Individual differences |
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Variations in growth hormone are associated with depression. The direction of causality is unclear. Do aspects of depression affect growth hormone or does growth hormone affect mood, or do both reflect the activity of the same underlying mechanisms?
It is interesting to note that the main neurotransmitters involved in mood regulation (e.g.,norepinephrine, serotonin, and dopamine) all affect growth hormone release as well as being implicated in depression.
- Diurnal rhythms of growth hormone, as measured in plasma, are disrupted in depression. Nocturnal growth hormone is elevated in depression
(Schillkrat et al 1975), but daylight-stimulated growth hormone levels are increased in both unipolar and bipolar depressives (Mendlewicz et al 1985).
- Growth hormone responses to growth hormone releasing factor have also been explored
in people with major depression but only some groups have reported blunted growth hormone responses (Lesch et al, 1987; Conteras et al, 1996; Krishnan et al 1988).
- Cerebral spinal fluid levels of somatostatin, which inhibits growth hormone, CRH, and ACTH release, are also reduced in depression (Agren & Lundquist, 1984;Runinow et al 1983),
- It is thought that low somatostatin levels in depression may reflect increased cortisol activity (Musselman et al, 1998;Rubinow 1986) which tends to normalize with treatment
(Garlow & Nemeroff, 2007).