Chronotoxicity of beta-adrenoceptor blocking agent in spontaneously hypertensive rats.

1. Chronotoxicity of a single LD50 dosage of beta-adrenoceptor blocking agent, pindolol, was determined in spontaneously hypertensive rats (SHR) and Wistar-Kyoto control rats (WKY). 2. The 24 h mortality was greater when pindolol was administered at 00.00 h than when it was administered at 12.00 h in both SHR and WKY. 3. The chronogram of the mortality in SHR was similar to that in WKY. 4. These results indicate that the mode of circadian variation in the acute toxicity of pindolol in SHR is not different from that in WKY.