Adrenocorticotropin receptors in rat adrenal glomerulosa cells

The results presented here demonstrate, for the first time, the presence of ACTH receptors in the zona glomerulosa of adrenal glands. We obtained the surprising result that the glomerulosa cells carry a higher concentration of ACTH receptors than the fasciculata cells. The analog [Phe2,Nle4]ACTH was iodinated by the iodogen method and separated by HPLC; it was obtained carrier-free and has a specific activity of 600 muCi/micrograms, retaining full biological potency. After 30 min of incubation at 22 C for concentrations of 2 X 10(-11) M [125I]ACTH, specific binding values were 4.85 +/- 0.44% (n = 15) and 1.85 +/- 0.18% (n = 15), respectively, for 50,000 glomerulosa or fasciculata cells. For the glomerulosa, our results indicated a density of 6.5 X 10(4), receptors/cell of the high affinity type (Kd1 = 7.6 X 10(-11) M) and 1.0 X 10(6) receptors of the low affinity type (Kd2 = 1.2 X 10(-9) M). In the zona fasciculata, we found 7.2 X 10(3) receptors of high affinity (Kd1 = 1.1 X 10(-11) M) per cell and 6.3 X 10(5) of low affinity (Kd2 = 2.9 X 10(-9) M). The dissociation constant for the high affinity site of the glomerulosa cells was in excellent correlation with the half-maximal stimulation dose of ACTH for aldosterone and corticosterone (Kd1 = 7.6 X 10(-11) M vs. ED50 of 8 X 10(-11) and 3 X 10(-11) M). Results from primary cultures showed a decrease in binding capacity after 1 day in culture and then an increase to the initial value after 3 days in culture.