Lung tissue guanosine 3',5'-monophosphate: effects of ventilation and anesthesia

In vivo levels of guanosine 3',5'-cyclic monophosphate (cGMP) in rat lung were measured by radioimmunoassay. The basal levels of this agent were found to change depending on the method of killing or anesthesia used. Lowest values were found after microwave irradiation to the head (10.2 fmol/mg wet wt). Values after pentobarbitol anesthesia, with or without atropine, were significantly higher (19-24 fmol/mg). In animals anesthetized with pentobarbital and ventilated at pressures of 7 cmH2O with no end-expiratory pressure, lung cGMP was 42-49 fmol/mg. Ventilation at higher pressures resulted in much higher levels of cGMP (20 cmH2O, 105 fmol/mg; 30 cmH2O, 233 fmol/mg). The response of cGMP to ventilation was not blocked by pretreatment of the animals with atropine. High-pressure ventilation was without effect on lung adenosine 3',5'-cyclic monophosphate.