As you know, several classes of agents stimulate or inhibit growth-hormone secretion. In particular, the hypothalamic action of dopamine leads to an inhibition of somatostatin, allowing Growth hormone-releasing hormone (GHRH) to elicit growth hormone secretions (more later). Furthermore, amines, whether catecholamines (for example, dopamine) or indolamines (for example, serotonin), can promote growth hormone secretion via alpha adrenergic stimulation (for catecholamines), beta-adrenergic inhibition (for catecholamines), dopaminergic stimulation (for catecholamines), or serotoninergic stimulation (for indolamines). The reverse cases (beta-adrenergic stimulation, alpha-adrenergic inhibition, dopamine inhibition, and serotonin inhibition) may lead to inhibition of growth-hormone release.
Other factors that may stimulate growth-hormone secretion may include amino acids, the condition of hypoglycaemia, exercise, sleep, certain hormones, and so on. Of course, all these agents do not produce an equal boost in growth hormone. Dopamine, for instance, is known to be a potent growth-hormone agonist. [1-carboxy] uses this mechanism. Taken pre-bed, the potent GH-stimulating effects ensure a deep, restful sleep, and promotes superior repair of cellular damage. Taken pre-workout in a fasted state, growth-hormone release is equally induced, and acts in concert with the growth-hormone produced by exercise.
...As you correctly implied, dopamine is derived from the synthesis of tyrosine. Put differently, dopamine is a tyrosine-derived neurotransmitter. As you also know, tyrosine can be incorporated into proteins, can be broken down for energy production, or can be converted into catecholamines. These catecholamines are neurotransmitters such as dopamine, norepinephrine, and epinephrine. The conversion of tyrosine into catecholamines is made possible by the action of the enzyme, tyrosine hydroxylase. The ensuing reaction produces DOPA (3,4-dihydrophenylalanine). Via the enzymatic action of DOPA decarboxylase, DOPA is converted to dopamine, which is, in turn, converted by dopamine ß-hydroxylase into norepinephrine. Finally, norepinephrine is converted by phenyletanolamine N-methyltransferase into epinephrine. However, the full conversion from tyrosine to epinephrine is only realized in the adrenals. In the brain, the conversion ends at dopamine! Furthermore, catecholamines can exhibit excitatory and inhibitory effects, which is why they can support higher metabolic activity and rest. Dopamine can act as an inhibitory and as an excitatory neurotransmitter. The dopamine receptors determine which pathway to utilize.
Dopamine has been shown severally to support growth hormone secretion via somatostatin secretion. As somatostatin blunts growth hormone secretion, the dopamine inhibition of somatostatin enhances the action of the dipeptide, Growth hormone-releasing hormone (GHRH). This leads to an elevated release of growth hormones.
On its own, serotonin (5-hydroxytryptamine) is a tryptophan-derived neurotransmitter. Although it is a monoamine neurotransmitter like dopamine, it is regarded as an indolamine, and not as a catecholamine (like dopamine). Serotonin is derived from tryptophan via a hydolation reaction (tryptophan hydroxylase) and a decarboxylation reaction (amino acid decarboxylase). Consequently, melatonin (N-acetyl-5-methoxytryptamine) is derived from serotonin in the pineal gland via the actions of the enzymes, serotonin-N-acetyltransferase and hydroxyindole-o-methyltransferase, both of which are most active in the dark. Furthermore, serotonin is primarily found in the gastrointestinal tract. Only small amounts are found in the brain. As tyrosine and tryptophan (as well as methionine, the branched-chain amino acids, and so on) depend on a neutral protein transporter to reach the brain for synthesis, a large amount of one of these can crowd-out the others, favouring its synthesis in the brain.
To summarize, dopamine is a powerful stimulus for growth-hormone secretion, via a series of steps. [1-carboxy]'s impact on growth-hormone secretion is dopaminergic. Taken in a fasted state, [1-carboxy] can induce a significant increase in dopamine, and consequently, growth-hormone, whether pre-workout, or pre-bed.
