Muscle growth in response to mechanical stimuli.

The relative merits of the separate and combined uses of stretch and electrical stimulation at 10 Hz in influencing the rates of protein synthesis in vivo, proteolysis, and the growth of the extensor digitorum longus muscle have been investigated after 3 days in the rabbit. Continuous electrical stimulation failed to change muscle protein turnover or growth. Static stretch caused significant adaptive growth, with increases in c-fos, c-jun, and insulin-like growth factor I (IGF-I; 12-fold) mRNA levels, and protein (19%), RNA (128%), and DNA (45%) contents. Both the fractional (138%) and total (191%) rates of protein synthesis increased with stretch, correlating with increased ribosomal capacities. Combining stretch and electrical stimulation increased the mRNA concentration of IGF-I (40-fold). The adaptive growth was greater (35%), with massive increases in the nucleic acids (185 and 300%), ribosomal capacities (230%), and the rates of protein synthesis (345 and 450%). Large increases (i.e., 200-400%) in cathepsins B and L and dipeptidyl aminopeptidase I activities during stretch, with or without stimulation, suggest a role for these enzymes in tissue remodeling during muscle hypertrophy.

The fibre type composition of the rabbit latissimus dorsi muscle.

The fibre type distribution has been mapped in the latissimus dorsi muscle of the Dutch rabbit. Using the myosin ATPase stain, a distinct border was found to run in a cranial to caudal direction, which effectively divided the muscle into 2 segments of different fibre type proportions. Although both segments contained mostly fast twitch fibres, the medial areas were found to contain approximately 10-20% slow (i.e. type I) fibres while the lateral portions contained very few, if any, slow fibres. Significantly fewer type IIa fibres were also found in the lateral areas of the muscle. These histochemical findings were confirmed by the use of the reverse transcriptase polymerase chain reaction, which demonstrated that more messenger RNA of the slow myosin heavy chain was found in the medial regions compared with the lateral segment. These results demonstrate the importance of choosing well defined sampling sites when evaluating regimes designed to transform this heterogeneous muscle for use in subsequent myoplasty procedures.

The detection of AKH/HrTH-like peptides in Ascaridia galli and Ascaris suum using an insect hyperglycaemic bioassay.

Evidence for the presence of adipokinetic hormone/hypertrehalosaemic hormone (AKH/HrTH)-like peptides in the parasitic nematodes Ascaridia galli and Ascaris suum has been obtained using insect bioassays which measure hyperglycaemic responses to peptides belonging to the AKH/HrTH family of insect hormones. A peptide fraction extracted from heads and tails of Ascaridia galli evoked a dose-dependent hyperglycaemic response when injected into the cockroach, Periplaneta americana. Maximal bioactivity was obtained with material that was equivalent to 38 mg (wet weight) of nematode. Bioactivity appeared to be highest in extracts from heads and tails of both male and female worms and could be fractionated into at least three peaks of hyperglycaemic activity by reversed-phase high-performance liquid chromatography. An extract from heads and tails of A. suum also evoked a hyperglycaemic response when injected into the cockroach, Blaberus discoidalis. The bioactivity was inactivated on incubation with pure endopeptidase 24.11, confirming the peptidic nature of the bioactive material. These results provide evidence for the existence of peptides related to the insect AKH/HrTH family of peptides in parasitic nematodes.