Binding of 125I-labeled insulin and growth hormone to membranes from liver and hearts of C57BL/6J mice was measured and the data analyzed by the graphical method of Scatchard. Animals were studied at ages 2, 10, 20, and 31 months; preparations from each animal were analyzed individually. There was no significant and progressive age-related difference in either dissociation constant or binding capacity for insulin in heart and liver, or for growth hormone in liver. Variations among individual animals were large; in some cases, the standard deviation exceeded the mean for a particular age group. We conclude that there are no large age related differences in binding of these anabolic hormones to the target tissues studied, and that any small changes would be masked by the large variations among individual animals.

Mice selected genetically for high and low blood pressure (BP) were compared with regard to heart weight and heart/body ratios. Two experiments were performed with mice ranging in age from 1.3 to 9 months and 11 to 23 months respectively. In a third experiment C57BL/6J mice were compared to the high and low BP mice. Heart/body ratios and heart weights, adjusted fo body weight via covariance analysis, were significantly greater for the high BP mice, but no Age x BP Genotype interaction was observed. Results were discussed in terms of a possible relationship between heart weight and BP via genetic linkage or pleiotropy. The possibility was also raised that compensatory mechanisms for high blood pressure, e.g., cardiac hypertrophy, may operate very early in development for animals who are hypertensive by virtue of selective breeding for blood pressure extremes.

Heart weight and heart/body weight ratios were determined for stocks of mice bred from Schlager's high and low blood pressure mice. Results of an analysis in which three different age groups (means = 15, 17, and 28 months) were compared indicated a nonsignificant interaction between age and blood pressure for heart weight and between age and blood pressure for heart/body weight ratios. Heart weight and heart/body weight ratios were significantly higher for the high than for the low BP mice at all ages with one exception; heart weights did not differ between the two lines at mean age 28 months. It was concluded that high blood pressure mice do not exhibit cardiac hypertrophy in the strictest sense of a disproportionately greater increase in heart/body weight ratios across the life span than low blood pressure for this particular stock.

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