Enterogastrone-like effect of peptide YY is vagally mediated in the dog.

Intraluminal fat inhibits gastric secretion through as yet undetermined mechanisms which involve release of one or more hormonal enterogastrones. As intraluminal fat releases Peptide YY (PYY) in amounts sufficient to inhibit meal-stimulated acid secretion, this ileo-colonic peptide exhibits the characteristics required of an enterogastrone. The present study seeks to determine the mechanism by which PYY inhibits acid secretion by examining the effects of PYY on gastric acid stimulated by pentagastrin, histamine, and bethanechol. In addition, effects of PYY on the acid response to sham feeding and distention of a denervated gastric pouch were examined. A dose of PYY (400 pmol X kg-1 X h-1) was employed that reproduced blood levels observed after intestinal perfusion with oleic acid and inhibited the acid secretory response to an intragastric meal by 35 +/- 6%. This same dose of PYY maximally inhibited histamine- and pentagastrin-stimulated acid secretion by 28 +/- 7% (P less than 0.05), and 17 +/- 4% (P less than 0.05), respectively. Although PYY had no effect on bethanechol-stimulated secretion it markedly inhibited the secretory response to sham feeding, maximally reducing secretion by 90 +/- 4% (P less than 0.01). We speculate that PYY acts by inhibiting acetylcholine release from vagal nerve fibers rather than by inhibiting acetylcholine's action on the parietal cell. The demonstration that PYY virtually abolishes cephalic phase acid secretion while having little if any effect on the response to exogenous secretogogues gives PYY unique characteristics among the known hormonal inhibitors of gastric secretion.

Effect of atropine on vagal release of gastrin and pancreatic polypeptide.

We studied the effect of several doses of atropine on the serum gastrin and pancreatic polypeptide responses to vagal stimulation in healthy human subjects. Vagal stimulation was induced by sham feeding. To eliminate the effect of gastric acidity on gastrin release, gastric pH was held constant (pH 5) and acid secretion was measured by intragastric titration. Although a small dose of atropine (2.3 mug/kg) significantly inhibited the acid secretory response and completely abolished the pancreatic polypeptide response to sham feeding, this dose of atropine significantly enhanced the gastrin response. Higher atropine doses (7.0 and 21.0 mug/kg) had effects on gastrin and pancreatic polypeptide release which were similar to the 2.3-mug/kg dose. Atropine (0.78 and 2.3 mug/kg) without sham feeding significantly inhibited basal acid secretion and also led to significant increases in serum gastrin above basal levels. The gastrin response to sham feeding with 2.3 mug/kg atropine was significantly greater than the sum of the gastrin responses to sham feeding alone and to 2.3 mug/kg atropine alone, indicating potentiation of vagal gastrin release by atropine. We conclude: (a) Unlike vagally mediated gastric acid secretion and pancreatic polypeptide release which can be blocked by atropine, vagal gastrin release is potentiated by atropine. This observation suggests the existence of a vagal-cholinergic pathway which normally (i.e., in the absence of atropine) inhibits gastrin release. (b) Because atropine (without sham feeding) increased basal gastrin levels, it is likely that the cholinergic pathway which inhibits gastrin release is active even when the vagus nerve is not stimulated by sham feeding.

Impaired expression and functional activity of the beta 3- and beta 1-adrenergic receptors in adipose tissue of congenitally obese (C57BL/6J ob/ob) mice.

Adipocytes from genetically obese (ob/ob) mice display an impaired response to beta-adrenergic stimulation, but the molecular defects have not been unequivocally identified. The expression and functional activity of the beta 1-, beta 2-, and beta 3-adrenergic receptor (AR) subtypes in white and brown adipose tissue from genetically lean and obese (ob/ob) mice were compared. Three beta 3AR transcripts of 2.1, 2.6, and 3.5 kilobases were identified in adipose tissue from lean mice by Northern blotting. All three beta 3AR mRNA species were dramatically reduced (by approximately 300-fold) in 12-week-old obese mice compared to those in lean animals. beta 1AR mRNA levels were also reduced (by approximately 4-fold) in obese mice, whereas beta 2AR mRNA levels were not significantly changed. The functional consequences of these changes in beta 3AR and beta 1AR expression were assessed by measuring beta-agonist-stimulated adenylyl cyclase activity in adipocyte plasma membranes with subtype-selective beta-adrenergic agonists and antagonists. Dose-response curves with epinephrine from lean mice were best fit to a two-component model comprised of 23% high affinity (K(act) = 1.42 x 10(-7) M) and 77% low affinity (K(act) = 1.67 x 10(-5) M) components, corresponding to activation of beta 1AR and beta 2AR conjointly, and beta 3AR, respectively. The beta 1AR-selective antagonist CGP20712A reduced the high affinity component to about 10%, whereas the nonselective beta-antagonist propranolol eliminated the high affinity component. The beta 3AR-selective agonist BRL37344 stimulated adenylyl cyclase activity in lean membranes to a slightly lesser extent than epinephrine, but was more potent (73% high affinity component; K(act) = 3.61 x 10(-8) M). In obese mice, stimulation of adenylyl cyclase by all agonists was severely blunted and was best fit to a single class of sites. Studies with CGP20712A or the beta 2AR-selective antagonist ICI118,551 indicated that this residual response was predominantly beta 2AR in character. Expression of beta AR subtypes in both brown and white adipose tissue of weanling obese mice (4-5-weeks of age) was also affected, but to a lesser extent, consistent with the progressive severity of obesity with age. Together the reduction in expression of the beta 3AR and beta 1AR impairs the beta-agonist-stimulated adenylyl cyclase response over a broad concentration range by greatly lowering the maximum stimulation and shifting the adrenergic sensitivity at low concentrations from a mixed beta 1AR/beta 2AR response to predominantly beta 2AR.

Peptide-YY, a new partner in the negative feedback control of pancreatic secretion.

Peptide YY (PYY), a newly discovered ileocolonic peptide, is released by nutrients in the proximal and distal intestine and inhibits pancreatic secretion. However, it is not clear whether PYY can be released in the absence of nutrients in the intestine or whether a physiological role exists for endogenous PYY in negative feedback regulation of pancreatic secretion by pancreatic proteases. In the present study we measured plasma PYY concentrations and determined the effects of anti-PYY serum during stimulation of pancreatic secretion by pancreatic juice diversion (PJD). The effect of SMS 201-995 (SMS; an analog of somatostatin), another inhibitor of pancreatic secretion, on regulation of PYY release induced by PJD was also investigated. Male Wistar rats equipped with pancreatic, biliary, duodenal, and jugular venous cannulas were studied 4-6 days postoperatively. After 90 min of basal collection, pancreatic juice was diverted for 4 h with or without infusion of SMS (2 micrograms/kg.h), given either iv or intraduodenally (ID). Plasma PYY concentrations were significantly increased from a basal level of 177 +/- 15 pg/ml to a peak level of 328 +/- 43 pg/ml 2 h after PJD. These increases in PYY concentration paralleled those in pancreatic protein and fluid outputs. Both iv and ID infusion of SMS during the first 2 h of PJD markedly decreased the plasma PYY concentration to 134 +/- 27 pg/ml and 156 +/- 19 pg/ml, respectively; the total incremental PYY release during 4 h of PJD was inhibited by 100% and 84% by iv and ID SMS, respectively. One milliliter of anti-PYY serum given iv significantly augmented the increment in protein and fluid output during PJD. These results suggest that endogenous PYY released by PJD may play a physiological role in negative feedback regulation of pancreatic secretion in rats.

Age-dependent changes in beta-adrenergic receptor subtypes and adenylyl cyclase activation in adipocytes from Fischer 344 rats.

Epididymal adipocytes were isolated from Fischer 344 rats aged 3, 6, 12, and 24 months, to study the mechanisms responsible for age-dependent diminution in cellular adrenergic responsiveness. Messenger RNA (mRNA) levels for the beta 1-, beta 2-, and beta 3-adrenergic receptors (ARs) were compared across age groups and related to adenylyl cyclase activation by selective receptor agonists in adipocyte plasma membranes and activation of lipolysis in intact cells. mRNA levels for the beta 1-AR decreased by 60% between 3-6 months and remained at this reduced level through 12 and 24 months. A modest increase in beta 2-AR mRNA was noted between 3-12 months, but decreased between 12-24 months to levels seen in the 3-month-old group. mRNA for the beta 3-AR did not change between 3-6 months, but decreased by about 40% between 6-12 months, and by a further 50% between 12-24 months. Lipolytic responsiveness also diminished with age, and regardless of whether beta 3-selective or beta 1/beta 2-selective agonists were used, the maximal release of glycerol was most severely blunted in adipocytes from 24-month-old rats. The age-dependent changes in adenylyl cyclase activation by beta-adrenergic agonists mirrored the observed changes in lipolytic responsiveness with respect to diminished efficacy. These results together with the similar forskolin-stimulated adenylyl cyclase activity among the groups suggest age-dependent changes in activation of adenylyl cyclase at a prior step. This suggestion is also supported by the comparable inhibitory capacities of the alpha 2-adrenergic and A1-adenosine signaling systems among the age groups. In view of the similar levels of Gs alpha, the age-dependent decrease in adrenergic responsiveness in rat adipocytes appears to result primarily from specific decreases in the expression of both beta 3-AR and beta 1-ARs.

Adrenalectomy after weaning restores beta3-adrenergic receptor expression in white adipocytes from C57BL/6J-ob/ob mice.

The role of hypercorticism in the development of compromised beta-adrenergic signaling in adipose tissue was assessed in ob/ob mice adrenalectomized at 4 weeks of age and studied 1 and 3 weeks thereafter. Adrenalectomy prevented the rapid increase in body weight and fat deposition between 4 and 5 weeks of age in ob/ob mice and produced a phenotype indistinguishable from that of lean mice. However, adrenalectomized ob/ob mice became intermediate between lean and ob/ob mice by 7 weeks of age. Adipocyte beta3-adrenergic receptor (AR) messenger RNA levels were similar between lean and adrenalectomized ob/ob mice at both time points and were 4- to 8-fold higher than messenger RNA levels in ob/ob mice. As judged by maximal activation of adenylyl cyclase by a beta3-AR-selective agonist, adrenalectomy also restored functional activity of the beta3-AR to levels above or equivalent to those seen in lean mice at both time points. The present results suggest that development of hypercorticism at or before weaning in ob/ob mice represses expression of the beta3-AR and prevents the normal postweaning development of this signaling system in the adipocyte.

Pancreatic polypeptide from rat pancreas.

Pancreatic polypeptide (PP) has been isolated from rat pancreas by gel filtration, ion exchange chromatography, and high performance liquid chromatography. The isolation was monitored with a RIA, using antibody to the carboxyl-terminal hexapeptide of bovine PP. Rat PP contains 36 amino acids and is similar in composition to PP from other mammalian sources. The single methionine residue in the peptide appears to oxidize easily to the sulfoxide, thereby giving rise to two immunoactive peaks on high performance liquid chromatography. Reduction to the native peptide can be accomplished with mercaptoethanol. The PP content of rat pancreas is about 2 mg/kg. The amino acid sequence of rat PP is Ala-Pro-Leu-Glu-Pro-Met-Tyr-Pro-Gly-Asp- Tyr-Ala-Thr-His-Glu-Gln-Arg-Ala-Gln-Tyr-Glu-Thr-Gln-Leu-Arg-Arg-Tyr-Ile- Asn-Thr-Leu-Thr-Arg-Pro-Arg-Tyr-NH2. This sequence preserves characteristics necessary for stabilization of the compact globular conformation found in avian PP.

Effect of cephalic-vagal stimulation on insulin, gastric inhibitory polypeptide, and pancreatic polypeptide release in humans.

The purpose of the present study was to determine whether there is a cephalic phase of insulin or gastric inhibitory polypeptide release in man. Seven healthy, normal weight volunteers were sham fed an appetizing steak meal, and serum insulin, gastric inhibitory polypeptide, and pancreatic polypeptide concentrations were measured. A pancreatic polypeptide response to sham feeding was employed as marker of adequate cephalic-vagal stimulation. Although serum pancreatic polypeptide concentrations increased significantly (P less than 0.05) in response to sham feeding, sham feeding had no significant effect on serum insulin and gastric inhibitory polypeptide levels. In addition, sham feeding did not affect insulin or gastric inhibitory polypeptide responses to intragastric glucose, although sham feeding did augment the pancreatic polypeptide response to this meal. These experiments were, therefore, unable to demonstrate insulin or gastric inhibitory polypeptide release in response to cephalic-vagal stimulation in humans.

Dopaminergic modulation of meal-stimulated and circadian secretion of pancreatic polypeptide in man.

This study investigated dopaminergic control of human pancreatic polypeptide (hPP) secretion in normal male volunteers. Dopamine infusion blunted the hPP response to a protein-rich meal. Dopamine antagonism with metoclopramide resulted in a hPP response at 5 min and a peak elevation of hPP 10 min after drug administration. Bromocriptine (2.5 mg, three times daily for 5 days) suppressed meal-induced secretory responses of hPP. Although bromocriptine did not alter the basic circadian pattern of hPP secretion, it did slightly increase nocturnal levels of this hormone. These results suggest that dopaminergic mechanisms exert a tonic inhibitory effect on hPP secretion in normal subjects.

Pancreatic polypeptide responses to hypoglycemia in chronic autonomic failure.

Pancreatic polypeptide (PP) and catecholamine responses to insulin-induced hypoglycemia have been measured in 15 patients with neurogenic orthostatic hypotension. Eight of the patients had idiopathic orthostatic hypotension, and 7 had multiple system atrophy, a condition characterized by the presence of central nervous system lesions in addition to the orthostatic hypotension common to both diseases. Eleven healthy subjects exhibited rapid and substantial elevations in plasma epinephrine, norepinephrine, and PP concentrations in response to insulin hypoglycemia. In contrast, patients with neurogenic orthostatic hypotension exhibited impaired catecholamine and PP responses to insulin hypoglycemia. There was no correlation between the catecholamine and PP responses in either the normal subjects or the patients, suggesting that PP release during hypoglycemia is independent of the sympathoadrenal medullary response. As PP release in response to insulin hypoglycemia is abolished by truncal vagotomy and unaffected by splanchnic nerve section, our results suggest that patients with chronic autonomic failure may have a diffuse autonomic dysfunction involving the parasympathetic as well as the sympathetic nervous system.

Regulation of pancreatic endocrine function by cholecystokinin: studies with MK-329, a nonpeptide cholecystokinin receptor antagonist.

A cholecystokinin (CCK) receptor antagonist, MK-329, was used to explore the physiological role of CCK in regulating pancreatic endocrine function in humans. The ability of CCK to increase plasma pancreatic polypeptide (PP) concentrations and blockade of this effect with MK-329 were evaluated in a double blind, balanced, four-period cross-over study. Eight subjects received single oral doses of 0.5, 2, or 10 mg MK-329 or placebo, followed by an iv infusion of CCK-8 (34 ng/kg.h). In placebo-treated subjects, PP increased from basal levels of 70 +/- 15 (+/- SE) to peak values of 291 +/- 58 pg/mL after CCK infusion (P less than 0.05 compared to basal). This increase in plasma PP concentration was inhibited in a dose-dependent fashion by MK-329, with 10 mg antagonizing the stimulatory effect of CCK infusion by nearly 80%. Second, the effect of MK-329 on meal-stimulated pancreatic endocrine responses was evaluated by giving placebo or 10 mg MK-329 2 h before ingestion of a mixed meal. Eight subjects were treated in a randomized two-period cross-over fashion. With placebo treatment, peak postprandial plasma insulin, glucagon, and glucose concentrations were 101 +/- 8 microU/mL, 195 +/- 15 pg/mL, and 150 +/- 10 mg/dL, respectively (all P less than 0.05). The integrated PP response following the meal was 56.3 +/- 11.1 ng/mL.minute. With MK-329 treatment, the integrated PP concentration was reduced to 33.9 +/- 2.2 ng/mL.min (P less than 0.05 compared to placebo treatment). Mean postprandial insulin, glucagon, and glucose concentrations did not differ between placebo and MK-329 treatments. We conclude that CCK receptor blockade with 10 mg MK-329 does not alter plasma insulin, glucagon, or glucose responses to a mixed meal. However, the observation that physiological concentrations of CCK increase plasma levels of PP, and the finding that CCK receptor blockade selectively attenuates the postprandial increase in plasma PP concentrations support a physiological role for CCK in regulating PP secretion.

Intragastric vs intraintestinal viscous polymers and glucose tolerance after liquid meals of glucose.

To determine whether viscous fibers improve glucose tolerance by slowing gastric emptying or impeding intestinal uptake of glucose, 800 mL of 0.2 mol glucose/L were instilled into the stomachs of the dogs and allowed to empty from the stomach out the proximal limb of a duodenal fistula while simultaneously fresh solution was instilled into the distal duodenum at the same rate. This technique allowed us to study 33 g pectin/L, isoviscous 400 g PEG 20,000/L, or 11 g guar/L when present with glucose in the stomach only, the intestine only, or in both stomach and intestine. Rates of gastric emptying and plasma glucose were lower when viscous polymer was present at both sites than at either site separately. Slowing of gastric emptying was an interactive outcome of viscosity at both loci, probably from slowed intestinal absorption of glucose with its exposure to more intestinal sensors. Reductions in postcibal glucose concentrations depended on slowing of both gastric emptying and intestinal absorption.

Neuropeptide Y/peptide YY receptor binding sites in the heart: localization and pharmacological characterization.

[125I]Peptide YY was used to localize and characterize peptide YY and neuropeptide Y receptor binding sites in the heart. In the rat and rabbit heart, nearly every artery and arteriole that could be histologically identified also expressed saturable binding sites for [125I]peptide YY. In the arteries, these [125I]peptide YY binding sites were primarily associated with the smooth muscle layer. Pharmacological experiments demonstrated that peptide YY and neuropeptide Y were equipotent in competing for [125I]peptide YY binding in the heart. In another competition series, [Leu31,Pro34]-neuropeptide Y (a Y1 receptor-specific agonist when used with [125I]peptide YY) was significantly more potent than neuropeptide Y (a Y2 receptor-specific agonist when used with [125I]peptide YY) in competing for [125I]peptide YY binding from coronary arteries, suggesting that the receptor binding sites on cardiac arteries and arterioles are of the Y1 subtype. These results demonstrate that smooth muscle cells of the atrial and ventricular arteries and arterioles in rat and rabbit heart express Y1 receptors and suggest a possible direct effect of neuropeptide Y on coronary blood vessels to induce vasoconstriction.

Immunochemical characterization of gastrin in pancreatic islets of normal and genetically obese mice.

Material with gastrin-like immunoreactivity has been extracted from micro-dissected islets and from antral mucosa of normal and genetically obese mice. The islet and antral extracts cross-reacted with antisera specific for the CO2H-terminal portion of human heptadecapeptide gastrin, but did not cross-react with antisera specific for the NH2-terminal region or with an antiserum specific for the entire, intact, molecule. With the antiserum showing highest cross- reactivity, the concentration of immunoreactive gastrin in normal islet tissue (138 pmol/g, standard human G17-I) was approximately 50% that in obese mouse islets (204 pmol/g) and 2% that in normal antral mucosa (6-1 nmol/g). Following fractionation on Sephadex G-50 the principal forms of gastrin in the islet and antral extracts had similar elution volumes to human heptadecapeptide gastrin, although other, probably smaller, forms of gastrin were also noted in the islet extracts.

Comparison of the neuropeptide Y receptor in the rat brain and intestine.

Neuropeptide Y (NPY) is widely distributed in the central and peripheral nervous systems where it serves neuromodulator and neurotransmitter functions. NPY is contained within intrinsic nerves of the small intestine and can be demonstrated to inhibit intestinal secretion when added to the serosal side of intestine mucosa mounted in Ussing chambers. When injected centrally it has potent effects on food intake, blood pressure, sexual activity and circadian rhythms. Using NPY radiolabeled with iodogen, lactoperoxidase, or the Bolton-Hunter reagent, we have localized high-affinity NPY receptors on brain membranes and on the serosal laterobasal membranes of the rat intestinal epithelial cell. We have demonstrated that enzymatic degradation may limit the ability to demonstrate NPY binding to brush border membranes. In other experiments NPY was cross-linked to its receptors in brain and intestine using disuccinimido suberate and the resulting complexes analyzed on SDS polyacrylamide gel electrophoresis followed by radioautography. We identified two main NPY receptor species in the intestine with molecular sizes of 52-59 kDa and 37-39 kDa. The 37-39 kDa species may possess a disulfide bond which gives the receptor a fixed conformation, or it may be composed of two subunits (37-39 kDa and approximately 5 kDa subunits). This conclusion is based on the different migration of the smaller band in the presence of the reducing agent, dithiothreitol. The intestinal NPY receptor exhibits differences from the rat brain receptor previously characterized by us using similar techniques. The brain receptor has a molecular weight of approximately 58 kDa with a smaller species of about 35 kDa which shows no differences in migration after exposure to dithiothreitol. The localization of NPY receptors on laterobasal membranes and brain membranes is consistent with previous anatomic and physiologic findings. The different characteristics of each receptor type provides physical evidence of receptor heterogeneity. However, it is possible that the greater enzymatic degradation observed in intestinal membranes might explain the differences in receptor sizes in the two organs.

Evidence for vagus-dependent pancreatic polypeptide-releasing factor in the antrum: studies with the autotransplanted dog pancreas.

Pancreatic polypeptide (PP) response to food is suppressed by truncal vagotomy, antral vagotomy, and antrectomy. The inhibitory effect of antral vagotomy and of antrectomy may be due to inadvertent vagal denervation of the pancreas, disruption of antropyloric neural reflexes, or inhibition of release of a PP-releasing factor from the antrum. In this study we examined the latter hypothesis by achieving total extrinsic pancreatic denervation by orthotopic autotransplantation of the entire pancreas in four dogs. Total extrinsic pancreatic denervation, which abolished the pancreatic juice protein response to insulin, did not significantly alter plasma PP response to a meal (peak 30-minute PP of 696 +/- 192 pg/ml before transplantation versus 961 +/- 80 pg/ml after transplantation). Therefore, postprandial release of PP is, to a large extent, not mediated either by direct vagal innervation of the pancreas or by neural communications between the pancreas and antrum or the pancreas and the small intestine. In two of the dogs with pancreatic transplants, subsequent antral vagotomy resulted in greater than 80% inhibition of postprandial PP response. These findings are consistent with the hypothesis that a PP-releasing factor is present in the antrum and that the release of this factor is dependent on intact antral vagal innervation.

Peptide YY inhibits cholecystokinin-stimulated sphincter of Oddi activity in the prairie dog.

Peptide YY (PYY), a recently discovered gut peptide, has been shown to have a number of actions that are antagonistic to the effects of cholecystokinin. This study was designed to determine whether PYY would inhibit cholecystokinin-stimulated sphincter of Oddi activity in the prairie dog. In 12 prairie dogs PYY was infused intravenously at 1, 10, and 100 ng/kg/min, and arterial blood samples were obtained. A dose-response curve was obtained, with the 10 ng/kg/min dose producing serum levels of 725 pg/ml. In seven additional prairie dogs a side-hole, pressure-monitored perfusion catheter was passed into the duodenum through a choledochotomy and positioned in the sphincter of Oddi. A perfusion catheter was also placed in the gallbladder fundus. Sphincter of Oddi and gallbladder pressures were recorded before and during 20-minute infusions of cholecystokinin and then cholecystokinin plus PYY at 10 ng/kg/min. PYY significantly inhibited cholecystokinin-stimulated sphincter of Oddi phasic wave frequency (3.8 +/- 0.2 vs 3.3 +/- 0.4; p less than 0.05) and sphincter of Oddi motility index (26.2 +/- 4.3 vs 18.7 +/- 4.8; p less than 0.025) but did not affect the increase in gallbladder pressure induced by cholecystokinin. These findings are consistent with other known anticholecystokinin effects of PYY. We conclude that PYY may also inhibit sphincter of Oddi activity in the prairie dog by an anticholecystokinin effect, thus reducing flow through the sphincter.

Tissue-specific alterations in G protein expression in genetic versus diet-induced models of non-insulin-dependent diabetes mellitus in the mouse.

Various tissues were obtained from the well-characterized genetic model (C57BL/6J-ob/ob) of non-insulin-dependent diabetes mellitus (NIDDM) and from a diet-induced model of NIDDM produced in the same genetic background (C57BL/6J). The objectives were to determine whether the previously observed changes in guanine nucleotide-binding regulatory protein (G protein) expression in adipose tissue from ob/ob mice were mirrored by concomitant changes in other tissues, and whether NIDDM of a different etiology would share similar alterations in G protein expression. Plasma membranes from adipocytes, brain, heart, liver, and testes were probed with alpha-subunit-specific antisera, and the level of G protein expression in each model was compared with that in its lean littermate control. Adipose, heart, and liver cell membranes from ob/ob mice contained significantly less alpha-subunit of stimulatory G protein (Gs alpha) than those from their lean littermates. As compared with the lean littermates, heart alpha-subunit-2 of inhibitory G protein (Gi alpha-2), liver Gi alpha-3, and adipocyte G1 alpha-1 and Gi alpha-3 were also reduced in ob/ob mice. In contrast, Gi alpha-2 and Go alpha were increased over lean-control levels in brain tissue from ob/ob mice, whereas Gs alpha was unchanged. G protein expression in the testes did not differ between lean and ob/ob mice. In the diet-induced model of NIDDM, Gs alpha expression in the liver was twofold greater in obese/diabetic mice as compared with lean controls. However, G protein expression in all other tissues examined did not differ between obese/diabetic animals and lean littermates.(ABSTRACT TRUNCATED AT 250 WORDS)

Pancreatic polypeptide release by intraluminal fatty acids.

The question of whether the response of pancreatic polypeptide to intestinal fatty acids is influenced by the site of intestinal perfusion or the chain length of the fatty acid was investigated. Six dogs with chronic gastric, pancreatic, and intestinal fistulas were studied. Proximal perfusates were administered at the pylorus and diverted via a Foley catheter in the orad stoma of an intestinal fistula placed 45 cm beyond the pancreatic cannula. Distal perfusates were administered into the caudal stoma of the intestinal cannula. Three experimental protocols were used: proximal fatty acid perfusion (20, 40, or 80 mmol/L) combined with distal saline perfusion; distal fatty acid perfusion (20, 40, or 80 mmol/l) combined with proximal saline perfusion; or distal fatty acid perfusion combined with proximal fatty acid perfusion of 80 mmol/L. Each dose of fatty acid was given in random order and the two fatty acids (dodecanoate and oleate) were tested on different days. Blood samples were drawn for pancreatic polypeptide radioimmunoassay, and pancreatic secretion was collected for determination of bicarbonate and protein outputs. Pancreatic polypeptide responses to perfusion of both proximal and distal segments with oleate exceeded (P less than 0.05) those evoked by dodecanoate. The responses of pancreatic polypeptide to dodecanoate administration into either the proximal segment or the distal intestine were not significantly different. In contrast, perfusion of the proximal intestinal segment with oleate release significantly (P less than 0.05) less pancreatic polypeptide than did distal intestinal perfusion with oleate.(ABSTRACT TRUNCATED AT 250 WORDS)

Demonstration of carboxyl-terminal PP-like peptides in endocrine cells and nerves.

Pancreatic polypeptide (PP) has been isolated from the pancreas of several species, and has been localized by immunohistochemistry to a distinct population of pancreatic endocrine cells. Recently, PP-like immunoreactivity has been demonstrated outside the pancreas, in gut endocrine cells and central and peripheral nerves, in studies using antisera raised to natural PPs. The antigenic determinants recognised by these antisera are not known in any detail, and, therefore, the identity of the molecules in these extrapancreatic localizations is also unknown. We have raised an antiserum to the synthetic COOH-terminus of PP (PP6), which, therefore, is directed exclusively towards the biologically active, invariant region of mammalian PPs. PP6-like immunoreactivity was localized in pancreatic cells which were revealed also by antiserum to human PP (hPP). Outside the pancreas, no localizations were obtained with anti-hPP antiserum, whereas antiserum to PP6 demonstrated immunoreactivity in a variety of tissues including gut glucagon cells, adrenal chromaffin cells, and nerve fibres in the gastrointestinal tract and adrenal gland. We would suggest that the wide distribution in nerves and endocrine cells of PP6-immunoreactive material, which may be biologically active, should be taken into account in the search for a physiological role for PP.