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

Pancreatic Polypeptide in Parkinson's Disease: A Potential Marker of Parasympathetic Denervation

BACKGROUND AND OBJECTIVES

Parkinson's disease (PD) patients experience several non-motor symptoms from the gastrointestinal tract that may partly be caused by parasympathetic deficiency. The pancreas is densely innervated by the vagus nerve, which mediates early meal-induced secretion of pancreatic polypeptide (PP). Early secretion after sham feeding has been validated as a marker of vagal integrity. Thus, the aim was to evaluate the ratio of increased PP plasma levels after sham feeding in PD and correlate findings with gastrointestinal transit time (GITT).

METHODS

Twenty-five PD patients and 17 controls were included. PP, insulin, and blood glucose levels were measured before, during, and after sham feeding with white bread and chocolate spread. GITT was measured using radiopaque markers. Furthermore, faeces samples were analyzed for pancreatic elastase enzyme as a marker of exocrine pancreatic function.

RESULTS

PD patients showed significantly lower PP ratio levels after sham feeding, which was most pronounced at 10 minutes. No significant association was seen between attenuated PP response and GITT in PD patients. No between-group differences were seen in glucose or insulin levels over time, but PD patients showed generally lower insulin levels compared to controls. No difference was found in faeces pancreatic elastase.

CONCLUSIONS

Early-to-moderate stage PD patients demonstrated significantly decreased PP response after sham feeding suggestive of vagal denervation.

Human sex hormone-binding globulin does not provide metabolic protection against diet-induced obesity and dysglycemia in mice

BACKGROUND

Sex hormone-binding globulin (SHBG) is the main transporter of sex hormones in most vertebrates. Low SHBG levels have been linked to increased risk for diabetes and metabolic syndrome. Polymorphisms of the SHBG gene linked to low SHBG protein levels also strongly predicted increased risk of type 2 diabetes, thus raising the possibility that SHBG may play a role in the pathogenesis of insulin resistance and diabetes.

AIM

To examine whether expression of human SHBG in mice may ameliorate the development of diabetes and metabolic syndrome in response to a high-fat diet (HFD).

METHODS

Transgene mice expressing a human SHBG transgene (SHBG+) (N = 10/11; males/females) and their wild type littermates (N = 12/8; males/females) were fed HFD for 4.5 months.

RESULTS

HFD induced comparable obesity in control and SHBG+ mice. Male transgenes had higher muscle mass after 2-3.5 months HFD (0.43 ± 0.028 (n = 4) vs 0.38 ± 0.053 g (n = 7), P = 0.05). Fasting blood glucose, as well as insulin or HOMA-IR, was not different in transgenic vs wild-type males after 4-5 months HFD. Female transgenes had higher fasting glucose (152 ± 29 (n = 7) vs 115 ± 27 mg/dL, P = 0.01 (n = 8)), but mean insulin and HOMA-IR were not different. Likewise, insulin tolerance test and intra-peritoneal glucose tolerance test (GTT) were not different. Finally, SHBG+ mice were not different from controls in terms of liver enzymes, serum triglyceride levels and blood pressure.

CONCLUSION

In mice with diet-induced obesity, human SHBG did not protect against development of obesity or dysglycemia.

GENDER DETERMINES SERUM FREE CORTISOL: HIGHER LEVELS IN MEN

OBJECTIVE

Because only the free fraction of serum cortisol can readily access glucocorticoid receptors, we investigated whether or not a gender-related difference in serum free cortisol (FC) exists in the basal and adrenocorticotropic hormone (ACTH)-stimulated state.

METHODS

Serum total cortisol (TC) and FC were measured in 323 subjects (175 men; 148 women). Additionally, the low-dose 1-μg ACTH test was performed in 56 subjects (30 women, 26 men). Subjects were healthy volunteers, recruited in a preventive medicine screening program and an outpatient clinic.

RESULTS

Overall, basal serum TC and FC level were ~18 and ~33%, respectively, higher in men than in women (TC, 14.5 ± 0.33 μg/dL vs. 12.3 ± 0.33 μg/dL; P<.0001; FC, 0.68 ± 0.02 μg/dL vs. 0.51 ± 0.02 μg/dL; P<.0001). The higher FC in men relative to women was apparent across a wide age range (17 to 86 years) and persisted after adjustment for age and body mass index. The FC fraction (%FC, out of TC) was concordantly higher in men (5.4 ± 0.09% vs. 4.8 ± 0.3%; P = .046). FC was not related to the estimated menopausal status (women age below and above 47, 50, or 53 years). ACTH-stimulated FC levels were significantly higher in men compared to women, as reflected by the area under the response curve (49.4 ± 3.4 μg × min vs. 39.6 ± 2.2 μg × min; P = .0014).

CONCLUSION

Gender is an unrecognized determinant of serum FC in humans. The possibility of lifelong exposure to the higher bioactive fraction of cortisol under basal conditions or daily stress involving ACTH stimulation should be further investigated in the context of gender-related phenotypic features such as "android" (visceral) fat deposition and longevity.

ABBREVIATIONS

ACTH = adrenocorticotropic hormone BMI = body mass index CBG = cortisol-binding globulin FC = free cortisol HPA = hypothalamic-pituitary-adrenal TC = total cortisol.

Unimpaired postprandial pancreatic polypeptide secretion in Parkinson's disease and REM sleep behavior disorder

BACKGROUND

Pancreatic polypeptide is released immediately after food ingestion. The release is operated by vagal-abdominal projections and has therefore been suggested as a test for vagal nerve integrity. Pathoanatomical and clinical studies indicate vagal dysfunction in early Parkinson's disease (PD).

METHODS

We assessed the postprandial secretion of pancreatic polypeptide and motilin in healthy controls (n = 18) and patients with idiopathic rapid-eye-movement sleep behavior disorder (iRBD, n = 10), a potential premotor stage of PD, as well as in drug-naive (n = 19) and treated (n = 19) PD patients.

RESULTS

The postprandial pancreatic polypeptide secretion showed a physiological pattern in all groups and even an enhanced response in drug-naive PD and iRBD. Motilin concentrations correlated with pancreatic polypeptide concentrations.

CONCLUSIONS

Postprandial pancreatic polypeptide secretion is not a suitable test for vagal nerve integrity in PD. The unimpaired pancreatic polypeptide response in iRBD and PD might be explained by partially intact vagal-abdominal projections or compensatory mechanisms substituting a defective neuronal brain-gut axis.

Splanchnic neural regulation of pancreatic polypeptide release in the isolated perfused human pancreas

The isolated perfused human pancreas was employed as a model in which electrical stimulation of the celiac mixed neural bundle was performed in the presence and absence of selective neural antagonists. Stimulation of the celiac neural bundle in the presence of hyperglycemia resulted in augmentation of pancreatic polypeptide release. Cholinergic stimulation appears to predominate, whereas beta-adrenergic fibers stimulate pancreatic polypeptide-cell secretion, and alpha-adrenergic fibers inhibit pancreatic polypeptide release. During euglycemia, both cholinergic stimulation and gastric inhibitory polypeptide infusion resulted in a marked release of pancreatic polypeptide. These stimulatory effects were additive, which suggests a linked hormonal and neural mechanism of pancreatic polypeptide release after a meal. In this in vitro human model, our data confirm that the splanchnic innervation of the pancreas has a potent regulatory role in pancreatic hormone release in man.

Apomorphine-induced nausea in humans: release of vasopressin and pancreatic polypeptide

Based on studies in animals and humans, it has been suggested that nausea activates the hypothalamo-neurohypophyseal system with resultant increases in circulating concentrations of oxytocin or vasopressin. The purpose of these studies was to determine in humans whether nausea is associated with increases in circulating concentrations of neurohypophyseal hormones or various enteropancreatic peptides (vasoactive intestinal polypeptide, substance P, or pancreatic polypeptide). Nausea, induced by intravenous infusion of apomorphine, was associated with fivefold to 75-fold increases in plasma vasopressin concentrations in 7 subjects (mean increase, 41-fold), with no change in plasma oxytocin levels. Furthermore, nausea was associated with sevenfold to 16-fold increases in plasma pancreatic polypeptide concentrations (mean increase, ninefold), with no change in plasma levels of vasoactive intestinal polypeptide or substance P. In 1 subject refractory to nausea, there was no increase in plasma vasopressin or pancreatic polypeptide concentrations with apomorphine. These studies indicate that nausea in humans is associated with vasopressin and pancreatic polypeptide release.