Abnormal phosphoinositide turnover in schizophrenia.

IO the Editor: We read with h,terest the recent article by Kaiya et al (26: 669-676; 1989), documenting abnormal phosphoinositide (PI) turnover in schizophrenia. The authors noted increased P! turnover and accumulation of diacylglycerol (DC_,) m plateiets of a subgroup of acute schizophrenic patients, and observed that patients with abno.,'mat PI turnover had a significantly better outcome than other acute schizophrenic p~tients. The authors further observed that this abnormality was unrelated to neuroieptic treatment or stress, and appeared to be related to the pathophysiology of ~e psychotic state. According to the authors, DG is a secondary messenger but they did not elaborate on possible neurotransmitters that this finding may implicate in the pathophysiology of schizophrenia. Several neurotransmitters act via the PI system by increasing phospholipase C (Baraban et al 1989), thereby generating DG and inositol triphosphate. If there is a parallelism between the platelet and brain with regard to the increased phosphoinositide tumo~'er and DG production in schizophrenic patients, this finding would suggest that the activity of any one of these various neurotransmitters (that act by increasing phospholipase C) may be increased in schizophrenia. Acetyicholine (M-1 muscarinic) and serotonin are two candidates, as both act via the pho~pholipase secondary messenger system (Baraban et al 1989). Increased 5HT-2 activity has been impiicated in the pathophysiology of schizophrenia (Meibach 1989). Recently, increased muscarinic (M-1) activity has been reported in the psychotic phase of schizophrenic illness (Berger et al 1989; Tandon and Greden 1989). It is suggested that dopamine (DA)/acetylcholine (ACh) balance is important in schizophrenia and that ACh activity increases as a homeostatic response in an effort to maintain this balance in the face of increasing DA activity that occurs in the psychotic phase (Tandon and Greden 1989). This increased muscarinic M1 activity may be reflected in increased PI turnover and DG accumulation, as the M-I receptors use the PI system a~ a secondary messenger. Furthe.qnore, the increase in muscarinic activity would be associated with a better outcome as it would reflect a homeostatic cesponse. If DG accumulation is indicative of incree~_¢d muscarinic activity, it would be associated with a better outcome, as observed by the authors in this study. This interpretation is admittedly speculative and alternative e:~planations are possible; however, it is consistent with current knowledge and provides an explanation for the occurrence of DG accumulation and atmo,.-maJ FI tm~aover, and t_h~ e,s~ociation of'.his finding with good outcome in schizophrenia.