Determination of beta-adrenoceptors and cAMP in muscle from normal and splayleg Belgian Landrace pigs.

beta-Adrenoceptors were identified and characterized by [3H]dihydroalprenolol ([ 3H]DHA) binding experiments in muscle membrane preparations from piglets. The [3H]DHA binding was rapid, reversible and stereoselective. Catecholamines competed for specific binding with a rank order of potency (-)-isopropylnoradrenaline greater than (-)-epinephrine much greater than (-)-norepinephrine, indicating a beta 2-subtype of adrenoceptor. Saturation binding experiments with [3H]DHA showed no significant difference for either the number of binding sites or the equilibrium dissociation constants in normal and splayleg pigs. Adenylate cyclase assays indicated that the basal adenylate cyclase activity and the prostaglandin E1 (PGE1)-, (-)-isopropylnoradrenaline (ISO)-, 5'-guanylyl-imidodiphosphate (GppNHp)- and sodium fluoride (NaF)-stimulated values were not significantly different in normal and splayleg pigs. In both groups, PGE1 did not affect basal activity, whereas ISO and GppNHp stimulated adenylate cyclase activity significantly (p less than 0.001) to about 40% above basal level. NaF induced a significant (p less than 0.001) increase of cAMP in normal and splayleg pigs amounting to 48% and 61% respectively. Significant correlations between absolute adenylate cyclase responses to ISO (r = 0.83***), NaF (r = 0.72**) and GppNHp (r = 0.61*) and basal activity in the splayleg pigs were the most striking findings. In contrast, these correlations could not be detected in the normal pigs. Whether or not this observation reflects an alteration in the signal transduction system needs to be further investigated. To the best of our knowledge this is the first biochemical study which relates an altered beta-adrenoceptor function and porcine splayleg.