Echocardiographic findings in 103 cats with hyperthyroidism.

Using M-mode echocardiography, cardiac abnormalities were studied in 103 cats with untreated hyperthyroidism. In addition, follow-up echocardiography was performed on 24 of these cats to assess the long-term (4 to 21 months) effect of treatment (thyroidectomy or radioiodine) on thyrotoxic cardiac disease. The most common echocardiographic abnormality in the 103 untreated hyperthyroid cats was hypertrophy of the left ventricular caudal wall (71.9%). Hypertrophy of the interventricular septum also was documented in 39.8% of the 103 cats. Other abnormalities included high values for left atrial diameter (70.0%), aortic root diameter (18.5%), and left ventricular diameter at end diastole (45.6%). In some of these cats, indices of contractility were enhanced; in 21.4% and 14.6% of the cats, values for shortening fraction and velocity of circumferential fiber shortening, respectively, were greater than those values measured in clinically normal cats. After treatment of the hyperthyroidism, left ventricular hypertrophy resolved or improved in many of the cats, as indicated by decreases in left ventricular caudal wall and interventricular septum thicknesses. Hyperdynamic wall motion resolved in all cats after treatment, as evidenced by consistent decreases in shortening fraction and velocity of circumferential fiber shortening. Despite these improvements, some cats had one or more persistently abnormal echocardiographic values after treatment. These results suggested that in cats, hyperthyroidism commonly is associated with largely reversible cardiomyopathy. In those cats in which cardiomyopathy persists or worsens after treatment, underlying primary cardiomyopathy or thyroid hormone-induced cardiac structural damage may exist.

Random partitioning of cytoplasmic organelles at cell division: the effect of organelle and cell volume.

When a cell divides, some cytoplasmic organelles may be partitioned randomly between the daughters. The number of organelles in each daughter is usually calculated from the binomial distribution, which assumes that the organelles occupy zero volume. We developed equations to predict numerical partitioning taking the volume of the organelles and of the cell into account. The effect of large organelle volume is that daughter cells receive equal or nearly equal numbers of organelles more often than predicted by the binomial distribution. However, numerical solutions show that volume effects are very small unless the number of organelles is very small or they occupy more than about 50% of the available cell volume.

Computer simulation of within family selection in finite populations.

The relative efficiency, in terms of selection limits, between mass selection and within family selection was compared by computer simulation methods. A 20-locus additive model was used to simulate a quantitative trait under selection. It was assumed that 50-75 percent of the genetic variance in the base population was controlled by four major genes initially at low frequencies.In populations of size N=100 no loss of major genes was found when either method of selection was used. When N=50 within family selection was generally superior to mass selection but when N=10 the situation was reversed. For N=30 within family selection was more efficient only under high selection intensity or high heritability situations.