Different effects of metoclopramide and domperidone on arginine-vasopressin secretion in man

Copeptin is increased by nausea and vomiting during hypertonic saline infusion in healthy individuals

OBJECTIVE

Measurement of hypertonic saline-stimulated copeptin has recently been described for the differentiation of polyuria-polydipsia syndrome. This study aims to determine the copeptin response to intravenous 3% hypertonic saline, including evaluation of adverse effects, in a local cohort of healthy adults >18 years in Australia.

DESIGN

Prospective clinical study.

METHODS

Twenty healthy volunteers (10 males and 10 females) were recruited. Participants underwent infusion of 3% hypertonic saline via a previously described standardized protocol, until the plasma sodium was ≥150 mmol/L, with measurement of plasma copeptin.

RESULTS

Mean peak sodium was 152 mmol/L ± SD 1.4 with osmolality 315 mmol/kg ± SD 3.9. Median volume of hypertonic saline infused to reach target sodium ≥ 150 mmol/L was 1536 mL (IQR 1362, 1992). Mean rate of plasma sodium rise was 5.9 mmol/L/hour ± SD 1.5. Hypertonic saline-stimulated copeptin had non-parametrical distribution with median of 33.8 pmol/L (IQR 27.6, 63.6). Overall median symptom burden was 6/10 (range 3/10-9/10). Copeptin was significantly higher for those who experienced nausea and/or vomiting (n = 13) (median 39.0 pmol/L; IQR 32.5, 90), compared to those participants who did not experience either (median 20.0 pmol/L; IQR 13.0, 31.0) (P = 0.003). There were no serious adverse events.

CONCLUSION

Hypertonic saline-stimulated copeptin measurements were similar in our population compared with previously reported reference intervals in healthy volunteers. There is a wide range of stimulated copeptin measurements in the healthy population. Nausea and vomiting are common adverse effects which enhance the copeptin response.

Metoclopramide as pharmacological tool to assess vasopressinergic co-activation of the hypothalamus-pituitary-adrenal (HPA) axis: a study in healthy volunteers

The synthetic vasopressin (AVP) analogue desmopressin (dDAVP) has been used as pharmacological function test to quantify vasopressinergic co-activation of the hypothalamus-pituitary-adrenal (HPA) axis in the past. Such exogenous vasopressinergic stimulation may induce confounding cardiovascular, pro-coagulatory and anti-diuretic effects and low endogenous corticotrophin-releasing-hormone (CRH) levels may limit its potential to reliably assess co-activation. Alternatively, the dopamine-2-(D2)-antagonist metoclopramide is believed to induce co-activation indirectly by releasing endogenous AVP. We investigated this indirect co-activation with metoclopramide under conditions of low and enhanced endogenous CRH release in healthy volunteers. A randomized, double-blind, placebo-controlled, four-way crossover study was performed in 12 healthy males. CRH release was induced by administering an oral 5-hydroxytryptophan (5-HTP) 200 mg function test. Co-activation was investigated by administering metoclopramide 10mg intravenously around the expected maximal effect of 5-HTP. The neuroendocrine effects were compared to those of metoclopramide alone, the 5-HTP test alone and matching placebo. Metoclopramide safely induced HPA-axis activation by itself, and potently synergized 5-HTP-induced corticotrophinergic activation of the HPA axis. These findings are indicative of vasopressinergic co-activation and suggest a role for metoclopramide as a practical function test for co-activation of the HPA axis. However, its application will be hampered pending clarification of the exact pharmacological mechanism by which metoclopramide induces co-activation of the HPA axis.

Domperidone. A review of its use in diabetic gastropathy

Domperidone is a selective antagonist at peripheral dopamine D2 receptors, with gastroprokinetic and antiemetic properties. It increases the frequency and duration of antral and duodenal contractions, thus decreasing/improving transit time of food through the gastrointestinal tract. Gastric emptying of liquids and solids is significantly improved with oral domperidone 40 to 120 mg/day in patients with diabetic gastropathy. Oral domperidone 40 to 80 mg/day significantly decreased the severity of symptoms of gastropathy from baseline values in 66 to 88% of patients with type 1 (insulin-dependent) or insulin-requiring diabetes mellitus. Double-blind withdrawal of domperidone from patients who had responded previously led to greater deterioration of symptoms in patients with delayed gastric emptying than in those who continued receiving the drug. Quality of life was significantly improved in patients who showed a symptomatic response to domperidone. The administration of domperidone 40 to 120 mg/day significantly reduced hospitalisation rates in patients with gastropathy. The symptomatic improvement with domperidone 80 mg/day was similar to that seen with cisapride 40 mg/day or metoclopramide 40 mg/day, and therapeutic benefits seen in symptoms of gastropathy were maintained with domperidone for up to 12 years. Domperidone 40 to 80 mg/day may be effective in patients who are refractory to metoclopramide, and a combination of domperidone 80 mg/day with cisapride 80 mg/day may improve some symptoms in patients who do not respond to either agent alone. Domperidone 40 to 120 mg/day was well tolerated for periods up to 12 years in trials in patients with diabetic gastropathy. Adverse events with domperidone 80 mg/day were similar to those seen in placebo recipients and significantly fewer than in patients receiving metoclopramide 40 mg/day. Although significant elevation of plasma prolactin levels (unrelated to dosage and duration of treatment) occurred in all domperidone recipients, prolactin-related adverse events were observed in only 10 to 20% of patients.

CONCLUSIONS

The available data suggest that domperidone 40 to 80 mg/day is an effective agent for the management of symptoms of gastropathy in patients with type 1 diabetes mellitus. In addition, it may provide symptom improvement in patients with gastropathy refractory to other gastroprokinetic agents. Domperidone maintains efficacy in the long term (up to 12 years) and appears to have a better tolerability profile than metoclopramide 40 mg/day.

Altered vasopressin response to metoclopramide in multiple system atrophy: evidence of a cholinergic defect in the hypothalamus

Multiple system atrophy (MSA) is a heterogeneous group of central neurological degenerations often associated with diffuse deterioration of the hypothalamic cholinergic neurons. In the hypothesis of an altered cholinergic regulation of vasopressin release, we evaluated vasopressin response to metoclopramide (20 mg i.v.), a cholinomimetic agonist, in 12 MSA patients. In the same patients the hemodynamic and osmolal control of vasopressin was also evaluated. We found that MSA patients had significantly lower basal plasma vasopressin values and higher plasma osmolality than control subjects. However, they displayed a normal vasopressin response to osmotic stimulation. During head-up tilting, orthostatic hypotension occurred in all patients, and the vasopressin response to hypotension was severely blunted in 5 of 12 patients, thus demonstrating the presence of a lesion of the afferent noradrenergic pathways. Metoclopramide increased vasopressin in control subjects, whereas MSA patients did not display any increase in vasopressin. These results clearly indicate that cholinergic neurons that regulate vasopressin release are damaged in MSA. Such an alteration may be dissociated from the lesion of the afferent noradrenergic pathways. As a consequence of the altered vasopressin release, MSA patients show lower plasma vasopressin levels with consequent propensity to dehydration and hypovolemia, which may further aggravate their hypotension.

Involvement of vasopressin in the cardiovascular effects of quinpirole

The effects of quinpirole, a specific dopamine D2 receptor agonist, were investigated on cardiovascular responses and plasma levels of catecholamines and vasopressin in two groups of conscious dogs: (1) control dogs and (2) dogs with diabetes insipidus (i.e. animals surgically deprived of vasopressin). In normal dogs, i.v. quinpirole (30 micrograms/kg) elicited a decrease in blood pressure associated with a rise in both plasma catecholamine and vasopressin levels. In dogs with diabetes insipidus, i.v. quinpirole induced a more marked decrease in blood pressure than in normal dogs. Quinpirole did not change plasma noradrenaline and vasopressin levels in dogs with diabetes insipidus. The present study demonstrates that the decrease in blood pressure elicited by quinpirole is associated with an increase in vasopressin release, which counteracts the hypotensive effect of the the dopamine D2 receptor agonist.

Muscarinic cholinergic, but not serotoninergic mediation of arginine vasopressin response to metoclopramide in man

The possibility that metoclopramide (MCP) stimulates arginine vasopressin (AVP) secretion in man through a serotoninergic and/or a cholinergic muscarinic pathway was studied. Twenty normal male subjects were tested with MCP (10 mg in an i.v. bolus) alone or in the presence of the 5HT1 serotoninergic antagonist metergoline (10 mg/day p.o. in five divided doses for 4 days), the 5HT2 receptor blocker ketanserin (10 mg i.v. 5 min before MCP) (n = 10), the M1 and M2 muscarinic antagonist atropine (1.2 mg i.v. just before MCP administration) or the M1 muscarinic receptor blocker pirenzepine (40 mg i.v. 10 min before MCP) (n = 10). AVP doubled in response to MCP. the MCP-induced AVP rise did not change after metergoline, ketanserin or pirenzepine administration, whereas it was abolished by atropine. Additional experiments were performed in order to evaluate the effect of 1.2 mg atropine, given alone, on circulating AVP levels and whether the effect of atropine on the AVP response to MCP depends on the amount of the muscarinic antagonist (dose-response study). For these purposes, atropine was given alone to the same subjects previously tested with MCP plus atropine; furthermore, eight additional male subjects were tested with MCP plus atropine given in doses ranging from 0.8 to 1.4 mg. The results of these additional studies failed to show an effect of atropine alone on AVP secretion and demonstrated a dose-related inhibition of MCP-induced AVP rise by increasing atropine administration from 0.8 mg to 1.2 mg.(ABSTRACT TRUNCATED AT 250 WORDS)