, the sensitivity to the acute hypophagic action of CCK-8S was weaker or abolished compared to adults treated with saline during suckling. In adult rats given CCK-8S during suckling acute treatment with CCK-8S reduced food intake to the same extent as in the group treated with saline postnatally. 4. These data show that early postnatal treatment with the CCK-A receptor antagonist L364.718 has an impact on the hypophagic response to CCK-8S in later life.

Central and NO mediated mechanisms are involved in the inhibitory effects of CCK on the chicken cecorectal area

In chickens CCK-8s induces defecation and causes an inhibition of rectal electrical activity (EA) and an increase in cecal motility. In contrast, CCK-4 inhibits the motility of both rectum and ceca. The cecorectal responses to CCK-8s and CCK-4, given intravenously (i.v.), were studied in conscious chickens prepared with electrodes for electromyography; the influence of atropine, phentolamine plus propranolol, hexamethonium and L-NAME on such responses was determined. Atropine and phentolamine plus propranolol did not cause any change in the response to CCK-8s or CCK-4 in the cecorectal area. Hexamethonium only induced a significant decrease in the number of defecations (ND) induced by CCK-8s. L-NAME slightly modified the decrease in rectal EA due to CCK-8s. The effects of intracerebroventricular (i.c.v.) administration of CCK-8s and CCK-4 were also studied. CCK-8s and CCK-4, given i.c.v., caused, in conscious chickens, a slight decrease in cecal EA, in the 15 minutes following administration. This effect was similar to that seen after i.v. administration of CCK-4. In conclusion, our results suggest that the inhibitory action of CCK on chicken rectum is mediated, at least in part, through nitric oxide release. In addition, nicotinic receptors mediate the increase in the ND caused by CCK-8s. Ganglionic, muscarinic, adrenergic and nitrergic blockade were not able to modify the excitatory cecal response to CCK-8s, which may indicate that the receptor mediating this effect is located on the cecal smooth muscle. Finally, the inhibitory action of i.v. CCK-4 on chicken cecum seems to be centrally mediated, as suggested by the fact that i.c.v. administration of either CCK-8s or CCK-4 induce a similar effect.

Several roles of CCKA and CCKB receptor subtypes in CCK-8-induced and LiCl-induced taste aversion conditioning

Administration of a relatively large IP dose of sulfated cholecystokinin (26-33) (CCK-8; 1.0 mumol/kg) consistently induced moderate taste aversion conditioning (TAC) using a 20-min, one-bottle test in Long-Evans rats. Because CCK-8 has affinity for both CCKA and CCKB receptor subtypes, we wanted to determine the subtype involved in CCK-8-induced TAC. Pretreatment with the selective CCKA antagonist MK-329 (L-364, 718 or devazepide), at doses of 0.1, 1.0, or 10.0 mumol/kg, markedly antagonized (> 70%) CCK-8-induced TAC. Pretreatment with the selective CCKB antagonist L-365,260, at doses of 0.1 or 1.0 mumol/kg, partially antagonized (approximately 50%) CCK-8-induced TAC, although the highest dose of L-365,260. 10.0 mumol/kg, did not. These partial antagonistic effects of L-365,260 on CCK-8-induced TAC were replicated in our second study. In our third study, we observed that another CCKB antagonist, the dipeptoid CI-988, also partially antagonized CCK-8-induced TAC at a dose of 0.1, but not 1.0 or 10.0, mumol/kg. In our final study, pretreatments with a single dose (i.e., 10.0, but not 0.1 or 1.0, mumol/kg) of either MK-329 or L-365,260 were also shown to partially antagonize the formation of moderate TAC induced by treatment with LiCl at 708 mumol/kg. Marked antagonism of LiCl-induced TAC was also observed following pretreatment with the known anxiolytic chlordiazepoxide HCl at 7.4 mumol/kg. Considering the existing data on the induction of TAC by various CCK analogues, we consider an action of CCK-8 on peripheral CCKA, but not CCKB, receptors necessary for the induction of TAC. Our results of partial antagonism of CCK-8- and LiCl-induced TAC by L-365,260, CI-988, or MK-329 suggest, but do not prove, that both CCKA and CCKB mechanisms may be operative during TAC. Because the CCK antagonists affected TAC like chlordiazepoxide, blockade of CCKA and CCKB mechanisms may produce a mild anxiolytic effect.