on of dopamine receptor subtypesAdenosine is a purine nucleoside produced by all cells that plays an important role in cellular metabolism and functions as an extracellular physiological regulator. Intracellular adenosine is then transported into the local extracellular space where it activates P1 purinergic receptors, which include A1 and A3 which couple with Gi and Go respectively A2A and A2B couple to Gs. During fetal life adenosine is very important, fetal plasma levels are fourfold greater than maternal levels. A1 receptors have been found in rat hearts as early as post conception 7.5 days when the developing heart is a primitive tube that has not initiated rhythmic beating. A1 are amongst the earliest expressed G - protein coupled receptors in mammalian heart. In mature hearts a1 activation has been shown to slow atrioventricular conduction and alter the pacemaker current. Adenosine receptor subtypes have been characterised which the adenosine acts upon to regulate cardiac activity. The procedure for investigating this was produce fetal culture conditions, a heart rate assessment, statistical analysis, use of various ligands. The results attained included; influences of A1A agonists on heart rates, P2 purinergic receptor ligand studies, adenosine influences on heart rates, influences of Gi/Go and cAMP on A1 action and influences of ion channel blockade on A1 action.Dose response curves generated using a variety of adenosine agonists revealed that A1 activation potently regulated fetal heart rates. Agonist n6-cyclopentyladenosine, inhibited heart rate and stopped fetal cardiac contraction in 63% of preparations. A2A & A2B receptor activation did not alter heart rates, activation of A3 produced modest declines in heart rate. Endogenous adenosine acts tonically to supress fetal heart rates demonstrated by the use of A1 antagonists 1,3-dipropyl-8-cyclopentylxanthine, increasing heart rates while adenosine reuptake inhibitors dipyridam...
