Hormonal regulation of skeletal muscle hypertrophy in rats: the testosterone to cortisol ratio

Abstract

This study determined the influence that the catabolic hormone, corticosterone (C), and the anabolic hormone, testosterone (T), had in regulating skeletal muscle hypertrophy using the rat hind limb ablation model. Specifically, the ratio of T:C (TCR) was manipulated via hormone implants and injections and concentrations measured to evaluate the relative contribution of each hormone to skeletal muscle protein balance. Skeletal muscle growth was measured 16 days after gastrocnemius muscle ablation. Elevations in plasma concentrations of C (via daily C injections, 50 mg kg*kg(-1) body mass) resulted in TCR of 0.007 that was less than the control group TCR of 0.249. In this C-injected group, whole body and skeletal muscle atrophy was elicited-this being greater in the fast-twitch plantaris muscle than in the slow-twitch soleus muscle. The overloaded leg resisted the C-induced atrophy. Castration of animals (TCR 0.024) resulted in less whole body and skeletal muscle growth. However, elevations in plasma concentrations of T (two groups, with TCR of 1.35 and 1.64) did not result in significantly greater muscle growth. Furthermore, T was also ineffective in antagonizing the C-induced atrophy in a group that received both T implants and C injections. This group had a TCR of 0.175 that was similar to the control group ratio of 0.249 that received no manipulations. We concluded that glucocorticoids were able to induce pronounced atrophy, but at the same time overloaded muscles were able to over-ride the glucocorticoid signal. Plasma concentrations of C were a better predictor of muscle growth/atrophy than T and/or the TCR. In addition, it is suggested that the volume of contractile activity of the muscle is perhaps an important determinant of C-induced atrophy, because less atrophy occurs in the more active slow twitch muscles.

Leg extensor power and dehydroepiandrosterone sulfate, insulin-like growth factor-I and testosterone in healthy active elderly people

“…However, some trend towards a negative relationship with cortisol and a positive relationship with the T:C ratio should be noted. This may re¯ect the hormonal regulation of muscle hypertrophy that has been described in animals (Crowley and Matt 1996) and observed in younger men (Busso et al 1990). The T:C ratio and DHEAS:C ratio have been proposed to be useful indicators of anabolic/catabolic balance (Busso et al 1990;Morales et al 1998).…”

Effect of concurrent strength and endurance training on skeletal muscle properties and hormone concentrations in humans

“…Conversely, anabolic hormones such as T and hGH, have been associated with enhanced synthesis of muscle protein leading to hypertrophy (Crowley and Matt 1996). It has been shown that concurrent strength and endurance training can elevate post-exercise serum cortisol concentration (Kraemer et al 1995) and resting UC concentrations (Bell et al 1997).…”

Hormonal Responses after a Strength Endurance Resistance Exercise Protocol in Young and Elderly Males

“…In contrast, others did not observe an increase in testosterone [2,12,31] and hGH concentrations [12,32] after resistance exercise. Cortisol concentrations, which suppresses protein synthesis [3,24], do not appear to be altered with resistance exercise in elderly males [12,14,32]. There is one report, however, where an increase in cortisol concentrations was observed following resistance exercise [26].…”