Phosphodiesterases in the rat renal vasculature

The objective this investigation was to determine the relative importance of type I, III, and IV phosphodiesterases in the regulation of cyclic adenosine monophosphate (cAMP) in the renal circulation. In the first experimental series, four groups of isolated rat kidneys perfused with Tyrode's solution were stimulated with isoproterenol(3, mu M) and then treated with increasing concentrations (from the similar to IC50,, to 30 times the similar to IC50 in threefold increments) of one of four phosphodiesterase inhibitors: group I, 3-isobutyl-1-methylxanthine, a "broad-spectrum" phosphodiesterase inhibitor (10-300 mu M); group 2, Ro 20-1724, a selective type IV phosphodiesterase inhibitor (3-100 mu M); group 3, 8-methoxymethyl-3-isobutyl-1-methylxanthine, a selective type I phosphodiesterase inhibitor (3-100 mu M); and group 4, milrinone, a selective type III phosphodiesterase inhibitor (0.3-10 mu M). In the second experimental series, five groups of cultured preglomerular (interlobular and afferent arteriolar) vascular smooth-muscle cells were stimulated with isoproterenol (1 mu M) and treated with vehicle or supra maximal concentrations (30 times IC50) of either 3-isobutyl-1-methylxanthine (300 mu M), RO 20-1724 (100 mu M), 8-methoxymethyl-3-isobutyl-1-methylxanthine? (100 mu M), or milrinone (10 mu M). In perfused kidneys and cultured preglomerular vascular smooth-muscle cells, 3-isobutyl-1-methylxanthine and Ro 20-1724 similarly increased renal cAMP release and total cellular (extracellular + intracellular) cAMP levels, respectively. In contrast, neither 8-methoxymethyl-3-isobutyl-1-methylxanthine nor milrinone affected renal cAMP release or total cellular cAMP levels. These data indicate that in the renal circulation, type IV phosphodiesterase is the predominant phosphodiesterase isozyme.