In vitro contractile responses of the uterus from 'restricted diet' rats to adrenoceptor agonists. Influence of cyclo-oxygenase inhibitors.

The experiments concerned the effects of 15 days of restricted diet (50% of the normal food intake) on the magnitude of phasic contractions (Isometric Developed Tension, IDT) of uterine horns isolated from estrous rats. During 60 min following isolation, the IDT of normally fed controls diminished significantly whereas preparations from animals on the restricted diet had a better contractile constancy. This improved motility was prevented by blockers of prostaglandin (PG) synthesis as well as by return to a normal diet. Cumulative dose-response curves for isoproterenol, norepinephrine and methoxamine were made for the different groups. Isoproterenol and norepinephrine evoked a dose-dependent inhibition of IDT. This response was significantly shifted to the right with uteri from restricted diet animals. Following incubation with propranolol, norepinephrine stimulated the magnitude of contractions significantly more in uterine horns from restricted diet rats than in those from controls. The dose-response curve showing the enhancement of motility induced by methoxamine was displaced to the left in preparations from animals on a restricted diet. This shift was abolished by restoring the normal diet as well as by the presence in vitro of indomethacin or acetylsalicylic acid. The results suggest that tissue PGS, the prevalence of alpha-adrenoceptor mechanisms and the reduction of beta-ones, are involved in the contractile behavior of the uterus isolated from restricted diet rats.