Effects of delta-aminolaevulinic acid on contractile activity in the isolated small intestine of the rabbit. Role of adrenergic receptors.
The porphyrin precursor, delta-aminolaevulinic acid (ALA) at concentrations of 0.23-7.6 mM caused dose-dependent inhibition of spontaneous contractions in isolated preparations of rabbit small intestine, suspended in Ringer-Locke solution. Contractions which returned after inhibition from 3.8 and 7.6mM ALA showed increased amplitude and from 7.6 mM ALA a reduction in rate. Pretreatment with prazosin (10(-7) M) significantly reduced the duration of inhibition exerted by 3.8 and 7.6 mM ALA and also the amplitude of contractions returning after this inhibition. Pretreatment with yohimbine (10(-6) M) and propranolol (7 X 10(-6) M) had no significant effects. Blocking of the release of noradrenaline in preparations by incubation with 6-hydroxydopamine (10(-3) M) or guanethidine (1.5 X 10(-5) M) did not prevent the inhibitory effects of ALA. The alpha 1 agonist, cirazoline (10(-5) M), inhibited contractile activity. This effect was blocked by prazosin (10(-7) M). The alpha 2 agonist, guanoxabenz (10(-5) M) had no detectable effect, in the presence of prazosin, to block any residual alpha 1 actions. It is concluded that alpha 1 receptors mediate inhibitory effects in this preparation and that ALA appears to have direct effects upon these receptors.
D000622:Aminolevulinic Acid / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D004347:Drug Interactions; D005769:Gastrointestinal Motility / Q000187:drug effects*; D066298:In Vitro Techniques; D007421:Intestine, Small / Q000187:drug effects* / Q000294:innervation / Q000378:metabolism; D007982:Levulinic Acids / Q000494:pharmacology*; D009638:Norepinephrine / Q000378:metabolism; D011433:Propranolol / Q000008:administration & dosage; D011817:Rabbits; D011941:Receptors, Adrenergic / Q000187:drug effects*; D015016:Yohimbine / Q000008:administration & dosage
D007982:Levulinic Acids; D011941:Receptors, Adrenergic; D015016:Yohimbine; D000622:Aminolevulinic Acid; D011433:Propranolol; D009638:Norepinephrine