Protein intake key factor in growth hormone's anabolic effect
Increasing protein intake may increase the anabolic impact of synthetic growth hormone. We formulate things cautiously, because the study on which we base this statement has been done with sick and malnourished people, not with fit athletes. Nevertheless, we would like to share the results of the research published in Nephrology, Dialysis, Transplantation in 2005 by American nephrologist Joel Kopple.Study

The researchers, affiliated with the Harbor-UCLA Medical Center, injected 6 adult kidney patients with growth hormone every day for 21 days. During this period, and during the 14 days, the researchers measured how much protein the patients consumed and the amount of IGF-1 in their blood.The liver manufactures most of the IGF-1 molecules in the blood. The liver produces more IGF-1 as the concentration of growth hormone in the blood is higher. The muscle building effects of growth hormone are mainly the work of IGF-1.
Here's how the body regulates growth hormone and IGF-1 release.
The figure below shows that administration of growth hormone increased the concentration of IGF-1 in the blood in most study subjects, but that 2 patients did not respond to growth hormone. These were Pt 3 and Pt 4.

Best respondes were Pt 1, Pt 2 and Pt 5.

Below you can see how much nitrogen (say dietary protein) the subjects consumed daily and how much nitrogen the subjects could retain (say: whether they were in an anabolic or catabolic state). All patients were malnourished, which is typical of their illness.
1 gram of nitrogen is approximately equal to 6.25 grams of protein.
The figure suggests that protein intake is an important factor in the anabolic activity of growth hormone. The subjects who did not respond to growth hormone, Pt 3 and Pt 4, had the lowest protein intake. The subjects who responded best to growth hormone treatment, Pt 1, Pt 2 and Pt 5, had the highest protein intake.

The researchers do not claim, however, that kidney patients should 'use' growth hormone. There is no evidence that growth hormone treatment makes this group healthier or makes it live longer.

J Nutr 2020;150:1871-9.