Intestinal absorption and metabolism of 6-mercaptopurine in the rat small intestine

The intestinal absorption of 6-mercaptopurine was examined in the rat by in vitro and in situ techniques for the purpose of establishing absorption characteristics which might explain the poor systemic oral availability of this drug. Experiments were designed to evaluate the significance of intestinal metabolism and active secretion processes. Since mucosal/serosal drug concentration gradients across in vitro segments were not significantly different (P greater than 0.05) for everted and noneverted preparations, with values of 1.21 +/- 0.27 and 0.91 +/- 0.12, respectively, it was concluded that active secretion or absorption mechanisms were absent. Varying the concentration of 6-mercaptopurine from 0.24 to 5.88 mM demonstrated saturability of the biotransformation of 6-mercaptopurine to 6-thiouric acid with a maximum rate of 1.6 X 10(-5) mmoles per min g for jejunal portions. Distal segments displayed 85% higher rates of biotransformation at concentrations of 1.47 mM. Inclusion of allpurinol (2 mM) completely inhibited biotransformation. With in situ loops perfused with 1.47 mM drug, collection of mesentery blood showed that absorption rates of 6-thiouric acid were 0.67 that of the parent drug.

Comparative cardiovascular effects of propranolol and practolol in puppies

The present results indicate that in 3-4-weeks-old puppies propranolol induces a significant depression of cardiovascular function expressed by a decrease in heart rate, myocardial contractility, and cardiac output, and an increase in systemic vascular resistance, in doses beyond beta-blocking levels. In contrast, practolol, in the same dose range, did not induce further cardio-circulatory depression, as shown by levels of heart rate, myocardial contractility, and cardiac output similar to the values obtained with beta-blocking doses of this agent. The cardio-depressant activity observed in puppies with doses of propranolol beyond blocking levels is thought to be due to direct negative inotropic and chronotropic effects of this agent, not related to influences on beta receptor sites. Such effect not observed with practolol at doses well beyond beta-blocking levels suggests that this drug exerts a more selective influence on cardiac sympathetic beta receptors.

Seasonal infection of Culex mosquitos and swine with Japanese encephalitis virus

A year-round study of the infection rates of JE virus in Culex mosquitos was made during 1970-71 in 2 hamlets in Taoyuan County, China (Province of Taiwan). JE virus was recovered from 5 of 314 pools of C. annulus, and from 1 of 22 pools of C. tritaeniorhynchus; these recoveries occurred during a 14-day period in July 1971. None of the 288 pools of C. p. fatigans, which had been collected between October and April, was positive. In addition, sentinel swine were assessed for antibody and virus. All the pigs became highly immune by 23 July; in each hamlet all the pigs had become infected within 1 week, virus being detected in them for only 1-2 weeks. Virus-positive mosquitos appeared to have obtained their infections at about the time that viraemia was occurring in the sentinel swine. These observations illustrate once again the lower infection rate and shorter duration of virus-positive mosquitos in China (Province of Taiwan) as compared with Japan.