No abstract

Specific binding sites for calcitonin gene-related peptide (CGRP) were demonstrated in the rat heart and spleen. Autoradiography revealed rat [125I]iodo CGRP binding associated with the intima and media of the aorta, the coronary arteries and the heart valves, and the red pulp of the spleen. Half-maximal inhibition of rat [125I]iodo-CGRP binding to membranes of the rat atria and the spleen was obtained with, respectively, 5 and 0.35 nM unlabeled rat CGRP; these values correspond to EC50 values of 3 and 0.14 nM for activation of adenylate cyclase by CGRP. In the isolated, spontaneously beating right atrium, the EC50 values of stimulation of the force and rate of contraction by rat CGRP were 120 and 70 nM, respectively. Rat CGRP caused relaxation of splenic strips, precontracted with noradrenaline; the EC50 was 50 nM. The beta-adrenergic blocking agent metoprolol, while obliterating the increase in the force and rate of contraction evoked by noradrenaline in the right atrium, did not significantly change the action of CGRP. Similarly, preserved action of CGRP in the presence of indomethacin as well as mepyramine and cimetidine argues against a role of prostaglandins or histamine in the functional responses of CGRP. Much like CGRP, capsaicin, which releases mediators from sensory neurons, caused stimulation of the force and rate of contraction of the isolated right rat atrium. After tachyphylaxis to CGRP, the response to noradrenaline was intact, while the positive chronotropic and inotropic effects of capsaicin were suppressed. The results indicate that the cardiac effects of capsaicin may be due to the release of endogenous CGRP through a local mode of action.

Binding sites for synthetic human 1251-labeled calcitonin gene-related peptide (125I-CGRP) have been demonstrated in membranes of the human nervous system. Binding was high in the cerebellar cortex (1.35 ± 0.27 fmol/mg of tissue; mean ± SEM), spinal cord (1.06 ± 0.27 to 1.27 ± 0.23 fmol/mg), and nucleus dentatus (1.02 ± 0.15 fmol/mg), intermediate in the inferior colliculus (0.80 ± 0.14 fmol/mg) and substantia nigra (0.75 ± 0.14 fmol/mg), low in the neocortex, globus pallidus, nucleus caudatus, hippocampus, amygdala, superior colliculus, thalamus, and hypothalamus (0.15-0.32 fmol/mg), and negligible in spinal and sympathetic ganglia and pituitary (<0.04 fmol/mg). Autoradiography showed distinct 1251-CGRP binding over the molecular and Purkinje cell layers of the cerebellar cortex and over the substantia gelatinosa posterior of the spinal cord. The highest levels of CGRP-like components were recognized in the dorsal part of the spinal cord and the pituitary gland. In the ventral part of the spinal cord as well as in the pituitary and thyroid glands, CGRP values were higher when measured by radioreceptorassay as compared to RIA, indicating that at least two CGRP-like components are present. The predominant CGRPlike peak on HPLC had the retention time of synthetic human CGRP. Immunohistochemistry revealed the presence of a dense plexus of CGRP immunoreactive nerve fibers in the dorsal horn of the spinal cord.The existence of rat and human calcitonin gene-related peptide (CGRP) has been predicted by analysis of the nucleotide sequence of the calcitonin gene (1, 2). CGRP is a unique 37 amino acid peptide that shares greater structural homology with salmon calcitonin-(1-32) than with rat and human calcitonin-(1-32) (1-3). Expression of CGRP was shown immunohistochemically and by specific RIA in combination with gelpermeation chromatography and HPLC in the nervous system and in the pituitary and thyroid glands (4-6). The amino acid sequence was derived from human medullary carcinoma of the thyroid (7).Here we report distinct regional distribution of CGRP and calcitonin (CT) binding sites in the human central nervous system. The presence of endogenous CGRP-like components in the nervous system, pituitary, and thyroid was revealed by a radioreceptorassay (RRA) using human cerebellar membranes, by RIA, and by immunohistochemistry. MATERIALS AND METHODSTissues and Peptides. Tissue obtained at autopsy within 20 hr postmortem was frozen on dry ice and stored at -80°C for a maximum of 3 wk. Patients with malignant tumors, chronic renal insufficiency, or metabolic bone disease were excluded from the study.Synthetic salmon CT-( Receptor Binding Studies. Membranes were prepared and incubated as described (8, 9) with 17,000 dpm (1 dpm = 16.7 mBq) of human 125I-labeled CGRP (125I-CGRP) Ci/mmol) or salmon 125I-labeled CT (125I-CT) Ci/mmol). Specific binding was defined as total binding minus binding in the presence of 0.7 ,uM unlabeled human CGRP or salmon CT, respectively. A RRA for CGRP was developed using membranes fro...

Immunoreactive calcitonin (CT), indistinguishable from human CT-(1-32) and its sulfoxide, has been identified in extracts of the hypothalamus, the pituitary, and the thyroid obtained from human subjects at autopsy. CT concentrations were highest in a region encompassing the posterior hypothalamus, the median eminence, and the pituitary; intermediate in the substantia nigra, the anterior hypothalamus, the globus pallidus, and the inferior colliculus; and low in the caudate nucleus, the hippocampus, the amygdala, and the cerebral and cerebellar cortices. Specific CT binding measured with "MI-labeled salmon CT was high-