Biphasic effects of chronic saccharin intake on pain responses of healthy and diabetic rats of two genetically selected strains.
Rats of the LC-2-HI strain, selected for high rates of self-stimulation, were supplied with a 3 mM saccharin solution. Within 1 week they developed markedly prolonged latencies to painful stimuli on a hot-plate. In contrast, a similar effect became manifest in LC-2-LO rats only after 3 weeks. Both strains of rats were made diabetic by injection of streptozotocin. LO rats showed more polydipsia and hyperglycemia than HI rats and, when drinking saccharin solution, developed cross-tolerance to morphine within about 2 weeks. It is assumed that saccharin consumption stimulates the release of endogenous opioid peptides, probably via stimulation of gustatory sweet receptors. The opioid peptides exert a biphasic effect: initially they raise the pain threshold, but at a later stage they cause chronic cross-tolerance to morphine.
D000698:Analgesia; D000818:Animals; D003921:Diabetes Mellitus, Experimental / Q000503:physiopathology*; D004361:Drug Tolerance; D005260:Female; D009020:Morphine / Q000494:pharmacology; D010146:Pain / Q000503:physiopathology*; D051381:Rats; D012439:Saccharin / Q000008:administration & dosage*; D012684:Sensory Thresholds / Q000187:drug effects; D013311:Streptozocin; D013997:Time Factors
D013311:Streptozocin; D009020:Morphine; D012439:Saccharin