Biochemistry and physiology of anabolic hormones used for improvement of meat production.
A number of hormones are involved in endocrine regulation of growth. In general, these hormones enhance body protein accretion and metabolise fat stores resulting in increased lean growth rates. Most practical importance was obtained by sex hormones (oestrogens and androgens), beta-agonists and growth hormone - whether legally or illegally. Efficiency of growth promotion ranges between 0% and +20% depending on the prerequisites such as species, breed, gender, age, reproductive status, body score or feeding of the animals. Oestrogens and androgens mediate their activity via intracellular receptors - directly in muscular tissue as well as indirectly via stimulation of growth hormone from the hypophysis and other growth factors from liver plus several further organs. In addition, mineral absorption in the gut is improved. The outstanding efficiency of trenbolone is based on its androgenic plus antiglucocorticoid activity. Melengestrolacetate is thought to act indirectly via stimulation of endogenous ovarian oestradiol in non-pregnant heifers. The necessary dosages and residue formations depend on the pharmacokinetic parameters of each substance and extrapolations between compounds are hardly possible. Growth hormone and beta2-agonists use independent pathways for growth promotion not related to steroid biochemistry.