Adrenocorticotropin Receptors in Rat Adrenal Glomerulosa Cells*

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Abstract
The presence of ACTH receptors in the zona glomerulosa of adrenal glands was demonstrated. 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 high performance liquid chromatography; it was obtained carrier-free and has a specific activity of 600 .mu.Ci/.mu.g, retaining full biological potency. After 30 min of incubation at 22.degree. C for concentrations of 2 .times. 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, a density of 6.5 .times. 104, receptors/cell of the high affinity type (Kd1 = 7.6 .times. 10-11 M) and 1.0 .times. 106 receptors of the low affinity type (Kd2 = 1.2 .times. 10-9 M) was indicated. In the zona fasciculata, 7.2 .times. 103 receptors of high affinity (Kd1 = 1.1 .times. 10-11 M) per cell and 6.3 .times. 105 of low affinity (Kd2 = 2.9 .times. 10-9 M) were found. 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 .times. 10-11 M vs. ED50 of 8 .times. 10-11 and 3 .times. 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.