RAPID STIMULATORY EFFECTS OF TESTOSTERONE UPON MYOTUBULE METABOLISM AND SUGAR-TRANSPORT, AS ASSESSED BY SILICON MICROPHYSIOMETRY

A considerable number of studies have revealed behavioral circumstance s that give rise to small or transient differences in circulating test osterone concentrations; however, careful consideration of androgen ph ysiology leads to the disquieting conclusion that these differences ar e often unlikely to have much physiologic or behavioral significance. In the present report, we observe that small transients of testosteron e secretion could have very rapid anabolic effects on a cultured muscl e-derived cell line. Specifically, we have examined the effects of tes tosterone on metabolism in cultured C2C12 myotubules, using a silicon microphysiometer. The instrument monitors cellular extrusion of proton s and acidic metabolites, and such extrusion is directly linked to ATP hydrolysis, thus providing a real-time measure of cellular metabolism . Testosterone caused a small but significant increase in metabolism. The most striking feature of this effect was its rapidity, in that it occurred within 3 hr. This rapid enhancement of metabolism suggested t hat testosterone might be enhancing substrate uptake even more rapidly . Indeed, we found that testosterone increased 2-deoxyglucose uptake w ithin 1 min. The rapidity of this effect seemed to preclude mediation by classical intracellular steroid receptors. In support of this, we w ere unable to detect specific intracellular binding of testosterone. T hese findings show that testosterone can exert rapid anabolic effects on substrate transport and metabolism in myotubules. Should this findi ng general to muscle in vivo, it suggests that relatively small indivi dual differences in testosterone profiles, in response to various soci al interactions, may have very real consequence for subsequent muscle physiology. (C) 1996 Wiley-Liss, Inc.