Neuroendocrine responses to laboratory panic: cognitive intervention in the doxapram model

Doxapram is a respiratory stimulant that appears to be a potent and specific panicogenic agent. It also elicits an abnormal ventilatory response in patients with panic. A replication study confirmed these findings and demonstrated that behavioral and ventilatory responses to doxapram were significantly modified by a psychological intervention designed to cognitively block panic. The replication study provided an opportunity to simultaneously investigate the neuroendocrine effects of the illness, the drug, the drug-induced panic attacks, and the cognitive intervention. Epinephrine (EPI), norepinephrine (NE), growth hormone (GH), adrenocorticotropin (ACTH), and cortisol were studied in patients with panic and control subjects given placebo and doxapram injections after receiving either standard instructions or a brief cognitive intervention. Patients with panic had elevated levels of EPI, ACTH, and cortisol throughout the study. Doxapram had little or no detectable effects on plasma NE, GH, ACTH, and cortisol. Doxapram-induced panic attacks were not associated with elevations in NE, GH, ACTH, or cortisol. Doxapram led to a rapid and very brief rise in plasma EPI, which was small in subjects who did not panic and pronounced in patients who did panic. The cognitive intervention attenuated the EPI response to doxapram, perhaps through its effect on panic, and modified the temporal pattern of ACTH and cortisol secretion. These results suggest that: (1) further study of catecholamine responses within the first few minutes after panic induction is needed; (2) intense panic can occur without significant activation of the hypothalamic-pituitary-adrenal axis; and (3) cognitive factors can modulate neuroendocrine activity in laboratory studies of patients with panic.

Hypothalamic-pituitary-adrenal axis activity in panic disorder. 24-hour secretion of corticotropin and cortisol

BACKGROUND

Oversecretion of corticotropin-releasing hormone and/or dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis may contribute to pathophysiologic processes in panic disorder, but documentation of HPA axis disturbance in panic has been inconsistent. In the current study we examined HPA axis activity in panic disorder over a full circadian cycle, using frequent blood sampling to provide detailed assessment of corticotropin and cortisol secretion.

METHODS

Twenty patients with panic disorder and 12 normal control subjects were studied. Blood samples were drawn every 15 minutes for 24 hours and assayed for corticotropin and cortisol levels.

RESULTS

Patients with panic disorder had elevated overnight cortisol secretion and greater amplitude of ultradian secretory episodes. Patients who entered the study through clinical referral channels had greater cortisol secretion than those recruited by advertisements. Patients with panic disorder who had a low frequency of panic attacks had elevated daytime corticotropin levels and elevated corticotropin ultradian amplitude. Patients with a high frequency of attacks had shifted corticotropin circadian cycles.

CONCLUSIONS

Patients with panic disorder demonstrate subtle alterations in HPA axis activity, characterized by overnight hypercortisolemia and increased activity in ultradian secretory episodes, but HPA axis alterations in panic are modulated by illness severity and treatment seeking. It remains unclear whether HPA axis dysregulation in panic represents a pathogenic defect within the axis itself. Inconsistencies in prior work may reflect the subtlety of the abnormalities seen, differences in clinical characteristics of patients studied, and the use of different probes and measurement contexts.

Hypothalamic-pituitary-adrenal axis activity in panic disorder: effects of alprazolam on 24 h secretion of adrenocorticotropin and cortisol

Pre-clinical and some clinical evidence suggests that central overdrive within the hypothalamic-pituitary-adrenal (HPA) axis may play a role in panic disorder, and that the anti-panic efficacy of alprazolam may involve its ability to inhibit this drive. Detailed examination of 24 h secretion of adrenocorticotropin (ACTH) and cortisol in 20 panic patients had revealed subtle HPA axis abnormalities prior to treatment. In order to determine whether these abnormalities resolve with alprazolam therapy, these patients were re-studied over a full circadian cycle after 12 weeks on alprazolam. Alprazolam produced substantial improvement in clinical status which was accompanied by nearly full resolution of pre-treatment hypercortisolemia. The impact of treatment on ACTH was more complex and influenced by symptom severity. The results are consistent with the hypotheses that HPA axis regulation is subtly disturbed in panic disorder and that impact on the HPA axis may play a role in alprazolam's mechanism of efficacy.

Hypothalamic-pituitary-adrenal axis activity in panic disorder: prediction of long-term outcome by pretreatment cortisol levels

OBJECTIVE

The authors sought to determine whether hypothalamic-pituitary-adrenal (HPA) axis activity in patients before their treatment for panic disorder can predict follow-up functional status. Although baseline HPA axis disturbances in patients with panic disorder appear to attenuate with treatment, there is evidence that they may be linked to poorer long-term outcomes.

METHOD

Follow-up clinical data were obtained for 18 of 20 patients with panic disorder who participated in a detailed study of HPA axis activity in panic, both before and during their treatment with alprazolam. HPA axis assessment included monitoring of adrenocorticotropin and cortisol over a full circadian cycle. The relationships between disability and clinical status at 2-year follow-up and HPA axis overactivity at entry were examined.

RESULTS

Mean 24-hour cortisol levels before treatment provided a strong, positive predictor of disability scores at follow-up. Those patients who achieved the treatment goal of medication-free remissions had less evidence of HPA axis overactivity at entry than those who were not in remission.

CONCLUSIONS

HPA axis activity before treatment did predict outcome 2 years later. This relationship appears robust and reproducible. Further work is needed to define the neuroendocrine mechanisms underlying the HPA axis markers that are linked to long-term functioning and to determine the biological, psychological, and social processes that link HPA axis disturbance to poorer outcomes.

Cholecystokinin in psychiatric research: a time for cautious excitement

Cholecystokinin (CCK) is a peptide neurotransmitter that was originally isolated from the gastrointestinal system, but which is extensively and abundantly distributed within the central nervous system (CNS). Stimulated by the fairly recent recognition of receptor subtypes (A and B), and the development of receptor-specific antagonists, CCK research has been advancing rapidly; and its potential importance to psychiatric neuroscience has been increasingly recognized. CCK participates in the mediation of satiety; it interacts with dopamine and may modulate psychosis; it interacts with opiate systems and may be an "anti-analgesic": and it appears to play a role in the mediation of anxiety. Highly specific, CCK-B receptor antagonists have reached clinical trials and have potential clinical utility as anxiolytics, antipsychotics, anti-anorexics, or analgesics. There are grounds for excitement, but many obstacles remain to be overcome and clinical potential may not be fulfilled. However, we must not allow clinical disappointments to slow the accelerating pace of scientific progress in CCK research. Regardless of clinical payoffs, the CCK receptor is clearly of great importance to human CNS functioning and deserves ongoing scientific attention.

Pentagastrin infusions in patients with panic disorder. I. Symptoms and cardiovascular responses

Cholecystokinin (CCK) may mediate human anxiety and animal data suggest that cholecystokinin antagonists could provide an important advance in the treatment of anxiety disorders. The study of CCK receptor systems in psychiatric patients has, however, been severely limited by the lack of available probes. We utilized intravenous infusions of pentagastrin, a selective CCK-B receptor agonist, and studied behavioral and cardiovascular responses in 10 patients with panic disorder and 10 normal controls. Pentagastrin produced substantial symptomatology, including anxiety, and increases in heart rate and blood pressure, in both patients and controls. Patients were more sensitive to the panicogenic effects of the pentagastrin. Panic attacks occurred in 70% of patients and 0% of controls. Patients' symptom responses were very similar to their "typical" panic attacks and to symptoms produced by CCK4. Pentagastrin provides a readily available alternative to CCK4 for studying the CCK receptor system and exploring its involvement in human anxiety.

Pentagastrin infusions in patients with panic disorder. II. Neuroendocrinology

Cholecystokinin (CCK) has well-documented anxiogenic effects in animals and normal people, and panicogenic effects in patients with panic disorder, but little is known about its neuroendocrine profile. We examined neuroendocrine responses to intravenous infusions of pentagastrin, a selective CCK-B receptor agonist, in 10 patients with panic disorder and 10 normal control subjects. Pentagastrin potently activated the hypothalamic-pituitary-adrenal (HPA) axis, but did not release growth hormone or any of several vasoactive peptides (neurokinin A, substance P, vasoactive intestinal peptide). The HPA axis response was unrelated to increases in symptoms. Panic patients did not differ from controls in neuroendocrine responses to the CCK agonist. Differential sensitivity to novelty stress accounted for the only patient-control differences in neuroendocrine profiles. The data suggest that CCK may help modulate normal HPA axis activity, but its anxiogenic effects are unrelated to its stimulatory effects on the HPA axis. Pentagastrin provides a safe and readily available probe for further study of CCK receptor systems in humans.

Endocrine, cardiovascular, and behavioral responses to clonidine in patients with panic disorder

We examined adrenergic regulation in patients with panic disorder by challenging 10 patients and 14 age-matched and sex-matched controls with intravenous infusions of clonidine hydrochloride (2 micrograms/kg), an alpha 2-adrenoreceptor agonist. Growth hormone, 3-methoxy-4-hydroxyphenylglycol (MHPG), blood pressure, heart rate, and behavioral (anxiety, sedation) responses were monitored. The data replicated the previously reported finding of blunted growth hormone (GH) responses to clonidine in patients with panic disorder. Reported abnormalities in MHPG, cardiovascular, and behavioral responses of panic patients to clonidine infusion were not replicated. The robustly blunted GH response to clonidine in panic patients supports the adrenergic dysregulation hypothesis of panic disorder, but alternative interpretations of this finding are available and further study is needed.

Blunted growth hormone response to clonidine in patients with generalized anxiety disorder

Patients with panic disorder or depression have abnormal responses to the alpha 2-adrenergic receptor partial agonist clonidine. Evidence linking anxiety to noradrenergic dysfunction and the presence of anxiety symptoms in both depression and panic suggest that abnormal responses to clonidine in these disorders could be due to the anxiety symptoms. To explore a possible link between "nonspecific" anxiety symptoms and abnormal responses to clonidine, patients with DSM-III-defined generalized anxiety disorder were given intravenous infusions of clonidine hydrochloride. Responses of plasma growth hormone, 3-methoxy-4-hydroxyphenylglycol, heart rate, blood pressure, and psychological states were determined in 11 patients with generalized anxiety disorder and 14 healthy subjects. Clonidine produced significantly smaller growth hormone responses in patients than in healthy controls. The two groups did not differ in 3-methoxy-4-hydroxyphenylglycol, heart rate, blood pressure, or psychological responses to clonidine. These results are compared with data from similar studies on patients with panic disorder and depression. The blunting of the growth hormone response to clonidine in all three disorders could be due to the presence of generalized anxiety symptoms. Subsensitivity of postsynaptic alpha 2-adrenoreceptors may be present in all three disorders; however, there are alternative interpretations of growth hormone blunting in response to clonidine. Blunting was observed in DSM-III-defined generalized anxiety disorder, whether or not the DSM-III-R criterion of excessive worry was also present.

Alpha 2-adrenoreceptor status in obsessive-compulsive disorder

Ten patients with obsessive-compulsive disorder (OCD) and 13 normal control subjects received intravenous infusions of 2 X 10(-6) g/kg of clonidine and normal saline on separate days. Responses to the drug relating to plasma growth hormone (GH), 3-methoxy-4-hydroxyphenylglycol (MHPG), heart rate, blood pressure, and several symptoms were determined. Additionally, platelet alpha 2-adrenoreceptor binding was measured in most of the subjects. GH, MHPG, blood pressure, and heart rate responses to clonidine did not differ between groups. As expected, patients reported more symptoms than normal subjects, and clonidine was sedating for both groups. Patients did not differ from normal subjects in the symptom response to clonidine. The maximum number of binding sites (Bmax) for tritiated clonidine was significantly greater in OCD patients than in normals. This pattern of alpha 2-adrenoreceptor status is different than the patterns in major depression and panic anxiety.

Treatment of panic-like attacks with a long-acting analogue of somatostatin

Psychiatric evaluations were completed on four patients who were treated for "idiopathic flushing" with a long-acting analogue of somatostatin. All four patients had symptom profiles consistent with a diagnosis of panic disorder. All four experienced clinically significant relief from panic-like attacks while on the experimental medication. These findings suggest a possible role for somatostatin in the pathophysiology and treatment of panic disorder.

Cardiac and neuroendocrine responses to exposure therapy in height phobics: desynchrony within the 'physiological response system'

Subjective, behavioral, cardiovascular and neuroendocrine responses were intensively monitored in two height phobics over a full course of exposure therapy and at follow-up. Both subjects showed rising cortisol responses and stable, non-extinguishing norepinephrine responses to height exposure over the course of treatment, while improvement occurred in subjective and behavioral response systems. They had differing heart rate responses. Despite desynchrony amongst anxiety response systems and within the physiological 'system' at treatment conclusion, both subjects had successful outcomes which were preserved at follow-up. Implications for the measurement of the 'physiological response system' in behavioral research are discussed.

Interpersonal and electrocardiographic responses of Type A's and Type B's in competitive socioeconomic games

Forty-eight subjects classified as either Type A (coronary-prone) or Type B (coronary-resistant) exchanged points worth money with a computer-simulated opponent while an electrocardiogram was computer-monitored and scored. Type A's were more aggressive during the socioeconomic exchanges than were Type B's. The more aggressive a subject during the interactions the greater was the shift toward depression of the ST segment of the electrocardiogram. Despite the relationship between aggression and ST response, and the greater aggressiveness of Type A's during the interactions, Type A's and Type B's did not differ significantly in ST response.