-adrenoceptors are G protein-coupled receptors whose functions are closely associated with caveolae in the heart and cultured cell lines. In the gut, they are responsible for the mediation of the sympathetic stimulation that might lead to intestinal paralysis postoperatively. We examined the effect of caveolin-1 knockout on the -adrenoceptor response in mouse small intestine. The relaxation response to (-)-isoprenaline in carbachol-contracted small intestinal tissue segments was reduced in caveolin-1 knockout mice (cav1^-/-) compared to their genetic controls (cav1^+/+). Immunohistochemical staining showed that -adrenoceptor expression was similar in both strains in gut smooth muscle. Selective -adrenoceptor blockers shifted the concentration response curve (CRC) of (-)-isoprenaline to the right in cav1^+/+ intestine, but not in cav1^-/-, with greatest shift in case of the ₃-blocker, SR59230A. The CRC of the selective ₃-agonist BRL 37344 was also shifted to the right in cav1^-/- compared to cav1^+/+. The cAMP-dependent protein kinase (PKA) inhibitor. H-89, shifted the CRC of (-)-isoprenaline to the right in cav1^+/+ but not in cav1^-/-. H-89 reduced the relaxation due to forskolin and dibutyryl cAMP in cav1^+/+ but not in cav1^-/-, suggesting a reduction in PKA activity in cav1^-/-. In cav1^+/+, PKA was colocalized with caveolin-1 in the cell membrane, but PKA immunoreactivity persisted in cav1^-/-. Examination of PKA expression in the lipid raft-rich membrane fraction of the jejunum revealed reduced PKA expression in cav1^-/- compared to cav1^+/+. The results of the present study show that the function of -adrenoceptors is reduced in cav1^-/- small intestine likely due to reduced PKA activity.