Evidence of combined growth hormone & testosterone anabolic action.
Metabolism, a continuous process of creating energy from food, storing energy, building up and breaking down different substances that the organism needs, have two distinct phases: anabolism and catabolism. Anabolism is the building-up aspect of metabolism, whereas catabolism is the breaking-down aspect. Both growth hormone and T are anabolic hormones, helping in building up active metabolic substances.
The first evidence for a possible combined anabolic action between the growth hormone and T might have been assumed from the observation that at puberty in boys (rather than girls) there is higher state of growth with higher linear growth rates, higher muscle and bone accumulation. It might also be argued that the higher anabolic effect and sexual development seen in boys during puberty is due solely to high T levels.
Interestingly however, in cases of isolated severe growth hormone deficiency, despite normal T secretion, there is no pubertal growth shot and the anabolic effect of T is attenuated. For this reason, it is the combination of these two hormones that brings the higher anabolic action observed physiologically in men.
Puberty and GH & testosterone synergism
Puberty offers plenty of evidence for the close interrelation of these two hormone systems, as daily GH secretion more than doubles mainly because of higher GH pulse amplitude, The highest rates of GH secretion coincide with the highest rates of linear growth during puberty in coordination with the higher secretion rates of testosterone.
Muscle growth and GH and testosterone synergism
Growth hormone and testosterone are all strong anabolic agents that promote muscle protein synthesis and growth. It appears that both of these hormones have a common target as they act to activate some specific muscle cells, called satellite cells, absolutely necessary for muscle growth. New data have clearly demonstrated that one hormone helps the other on activating these muscle satellite cells.
In a similar fashion both, growth hormone and testosterone have an additive effect on lipolysis (breaking down of lipids) and the presence of one is required for the fully expressed lipolytic action of the other.
Combined growth hormone & testosterone replacement therapy
Growth hormone Testosterone replacement therapy in suitable individuals, preferentially affects skeletal muscle mass and indeed, physical performance and exercise capacity change for the better.