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Plasma MHPG levels in lactate and isoproterenol anxiety states
R Pohl1, E Ettedgui, M Bridges
1Lafayette Clinic, Detroit, MI 48207.
Abstract:
It has been claimed that an increase in brain noradrenergic activity plays a role in panic disorder and that enhanced noradrenergic activity may be reflected by plasma levels of MHPG. We investigated plasma MHPG levels in panic disorder patients at baseline and during lactate- and isoproterenol-induced anxiety states. These infusions and 5% dextrose infusions were given to 10 panic disorder patients and 9 healthy control subjects. Each subject received all three infusions, double-blind, in random order, and at 1-week intervals. When compared to controls, plasma free MHPG levels in panic patients were not elevated at baseline, during lactate or isoproterenol infusions, at the point of panic, or up to 20 min after the onset of panic. MHPG values were also not elevated in subjects who panicked compared to those who did not. MHPG values were significantly lower in three patients who failed to panic with isoproterenol, but the patient panickers had MHPG values similar to those of controls. Significant correlations between MHPG levels and anxiety ratings were infrequent and could be accounted for by chance alone. These results did not support the noradrenergic model for panic anxiety states induced by lactate or isoproterenol.
Insights
This study found no evidence that higher MHPG levels indicate panic disorder. Plasma MHPG levels did not increase in panic disorder patients during induced anxiety, challenging the noradrenergic model.
Area of Science:
- Neuroscience
- Psychiatry
- Pharmacology
Background:
- The noradrenergic system is implicated in panic disorder.
- Plasma levels of 3-methoxy-4-hydroxyphenylglycol (MHPG) are proposed as a marker for noradrenergic activity.
- Previous research suggests a link between elevated MHPG and panic attacks.
Purpose of the Study:
- To investigate plasma MHPG levels in panic disorder patients.
- To assess MHPG levels during lactate- and isoproterenol-induced anxiety.
- To determine if MHPG reflects noradrenergic activity in panic disorder.
Main Methods:
- 10 panic disorder patients and 9 healthy controls participated.
- Subjects received lactate, isoproterenol, and dextrose infusions double-blind and in random order.
- Plasma MHPG levels were measured at baseline, during infusions, and after panic onset.
Main Results:
- Panic disorder patients showed no elevated baseline or infusion-induced MHPG levels compared to controls.
- MHPG levels did not correlate with anxiety ratings or panic onset.
- Lower MHPG was observed in patients who did not panic with isoproterenol, but panickers had normal MHPG levels.
Conclusions:
- The findings do not support the noradrenergic model of panic disorder.
- Plasma MHPG levels do not appear to be a reliable marker for panic anxiety states induced by lactate or isoproterenol.
- Further research is needed to understand the neurobiology of panic disorder.