Ontogeny of glucagon and isoproterenol induced cyclic 3'-5' adenosine monophosphate production in adipocytes isolated from the inguinal adipose tissue of developing rats.

To investigate any differences that might exist between the maturation of receptors coupled to the cyclic-AMP system, the effects of glucagon and isoproterenol (specific beta-adrenergic agonist) on the stimulation of cyclic-AMP production in adipocytes and stromal cells isolated from 3, 10 and 24 days-old rats were studied. In the presence of 0.5 mM 3-isobutyl-1-methylxanthine and at a cell concentration of approximately 5 X 10(5) cells/ml, the cyclic-AMP accumulation produced by 100 microM isoproterenol in the stromal vascular cells represented a two-fold and a four-fold increase above basal at 3 days and 24 days respectively, after 10 min incubation at 37 degrees C. In the same conditions, at a cell concentration of 1.7 X 10(5) cells/ml, the increase of cyclic-AMP concentration was maximum in the mature adipocytes after 10 min incubation and represented a 12-fold increase above basal values at all ages. In the latter cells, a striking difference was observed in the level of cyclic-AMP concentrations, induced by maximal doses of glucagon (0.3 microM), according to age. Indeed, at 24 days, the values of glucagon-stimulated cyclic-AMP concentrations, as well as the ratio of stimulated to basal values, was significantly higher than at 3 or 10 days. After 5 min incubation, this increase was two-fold for 3 and 10 days. After 5 min incubation, this increase was two-fold for 3 and 10 days old and four-fold for 24 days-old animals. These results suggested that the beta-adrenergic receptors develop very early in life since they are efficient even in the stromal cells, whereas a progressive development of the glucagon-induced effect could be observed during the suckling period in the lipid laden cells.