The role of cyclic nucleotides and prostaglandins in heart function.

A short review of the role of cyclic nucleotides and prostaglandins (PGs) in normal and pathological functions of the heart is given. Possible interrelationships of these two regulatory systems have been studied by using spontaneously beating rat atria preparations. Addition of noradrenaline (NA) to the incubate (1 . 10(-6) M) caused an increase in amplitude and frequency which was preceded and parallelled by an elevation of the tissue cAMP level. A transient increase in cGMP and PGE values was also seen. Propranolol (5 . 10(-6) M) abolished the increase in amplitude and frequency as well as in cAMP and PGE concentrations. Indomethacin (1 . 10(-5) M) inhibited the formation of PGE. The increase in cGMP was blocked by phenoxybenzamine. Interchange between beta- and alpha-receptors according as the temperature is lowered has been described earlier. Hypothermia (20 degrees C) had a positive inotropic effect on the atria and increased the tissue cAMP concentration. Loading of the atria caused an increase in cAMP without any effects on cGMP or PGs. Slight hypoxia did not change the cAMP or PG levels, but elevated the cGMP values. Arrhythmias induced by hypo- or hyperpotassemia did not modify the biochemical parameters measured. PGF2alpha (1. 10(-5) M) normalized the atrial rhythm and increased the amplitude without changing cyclic nucleotide or PG levels. PGE1 (1 . 10(-4) M) increased the amplitude of normorhythmic atria and the tissue concentration of cAMP. PGE2 was the only PG tested which stimulated the heart adenylate cyclase in vitro. There seems to be close but complicated relationships between cyclic nucleotides and PGs in the heart.