NATURAL RESISTANCE OF ALBINO RATS AND MICE TO HISTAMINE, PITUITARY AND CERTAIN OTHER POISONS

¹ Division of Pharmacology, Hygienic Laboratory, United States Public Health Service

Albino rats and mice exhibit a very great natural resistance to poisoning by histamine and pituitary extract.

The isolated uterus of the rats responds to histamine by relaxation instead of contraction, and pituitary extract is much less effective than on the uterus of guinea-pigs. The isolated intestinal loop of rats required about ten times the concentration of histamine phosphate to produce contraction as would be required in the case of intestinal loops of cats.

The active principle of the posterior lobe of the pituitary gland produces relaxation of the intestinal loop of the rat. Atropin, pilocarpin and epinephrine produce the same response of the intestinal loop of the rat as that obtained in other species of animals.

The minimum lethal dose of epinephrine, atropine, morphine and arsenic is of the same order in rats as in other animals.

Attempts to produce secondary traumatic shock in albino rats have failed in our hands.

We have come to the conclusion that the resistance of rats to poisoning with histamine, pituitary or diphtheria toxin is connected with the behavior of the smooth muscle and capillaries of this species. Further work is necessary to elucidate the cause of this peculiarity of the rat.