INHIBITION OF ADENYLATE-CYCLASE IN PREFUSION MOUSE PALATE BY SECALONIC ACID-D

Glucocorticoids (GC) induce cleft palate (CP) in the offspring of expo sed pregnant mice. Glucocorticoids induce prostaglandin (PG) synthesis inhibition via reduced arachidonic acid (AA) release from membranes, and this results from inhibition of phospholipase A(2). This metabolic event is associated with reduced palatal cAMP levels in the prefusion stages (d 13 of gestation). The mycotoxin secalonic acid D (SAD) indu ces CP in the offspring born to treated mothers, elevates maternal pla sma corticosterone levels, and reduces prefusion palatal cAMP levels. In addition, an increase in cAMP was noted in the postfusion period (d 15 of gestation). Since exogenous AA given simultaneously to GC-expos ed mothers may protect against CC-induced CP in the offspring, such a possibility was tested for SAD. Pregnant CD1 mice given a teratogenic dose of SAD (30 mg/kg, ip, on gestational d 11) were simultaneously tr eated with maximal tolerated doses of AA (200 mg/kg, sc, on gestationa l d 11, 12, and 13). At term, no significant reduction in SAD-induced CP was seen as a result of AA treatment. To evaluate if SAD-induced al terations in palatal cAMP are due to reduced palatal membrane-associat ed adenylate cyclase(AC) activity during pre- and postfusion periods, SAD-treated mothers were sacrificed at 12-h intervals between gestatio nal d 13.5 and 15.5, palate shelves were collected from the fetuses, a nd AC activity (cAMP formed/mg protein/min) was assayed in the presenc e or absence of the enzyme stimulator, sodium fluoride (NaF). Although SAD did not alter unstimulated AC activity, it significantly reduced the NaF-induced stimulation of enzyme activity in the prefusion period . This inhibition could not be reversed by excess CTP in the incubatio n mixture. Since NaF stimulation of AC indicates post-receptor-site fu nction involving CTP-binding and catalytic units, and since addition o f CTP failed to correct SAD-induced alteration of NaF stimulation of t he enzyme, it is suggested that SAD may inhibit the AC sensitivity to stimuli by its effect on the catalytic unit in a manner that does not affect enzymic basal activity.