Here’s an excerpt from an article that I think is pretty good.
GH seems to be one of the most misunderstood hormones in the body with some so-called “fitness gurus” claiming it isn’t anabolic at all or even beneficial from a health standpoint (which is quite an arrogant thing to say given the body of scientific evidence against such claims). GH does indeed have a variety of anabolic actions in the human body, but they are mechanistically different from those of insulin. GH may be viewed as the primary anabolic hormone during stress and fasting, whereas insulin is the major anabolic hormone in the periprandial timeframe.
Research has shown that GH strongly inhibits amino acid oxidation (recall from earlier that amino acids may be oxidized for energy). Thus, GH acts to spare crucial amino acids in the amino acid pools, resulting in a greater availability of those amino acids for incorporation into proteins. 
That being said, it appears that GH is a promoter of whole-body protein synthesis in the short-term and any increases in muscle protein synthesis from GH administration are likely the result of downstream paracrine (local) IGF-1 release. Both GH and testosterone (which we will cover later in this guide) increase paracrine IGF-1 which could be of benefit for anabolic effects in skeletal muscle tissue.
A curious finding is that in studies that give subjects exogenous doses of IGF-1, the expression of paracrine IGF-1 is suppressed and thus no increase in muscle protein synthesis is observed. [7, 12, 13] Therefore, the use of IGF-1 as a performance-enhancing drug does not seem very pragmatic, at least for someone looking to acquire more skeletal muscle tissue.
It has been shown that GH not only promotes protein synthesis but also inhibits protein degradation, and it is likely that this effect is seen in skeletal muscle tissue due to paracrine expression IGF-1.  The reason for attributing these anabolic effects to GH is quite simply because GH subsequently creates IGF-1.
A final point to consider with regards to the anabolic actions of GH is that it accelerates the transport of several essential amino acids across the cell membrane, specifically those mediated by System L—the major transport system responsible for sodium-independent transport of neutral amino acids (such as leucine, isoleucine and valine). 
GH is a highly complex hormone that’s under much investigation as many of its in vivo actions are yet to be elucidated.
To recap, GH is a potent hormone that promotes whole-body protein synthesis and decreases whole-body protein breakdown, and it is likely that those effects could be induced in skeletal muscle tissue as well once the downstream production of paracrine IGF-1 kicks in (hopefully more research will be directed towards this concern in the coming years).
GH also strongly inhibits the oxidation, and increases the transmembrane transport, of important amino acids such as the branched-chain amino acids leucine, isoleucine and valine. Also of note is that GH is a major influencer on fat loss since it promotes the use of free fatty acids for energy.
As was noted in the above IGF-1 section, a variety of factors play into when and how much GH is secreted. Given that GH is secreted in a pulsatile fashion (with about 50% of the total daily secretion occurring during deep sleep) it is worthwhile to consider the following list of GH secretion stimulators and inhibitors:
Stimulators of GH secretion: [16-22]
Sex hormones (androgens and estrogen)
Peptide hormones such as ghrelin and growth hormone-releasing hormone (GHRH)
L-DOPA, the precursor to the neurotransmitter Dopamine
Nicotinic acid (Vitamin B3)
Nicotinic receptor agonists
Inhibitors of GH secretion: [18, 23-26]
Hyperglycemia (e.g. carbohydrates in the bloodstream)
IGF-1 and GH (due to negative feedback inhibition on the pituitary gland)
Certain sex hormone metabolites, such as dihydrotestosterone (DHT)