Cellularity of adipose depots in six strains of genetically obese mice

Adipocyte cell size and number of three adipose depots, gonadal, subcutaneous, and retroperitoneal, were determined in several strains (aA(y), aA(iy), dbdb, obob, and NZO) of adult genetically obese mice, male and female, and in male gold thioglucose-treated mice. Epididymal pad cellularity was determined during development in yellow and viable yellow obese mice and their lean littermates, as well as in the NCS/R mouse. Cell number in the mouse epididymal pad in both lean and genetically obese animals is determined early in development, i.e., before weaning. Cell enlargement is the consistent and usually dominant morphological explanation for adipose depot enlargement in genetic and in gold thioglucose-induced mouse obesity. In some instances, hyperplasia accompanied the hypertrophy, occurring most often in the subcutaneous depot. Cell number in the subcutaneous pad of the obese-hyperglycemic female is four times that of the lean control and represents the most extreme case of hyperplasia observed. In fact, hyperplasia was consistently seen in the obob mouse. A classification for genetic obesity based primarily upon the cellularity characteristics of the adipose depots is proposed.

Cellularity of adipose depots in the genetically obese Zucker rat

Cell size and number of three adipose depots, epididymal, retroperitoneal, and subcutaneous, were determined during growth of the obese Zucker rat ("fatty") and nonobese Zucker control. Cellularity of these depots in the adult "fatty" was compared with that in nonobese controls and in nonobese Zucker rats made obese by ventromedial hypothalamic lesions. Epididymal and retroperitoneal depots in the nonobese rat grew by cell enlargement and increase in cell number until the 14th wk, when number became fixed; further increase in depot size occurred by cell enlargement. The subcutaneous depot added cells until the 26th wk. In the Zucker "fatty," cell number increased until the 26th wk in all depots, accompanied by extreme cell enlargement. The enlarged adipose depots of the adult Zucker "fatty," when compared with the nonobese control, are the result of both hypertrophy and hyperplasia. Depot enlargement in the lesioned animal is the result of hypertrophy. "Fatties" have more cells in adipose depots than do lesioned rats. Genetic obesity in the Zucker rat is clearly different from the obesity produced by hypothalamic lesioning.

Cellularity of rat adipose tissue: effects of growth, starvation, and obesity

The size, number, and rate of formation of mature adipocytes were studied in the epididymal pads and retroperitoneal adipose depots of the Sprague-Dawley rat. Early growth of these depots was accompanied by progressive enlargement of adipose cells as well as by increases in number. Beyond the 15th wk of life, the depot grew exclusively by the process of cellular enlargement, with no further change in cell number. Severe starvation during the 6th wk of life followed by normal feeding had no lasting effect on cell size or cell number; prolonged semistarvation beginning in the 15th wk greatly reduced cell size while cell number was unaffected. Likewise, extreme increases in depot size produced by hypothalamic lesions did not change cell number, but only cell size. The concept of a fixed number of mature adipocytes in the adult organism may be of central importance in caloric and metabolic equilibrium.

Effect of early nutrition on the development of rat epididymal fat pads: cellularity and metabolism

The effect of infantile nutritional levels on adipose tissue cellularity and metabolism was studied in two groups of Sprague-Dawley rats. Caloric intake was varied during the suckling period by manipulating litter size immediately after birth; however, all animals had free access to food after weaning. The epididymal fat pads of animals raised in small litters were heavier than those of their paired siblings raised in large litters. Initially, the differences in pad weight were accounted for primarily by differences in total cell number; however, at 20 wk both cell number and cell size contributed equally. The rate of glucose incorporation into CO(2) and triglyceride during in vitro incubations was the same for both groups if expressed on a per cell basis; therefore total tissue incorporation was greater in animals with more cells. The results support the hypothesis that early nutritional experiences can effect permanent changes in the cell number and size of the epididymal fat depot and that total cell number is important in the total metabolism of this organ. These findings and the fact that extreme human obesity is accompanied by similar alterations in cellularity and metabolism indicate that early nutritional experiences should be studied further as a guide to the etiology of obesity in man.

Methods for the determination of adipose cell size in man and animals

Four methods for the sizing of adipose cells in small samples of human or animal adipose tissue are compared. These methods depend on the preparation of cell suspensions by incubation of the tissue with collagenase or by prolonged fixation with osmium tetroxide and separation of the fixed cells. A Coulter electronic counter was used to count and size the suspended cells and a Zeiss particle size analyzer for the sizing of cells in photomicrographs. The use of the Coulter counter to count cells in a suspension derived from a known amount of tissue and subjected to osmium tetroxide fixation is recommended for accuracy and general applicability to adipose cells of all sizes in man and animals.