CONTRACTILE PROPERTIES OF THE QUADRICEPS MUSCLE IN GROWTH HORMONE-DEFICIENT HYPOPITUITARY ADULTS

1. Growth hormone-deficient hypopituitary adults often complain of wea kness and fatigue. The cause of the fatigue is unknown but could be an increased proportion of fast, fatiguable, type 2 fibres in the muscle , The aim of this study was to examine the contractile properties of t he quadriceps muscle in a group of these patients compared with health y controls, Changes in these properties were also examined in a small subset of the patients following growth hormone replacement. 2. Isomet ric strength, half-relaxation time from a twitch (t1/2) and the force- frequency relationship were measured using electrically evoked contrac tions in 14 growth hormone-deficient patients and 14 age- and sex-matc hed controls, Six patients were restudied following 6-24 month's repla cement therapy with growth hormone (daily dose 0.04 +/- 0.01 i.u./kg). 3. The growth hormone-deficient patients had a significantly lower t1 /2, than the controls (46.1 +/- 6.1 ms versus 56.1 +/- 10.5 ms respect ively; P = 0.0072; mean +/- SD), The 10/100% ratio was also significan tly lower in growth-hormone-deficient patients (38.6 +/- 9.9% versus 5 2.3 +/- 8.0%; P = 0.0005), as was muscle strength (349 +/- 99 N versus 493 +/- 215 N; P = 0.036), Following growth hormone replacement, musc le strength increased significantly (P < 0.05), The 10/100% ratio also increased towards control values, but this change was not significant . 4. These results demonstrate that the relaxation times of the quadri ceps are significantly shorter and that the force-frequency relationsh ip shifted to the right in growth hormone-deficient patients, which is consistent with a greater proportion of type 2 fibres within the musc le, Preliminary data on a small group suggest that replacement with gr owth hormone results in a change in these properties towards that of c ontrols,