Ontogenetic studies on adrenergic lipolysis in rat adipocytes from subcutaneous adipose tissue

The in vitro release of free fatty acids from small adipocytes (mean diameter 24.4 +/- 0.4 micrometer; 11-42 micrometer) isolated from subcutaneous adipose tissue of rats aged 5, 14, 21 and 35 days was induced by l-isoprenaline (ISO), l-noradrenaline (NA) or l-adrenaline (ADR). The results were related to a cell count of 10(6) and compared to results in adult rats [both sexes, fed ad libitum, mean weight 180-210 g). The cell yield decreased with development, i.e. it was highest in the youngest rats. In adult rats, increasing catecholamine (CA) concentrations produced pronounced concentration-dependent lipolysis in the potency order ISO greater than NA greater than ADR which is typical of beta 1-adrenergic functions. Qualitatively the same results in 5- and 35-day-old rats were observed, the latter showing greater sensitivity towards CA. Practically no lipolytic response was recorded in 14 and 21-day-old animals, however. Not one of the CA, nor any of the concentrations used, could evoke lipolysis in these animals. The experiments were carried out simultaneously on different age groups, technical errors can therefore be excluded.