Which effect does theophylline have on urinary output?

Theophylline has a known effect of increasing urinary output through diuresis. This occurs primarily because theophylline is a methylxanthine that inhibits phosphodiesterase, leading to an increase in cyclic AMP levels in various tissues, including the kidneys. This heightened level of cyclic AMP promotes renal blood flow and enhances the glomerular filtration rate, resulting in increased urine production.

Additionally, theophylline has mild diuretic properties, which can further contribute to increased urinary output. It works by inhibiting the reabsorption of sodium in the renal tubules, which also increases the amount of water excreted in the urine. Such properties make it a compound of interest when considering fluid balance and renal function in patients, especially those with conditions where fluid management is important.

The other options do not accurately reflect the pharmacological effects of theophylline regarding urinary output, as it does promote increased urinary output rather than decreasing it or having no effect.