A combination of pharmacological, molecular biological and biochemical approaches were used to investigate the differential expression of two cyclic GMP‐inhibited cyclic nucleotide phosphodiesterase genes (PDE3A and PDE3B) in the rat.

RT–PCR using PDE3A‐ or PDE3B‐specific oligonucleotide primers allowed amplification of products encoding PDE3A (508 bp) or PDE3B (499 bp) sequences from several rat tissues (heart, aorta, liver, kidney and epididymal fat), from primary cultures of aortic vascular smooth muscle cells (VSMC) as well as from an SV40 large T‐antigen immortalized aortic VSMC line.

Immunoblotting experiments with PDE3‐selective antisera allowed the detection of both PDE3A and PDE3B immunoreactive proteins in several rat tissues, including tissues of the cardiovascular system, in primary cultures of aortic VSMC and in an SV40 large T‐antigen immortalized aortic VSMC line. In all cases, PDE3A was expressed as a 120 kDa protein which was only detected in the cytosolic fraction. PDE3B was expressed as a 135 kDa protein and its expression was limited to the particulate fraction of all tissues and cells studied.

Prolonged incubation of cultured aortic VSMC with agents that increase VSMC cyclic AMP (forskolin or 8‐bromo‐cyclic AMP) produced marked time‐dependent increases in PDE3 activity which correlated with increases in PDE3A and PDE3B RT–PCR signals and a marked increase in particulate PDE3 activity and PDE3B protein.

The physiological, pharmacological and biochemical implications of these findings are discussed based on previous reports of the effects of PDE3 inhibitors in the cardiovascular system and the relevance of our findings are presented in the context of the development of PDE3A and/or PDE3B‐selective pharmacological agents.