The impact of insulin-independent, glucagon-induced suppression of total ghrelin on satiety in obesity and type 1 diabetes mellitus

AIMS/HYPOTHESIS

The mechanisms underlying glucagon-induced satiety are incompletely understood. The glucagon-induced reduction in total ghrelin exerted at the hypothalamo-pituitary level might be responsible for this effect. Here we investigated glucagon-suppressive effects on circulating total and acyl-ghrelin, both in obesity and in type 1 diabetes mellitus (T1DM), with respect to the role of glucagon in appetite control. We further aimed to identify a possible mechanistic impact of changes in endogenous insulin.

METHODS

In our prospective, double-blinded, placebo-controlled study, we investigated the endocrine and metabolic responses to intramuscular glucagon administration in 13 patients with T1DM (6 males, 7 females; body mass index [BMI] 24.8 ± 0.95 kg/m(2)), 11 obese participants (OP; 5 males, 6 females; BMI 34.4 ± 1.7 kg/m(2)), and 13 healthy lean participants (LP; 6 males, 7 females; BMI 21.7 ± 0.6 kg/m(2)).

RESULTS

As compared with placebo, glucagon significantly increased satiety index in T1DM and in LP (P < .001) but failed to induce satiety in OP (P = .152). Total ghrelin significantly decreased after glucagon administration in all study groups (P < .01). Similarly, acyl-ghrelin significantly decreased in LP (P < .01). However, acyl-ghrelin concentrations showed no change in OP (P = .248) and even increased substantially in T1DM (P < .01). Changes in acyl-ghrelin correlated positively with changes in nonesterified fatty acid concentrations in all groups (r = 0.31-0.43; P < .01).

CONCLUSIONS/INTERPRETATION

Glucagon-induced satiety was preserved in T1DM but not in obesity. This effect was unrelated to changes in total or acylated ghrelin and was independent of endogenous insulin release. In contrast to the insulin-independent glucagon-induced suppression of total ghrelin, glucagon- and/or insulin-induced modification of lipolysis may determine changes in acylated ghrelin.

Evidence for an additional effect of whole-body vibration above resistive exercise alone in preventing bone loss during prolonged bed rest

SUMMARY

The addition of whole-body vibration to high-load resistive exercise may provide a better stimulus for the reduction of bone loss during prolonged bed rest (spaceflight simulation) than high-load resistive exercise alone.

INTRODUCTION

Prior work suggests that the addition of whole-body vibration to high-load resistive exercise (RVE) may be more effective in preventing bone loss in spaceflight and its simulation (bed rest) than resistive exercise alone (RE), though this hypothesis has not been tested in humans.

METHODS

Twenty-four male subjects as part of the 2nd Berlin Bed Rest Study performed RVE (n = 7), RE (n = 8) or no exercise (control, n = 9) during 60-day head-down tilt bed rest. Whole-body, spine and total hip dual X-ray absorptiometry (DXA) measurements as well as peripheral quantitative computed tomography measurements of the tibia were conducted during bed rest and up to 90 days afterwards.

RESULTS

A better retention of bone mass in RVE than RE was seen at the tibial diaphysis and proximal femur (p ≤ 0.024). Compared to control, RVE retained bone mass at the distal tibia and DXA leg sub-region (p ≤ 0.020), but with no significant difference to RE (p ≥ 0.10). RE impacted significantly (p = 0.038) on DXA leg sub-region bone mass only. Calf muscle size was impacted similarly by both RVE and RE. On lumbar spine DXA, whole-body DXA and calcium excretion measures, few differences between the groups were observed.

CONCLUSIONS

Whilst further countermeasure optimisation is required, the results provide evidence that (1) combining whole-body vibration and high-load resistance exercise may be more efficient than high-load resistive exercise alone in preventing bone loss at some skeletal sites during and after prolonged bed rest and (2) the effects of exercise during bed rest impact upon bone recovery up to 3 months afterwards.

Resistive vibration exercise attenuates bone and muscle atrophy in 56 days of bed rest: biochemical markers of bone metabolism

During and after prolonged bed rest, changes in bone metabolic markers occur within 3 days. Resistive vibration exercise during bed rest impedes bone loss and restricts increases in bone resorption markers whilst increasing bone formation.

INTRODUCTION

To investigate the effectiveness of a resistive vibration exercise (RVE) countermeasure during prolonged bed rest using serum markers of bone metabolism and whole-body dual X-ray absorptiometry (DXA) as endpoints.

METHODS

Twenty healthy male subjects underwent 8 weeks of bed rest with 12 months follow-up. Ten subjects performed RVE. Blood drawings and DXA measures were conducted regularly during and after bed rest.

RESULTS

Bone resorption increased in the CTRL group with a less severe increase in the RVE group (p = 0.0004). Bone formation markers increased in the RVE group but decreased marginally in the CTRL group (p < 0.0001). At the end of bed rest, the CTRL group showed significant loss in leg bone mass (-1.8(0.9)%, p = 0.042) whereas the RVE group did not (-0.7(0.8)%, p = 0.405) although the difference between the groups was not significant (p = 0.12).

CONCLUSIONS

The results suggest the countermeasure restricts increases in bone resorption, increased bone formation, and reduced bone loss during bed rest.

The Simultaneous Measurement of Plasma-Aldosterone- and -Renin-Concentration Allows Rapid Classification of all Disorders of the Renin-Aldosterone System

OBJECTIVE

The determination of the plasma aldosterone (PAC) to the plasma renin concentration (PRC) ratio is an accepted screening tool for primary hyperaldosteronism (PHyperA).

DESIGN

To assess the diagnostic significance of this ratio for other disorders of the renin-aldosterone-system (RAS), we examined 60 patients with different adrenal diseases, 32 patients with essential hypertension and 76 normotensive healthy volunteers. The aldosterone (pmol/L) and renin (mU/L) concentrations were measured in one plasma sample by an automated chemiluminescence assay (Nichols Advantage).

RESULTS

Patients with PHyperA (n=31) had a PAC/PRC ratio between 105 and 2328 and could be distinguished without overlap from the essential hypertension group (ratio: range 2.7-49) and normal healthy volunteers (ratio: range 0.9-71). Fourteen patients with primary hypoaldosteronism showed low PAC/PRC ratios (range 0.21-0.98) and low PAC values (range: 42-100). Seven patients with secondary hypoaldosteronism had normal PAC/PRC ratios (range 2.8-23.2) and low PAC values (range: 42-116). Eight patients with secondary hyperaldosteronism had normal PAC/PRC ratios (range 7.8-67.9) and elevated PAC values (range: 803-2917). The graphic presentation of these data allowed the differentiation of all major disorders of the RAS.

CONCLUSIONS

The measurement of PAC/PRC ratios using this automated system provides a sensitive and rapid screening method for PHyperA. Moreover, the measurement of both the PAC and the PAC/PRC ratio allows differentiation of other disorders of the RAS.

Glucagon suppression of ghrelin secretion is exerted at hypothalamus-pituitary level

CONTEXT

The mechanisms underlying the well-known glucagon-induced satiety effect are unclear. Recently, we showed that glucagon induces a remarkable decrease in the orexigenic hormone ghrelin that might be responsible for this effect.

OBJECTIVE

The objective of this study was to evaluate the putative role of the hypothalamic pituitary axis in glucagon's suppressive effect on ghrelin secretion. DESIGN, SUBJECTS, AND METHODS: Prospectively, we studied the endocrine and metabolic responses to im glucagon administration in 22 patients (16 males; age, 21-68 yr; body mass index, 28.1 +/- 1.1 kg/m(2)) with a known hypothalamic-pituitary lesion and at least one pituitary hormone deficiency. Control experiments were performed in 27 healthy subjects (15 males; age, 19-65 yr; body mass index, 25.5 +/- 0.9 kg/m(2)).

RESULTS

The suppression of ghrelin by glucagon measured as area under the curve(240 min) was significantly greater in controls when compared with patients (P < 0.01). Although there was a significant decrease in ghrelin in controls (P < 0.001), ghrelin was almost unchanged in patients (P = 0.359). Changes in glucagon, glucose, and insulin levels were comparable between both groups.

CONCLUSIONS

We show that the hypothalamic-pituitary axis plays an essential role in the suppression of ghrelin induced by im glucagon administration. Glucagon significantly decreases ghrelin levels in healthy subjects. However, in the absence of an intact hypothalamic-pituitary axis, this effect was abolished. The mechanisms responsible for our observation are unlikely to include changes in glucose or insulin levels.

Endogenous inhibitors of 11 beta-OHSD: existence and possible significance

Inhibition of 11 beta-hydroxysteroid dehydrogenase (11 beta-OHSD) by licorice-derived compounds and in cases of idiopathic impairment of this enzyme is known to result in hypermineralocorticoid syndromes, reflecting corticosteroid receptor activation by excess intracellular glucocorticoids. In this paper we address the question of whether or not endogenous inhibitors of 11 beta-OHSD exist that might cause pathological glucocorticoid metabolism. Using microsomal preparations we have demonstrated that bile acids are potent inhibitors of rat renal and human hepatic 11 beta-OHSD, with lithocholic acid exerting the strongest effect. The human renal enzyme is affected to a lesser extent. Serum of patients with cholestatic liver cirrhosis also inhibited 11 beta-OHSD activity, in parallel with total bile acid concentration. Cholesterol and its precursor lanosterol inhibited the enzymatic activity in microsomes from rat and human kidney cortex and human liver. We conclude that bile acids could contribute to the abnormalities of cortisol metabolism observed in cholestatic liver cirrhosis.

Inhibition of rat renal 11 beta-hydroxysteroid dehydrogenase by steroidal compounds and triterpenoids; structure/function relationship

Various compounds with steroidal structure were tested for inhibitory effects on enzymatic activity of 11 beta-hydroxysteroid dehydrogenase (11 beta-HSD) from rat renal microsomes. Most substances exerting inhibitory potency on both the oxidative as well as the reductive activity can be classified into two main groups: pentacyclic triterpenoids of the oleane type and steroidal detergents of the CHAPS-series. Inhibition is competitive, as was shown for one compound of each group. The IC50 values of the various inhibitors range over five orders of magnitude. In all cases, oxidative activity was inhibited more effectively than reductive activity. An attempt has been made to correlate structural properties and inhibitory potency. In brief, inhibition seems to be enhanced by a C11-oxygen function, which is present in all endogenous glucocorticosteroids and a C7-OH function. Inhibition is reduced by a large and polar substituent at C3 in the A-ring. A large D-ring substituent, such as a bisgluconamidopropyl side chain or even an additional E-ring, does not prevent binding to the enzyme, although inhibition seems to be influenced by its steric conformation. The cardiac glycosides and steroidal antibiotics tested exert no inhibitory effect on 11 beta-HSD. Cholesterol and pentacyclic triterpenoids of the lupane type exhibit a very poor inhibition, probably caused by the localization of planar structures in the ring systems, which differs from that of the effective oleane type inhibitors.

Bile acids and their amidates inhibit 11 beta-hydroxysteroid dehydrogenase obtained from rat kidney

Recently it has been demonstrated that interaction of corticosteroids with extraadrenal target cells can effectively be modulated by metabolic transformation of the steroid hormone. As far as 11-hydroxylated glucocorticoids are concerned 11 beta-hydroxysteroid dehydrogenase (11 beta-HSD) is the most important enzyme charged with target cell metabolism. Inhibition of 11 beta-HSD function either by genetically transmitted deficiency or by exogenous enzyme inhibitors causes severe pathophysiological derangements, which result in a syndrome of "apparent mineralocorticoid excess". In the present paper we have tested whether or not endogenous inhibitors of this enzyme system might exist. The effects of the main naturally occurring mono-, di-, and trihydroxylated bile acids in man on 11 beta-HSD have been studied in in vitro experiments. Using rat renal microsomes it could be demonstrated that unconjugated bile acids of all three classes as well as the corresponding glycine and taurine amidates effectively inhibit oxidative as well as reductive activity of 11 beta-HSD, with lithocholic acid and chenodeoxycholic acid being the most potent compounds. It is concluded that bile acids are potent endogenous inhibitors of 11 beta-HSD and, therefore, could participate in abnormalities of cortisol metabolism observed in liver cirrhosis and extrahepatic biliary obstruction and, possibly, after ingestion of bile acids.