Increased Chromosome Number of Rat Parotid Cells After Isoproterenol. ∗

Summary

Administration of pharmacologic doses of the sympathetic amine, isoproterenol, to adult female rats resulted in a progressive enlargement of the gland with duration of treatment. Although this enlargement is the result of hypertrophy of acinar cells as well as proliferation of these elements, marked mitotic activity was generally confined to the early days of treatment (1-5 days) whereas hypertrophy was initiated almost immediately and persisted throughout the period of isoproterenol-administration. During the early phase of marked cellular proliferation, chromosome counts from squash preparations of tissue indicated that greater-than-diploid (>2n) as well as diploid (2n) cells were present. Furthermore, the proportion of 2n to >2n changed with time in a highly suggestive way, i.e., at 1-2 days, when mitotic activity was increased above normal, but low, 2n cells predominated; at 3 days, when mitotic rate was maximal, equal numbers of 2n and >2n cells were observed; and at 4-5 days, when mitotic rate dropped, the >2n cells were most evident. Culturing the hypertrophic cells (14 days of IPR treatment) produced only 2n cells. Measurements of nuclei of the enlarged cells, estimations of DNA content by visual examination, and the occurrence of polyploid cells in definite ratios with time all suggest the existence of polyploid nuclei in the enlarged glands.