Time‐response and dose‐response to acetazolamide in the WB/ReJ and C57BL/6J mouse strains: Genetic interaction in the ectrodactyly response
Authors: Biddle Fred G. , Mulholland Lynda R. , Eales Brenda A. 
Published: June 2005

The WB/ReJ and C57BL/6J strains were compared in their time and dose responses to acetazolamide administered in a single subcutaneous injection regime. WB/ReJ has a genetically determined, high‐frequency, transient fetal edema that has maximum expression on day 14 and is resolved by day 18. Acetazolamide, at 1,000 mg/kg, appears to induce edema in WB/ReJ with a time of response on days 9 and 10, and the induced edema follows the same time course of appearance and disappearance as the spontaneous trait. The dose‐response analysis is not interpretable in the WB/ReJ and C57BL/6J strains and their reciprocal F1 fetuses because there was significant response only at the highest dose (2,000 mg/kg) used in this study. The time of ectrodactyly response is maximal on day 9 in both WB/ReJ and C57BL/6J strains. The dose‐response analysis demonstrates that, for the usual measure of total fetuses with ectrodactyly (or penetrance), the WB/ReJ and C57BL/6J strains and the WB/ReJ × C57BL/6J F1 (WB.B6F1) have the same slope of the dose‐response curve and the strain difference in response can be interpreted as a difference in dosage tolerance. The tolerance of WB/ReJ is twofold greater than that of C57BL/6J, and the WB.B6F1 tolerance is fourfold greater than that of C57BL/6J. This overdominance of relative resistance to acetazolamide ectrodactyly supports the general finding of directional dominance of relative resistance among genetically different strain pairs. The median effective dose for penetrance of the ectrodactyly response of the reciprocal B6.WBF1 embryo is similar to the WB.B6F1, but the slope of the dose‐response curve is significantly different, and a different teratogenic mechanism of response may be involved. Ectrodactyly was predominantly right sided in all genotypes, and, in bilaterally affected fetuses, the right forelimb was more severely affected. An unexpected difference between WB/ReJ and C57BL/6J was found when the laterality of ectrodactyly was analyzed further. There is a significant increase with dosage in bilaterally affected fetuses (a measure of expressivity) in C57BL/6J but not in WB/ReJ, even though the dose‐response of total affected fetuses (penetrance) is similar in both strains. In C57BL/6J, the left and right forelimbs are correlated in their responses with the left, requiring approximately a threefold greater dose. The left and right forelimbs are symmetrical in response, and the difference can be interpreted in terms of a developmental (or teratogenic) gradient. In WB/ReJ, the right forelimb has the same dose response as C57BL/6J and requires a twofold greater dose than the right forelimb of C57BL/6J, but the left forelimb has a very flat slope and is not correlated with the response of the right. Therefore, the left and right forelimbs of WB/ReJ are asymmetrical in their response to acetazolamide. The WB/ReJ has a qualitatively different ectrodactyly response to acetazolamide. Doses and sample size were insufficient to analyze the laterality of response in the reciprocal F1 fetuses, which may provide clues to the apparent interaction in the response of total ectrodactyly and in the response of the right forelimb alone.