ABSTRACT
~3H-Clonidine, a potent and selective alpha2-adrenergic agonist was used to label alpha2-a-drenoceptors in intact lymphocytes isolated from rat spleen. Binding of ~3H-Clo-nidine was rapid(t1/2: 2min)and readily reversed by 10umol?L~(-1) clonidine(t1/2: 3-4min). ~3H-Clonidine saturationexperiments indicated a single c1ass of site with a K_D of 6.57?1.63nM and Bmax of 72.4?13.4 fmol/10~7 lymphocytes. Adrenergic agonists competed for ~3H-clonidine binding site with anorder of potency:epinephrine)norepinephrine)isoproterenol. These results show the presence ofalpha2-adrenoceptors in splenic lymphocytes. Computer analysis of competition experiments withadrenergic agonists revealed three classes of sites: high affinity site, medium affinity site and lowaffinity site. The affinity of high affinity site is 2-3 orders of magnitude higher than the one ofmedium affinity site, whereas the latter is the same orders higher than low affinity site Using im-proved Mishell-Dutton method, 10umol?L~(-1) clonidine suppressed the Ig M synthesis and thesuppression was blocked by 10 umol?L~(-1) phentolamine. These results indicate the suppression ofIg M antibody response to SRBC in vitro by clonidine is mediated by the alpha-adrenoceptors.
ABSTRACT
The Bmax and Kd of beta-adrenoceptors in splenie lymphocytes of rats were determined by direct binding of radioligand, ~3H-dihydroalpranolol. Bmax of beta-adrenoceptors was significantly increased on day+1, was peak on day+2 and gradually reduced to control values on day+ 6 after the intraperitoneal injection of 5?10~9SRBC. A positive correlation (r=0. 86) was found between the Bmax of beta-adrtenoceptors on day+1 to+3 and the amount of Ig M in s(?)rum after 72 hours. Both the Bmax of beta-adrenoceptors on day+2 and the amount of Ig M in serum on day+5 were reduced by the intraperitoneal injection of propranolol. In study on antibody response to SRBC.in vitro, Ig M Synthesis in mouse spleen cells was enhanced by norepinephrine (10?mol/L), and blocked by propranolol (1?mol/L). These results indicated that: (1) the immune response to SRBC in vivo up-regulates the density of beta-adrenoceptors in splenic lymphocytes; (2) the up-regulation of Bmax of beta-adrenceptors in splenic lymphocytes may increase its Ig M synthesis;(3) the enhancement of the Ig M antibody response to SRBC in vitro by norepinephrine was mediated by the beta-adrenoceptors.