Adenosine increases ventilation rate, cardiac performance and haemolymph velocity in the American lobster Homarus americanus.

The effects of adenosine and adenine nucleotides on haemolymph velocity and on heart rate and scaphognathite frequency were investigated in the American lobster Homarus americanus. The infusion of 0.25-2.4 nmol g(-1) min(-1) adenosine produced steady-state concentrations of 2-3 micromol l(-1) adenosine and approximately 80 micromol l(-1) inosine in the haemolymph. No hanges in haemolymph concentration of AMP, hypoxanthine, xanthine or IMP were observed. Adenosine increases haemolymph velocity in the sternal artery from 55+/-29 to 204+/-53 mm s(-1) and in the posterior aorta from 21+/-7 to 54+/-28 mm s(-1 )and reduces haemolymph velocity in the lateral arteries from 98+/-92 to 74+/-69 mm s(-1). Heart rate is increased from 69.3+/-7.4 to 81.2+/-6.2 beats min(-1) and scaphognathite frequency from 86.9+/-29.0 to 147.1+/-35.0 beats min(-1). The effects of adenosine are rapidly reversed after the cessation of the infusion of this purine. The adenylates cause similar but lesser changes and the effects are protracted, probably because of low in vivo activities of nucleotidases.