Neural control

POS-004-027 THE EFFECTS OF INTRACEREBROVENTRICULAR (ICV) INJECTION OF CARBACHOL, A STRESS STIMULUS, ON GLUCOREGULATION 1N NORMAL AND DIABETIC DOGS.

H.L.A. LICKLEY, P.D.G. MILES, K. YAMATANI AND M. VRANIC The Departments of Physiology, Surgery and Medicine and Women's College Hospital, University of Toronto, Toronto, Canada. Several neuroendocrine pathways take part in glucoregulation during stress. We have examined this in conscious normal and diabetic dogs with indwelling eannulae inserted into the third ventricle of the brain. In 7 studies in 3 normal dogs, a minimal dose of carbachol (l-lO pg), a stimulus to autonomic outflow from the brain, was given ICV. Hepatic glucose production (Ra) increased (2.8 ± 0.2 - 4.6 ~ 0.4 ~g/kg-min) by 12.5 min (p<O.O5), and remained significantly elevated for 45 min. Glucose disappearance (Rd) also increased significantly (2.8 i 0.2 - 4.1 ± 0.4 pg/kg-min, p~O.05), thus plasma glucose rose only slightly from 107 ± 2 - 114 Z 4 mg/d[ (p~O.05). Metabolic clearance of glucose (MCR) rose (2.5 ~ 0.2 - 3.6 ~ 0.3 ml/kg-min, p<O.05). The rise in Ra cor- related with an increase in plasma glucagon (IRG), epinephrine and norepinephr~ne. IRG rose from 148 i 32 to 204 ± 14 pg/ml (p<0.05). Both epinephrine and norepinephrine levels increased in each study although the timing of the increase was variable. There was also a small increase in plasma insulin (IRI) (10 ± I - 13 ~ 2 ~U/ml, p< 0.05), which could only partly explain the increase in Rd and MCR. Carbachol (ICV) was also given in two preliminary experiments after diabetes was induced by alloxan (65 mg/kg) with basal plasma glucose maintained between ]50 and 230 mg/dl with intravenous insulin. After ICV carbachol (5 pg), plasma glucose rose steadily by more than I00 mg/dl in each study, more than a |0-fold greater increase than in normal dogs. This was associated with increases in Ra (3.0 - 6.5 pg/kg-min) in both studies. However MCR rose only marginally. Rd increased by 2.6 and 2.8 >g/kg-min secondary to the increase in plasma glucose as there was no change in IRI. Increments in glucagon, epinephrine and norepinephrine were compar- able to those in normal dogs. Thus, ICV carbacho~, a model of stress, increased glucose turnover, in normal dogs. The hyperglycaemic response to ICV carbachol appeared to be greatly exaggerated in diabetes, both because of a greater increase in Ra and a diminished increase in MCR which, at least in part, reflected the lack of insulin response in diabetes.

POS-004-028 ROLE OF DIFFERENT REGIONS OF THE BRAIN IN DIRECTING HORMONE RELEASE AND GLUCOSE PRODUCTION DURING INSULIN-INDUCED HYPOGLYCEMIA (IIH).

R.T. FRIZZELL, D.W. BIGGERS, S.R. MYERS, J.B. JASPAN, P.E. WILLIAMS Vanderbilt University School of Medicine, Nashville, Tennessee, U.S.A.

IIH inc reases ep inephr ine(E) , norepinephr ine (NE), glucagon(G), c o r t i s o l ( C ) and p a n c r e a t i c polypept ide(PP) , as well as glucose production (Ra). To determine the ro le of various regions of the brain in directing these responses experiments were carried out on 18h fasted conscious dogs in which catheters had previously been placed in both carotld(C) and vertebral(V) arteries (without occlusion of blood flow). In each of 3 groups insulin (3.5 mU/kg-mln) was infused peripherally during a 3h test period. Brain hypoglycemia was minimized by glucose infusion into both the carotid and vertebral arteries (C+V; n=4), the vertebral arteries alone (V; n=5) or a peripheral vein (P; n=5). The arterial glucose level fell to a similar extent in all three groups (45±2, 46±2 and 48±3 mg/dl). The E, NE, G, C and PP responses in C+V were 14±6, 39±12, 21±8, 17±8 and 9±4% of those present in P (all p<0.05). In V the E, NE, G, C and PP responses were 92±18, 96±21, 49±41~ 88±16 and 84±23% of those in P. R;,, assessed using 3-3H glucose, fell in C+V from 2.7±0.2 to 2.0±0.3 mg/kg-min (p<0.05) by 3h, while in P it rose from 2.6ti.0 to 4.4±0.5 mg/kg-min (p<0.05), and in V it rose from 2.9±0.2 to 3.4±0.7 mg/kg-min (NS). In conclusion, the brain is the primary director of hormone release and glucose production during IIH, and areas of the brain supplied by the carotid circulation (forebrain, anterior hypothalamus) are necessary to the response since vertebral artery glucose infusion only modestly impaired counterregulation.

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POS-004-029 BRAIN CHOLINERGIC NEURONS AND INSULIN SECRETION IN ADRENALECTOMIZED RATS.

M GOTOH*, A IGUCHI, A YATOMI, K UEMURA, H MIURA, K KATO*, N SAKAMOTO Aichi Medical University* and Nagoya University School of Medicine, Japan.

Although the participation of vagus nerve in central nervous system (CNS)-mediated neural regulation of insulin release has been demonstrated, little is known of neuropharmacological characteristics in the CNS. Therefore, to investigate the effect of central cholinergic neurons on insulin secretion, neostigmine ( 5x10 -a mol; a cholinesterase inhibitor ) was injected into the third cerebral ventricle in adrenalectomized fed rats. Neostigmine (I ~i) injected intraventricularly produced hyperglycemia and hyperinsulinemia, whereas neostigmine (0.2ml) injected intravenously did not. Prior subdiaphragmatic vagotomy inhibited hyperinsulinemia, but not hyperglycemia. Intraperitoneal injection of methyl-atropine could inhibit hyperinsulinemia, but not hyperglycemia. Intraventricular coadministration of methyl-atropine in a dose, which was ineffective when administered intraperitoneally, suppressed hyperinsulinemia and hyperglycemia. Neither hyperinsulinemia nor hyperglycemia is suppressed by intraventricular injection of hexamethonium bromide. Hyperinsulinemia induced by neostigmine was not found in intact rats, indicating the inhibitory effect of concomitant epinephrine secretion on insulin release. These findings suggest that central cholinergic- muscarinic neurons could participate in the vagus nerve-mediated central regulation of insulin secretion.

POS-004-030 INCREASED SENSITIVITY TO NORADRENALINE INFUSION AND BASAL SYMPATHETIC TONE IN NONINSULIN DEPENDENT DIABETES MELLITUS (NIDDM).

DG BRUCE, DJ CHISHOLM, LH STORLIEN, GA SMYTHE, EW KRAEGEN. Garvan Institute of Medical Research, St Vincent's Hospital, Sydney

The sympathetic nervous system may play a role in hepatic glucose overproduction in NIDDM. The aim of this study was to determine whether subjects with NIDDM had normal sensitivity to noradrenaline (NA) infusion. NA was infused at 60 ng/kg/min for 60 mins into nondiabetic (C, n=6) and diabetic subjects (n=7) and cardiovascular, hormonal and metabolic responses determined. Basal levels of NA (NIDDM 2.7~0.4 vs C 2.3~0.2 nmol/l) and its metabolite dihydroxyphenylethylene glycol (DHPG, 6.8~i.i vs C 5.9~1.4 nmol/l) and NA levels during NA infusion (14.1±1.5 vs C 12.9~i.0 nmol/l) were the same in both groups. The diabetic subjects had significantly greater pressor (mean systolic elevation, 21_%3 vs llel mmHg, P<0.02) and glycaemic responses (mean glucose increments, 2.1±0.4 vs 0.6±0.1 mmol/l, p<0.005) than the nondiabetic subjects. There was a positive correlation between pressor and glycaemic responses for all subjects (r=0.64, p<0.02). The excess glycaemia was due to an increase in hepatic glucose production rather than an effect on glucose uptake. Glucagon levels rose (nonsignificantly) and insulin levels fell transiently (significant in NIDDM) in both groups. Basal plasma glucose levels correlated with basal DHPG (r=0.77, p<0.04) but not with NA levels, in the diabetic subjects only. We conclude that there is increased sensitivity to high (physiological) circulating NA levels in NIDDM which influence pressor reflexes and glycaemia; there may also be increased sensitivity to basal sympathetic tone. These data have implications regarding the pathogenesis of hyperglycaemia in NIDDM.

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POS-004-031 2-DEOXYGLUCOSE-INDUCED HYPERGLYCAEMIA IS MEDIATED BY DIRECT SYMPATHETIC NERVOUS SYSTEM ACTIVATION OF LIVER GLUCOSE OUTPUT.

WS PASCOE, GA SMYTHE AND LH STORLIEN. Garvan Institute of Medical Research, St.Vincent's Hospital, Sydney, Australia.

The hypothalamus is known to play an important integrative role in the control of peripheral metabolism, achieved by modulation of autonomic outflow to the endocrine pancreas, the liver and the adrenal medulla. This study was designed to determine the role of direct sympathetic nervous system control of hepatic glucose output during neuroglycopaenia induced by the non- metabolizable glucose analogue 2-deoxyglucose (2DG). Steady-state tracer methodology was used to directly measure hepatic glucose output (Ra) in pentobarbitone-anaesthetised male Wistar rats (220-320g). This involved a primed 90 minute continuous infusion of D-3-[3H]-glucose. Liver glucose output is calculated as the ratio of tracer infusion rate to steady-state plasma glucose specific activity. Administration of 500mg/kg 2DG i.p. produced an increase in Ra from a control value of 7.3 + 0.3 mg/kg.min (n=4) to 15.2 __. 2.2 mg/kg.min (n=8), corresponding to an increase in plasma glucose (PG) from 6.4 + 0.1 mmol/L to 10.1 + 0.4 mmol/L. This rise was effectively countered by the sympathetic noradrenergic blocker guanethidine (100mg/kg i.p.), reducing Ra to 10.4 + 0.9 mg/kg.min and PG to 6.1 + 0.3 mmol/L (n=8), even in the face of markedly lower plasma insulin (PI) levels (2DG: PI= 94.7+ 18.6 mU/L (n=7), 2DG+GU: PI= 41.4 + 3.3 mU/L (n=8)). Absence of adrenal-medullary influence was evident by the persistence of 2DG- induced hyperglycaemia in adrenalectomized (ADX) animals. Liver glucose output in intact and ADX animals treated with 2DG was virtually identical (2DG: Ra= 15.2 + 2.2 mg/kg.min, 2DG+ADX= 15.6 + 1.0 mg/kg.min). Elevated Ra in the 2DG+ADX group was maintained despite markedly elevated insulin levels (349.3 + 72.6 mU/L (n=7)).We conclude that 2DG-induced hyperglycaemia is mediated by direct sympathetic nervous system activation of liver glucose output.

POS-004-032 DIRECT CENTRAL NORADRENERGIC Vs. SYMPATHOADRENAL ROLES IN GLUCOREGULATION FOLLOWING STRESS IN THE RAT.

GA SMYTHE, WS PASCOE, LH STORLIEN Garvan Institute of Medical Research, St Vincent's Hospital, Sydney, Australia.

Central noradrenergic pathways play a significant role in mediating blood glucose levels following neuroglycopaenia. To further investigate hypothalamic noradrenergic neuronal activity (NNA) and sympathoadrenal influences in glucoregulation we studied the effects of acute stress on glucose and insulin levels in normal and adrenalectomized (ADRX) rats. Gas chromatography/mass spectrometry with deuterated internal standards was used to assay hypothalamic concentrations of noradrenaline (NA) and its primary neuronal metabolite, 3,4-dihydroxyphenylglycol (DH:PG). NNA was assessed from the hypothalamic ratio DHPG/NA and relationships with serum glucose and insulin levels were examined in adult male Wistar rats 5 min or 15 - 18 min after being subjected to either ether vapour (1 min) or cold swim (2 min) stress. Linear regression analysis of the combined data from these stress studies in intact rats revealed an highly significant positive correlation between hypothalamic NNA and serum glucose levels (F ratio = 55; p<0.0001). However, insulin responses were time-dependent. Five min following stress in the intact rat insulin release was inhibited (p<0.05) and serum insulin levels were inversely correlated with hypothalamic NNA (F ratio = 5.4). This relationship between insulin and NNA was no longer present 15 min after stress and serum insulin levels, being not significandy different from basal controls at this time, were inappropriately low in relation to the elevated serum glucose levels (approx. 30% above basal). Blockade of peripheral sympathetic nervous system pathways by treatment of intact rats with guanethidine prevented the rise in glucose 5 min following cold swim stress but did not prevent the inhibition of insulin release. When, on the other band, ADRX mts were subjected to cold swim stress they exhibited elevated hypothalamic NNA and serum glucose rises similar to intact animals but, in contrast to their intact counterparts, their serum insulin levels were significantly elevated (p<0.01). These results indicate that hepatic glucose release is mediated by central NNA via a direct neural pathway to the liver, but a similar neural pathway to the pancreas does not play a major role in inhibiting insulin release atter stress. In fact, adrenal catecholamines appear to be the principal mediators of insulin inhibition immediately following stress in the rat. We suggest that the negative relationship between NNA and insulin 5 min after stress reflects stimulation of the adrenal medulla by the CNS. Thus the data from this investigation are consistent with central noradrenergic neural pathways directly mediating hepatic glucose release and indirectly inhibiting pancreatic insulin release via activation of adrenal medullary catecholamines.

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POS-004-033 BARORECEPTOR-GOVERNED SYMPATHETIC NERVE ACTIVITY INCREASES AFTER CARBOHYDRATE INTAKE.

C Berne and Jan Fagius, Departments of Internal Medicine and Neurology, University Hospital, Uppsala, Sweden.

Carbohydrate intake is associated with increased plasma norepinephrine concentrations, suggesting enhanced sympathetic nervous system activity(SNS).

In order to examine directly changes in nerve function the sympathetic discharge in extremity nerves were recorded by microneurography in altogether 24 healthy subjects.The baroreceptor-regulated muscle nerve sympathetic activity (MSA)and the skin nerve sympathetic activity(SSA), which consists of sudomotor and cutaneous vasoconstrictor signals, were measured by a 5 I~m tungsten electrode placed in the peroneal nerve below the knee. The nerve activity was studied first during basal conditions and then for up to 90 min after 100 g oral D-glucose, an iso- osmolar load of D-xylose, after intravenous D-glucose(0.35 g/kg) and after water ingestion.

MSA increased significantly after oral D-glucose from 21 + 1 bursts/min(mean + SEM; n=7) at rest to a peak of 35 + 5 bursts/min at 30 min(p<0.05) followed by a gradual return to 27 + 2 bursts/min at 90 min, the activity parallelling the insulin response curve. In contrast, SSA(n=3) displayed no change after glucose ingestion. Also D-xylose(n=7), giving rise to a moderate insulin increase, elicited a MSA response, although lower and more protracted than after D-glucose, wheras ingestion of water was not associated with any significant change of MSA(n=3).lntravenous D-glucose(n=7) caused a variable response with great individual differences and with no apparent relation to insulin release. CONCLUSIONS: The present study has identified MSA as one major source of the norepinephrine increase after carbohydrate ingestion.The effect of carbohydrate intake may be mediated by the hyperinsulinaemia, but other mechanisms may also be involved.The lack of change of SSA shows that there is no overall SNS stimulation. The increase of the mainly vaso-constrictory MSA in response to feeding may contribute to the association of over-feeding with hypertension.

POS-004-034 RESPONSES OF THE HUMAN SYMPATHETIC NERVOUS SYSTEM TO GLUCOPENIA FOLLOWING 2-DEOXY-D-GLUCOSE INFUSION.

J. FAGIUS & C. BERNE, DEPARTMENTS OF NEUROLOGY AND INTERNAL MEDICINE, UNIVERSITY HOSPITAL, S-751 85 UPPSALA, SWEDEN

Microelectrode recordings of sympathetic outflow in human extremity nerves during insulin-induced hypoglycaemia have displayed an increase in muscle nerve sympathetic activity (MSA), composed of baroreflex-governed vasoconstrictor sig- nals. Skin nerve sympathetic activity (SSA), consisting of sudomotor impulses and vasoconstrictor signals to the skin, reacts with an increase in sudomotor outflow with simultaneous reduction of the vasoconstrictor component.

In order to detect whether these effects are due to glucopenia or depend on direct insulin action, 2-deoxy-D-glucose, 50 mg/kg b.w., was infused to healthy volunteers after an overnight's fast. Blood glucose rose successively from 5.0Z0.I (mean ZSE) to 7.9Z0.6 mmol/l at 90 min after the infusion (p<0.01) with subsequent increase in insulin level from 5.5Z0.5 to 15.4ZI.7 mU/l (p<0.01). Clinical symptoms of glucopenia appeared as expected.

MSA (n=6) increased from an initial level of 21+4.2 bursts/min to a maximum of 36+4.6 bursts/min at 30 min after the infusion (p~0.01) with a slow subsequent decline; i.e. another temporal course than that of the increase in insulin level. Preliminary observations of SSA (n=3) have shown qualitative changes of the temporal pattern of the activity, compatible with activation of sudomotor and inhibition of vasoconstrictor outflow. All changes were very similar to those observed during insulin-induced hypoglycaemia, albeit more protracted.

Conclusion. The present results suggest that the previously observed changes of sympathetic activity in human extremity nerves during insulin-induced hypo- glycaemia are primarily due to intracellular glucopenia (presumably in the CNS) and not to direct action of insulin.

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POS-004-035 INSULIN RESPONSE TO A SHORT STRESS P~RTOD

A ALVAREZ, L PORTILLA, R GONZALEZ

National Institute of Endocrinology, Havana, Cuba.

The present paper is @ preliminary report of a research program aimed to identify psychoneuroendocrine factors related to metabolic control in type II diabetics.

We studied in 24 volunteers, the insulin response to a short stress pe- riod (30 minutes), induced by a cognitive conflict under social pressure.

Insi~lin, Growth Hormone (GH), glycemia and blood pressure (BP) determin_a tions were performed before and after the stress period. Insulin and GH- were determined by RIA and gly~emia by the glucose oxidase method.

Results showed a significant increase of insulin levels following the stress period (p=O.02, paired observations t test). ~ multiple stepwise regression anelysis using insulin differences as the dependent variable and GH and glycemia as predictors showed that insulin variation was in- dependent of the latter.

The relation between emotional factors and metabolic control in type II diabetics are discussed.

POS-004-036 EFFECT OF NEUROPEPTIDE Y ON THE HYPOTHALAMIC-PITUITARY-ADRENAL AXIS IN THE DOG

T INOUE, A INUI, M OKITA, N SAKATANI, M OYA, H MORIOKA, S BABA Second Department of Internal Medicine, Kobe University School of Medicine, Kobe, Japan

There is increasing evidence that neuropeptide Y (NPY) may affect release of pituitary hormones. We previously reported that 0.119 to 1.19 mnol of NPY centrally administered to conscious dogs stimulated ACTH and cortlsol secretion dose-dependently (Sakatani et al., Aeta Endocrlnol 109: Suppl. 270, 38, 1985). Therefore, the present study was designed in order to clarify the mechanism by which NPY activates the hypothalamic-pitultary-adrenal (HPA) axis in the dog. Mongrel dogs were equipped with a chronic cannula allowing intra-third cerebro- ventricular (i.t.v) administration. A 1.19 nmol, i.t.v, dose of NPY produced as great an ACTH and cortisol response as did equimolar ovine CRF, but slightly less of a response than did insulin hypoglycemia. Intravenously (i.v.) administered NPY (1.19 - 11.9 nmol) was much less potent than i.v. CRF in stimulating ACTH and cortisol secretion. However, i.v. NPY produced a significant increase in plasma ACTH and cortisol concentrations, raising the possibility that NPY may modulate the activity of cortlcotrophs. Next, we have investigated the possible relationship between NPY and CRF on the HPA axis. Pretreatment with a novel CRF antagonist, 500 ~g alpha-helical CRF 9-41, partly but significantly attenuated the ACTH and cortlsol responses to 1.19 nmol i.t.v. NPY. Furthermore, adding a subthreshold dose of NPY (0.119 nmol) to 1.19 nmol of i.t.v. CRF resulted in a potentiation of CRF-induced ACTH secretion. These results indicate that NPY may activate HPA axis in concert with CRF. The present findings that NPY evokes ACTH secretion and potentiates the effectiveness of CRF as a secretagogue, together with the abundance of NPY in the hypothalamus, median eminence, and the portal blood, suggest that NPY may be involved in multihormonal control of ACTH release.

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POS-004-037 EFFECTS OF PANCREASTATIN ON PITUITARY-ADRENAL AXIS, ENDOCRINE PANCREAS, AND FOOD AND WATER INTAKE IN THE DOG

A INUI, M OKITA, T INOUE, N SAKATANI, M OYA, H MORIOKA, S BABA Second Department of Internal Medicine, Kobe University School of Medicine, Kobe, Japan

The present study was designed to seek evidence fer pancreastatin as a biologically active brain-gut peptide. Purified porcine pancreastatin in a single dose of 1.19 nmol was adminis- tered for 5 min into the third cerebral ventricle (i.t.v.) and its effects on pituitary-adrenal axis, endocrine pancreas, and food and water intake studied in the dog. Pancreaststin was kindly donated by Dr. Tatemoto (Stanford University, USA). The 1.19 nmol dosage was chosen since many peptides affect visceral and behavioral functions of dogs at this level, including cholecystokinin oetapeptide (CCK-8), corticotropin releasing hormone (CRH), and neuropeptide Y (NPY). Pancreastatin was also administered into the peripheral vein (i.v.) and the effects of the peptide compared with those after i.t.v, administration. Neither means of administration had any effect on basal ACTH, cortisol, insulin, pancreatic polypeptide (PP), or glucose concentrations. Nor did pretreatment with i.t.v, or i.v. pancreaststin affect the ACTH or cortisol responses to 1.19 nmol CRH. Nor did i.t.v, or i.v. pretreatment with pancreaststin reduce i.v. glucose-induced insulin release. However, i.v. pancreastatin did inhibit the i.v. CCK-8-induced insulin release without affecting PP release, suggesting it exerts a direct and preferential action on the islet. Like 1.19 nmol NPY, i.t.v, pancreastatin had no effect on food or water intake under fasting (16h) or non-fasting conditions, although it tended to increase water intake. However, i.t.v, pretreatment with pancreastatin was able to partly but significantly reverse the 1.19 nmol i.t.v. CCK-8-induced suppression of food intake, this effect not observed with i.t.v, pretreatment with NPY. These results suggest that pancreastatin may have modulatory effects on insulin release and feeding behavior in the dog.

POS-004-038 THE ROLE OF THE SPLANCHNIC NERVE IN REGULATION OF ENDOCRINE PANCREAS

T KUROSE, Y SEINO, G KOH, H FUKUMOTO, K TSUJI, T T,~ZiNATO, K TSUDA Y YAMADA, H YANO, H IMURA Department of Internal Medicine, Kyoto University School of Medicine, Kyoto Japan. Neural regulation of endocrine pancreas has been investigated in vivo and in vitro, but most of them were performed in vivo, and other phenomena induced by in vivo nerve stimulation make it difficult to evaluate the direct neural effect on pancreatic hormone secretion. We have, accordingly, established a new in vitro method using the isolated and vasculary perfused rat pancreas supplied with the left splanchnic nerve. Electrical stimulation of the nerve was performed by square wave impulse (10Hz, Ims, 30V). Perfusate volume decreased to 80% of a basal value in response to the splanchnic nerve stimula- tion. Insulin(IRI) and somatostatin (IRS) responses during perfusion with 16.7 mM glucose were inhibited by 75% and 40% respectively by nerve stimulation. In contrast, norepinephrine output increased 10-fold in response to nerve stimulation. Glucagon(IRG) response to nerve stimulation during perfusion with 5.5 mM glucose was augmented about 20-fold. Phentolamine reduced the inhibition of IRI and IRS release by nerve stimulation, by 50% and 30% respectively. In addition, IRG response to nerve stimulation was abolished by phentolamine. Propranolol did not affect the IRG response to nerve stimulation significantly, whereas 5 min sum of changes in IRI and IRS output induced by nerve stimulation were further inhibited by propranolol. In the presence of phentolamine and propranolol, IRI and IRS responses to nerve stimulation were still significantly inhibited. These results suggest that IRG release induced by splanchnic stimulation is through alpha adrenergic mechanism. Inhibition of IRI and IRS responses by splanchnic nerve stimulation seems to be mediated not only by alpha receptor mechanism but also by non-adrenergic mechanism.

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POS-004-039 THE EFFECT OF MUSCARINIC STIMULATION ON PLASMA INSULIN AND GLUCOSE IN OBESE-HYPERGLYCEMIC OB/OB MICE

S FUKUDO, R S SURWIT, C COCHRANE, C M KUHN, & M N FEINGLOS Departments of Psychiatry, Pharmacology, and Medicine, Duke University Medical Center, Durham, N.C., U.S.A.

The significance of the parasympathetic nervous system in glucoregulation is still unclear, although several authors have reported that muscarinic stimulation causes insulin secretion. We now report evidence of vagal impact on glucoregulation in physiological and pathological conditions. Plasma glucose and insulin responses to a muscarinic agonist (bethanechol) were evaluated in C57 BL/6J ob/ob mice (an animal model of type II diabetes, characterized by hyperinsulinemia and peripheral insulin resistance), C57 BL/6J ob/? mice (nondiabetic lean littermates of the ob/ob in which we have recently demonstrated an apparent genetic predis- position to diabetes), and A/J (normoglycemic) mice. In A/J mice, subcutaneous injection of bethanechol in various doses (0, 0.5, 1.0, 2.0 ug/g) caused a dose-dependent increase in insulin secretion and a significant decrease in plasma glucose (p < 0.001). In lean C57 mice, in contrast, insulin increased but there was little change in plasma glucose. In ob/ob mice, insulin increased remarkably in response to bethanechol administration (saline: 631.5 + 80.2 uU/ml: bethanechol 2.0 ug/g: 1793.8 + 97.4 uU/ml, n=10, p < 0.001), but surprisingly, plasma glucose rose significantly (salineT 230.1 + 14.0 mg/dl; bethanechol 2.0 ug/g: 362.8 + 17.6 mg/dl, n=10, p < 0.001). The etiology of thTs hypersensitivity to muscarinic-induced -- insulin secretion and the paradoxical glucose response seen in ob/ob mice is presently undefined. However, these findings suggest that excitation of the parasympathetic nervous system plays an important role in insulin secretion and glucose utilization in this animal model of type II diabetes.

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