The stability of plasma growth hormone and MHPG responses to repeated clonidine challenge in normal males

Mismatch negativity is not correlated with neuroendocrine indicators of catecholaminergic activity in healthy subjects

The identification of the brain structures and neurotransmitters responsible for the generation and/or modulation of the mismatch negativity (MMN) may contribute to a clearer understanding of its functional significance, and may have clinical implications. In this context, some findings suggest that the scalp-recorded MMN reflects activity from multiple neuronal ensembles within or in the immediate vicinity of the primary auditory cortex and with possible contribution from the frontal cortex. However, few data are available concerning the influence of neurotransmitter systems on the MMN. In this study, the relationship between both noradrenergic and dopaminergic systems and the MMN were investigated in 34 healthy volunteers. Noradrenergic and dopaminergic activities were assessed with the apomorphine and clonidine challenge tests. The results showed no significant relationship between either growth hormone (GH) responses to apomorphine or clonidine and the MMN amplitude or latency. Therefore, this study does not demonstrate the implication of dopaminergic and noradrenergic activities as assessed by GH response to apomorphine and clonidine for the generation and/or the modulation of the MMN. However, given the complexity of the central neurotransmitter systems, these results cannot be considered as definitive evidence against a relationship between dopaminergic and noradrenergic activity and the MMN.

Interpretative difficulties with growth hormone provocative retesting in childhood-onset growth hormone deficiency

A review of literature demonstrates that there are many ill-understood factors that determine the results of GH provocative (re)testing, so that these results should be interpreted with extreme caution when used for diagnosis or confirmation of diagnosis of GHD. GH provocation tests are probably of no value at all for what has been called 'partial GHD'. The phenomenon of 'normalization' of test results after long-term treatment with GH needs no 'transient GHD' hypothesis as it can be largely explained by the very low reproducibility of the tests and by a regression to the mean effect. Moreover, it is possible that 'normal values' increase with age. Other determinants of normal peak values may also change from childhood to adulthood and contribute to 'normalization'.

Growth hormone response to growth hormone-releasing hormone stimulation in obsessive-compulsive disorder

Two groups of 30 patients with obsessive-compulsive disorder and 30 age- and sex-matched healthy control subjects were given a growth hormone-releasing hormone (GHRH) stimulation test to determine: (1) whether the downstream function of the somatotropic axis (growth hormone = GH, somatomedin-C = SMD-C) was impaired; (2) what might be the central alteration responsible for such impairment; and (3) whether alterations might be linked to the etiopathogenesis of the disease. Basal values of GH and SMD-C were the same in patients and control subjects, but GH responses to GHRH stimulation were significantly lower in patients than in control subjects. The absence of a pathology of basal GH and SMD-C concentrations indicates that the blunted GH responses to GHRH stimulation are not due to a negative feedback mechanism and suggests that a central neurotransmitter-neuropeptide pathology might be involved in the phenomenon.

Clonidine challenge in childhood anxiety disorder

OBJECTIVE

To evaluate the neurohormonal and subjective mood response of children with anxiety disorder to clonidine challenge

METHOD

Children with DSM-IV diagnoses of anxiety disorder (ANX) (n = 24) and normal controls (n = 15) were given a challenge of intravenous clonidine (1.3 micrograms/kg) and provided neurohormonal and mood self-report assessment over a 180-minute period.

RESULTS

The ANX group differed from normal controls in Hamilton Anxiety Rating, Revised Children's Manifest Anxiety Scale score, and maximum change from baseline (delta max) in growth hormone (GH). Clonidine-stimulated GH concentration of the ANX group was significantly elevated compared with that of controls but returned to baseline within 2 hours. A subgroup with obsessive-compulsive disorder (OCD) (n = 9) had significantly higher delta max GH (17.5 +/- 10.1 ng/mL) than the group with other anxiety disorders (ANX-OCD) (9.1 +/- 5.8 ng/mL) and controls (5.7 +/- 4.1 ng/mL).

CONCLUSION

GH response to clonidine challenge is not blunted in ANX subjects. This finding is in contrast to adult disorder and suggests that adrenergic postsynaptic receptor down-regulation is not a feature of childhood anxiety. These findings suggest enhanced central adrenergic sensitivity in ANX which is most pronounced in OCD and argue against a neurobiological continuum from childhood to adult anxiety disorder.

Hormonal responses to meta-chlorophenylpiperazine (m-CPP) are undiminished by acute m-CPP pretreatment

Two challenges with meta-chlorophenylpiperazine (m-CPP, 0.5 mg/kg, p.o.) were performed in healthy volunteers to test the short-term stability of hormonal responses. Challenges were performed in an identical fashion and were conducted on sequential days. Circulating m-CPP plasma levels, as well as prolactin and cortisol responses to m-CPP, were correspondingly similar in magnitude on the 2 days. These data suggest that both prolactin and cortisol responses to single oral administrations of m-CPP are stable over at least a 24-h period.