Is there a no-effect dose for corticosteroid-induced cleft palate? The contribution of endogenous corticosterone to the incidence of cleft palate in mice.

Teratology and genetic counselors are frequently asked whether very low exposures of drugs and chemicals can cause a child's congenital malformations. One critical factor on which the counseling is based is the dose. Because teratogenic effects follow a toxicologic dose-response curve with a no-effect dose, frequently counselors can refute a causal relationship because the dose was far below the no-observable-effect dose. Recently, some investigators have suggested that some teratogens which are present in physiologic levels such as cortisone, glucose, insulin, or sex steroids may contribute to the background incidence of congenital malformations and, therefore, there is no safe dose. Using corticosteroid-induced cleft palate in mice as the model, we conducted experiments to test this hypothesis. Adrenalectomy of A/J or CD-1 dams resulted in a reduction of endogenous corticosterone, but did not reduce the spontaneous incidence of cleft palate in the offspring. In A/J mice, the incidence of isolated cleft palate increased with adrenalectomy indicating that the spontaneous incidence of this defect is not due to endogenous corticosterone. Adrenalectomy did not affect the susceptibility of CD-1 mice to cortisone induced cleft palate demonstrating that endogenous corticosterone did not contribute significantly to the incidence of cleft palate induced by the exogenous corticosteroid. Finally, results in CD-1 mice clearly indicate that cortisone, like other teratogens, has a no-effect level for teratogenesis. These studies support the concept of a threshold in the dose-response relationship for corticosteroid-induced cleft palate in mice.