Modulation of the three -adrenergic receptor subtypes (1&ARs) by Insulin was investigated in mouse 3T3-F442A adipocytes. Saturation and competition experiments measuring binding of 12I-abeled (-)-cyanopindolol to adipocyte membranes demonstrated that cell exposure to insulin for 4 days caused a 3.5-fold decrease in the density of the major P-AR component of the adipocyte, the #3-AR, while 1i-AR sites remained unchanged and P2-ARs were undetectable. This correlated with a lower potency of the 13-ARselective agonists CGP12177, IC1201651, and BRL37344 in stimulating adenylate cyclase. Northern blotting analysis indicated that insulin induced a rapid and sharp decrease in 13-AR mRNA levels. This effect was detectable at low insulin concentrations (EC5o = 3 nM) and was not observed in the presence of insulin-like growth factor I, sugging an insulin receptormediated phenomenon. Reverse transcriptase-PCR analysis showed that, in contrast to Its dramatic down-regulatory effect on (3-AR mRNA, insulin did not modify the levels of JR,-and SE-AR transcripts. As as d by nuclear run-on assays, insulin inhibited the 13-AR gene transcription rate by 90% within 30 min. mRNA turnover experiments showed that the half-life of P3-AR mRNA was short (90 min) and remained unaffected by insulin. These findings demonstrate the genetic control of a 3-AR subtype expression by insulin and reveal a mechanism for the regulation by this hormone of cAMPdependent biological processes in adipocytes.