Relaxant Effect of Adrenomedullin on Bovine Isolated Iris Sphincter Muscle Under Resting Conditions

Abstract

1. The mechanisms involved in the fine adjustment of iris sphincter muscle tone are largely unknown. The aim of the present study was to clarify the effects of adrenomedullin on the resting tension of the bovine isolated iris sphincter muscle. 2. The motor activity of the bovine isolated iris sphincter muscle was measured isometrically. The effects of adrenomedullin on resting tension were analysed in the presence of indomethacin. The presence of adrenomedullin mRNA in the preparation was determined by reverse transcription-polymerase chain reaction. Immunolabelling for adrenomedullin was also performed. 3. Adrenomedullin significantly decreased the resting tension of the muscle. The relaxant effect of adrenomedullin was significantly inhibited by adrenomedullin (22-52), a putative antagonist for the adrenomedullin receptor, or calcitonin gene-related peptide (CGRP) (8-37), a putative antagonist for the CGRP1 receptor. The relaxant effect was almost completely blocked by a combination of adrenomedullin (22-52) and CGRP (8-37). 4. The relaxant effect of adrenomedullin was also significantly diminished by 2',5'-dideoxyadenosine, an inhibitor of adenylate cyclase, N(G)-nitro-L-arginine, an inhibitor of nitric oxide synthesis, or 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, an inhibitor of soluble guanylate cyclase. 5. Reverse transcription-polymerase chain reaction analysis showed that adrenomedullin mRNA was expressed in the muscle strip. Immunopositive staining for adrenomedullin was detected in blood vessel cells and in the iris sphincter muscle cells. 6. These results suggest that adrenomedullin may be an autocrine and paracrine regulator of the resting tension of the iris sphincter muscle. Its biological effects may be due to the direct involvement of adrenomedullin receptors and also to the stimulation of CGRP1 receptors. The stimulation of these receptors by the peptide leads to the activation of adenylate cyclase and soluble guanylate cyclase and subsequent relaxation of the muscle strip.

Transgenic mice with ocular overexpression of an adrenomedullin receptor reflect human acute angle-closure glaucoma

“…PCR products representing the transgene had a predicted size of 880 bp ( Figure 1B). CLR SMαA × AM −/+ mice were obtained by mating hemizygote CLR SMαA mice with hemizygote AM-knockout animals [19]. Offspring with the AM +/+ or AM −/+ genotype were identified by PCR analysis of tail biopsy DNA with AM genespecific forward (5 -GGCTCCTTAAGTTGCGCA-3 ) and reverse (5 -ACGTAGAAGAACTTATTAAAC-CGCA-3 ) primers.…”

“…Furthermore, AM-induced cAMP production has been observed in the iris sphincter muscle from different mammalian species including humans [17,18]. In the cat, AM dosedependently inhibited carbachol-induced contraction of the isolated sphincter muscle, and the resting tension of the isolated bovine iris sphincter was transiently decreased by AM [18,19]. This indicates that the pupillary sphincter is a target of ocular AM.…”

Rho-Kinase, but not Protein Kinase C, is Involved in Generation of the Spontaneous Tone in the Resting Phase of the Isolated Pig Iris Sphincter Muscle

“…The prepared strips were suspended vertically in an organ bath containing 10 ml Krebs-Henseleit solution continuously aerated with 95% O 2 plus 5% CO 2 . The temperature of the bath was maintained at 37.0 • C ± 0.5 • C. 18 …”

“…A resting tension of 100 mg was applied to the prepared strips and maintained throughout the experiment. 18 An equilibration period of 90 min was allowed before the experiments were started. The effect of Y27632 (1 µmol/L or 10 µmol/L), a Rho-kinase inhibitor, on the carbacholinduced (from 10 nmol/L to 10 µmol/L) contraction of the isolated pig iris sphincter muscle was examined.…”