Myosin heavy chain isoforms expression and cyclic AMP concentrations in hypoxia-induced hypertrophied right ventricle in rats

Acute hypoxia modifies cAMP levels induced by inhibitors of phosphodiesterase-4 in rat carotid bodies, carotid arteries and superior cervical ganglia

BACKGROUND AND PURPOSE

Phosphodiesterase (PDE) inhibitors are useful to treat hypoxia-related diseases and are used in experiments studying the effects of oxygen on 3'-5'-cyclic adenosine monophosphate (cAMP) production. We studied the effects of acute hypoxia on cAMP accumulation induced by PDE inhibitors in oxygen-specific chemosensors, the carotid bodies (CBs) and in non-chemosensitive CB-related structures: carotid arteries (CAs) and superior cervical ganglia (SCG).

EXPERIMENTAL APPROACH

Concentration-response curves for the effects of a non-specific PDE inhibitor [isobutylmethylxanthine (IBMX) ], PDE4 selective inhibitors (rolipram, Ro 20-1724) and a PDE2 selective inhibitor (erythro-9-(2-hydroxy-3-nonyl)adenine) on cAMP levels were obtained in normoxic (20% O(2)/5% CO(2)) or hypoxic (5% O(2)/5% CO(2)) conditions.

KEY RESULTS

Responses to the PDE inhibitors were compatible with the presence of PDE4 in rat CBs, CAs and SCG but in the absence of PDE2 in CAs and CBs. Acute hypoxia enhanced the effects of IBMX and PDE4 inhibitors on cAMP accumulation in CAs and CBs. In SCG, acute hypoxia reduced cAMP accumulation induced by all the four PDE inhibitors tested. Differences between the effects of Ro 20-1724 and rolipram on cAMP were found in CAs and CBs during hypoxia.

CONCLUSIONS AND IMPLICATIONS

The effects of PDE4 inhibitors could be potentiated or inhibited by acute hypoxia depending on the PDE isoforms of the tissue. The similarities between the characterization of PDE4 inhibitors at the CBs and CAs, under normoxia and hypoxia, did not support a specific role for cAMP in the oxygen-sensing machinery at the CB and suggested that no direct CB-mediated, hyperventilatory, adverse effects would be expected with administration of PDE4 inhibitors.

Hypoxia-induced adaptational shift in MHC-beta isoform expression in rat ventricles

We investigated whether the shift of cardiac myosin heavy chain (MHC) isoform observed during exposure to hypoxia is secondary to hypertrophy, or whether it is directly related to the hypoxic stress. Twelve male Wistar-Kyoto rats, 14 weeks old, were randomly assigned to two groups: sea-level control group (CO) and hypoxia group (HX). The CO group was housed 4 weeks at 1,011 hPa, and the HX group was housed for 4 weeks at 701 hPa. The expression of MHC-beta was significantly increased (600%) in the HX group as compared to the CO group in the right ventricle (p < 0.01). An increased ventricular mass induced by hypoxic exposure was associated with an increased expression of MHC-beta in the right ventricle (p < 0.05). In the left ventricle, the MHC-b expression was significantly increased (295%) in the HX group as compared to the CO group without ventricular hypertrophy (p < 0.01). No differences were observed in the adenylyl cyclase activity or in the phosphodiesterase activities in both ventricles between the CO and HX groups (p > 0.05). Oxidative enzymatic activities (citrate synthase and three-hydroxyacyl-CoA dehydrogenase) were unchanged in both ventricles following 4 weeks of hypoxia (p > 0.05). These findings suggest that, besides cardiac hypertrophy, the hypoxia-induced adaptational change to the MHC-b isoform may be mediated through a specific mechanism related to the stress of hypoxia.