Glucose and scyllo‐inositol impair phosphoinositide hydrolysis in the 10.5‐day cultured rat conceptus: A role in dysmorphogenesis?

Culture of the postimplantation rat conceptus from gestational day 9.5–10.5 in media supplemented with d‐glucose or scyllo‐inositol decreases tissue myo‐inositol and phosphoinositides with a concomitant increase in dysmorphogenesis. A number of mitogenic agents initiate cellular proliferation and differentiation through receptors coupled to phosphoinositide hydrolysis. To test whether the decrease in conceptus phosphoinositides is associated with a reduced phosphoinositide hydrolytic response, we developed a protocol to stimulate phosphoinositide hydrolysis. Phosphoinositide hydrolysis was monitored by measurement of [³H]inositol phosphates after preincubation in serum free media. We examined the ability of serum, platelet‐derived growth factor (PDGF), epidermal‐derived growth factor (EGF), insulin‐like growth factor 1 (IGF‐1), insulin like growth factor 2 (IGF‐2), endothelin‐1 (ET‐1), and endothelin‐2 (ET‐2), to stimulate phosphoinositide hydrolysis. As measured by [³H]inositol monophosphate ([³H]InsP₁) accumulation, normal rat serum, ET‐1, and ET‐2 stimulated phosphoinositide hydrolysis 47%, 420%, and 154% above the basal rate observed in serum free controls. EGF stimulated a statistically insignificant 15% increase while PDGF, IGF‐1, or IGF‐2 were without effect. We further characterized ET‐1 stimulated phosphoinositide hydrolysis. Dose‐response studies disclosed that incremental increases in [³H]InsP₁ (129–420%) are observed over a concentration range of 10–1,000 nM. Maximal stimulation was not reached even at 1,000 nM. Temporally [³H]InsP₁ and [³H]InsP₃ levels increased linearly during incubation periods of 15‐60 min. We further analyzed ET‐1 stimulated phosphoinositide hydrolysis in 10.5‐day conceptuses cultured for 24 hr in media containing high concentrations of glucose (23.3‐56.6 mM) or scyllo‐inositol (0.55, 5.5 mM). Under these dysmorphogenic conditions that concomitantly decrease the phosphoinositide precursor pool the response to ET‐1 was blunted 28–76% for glucose and 29–65% for scyllo‐inositol. This suggests that the effect of glucose and scyllo‐inositol on lowering phosphoinositide precursor pools also results in a decrease in the response to agonists using the inositol/lipid intracellular pathway. This impaired signaling response may contribute to initiating dysmorphogenic events in diabetic embryopathy. © 1993 Wiley‐Liss, Inc.