ACTH receptors in nervous tissue. High affinity binding–sequestration of [¹²⁵I][Phe²,Nle⁴]ACTH 1–24 in homogenates and slices from rat brain

Abstract

We have demonstrated specific, high affinity binding of a biologically active Tyr23-monoiodinated derivative of ACTH, [125I][Phe2,Nle4]ACTH 1-24, in rat brain homogenates. Similarly, in metabolically inhibited and noninhibited rat whole brain slices there is a specific "binding-sequestration" process that is dependent on time, protein concentration, and pH. In homogenates, binding curves were best described by a two-site model and provided the following parameters: Kd1 = 0.65 +/- 0.47 nM, Bmax1 = 21 +/- 41 fmol/mg protein; Kd2 = 97 +/- 48 nM, Bmax2 = 3.5 +/- 1.8 pmol/mg protein. In metabolically viable brain slices, concentration-competition curves of [125I][Phe2,Nle4]ACTH 1-24 binding-sequestration can be described by three components (Kd1 = 14 +/- 24 nM, Bmax1 = 50 +/- 95 fmol/mg protein; Kd2 = 2.4 +/- 1.9 microM, Bmax2 = 44 +/- 49 pmol/mg protein; Kd3 = 0.16 +/- 1.0 mM, Bmax3 = 5.3 +/- 54 nmol/mg protein). Metabolic inhibition, by removal of glucose and addition of 100 microM ouabain, abolishes the lowest affinity, highest capacity binding-sequestrian component only (Kd1 = 7.1 +/- 14 nM, Bmax1 = 8.7 +/- 16 fmol/mg protein; Kd2 = 7.4 +/- 4.49 microM, Bmax2 = 37 +/- 27 pmol/mg protein). The two binding-sequestration parameter estimates obtained from metabolically inhibited tissue slices are not significantly different from those of the two higher affinity components obtained with noninhibited tissue. Thus, metabolic inhibition permits demonstration of ACTH receptor binding only, unconfounded by sequestration or internalization of ligand:receptor complexes.(ABSTRACT TRUNCATED AT 250 WORDS)

B‐50 (GAP‐43): Biochemistry and Functional Neurochemistry of a Neuron‐Specific Phosphoprotein

“…The discrepancies in the CD spectroscopy (plus detergent; Masure et al, 1986) and the NMR data (minus detergent, would support this suggestion. It is too early to say if these findings point to a role for B-I101 50 in non-receptor-mediated signal transduction for centrally acting ACTH and ACTH-related peptides, and there is one report (Hnatowich et al, 1989) of high-affinity binding of [ 1251]Phe2,Nle4-ACTH1-24 (but not native ACTH) to rat brain membranes, which suggests otherwise.…”

Identification of a receptor for gamma melanotropin and other proopiomelanocortin peptides in the hypothalamus and limbic system.

“…Thus far, MSH-R and ACTH-R mRNA expression has only been detected in melanocytes and in the adrenal cortex, respectively. Although specific high-affinity MSH and ACTH binding has been reported in brain, with highest levels in the hypothalamus (12,13), no MSH-R or ACTH-R mRNA was detected in the brain by either Northern hybridization or in situ hybridization (14,15). Additionally, melanocortin binding and biological action in the brain display pharmacological profiles that do not match those of either the adrenal The publication costs of this article were defrayed in part by page charge payment.…”

Characterisation of the Melanocortin 4 Receptor by Radioligand Binding

“…a-MSH, (melanocyte stimulating hormone) P-MSH, y-MSH and ACTH (adrenocorticotrophic hormone). Melanocortic peptides binds to specific sites in the brain (Hnatowich et al 1989;Tatro 1990;Lichtensteiger et al 1993) and their central administration influence many systems such as e.g. thermoregulation (Feng et al 1987), behaviour (Garrud et al 1974), and neuroendocrine systems (Wiegant et al 1979).…”