The function of corpus cardiacum peptides in horse flies

HPLC separation of corpus cardiacum homogenates from Tabanus lineola, T. proximus and T. calens all produced two peaks whose retention times corresponded to the retention times of the synthetic Tabanus atratus adipokinetic and T. atratus hypotrehalosaemic hormones. Corpus cardiacum extracts from T. proximus and from T. lineola produced hyperlipaemic and hyperglycaemic responses when injection into sucrose fed T. lineola. Synthetic T. atratus hypotrehalosaemic hormone induced strong hyperlipaemic and hyperglycaemic responses in T. lineola, but synthetic T. atratus adipokinetic hormone produced only a weak hyperglycaemic response. The current names of the tabanid metabolic peptides do not correspond to their action in T. lineola. Octopamine also elevated both lipids and sugars in the blood of sucrose fed T. lineola, indicating the sensitivity of storage tissues to both biogenic amines and to metabolic peptides. Lack of response to synthetic T. atratus hypotrehalosaemic by starved T. lineola suggests an inhibition of the hyperlipaemic/glycaemic response when the available tissue reserves falls below a given level.