Pharmacological evidence for the contribution of polyamines as mediators of the transcriptional component involved in smooth muscle relaxation elicited by forskolin.
To study whether cAMP-dependent transcriptional effect and polyamines might play a modulatory role on smooth muscle, the effect of forskolin on KCl (60 mM)-induced contractions in isolated rat uterus and its modification by inhibitors of cAMP-dependent protein kinase (PKA) (Rp-cAMPS and TPCK), transcription (actinomycin D), protein synthesis (cycloheximide) and ornithine decarboxylase (alpha-difluoromethyl-ornithine, DFMO), and a polyamine (spermine) have been assayed. Forskolin (0.1 to 6 microM) induced concentration-dependent relaxation on KCl-induced tonic contractions in rat uterus (IC50: 0.55 +/- 0.12 microM) which was antagonized (p<0.05) by Rp-cAMPS (30 microM), TPCK (3 microM), cycloheximide (300 microM), actinomycin D (4 and 12 microM) and TPCK (3 microM) plus actinomycin D (12 microM). The IC50 values of forskolin in the presence of these drugs were 3.75 +/- 1.53 microM, 12.08 +/- 8.18 microM, 6.88 +/- 5.02 microM, 3.80 +/- 2.35 and 5.31 +/- 2.80 microM, and 4.26 +/- 3.65 microM respectively. Furthermore, DFMO (10 mM) also shifted the relaxation curve to forskolin to the right (IC50: 3.06 +/- 2.66 microM, p<0.05) but DFMO (10 mM) plus actinomycin D (12 microM) (IC50: 1.78 +/- 1.33 microM) did not. However, DFMO (10 mM) and actinomycin D (12 microM) did not antagonize the spermine (1-30 mM)-elicited relaxation (IC50s: 7.8 +/- 0.7 mM vs 7.28 +/- 1.4 mM and 4.67 +/- 0.44 mM in the presence of DFMO and actinomycin D, respectively). Moreover, spermine (1 mM) did not decrease the forskolin induced relaxation and counteracted the antagonism produced by actinomycin D and DFMO. Our results suggest that, in rat uterus, forskolin: a) produced cAMP-dependent relaxation, as this is antagonized by Rp-cAMP and TPCK, and b) increased the activity of ornithine decarboxylase, as this is inhibited by DFMO. Therefore, polyamines could be the mediator of the cAMP-dependent transcriptional component involved in forskolin relaxation, since, as mentioned, DFMO antagonized this relaxation and spermine counteracted the displacement produced by DFMO and actinomycin D. Thus, a plasma membrane-nucleus interaction might, at least partially, explain the mechanisms involved in forskolin induced relaxation in smooth muscle of rat uterus under the present experimental conditions.
Revuelta
M P
MP
Laboratorio de Farmacología, Dpto Medicina, Facultad de Medicina, Universidad de Oviedo, Spain.
Cantabrana
B
B
Hidalgo
A
A
D000818:Animals; D005576:Colforsin / Q000494:pharmacology*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors; D003513:Cycloheximide / Q000494:pharmacology; D003609:Dactinomycin / Q000494:pharmacology; D000518:Eflornithine / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D066298:In Vitro Techniques; D009126:Muscle Relaxation / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects* / Q000502:physiology; D065108:Ornithine Decarboxylase Inhibitors; D011073:Polyamines / Q000494:pharmacology*; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D014158:Transcription, Genetic / Q000187:drug effects*
D004791:Enzyme Inhibitors; D065108:Ornithine Decarboxylase Inhibitors; D011073:Polyamines; D011500:Protein Synthesis Inhibitors; D003609:Dactinomycin; D005576:Colforsin; D003513:Cycloheximide; D017868:Cyclic AMP-Dependent Protein Kinases; D000518:Eflornithine