The following statements regarding methylxanthines are true except:

Methyl xanthines inhibit cyclic nucleotide phosphodiesterases and can antagonize receptor-mediated actions of adenosine. Long-term ingestion of methyl xanthines can produce tolerance and physical dependence. It can relax various smooth muscles including the bronchial muscles. It increases glomerular filtration rate and increases the excretion of electrolytes and water.