Rp Diastereomeric Analogs of cAMP Inhibit both cAMP- and cGMP-lnduced Dilation of Hamster Mesenteric Small Arteries

Abstract

Cross talk between the adenosine (3’,5’-cyclic monophosphate) (cAMP) and the guanosine (3’,5’-cyclic monophosphate) (cGMP) signalling pathways in vascular smooth muscle may occur such that cAMP may act through cGMP-dependent protein kinase rather than cAMP-dependent protein kinase to induce relaxation of this tissue. Therefore, it was hypothesized that due to this crosstalk, competitive antagonists of cAMP may not show much selectivity in inhibition of cAMP- or cGMP-induced vasodilation. To test this hypothesis, the effects of Rp-diastereomeric phosphorothioate derivatives of cAMP, putative competitive antagonists of cAMP at cAMP-dependent protein kinase, were assessed on vasodilation induced by Sp-phosphorothioate derivatives of cAMP, dibutyryl cAMP, 8-Br cGMP and sodium nitroprusside. Hamster mesenteric arteries (200–400 µm i.d.) were cannulated and pressurized to 75 mm Hg and constricted to ∼50% of maximum with 1 µmol/l phenylephrine. Vasodilators were then added in cumulative fashion and diameter responses recorded in the absence and presence of (Rp)-adenosine (3’,5’-cyclic monophos-phorothioate) (Rp cAMPs) or (Rp)-8-(parachlorophenylthio) adenosine (3’,5’-cyclic monophosphorothioate) (Rp 8CPT cAMPs). Rp cAMPs (0.1-0.5 mmol/l) inhibited dilations induced by the cAMP agonists, (Sp)-adenosine (3’,5’-cyclic monophosphorothioate) (Sp cAMPs) and dibutyryl cAMP, but also inhibited dilations induced by 8-Br cGMP and sodium nitroprusside (p < 0.05 and n > 4 for all). In a more detailed study we found that Rp 8CPT cAMPs (0.025-0.25 mmol/l) competitively inhibited dilations induced by both Sp 8CPT cAMPs and 8-BR cGMP with equal potency: the pA₂ for Rp8 CPT cAMPs against Sp 8CPT cAMPs (3.6 ± 1.2) was similar to the pA₂ for Rp 8CPT cAMPs against 8-Br cGMP (4.1 ± 1.2) (p > 0.05, d.f. = 37). These data support the hypothesis that both cAMP and cGMP act through a common protein kinase to cause vasodilation and urge caution in the use of Rp-diastereomeric analogs of cyclic nucleotides to dissect out specific signal transduction pathways in blood vessels.

Acute impairment of contractile responses by 17β‐estradiol is cAMP and protein kinase G dependent in vascular smooth muscle cells of the porcine coronary arteries

“…Rp‐8‐Br‐cAMPS competes for the cAMPS binding domain on PKA. However, binding of Rp‐8‐Br‐cAMPS results in the ‘locking’ of the regulatory subunit to the catalytic subunit (Jackson, 1996). KT5720 is a staurosporine‐like compound that binds to the ATP binding of the catalytic subunit of PKA (Spicuzza et al ., 2001), inhibiting the catalysis of its phosphorylation of target proteins.…”

Investigation of the interaction between nitric oxide and vasoactive intestinal polypeptide in the guinea‐pig gastric fundus

“…As (R) ‐p‐cAMPS has also been shown to inhibit protein kinase G (Boese et al ., 1996), an alternative possibility is that cyclic AMP acts through protein kinase G, that in turn could activate iNOS assuring a positive feedback loop. Several reports suggest that cyclic AMP may act through protein kinase G to induce smooth muscle relaxation (Jiang et al ., 1992; Boese et al ., 1996; Jackson, 1996).…”

Involvement of cAMP and β‐adrenoceptors in the relaxing effect elicited by flavonoids on rat uterine smooth muscle

“…At the concentrations assayed, Rp-CAMPS inhibits the smooth muscle relaxation elicited by drugs that increase cAMP in rat uterus and vascular smooth muscle (Jackson, 1996;Rodriguez, Garcia de Boto & Hidalgo, 1996;Ptrez-Vallina, Revuelta, Cantabrana & Hidalgo, 1997). Our results suggest the involvement of cAMP in the relaxation elicited by papaverine as occurring in other systems (Salaices, de Gregorio & Martin, 1985;Leroy, Cedrin, Breuiller, Giovagrandi & Ferre, 1989;Murray, 1990).…”