Adrenaline improves endurance of rabbit gastrocnemius: a study with continuous high frequency stimulation

Beta adrenoceptor agonists are well known for their potentiating effects on peak twitch and tetanic tension and defatiguing effects on skeletal muscles. Adrenaline (ADR) is one of these agonist which is known for inotropism but less described for fatigue. In addition, studies on high frequency stimulation (HFS) of skeletal muscles are scarce and not available for tetanization fatigue related with endurance and recovery under the influence of ADR. We hypothesized that ADR can maintain peak tetanic tension (PTT) produced by mammalian skeletal muscles for longer period as well as help in recovery from fatigue on continuous HFS. Gastrocnemius muscles (medial Belly) from both limbs were isolated from Rabbits (Oryctologus cunniculus) and continuously stimulated at High frequency of 80Hz for 20Sec. Tetanic tensions were recorded digitally with the measurement of PTT at different time points during this stimulation. Time (T50) was also noted at which muscle force was reduced to 50%. At 20Sec of continuous stimulation, mean PTT(% of initial) was declined significantly in both the ADR treated and control CTL muscles being greater in CTL ones. T50 was found 74.9% greater in ADR than CTL, being significant. When muscles, which were fatigued with same stimulation protocol, were allowed to recover with and without adrenaline, the PTT recovers by 3.4 folds in ADR and about 2 folds only in CTL. Significant differences between CTL and ADR treated-continuously stimulated high frequency fatigued muscles confirm the hypothesis that in mammalian muscles ADR increases the endurance by delaying the high frequency fatigue and helps in its recovery.