Secalonic acid D-induced changes in palatal cyclic AMP and cyclic GMP in developing mice.

Secalonic acid D (SAD) induces cleft palate in the developing mouse by an unknown mechanism. To investigate possible roles of cyclic nucleotides (cAMP and cGMP) in the teratogenesis of SAD, cAMP and cGMP levels were measured in the extracts of fetal palates of gestational age 13(0) through 16(12) (days(hours]. Fetuses were obtained from pregnant CD-1 mice treated on day 11(0) of gestation, with either 5% (wt./vol.) sodium bicarbonate (NaHCO3, control) or 30 mg/kg of SAD in 5% NaHCO3, intraperitoneally (i.p.). Radioimmunoassay was used to quantitate cyclic nucleotide levels. Cyclic AMP levels peaked on day 14(12) of gestation in controls. In the SAD group there was a significant decrease in cAMP levels on days 13(12) and 14(0) of gestation and a decrease of 30% in total cAMP on days 13(0) through 14(0) of gestation, with little or no change at the peak on day 14(12). On day 15(12), however, the SAD group had a 68% increase in palatal cAMP level over the control. Control levels of cGMP appeared to follow a diurnal pattern reaching maximal levels at the end of the dark cycle. In contrast, SAD decreased the cGMP level by 31% on day 13(12) (P less than 0.05) and increased it 100% above that of the control level on day 15(0) (P less than 0.01). Total cGMP during days 15(0) through 16(12) of gestation was 33% higher than control (P less than 0.01). The number of clefts in the SAD group was significantly higher at all points following palate closure in the control fetuses (14(0) through 16(12] with values ranging from 20% to 34% versus 0% in the control (P less than 0.01-0.005). Morphological changes on days 13(0) through 15(0) indicated a failure of shelf elevation in middle and posterior palatal regions of SAD-treated fetuses. These results suggest that the induction of cleft palate by SAD is associated with dynamic changes (initial decrease followed by later increase), in vivo, in established cyclic nucleotide patterns and support a mechanistic role for cyclic nucleotide-mediated cellular processes in normal as well as abnormal palate development.