Gastric acid and pancreatic polypeptide responses to modified sham feeding: indication of an increased basal vagal tone in a subgroup of duodenal ulcer patients

Auricular vagal nerve stimulation enhances gastrointestinal motility and improves interstitial cells of Cajal in rats treated with loperamide

BACKGROUND

Gastrointestinal (GI) motility disorders affect a large proportion of the population with limited treatment options. The aims of this study were to investigate the potential of a non-invasive method of auricular vagal nerve stimulation (aVNS) for treating GI dysmotility and to explore possible mechanisms involving slow waves and interstitial cells of Cajal (ICC).

METHODS

Normal rats were treated daily with loperamide for 1 week and then treated, while still on daily loperamide, with aVNS/Sham-aVNS for another 1 week. Gastric emptying (GE), small intestine transit (SIT), and GI slow waves were measured. The plasma level of pancreatic polypeptide (PP) and noradrenaline (NE) was assessed by ELISA. ICC in the gastric antrum were detected by immunohistochemistry.

KEY RESULTS

(a) aVNS significantly increased the percentage of normal GI slow waves (p < 0.05 for both fasting and postprandial states, vs. Sham-aVNS) and accelerated GE (p < 0.05, vs. Sham-aVNS) and SIT (p < 0.05, vs. Sham-aVNS) impaired by loperamide. (b) aVNS increased plasma PP (p < 0.01) and decreased plasma NE (p < 0.01), compared with Sham-aVNS. (c) Gastric ICC was decreased by loperamide (p < 0.01) but increased after aVNS (p < 0.01, vs. Sham aVNS).

CONCLUSIONS & INFERENCES

Loperamide induces upper GI dysmotility. aVNS accelerates upper GI transit and improving pace-making activity mediated via the ICC. Non-invasive aVNS may have a therapeutic potential for upper GI dysmotility.

Studying noninvasive indices of vagal control: the need for respiratory control and the problem of target specificity

Respiratory sinus arrhythmia (RSA) is a popular index of cardiac vagal control; however, research has rarely adequately addressed respiratory influences on RSA. In addition, simplistic views of the parasympathetic system have resulted in an overinterpretation of RSA as a general indicator of vagal control. Research using a respiration-corrected time-domain index of RSA has yielded plausible findings that substantially deviate from uncorrected RSA. Paced breathing, which is used for baseline calibration of RSA in this correction procedure, allows for a representative sampling of respiratory influences on RSA and has minimal impact on autonomic regulation. Past research has largely focused on cardiac vagal activity and ignored the extent of target specificity in the parasympathetic system. More research is needed on new noninvasive indices of vagal control at other organ sites. Studies also need to address muscarinic receptor sensitivity before noninvasive vagal indices can be interpreted as markers of central vagal outflow.

Counterregulatory hormone and symptom responses to insulin-induced hypoglycemia in the postprandial state in humans

Plasma counterregulatory hormones and symptoms were measured during hypoglycemia in the postprandial and in the fasting state in humans to establish differences in physiological responses. We studied 8 nondiabetic subjects and 10 subjects with type 1 diabetes on two different occasions during clamped insulin-induced hypoglycemia (2.4 mmol/l) in the sitting position. On one occasion, subjects ate a standard mixed meal, and on the other they remained fasting. In response to postprandial as compared with fasting hypoglycemia, nondiabetic subjects exhibited lower total symptom scores (6.6 +/- 0.4 vs. 11.5 +/- 0.8, P = 0.001), which was due to less hunger (1.1 +/- 0.1 vs. 4.2 +/- 0.2), lower suppression of plasma C-peptide (0.23 +/- 0.1 vs. 0.08 +/- 0.07 nmol/l, P = 0.032), and greater responses of plasma glucagon (248 +/- 29 vs. 163 +/- 25 ng x l(-1) x min(-1), P = 0.018), plasma adrenaline (4.5 +/- 0.6 vs. 3.1 +/- 0.4 nmol x l(-1) x min(-1), P = 0.037), norepinephrine (3.8 +/- 0.3 vs. 3.2 +/- 0.2 nmol x l(-1) x min(-1), P = 0.037), and pancreatic polypeptide (217 +/- 12 vs. 159 +/- 22 pmol x l(-1) x min(-1), P = 0.08). Except for plasma C-peptide, responses in diabetic subjects were similarly affected. Notably, in diabetic subjects responses of glucagon, which were absent in the fasting state, nearly normalized after a meal. In conclusion, in the postprandial compared with the fasting hypoglycemic state, total symptoms are less, but counterregulatory hormones are greater and responses of glucagon nearly normalize in type 1 diabetic subjects.

Autonomic control of heart period in duodenal ulcer patients insights from spectral analysis of heart rate variability

Beyond the fundamental pathogenetic importance of Helicobacter Pylori a possible additional role of vagal innervation in favouring or modulating the clinical history of duodenal ulcer (DU) has been suggested by old studies employing invasive methodologies. Aim of this study was to assess whether vagal prevalence in autonomic modulation was present in healed DU patients (n=20) as compared to controls,(n=50), using a validated non-invasive methodology, based on spectral analysis of cardiovascular variability. This approach provides markers of the sympathetic and vagal modulations of the SA node, respectively by way of the normalized low frequency (LF(RR)) and high frequency (HF(RR)) components of RR interval variability; LF/HF ratio furnishes a marker of sympatho-vagal balance. In addition, sham feeding (SF) provided a means to assess, in DU patients, neurally mediated acid secretion, as the SF acid output (SAO) to basal acid output (BAO) ratio (SAO/BAO). Results showed that LF(RR) was smaller in DU patients than in controls (40.3+/-3.9 vs. 52.3+/-2.3 normalized units, nu; P<0.05). On the contrary, HF(RR) was greater (52.1+/-3.7 vs. 35.7+/-2.3 nu; P<0.05). Conversely the LF component of SAP variability, a marker of sympathetic vasomotor modulations, and the index alpha, a measure of baroreflex control of the SA node, as well as respiratory patterns, were similar in the two groups. SAO/BAO ratio was significantly correlated with markers of autonomic control of the SA node (r = -0.67, P<0.0083 with HF(RR)). In conclusion results suggest an enhanced vagal modulation of heart period in DU patients at rest, that appears linked to indices of neurally mediated gastric acid secretion response.

Long-term intensive insulin therapy in IDDM: effects on HbA1c, risk for severe and mild hypoglycaemia, status of counterregulation and awareness of hypoglycaemia

The present studies were designed to assess the percentage of HbA1c, frequency, and awareness of hypoglycaemia (H) during long-term intensive therapy (IT) of insulin-dependent diabetes mellitus (IDDM). From 1981 to 1994, 112 IDDM patients were on IT. HbA1c was 7.17 +/- 0.16% (non-diabetic subjects 3.8-5.5%), the frequency of severe H 0.01 +/- 0.009 episodes/patient-year, frequency of mild symptomatic H 35.6 +/- 2.9 episodes/patient-year. IDDM patients with HbA1c < or = 5.5% (Group I, n = 10), between 6.1-7.0% (Group II, n = 12), and > or = 7.6% (Group III, n = 11) were studied to assess responses of counterregulatory hormones, symptoms and cognitive function during experimental, stepped H. Compared to 18 non-diabetic subjects, Group I exhibited high thresholds (plasma glucose had to decrease more than normal to evoke responses), and impaired responses of adrenaline, unawareness of H and delayed onset of cognitive dysfunction at the lowest glycaemic plateau (2.3 mmol/l). Group II had normal thresholds and responses, whereas Group III had low thresholds. Frequency of mild H was higher in Group I (54.5 +/- 1.9 episodes/patient-year) than in Group II and III (33.7 +/- 3.5 and 20.4 +/- 2.5 episodes/patient-year, respectively, p < 0.001) and correlated with percentage of HbA1c (r = -0.82).

IN CONCLUSION

IT can maintain near-normal HbA1c and is compatible with low frequency of severe H. However, if HbA1c is less than 6.0%, mild, symptomatic H is excessively frequent and causes impaired counterregulation and H unawareness. Efforts should be made not only to maintain HbA1c < or = 7.0%, but also to prevent, recognize and reverse iatrogenic H unawareness during long-term IT of IDDM by maintaining HbA1c > 6.0%.

Long-term recovery from unawareness, deficient counterregulation and lack of cognitive dysfunction during hypoglycaemia, following institution of rational, intensive insulin therapy in IDDM

Hypoglycaemia unawareness, is a major risk factor for severe hypoglycaemia and a contraindication to the therapeutic goal of near-normoglycaemia in IDDM. We tested two hypotheses, first, that hypoglycaemia unawareness is reversible as long as hypoglycaemia is meticulously prevented by careful intensive insulin therapy in patients with short and long IDDM duration, and that such a result can be maintained long-term. Second, that intensive insulin therapy which strictly prevents hypoglycaemia, can maintain long-term near-normoglycaemia. We studied 21 IDDM patients with hypoglycaemia unawareness and frequent mild/severe hypoglycaemia episodes while on "conventional" insulin therapy, and 20 nondiabetic control subjects. Neuroendocrine and symptom responses, and deterioration in cognitive function were assessed in a stepped hypoglycaemia clamp before, and again after 2 weeks, 3 months and 1 year of either intensive insulin therapy which meticulously prevented hypoglycaemia (based on physiologic insulin replacement and continuous education, experimental group, EXP, n = 16), or maintenance of the original "conventional" therapy (control group, CON, n = 5). At entry to the study, all 21 IDDM-patients had subnormal neuroendocrine and symptom responses, and less deterioration of cognitive function during hypoglycaemia. After intensive insulin therapy in EXP, the frequency of hypoglycaemia decreased from 0.5 +/- 0.05 to 0.045 +/- 0.02 episodes/patient-day; HbA1c increased from 5.83 +/- 0.18 to 6.94 +/- 0.13% (range in non-diabetic subjects 3.8-5.5%) over a 1-year period; all counterregulatory hormone and symptom responses to hypoglycaemia improved between 2 weeks and 3 months with the exception of glucagon which improved at 1 year; and cognitive function deteriorated further as early as 2 weeks (p < 0.05). The improvement in responses was maintained at 1 year. The improvement in plasma adrenaline and symptom responses inversely correlated with IDDM duration. In contrast, in CON, neither frequency of hypoglycaemia, nor neuroendocrine responses to hypoglycaemia improved. Thus, meticulous prevention of hypoglycaemia by intensive insulin therapy reverses hypoglycaemia unawareness even in patients with long-term IDDM, and is compatible with long-term near-normoglycaemia. Because carefully conducted intensive insulin therapy reduces, not increases the frequency of moderate/severe hypoglycaemia, intensive insulin therapy should be extended to the majority of IDDM patients in whom it is desirable to prevent/delay the onset/progression of microvascular complications.

Relative roles of insulin and hypoglycaemia on induction of neuroendocrine responses to, symptoms of, and deterioration of cognitive function in hypoglycaemia in male and female humans

To assess the relative roles of insulin and hypoglycaemia on induction of neuroendocrine responses, symptoms and deterioration of cognitive function (12 cognitive tests) during progressive decreases in plasma glucose, and to quantitate glycaemic thresholds, 22 normal, non-diabetic subjects (11 males, 11 females) were studied on four occasions: prolonged fast (n = 8, saline euglycaemia study, SA-EU), stepped hypoglycaemia (plasma glucose plateaus of 4.3, 3.7, 3 and 2.3 mmol/l) or euglycaemia during insulin infusion at 1 and 2 mU.kg-1.min-1 (n = 22, high-insulin hypoglycaemia and euglycaemia studies, HI-INS-HYPO and HI-INS-EU, respectively), and stepped hypoglycaemia during infusion of insulin at 0.35 mU.kg-1.min-1 (n = 9, low-insulin hypoglycaemia study, LO-INS-HYPO). Insulin per se (SA-EU vs HI-INS-EU), suppressed plasma glucagon (approximately 20%) and pancreatic polypeptide (approximately 30%), whereas it increased plasma noradrenaline (approximately 10%, p < 0.05). Hypoglycaemia per se (HI-INS-HYPO vs HI-INS-EU) induced responses of counterregulatory hormones (CR-HORM), symptoms and deteriorated cognitive function. With the exception of suppression of endogenous insulin secretion, which had the lowest glycaemic threshold of 4.44 +/- 0.06 mmol/l, pancreatic polypeptide, glucagon, growth hormone, adrenaline and cortisol had similar glycaemic thresholds (approximately 3.8-3.6 mmol/l); noradrenaline (3.1 +/- 0.0 mmol/l), autonomic (3.05 +/- 0.06 mmol/l) and neuroglycopenic (3.05 +/- 0.05 mmol/l) symptoms had higher thresholds. All 12 tests of cognitive function deteriorated at a glycaemic threshold of 2.45 +/- 0.06 mmol/l, but 7 out of 12 tests were already abnormal at a glycaemic threshold of 2.89 +/- 0.06 mmol/l. Although all CR-HORM had a similar glycaemic threshold, the lag time of response (the time required for a given parameter to increase) of glucagon (15 +/- 1 min) and growth hormone (14 +/- 3 min) was shorter than adrenaline (19 +/- 3 min) and cortisol (39 +/- 4 min) (p < 0.05). With the exception of glucagon (which was suppressed) and noradrenaline (which was stimulated), insulin per se (HI-INS-HYPO vs LO-INS-HYPO) did not affect the responses of CR-HORM, and did not influence the symptoms or the cognitive function during hypoglycaemia. Despite lower responses of glucagon, adrenaline and growth hormone (but not thresholds) in females than males, females were less insulin sensitive than males during stepped hypoglycaemia.

Vagal effects on acid and pepsin secretion and serum gastrin in duodenal ulcer and controls

To study whether the vagus sustains basal secretion and stimulates acid and pepsin differently in duodenal ulcer (DU) and non-DU, we tested 144 patients with DU and 92 nonulcer controls, using 1-hr basal secretion followed by 15 min of modified sham feeding (MSF) and after 1 hr followed by a reference maximum elicited by 6 micrograms/kg pentagastrin given subcutaneously and observed for another 1 hr. Of all subjects, 97.5% responded to MSF by raising basal acid output (BAO) at least 15%. MSF added amounts of acid equal to 26-30% of peak acid output and 30-43% of peak pepsin output, regardless of diagnosis or level of basal secretion (including hypersecretors). Speed and duration of responses were similar in DU and controls. MSF did not substantially alter serum gastrin. Males secreted more acid and pepsin than females under all conditions, differences that persisted in DU but not in controls when outputs were corrected for body weight. Male DU but not female DU patients secreted more than corresponding controls. Sham feeding is an effective stimulus with similar characteristics in controls and DU patients. There was no evidence for saturation of vagal pathways in basal hypersecretors. MSF stimulation does not appear to involve gastrin. Hypersecretion in DU derives largely from responses in male DU.

Neurohumoral control of gallbladder motility in healthy subjects and diabetic patients with or without autonomic neuropathy

Patients affected by diabetes mellitus are reported to have an increased incidence of gallbladder abnormalities. The pathophysiologic mechanisms for this phenomenon are unclear. In the present study ultrasonography was used to determine gallbladder emptying in response to a meal or separate cephalic or hormonal stimulation in 21 diabetic patients and 10 healthy subjects. Gallbladder emptying and refilling after a meal were similar in diabetic patients and healthy subjects. When diabetics were divided according to the presence or absence of cardiac autonomic neuropathy (AN), a significant reduction of gallbladder emptying in response to cephalic stimulation was found in diabetics with AN (P less than 0.01 in comparison with diabetics without AN or healthy subjects). A dose-response curve of gallbladder emptying in response cerulein, a cholecystokinin analog, at concentrations of 0.25, 1, and 4 micrograms/kg/min was evaluated. No differences of gallbladder emptying were found in the three groups of subjects, indicating that gallbladder sensitivity to hormonal stimulation is not changed in diabetic patients with or without AN. Diabetic patients with AN have a significant reduction of gastric acid output and pancreatic polypeptide (PP) secretion in response to cephalic stimulation (P less than 0.05 in comparison with diabetic patients without AN or healthy subjects). Cerulein-induced PP secretion was similar in all three groups of subjects (P greater than 0.05). This study indicates that in diabetic patients with AN, gallbladder emptying as well as gastric acid and PP secretions induced by neural stimulation are markedly reduced in comparison to diabetics without AN.

Gastric acid response to modified sham feeding in patients with duodenal ulcer: is increased vagal tone the cause of basal acid hypersecretion?

In order to test the hypothesis that increased basal vagal tone causes basal acid hypersecretion in duodenal ulcer (DU), the effect of sham feeding on gastric acid secretion was studied in 26 patients with DU and 20 healthy controls. Basal acid output (BAO), sham feeding-stimulated acid output (SAO) and peak histamine-stimulated acid output (PAO) were significantly higher in DU patients compared with healthy controls (P less than 0.01). The BAO/PAO ratio in DU patients (0.28 +/- 0.03) was not significantly different from that of healthy subjects (0.19 +/- 0.03), indicating that the higher BAO in DU patients group, as a whole, was due to a higher parietal cell mass. The basal subtracted response to sham feeding expressed as a fraction of secretory capacity [(SAO-BAO)/PAO], which correlates inversely with the basal vagal tone, was not significantly different in the patients and control subjects (0.27 +/- 0.03 versus 0.3 +/- 0.03; P greater than 0.05). Based on the data from the healthy controls, a ratio of BAO/PAO greater than 0.44 was defined as abnormal (using 95% confidence limits) and it indicated marked basal acid hypersecretion. Four of 26 DU patients had basal acid hypersecretion (that is, BAO/PAO greater than 0.44), but only two of them did not show an increase over their basal rate of secretion in response to sham feeding. All other DU patients, including two with marked basal acid hypersecretion, and all healthy controls showed an appreciable increase in their acid secretion in response to sham feeding.(ABSTRACT TRUNCATED AT 250 WORDS)

Sham feeding for testing gastric secretory capacities before and after parietal cell vagotomy

The usefulness of acid secretory data collected during a modified sham-feeding (MSF) test was examined in 50 patients suffering from duodenal ulcer before and after parietal cell vagotomy. In these patients basal acid output pentagastrin-stimulated acid output and MSF-stimulated acid output were measured. Preoperative MSF-stimulated acid output was found to be correlated with preoperative basal acid output, and postoperative MSF-stimulated acid output was correlated with both preoperative basal acid output and postoperative basal and pentagastrin-stimulated acid outputs. The addition of preoperative MSF-stimulated acid output to preoperative pentagastrin-stimulated acid output did not noticeably increase the close relationship between the latter and postoperative pentagastrin-stimulated acid output. It is concluded that basal and MSF-stimulated secretory rates overlap. Therefore, it is suggested that in both preoperative and postoperative conditions the addition of the sham-feeding test to the more simple basal and pentagastrin-stimulated studies could be discarded.

Basal and sham-feeding-stimulated salivary flow in duodenal ulcer patients and healthy subjects

Increased vagal (parasympathetic) stimulation of gastric secretion has been postulated in patients with duodenal ulcer disease. Since salivary secretion is influenced by parasympathetic nerves, we reasoned that duodenal ulcer patients also might have increased salivary secretion. Furthermore, if salivary secretion in duodenal ulcer patients is under nearly maximal parasympathetic stimulation basally, salivary volume might not increase with additional parasympathetic activation induced by sham feeding. To test these hypotheses, we measured basal and sham-feeding-stimulated salivary flow in duodenal ulcer patients and healthy subjects. Contrary to our hypotheses, both basal salivary flow and the salivary response to sham feeding were almost identical in duodenal ulcer patients and healthy subjects. Also, urogastrone concentrations in saliva were approximately the same in duodenal ulcer patients and normal subjects.

Modified sham feeding test after parietal cell vagotomy for juxtapyloric ulcer disease in patients with and without recurrent ulcers

The mean of individual coefficients of variation of acid output after modified sham feeding was 39% in 22 patients operated on with parietal cell vagotomy. The reproducibility of the interpretation of the sham feeding test as 'positive' or 'negative' was good. An intragastric infusion of a marker to correct for pyloric loss did not increase the accuracy of the test. The prognostic value of the qualitative estimation of the sham feeding test 2 months after operation to predict recurrent ulcer after parietal cell vagotomy was poor in 39 patients studied prospectively over 3 years. With the criterion sham feeding minus basal acid output over 1.0 mmol/30 min as a positive test, 63% of patients with a positive and 24% with a negative test later had recurrent ulcers. The consistency of the interpretation as either positive or negative was low in annual tests during the 3 years of follow-up study. After parietal cell vagotomy the sham-feeding-stimulated acid output was higher in patients with duodenal than in those with prepyloric recurrent ulcers and also in those without recurrences. This indicates that the amount of vagal innervation left after parietal cell vagotomy is of special importance in the occurrence of duodenal ulcer relapse.

Gastric acid and pancreatic polypeptide responses to modified sham feeding. Effects of truncal and parietal cell vagotomy

The effects of truncal vagotomy and parietal cell vagotomy on gastric acid secretion and plasma gastrin and pancreatic polypeptide release were studied in 28 duodenal ulcer patients under basal conditions and after modified sham feeding and infusion of pentagastrin (2 micrograms/kg/h). Before vagotomy gastric acid output in response to modified sham feeding was significantly higher than basal acid secretion in all subjects tested and reached about 45% of the pentagastrin maximum. No difference in the increase in acid response, or in the pancreatic polypeptide response to modified sham feeding was found between patients with high and low basal secretion. Plasma gastrin concentration was unaltered by modified sham feeding before and after truncal vagotomy or parietal cell vagotomy, although after vagotomy it tended to reach higher values than before this procedure. After truncal vagotomy, basal pancreatic polypeptide concentration was decreased and modified sham feeding-induced pancreatic polypeptide increment was completely eliminated. Four weeks after parietal cell vagotomy, the modified sham feeding-induced increment in plasma pancreatic polypeptide was significantly decreased and observed only in seven of 12 patients. Four to five years after parietal cell vagotomy all subjects responded to modified sham feeding with pancreatic polypeptide increment similar to that before vagotomy and in three of 12 patients acid response to modified sham feeding was seen. This study indicates that truncal vagotomy eliminates gastric acid and plasma pancreatic polypeptide responses to vagal excitation while parietal cell vagotomy abolishes gastric acid response and reduces temporarily the pancreatic polypeptide response to modified sham feeding (possibly because of transient impairment of the vagal innervation of the pancreas). (2) A high ratio of basal to maximal acid output in non-operated duodenal ulcer patients is not associated with a low acid response to modified sham feeding, nor with a high pancreatic polypeptide concentration, and (3) Restitution of the pancreatic polypeptide response to modified sham feeding five years after parietal cell vagotomy does not indication ineffective denervation of the parietal cells.

Pancreatic polypeptide response to a protein-rich meal in diabetic patients with and without neuropathy

A protein-rich meal and insulin-induced hypoglycemia (ITT) are two of the most important stimuli on pancreatic polypeptide (PP) secretion in diabetic patients. Previous studies have shown a reduced PP response to ITT in diabetic patients with autonomic neuropathy (AN). Twelve patients without AN (mean age 44 +/- 10.8 yr, mean duration of diabetes 11 +/- 5.6 yr), 9 with AN (51.4 +/- 6 yr, 15.8 +/- 6.9 yr) and 9 controls (N) were studied. AN was assessed by the evaluation of the beat-to-beat variation of the heart rate during deep breathing. PP secretion was stimulated by a protein-rich meal (200 g meat, 150 g milk). All insulin-dependent diabetic (IDD) patients lacked circulating PP antibodies. All diabetic patients showed a significant reduction in the early vagal phase compared to controls. This behavior was more evident in diabetic patients with AN and the secondary phase of these two groups overlapped with the response of controls. These data may be explained by the initial alterations of vagal functions not detectable by current methods.