Adipocyte responsiveness to norepinephrine in spontaneously hypertensive rats

The present study describes the effect of norepinephrine on lipolysis and adenylate cyclase activity in adipocytes from Wistar-Kyoto (WKY) and spontaneously hypertensive (SH) rats. The adipocytes were incubated in the presence of norepinephrine (10(-7) to 10(-4) mol/L) and the lipolytic activity was measured according to the accumulation of glycerol after one hour incubation. The results showed that norepinephrine induced a lower lipolytic activity in adipocytes from SH rats. cAMP-phosphodiesterase activities in adipocyte homogenates from WKY and SH rats were the same for both preparations. The effect of norepinephrine (10(-7) to 10(-4) mol/L) on adenylate cyclase activity in fat cell membranes from SH rats was decreased compared with WKY fat cell membranes. Adenylate cyclase activities in the presence of 10 mmol/L NaF were the same in both preparations. beta-receptor characteristics were examined, and the data demonstrate a statistically significant decrease in beta-receptor density in fat cell membranes from SH rats. The dissociation constants (Kd) were the same for WKY and SH preparations. This article suggests that adipocyte responsiveness to norepinephrine is decreased in SH rats. The decreased response to norepinephrine may be explained by a lower beta-receptor density in fat cell membranes from SH rats.