The effect of theophylline and cyclic adenosine 3,5-monophosphate on renin release by afferent arterioles

The effects of theophylline and cyclic adenosine 3ʼ,5ʼ-monophosphate (cAMP) on renin release by afferent arterioles were studied. Rabbit afferent arterioles (seven to 10), obtained by a microdissection technique, were incubated for three consecutive 20min periods in 100(µ of Medium 199 with 0.1% bovine serum albumin (BSA). Afferent arterioles exposed to theophylline, 1 x 10mol/l, produced a>100% increase in renin release (0.18 ± 0.04 to 0.42 ± 0.05 ng angiotensin l/h per arteriole per h incubation). The renin release stimulated by theophylline was completely abolished by indomethacin and meclofenamate. The stimulation of renin secretion was also blocked when extracellular calcium concentration was decreased to 10~7 mol/l and the arterioles were permeabilized with calcium ionophore. Dibutyryl cAMP (db-cAMP), 1 x 10 mol/l, and forskolin, 1 µ.mol/1 or 100µmol/l, failed to stimulate renin release by afferent arterioles. The results of this study therefore suggest that theophylline-stimulated renin release may be mediated through a prostaglandin pathway. The stimulation of renin secretion is also dependent on the extracellular concentration of calcium.