In vitro studies have shown that estrogen and progesterone can affect the contractile response and myoelectric activity of the gastrointestinal smooth muscle. The present study was designed to investigate the effect of sex steroid hormones on gastric emptying and gastrointestinal transit were assessed in rats 15 min after intragastric instillation of a test meal containing charcoal and 51Cr. Gastric emptying was determined by measuring the amount of labeled chromium contained in the small intestine as a percentage of the initial amount received. Gastrointestinal transit was evaluated by calculating both the geometric center of distribution of the radiolabeled marker and the charcoal transit in the intestine. The experimental animals included diestrus rats; ovariectomized rats treated with vehicle, estradiol, and/or progesterone; and normal male and orchiectomized rats treated with vehicle or testosterone. Female rats in diestrus had a slower gastric emptying and a lesser geometric center value than ovariectomized rats. Estradiol inhibited gastric emptying but did not affect gastrointestinal transit. Progesterone increased gastric emptying. Progesterone at lower dose (10 mg/kg) decreased the geometric center compared with higher doses (20 or 40 mg/kg) or vehicle controls. A mixture of estradiol (10 micrograms/kg) and progesterone (20 mg/kg) inhibited gastric emptying to a similar degree as estradiol (10 micrograms/kg) did. Testosterone had no influence on gastric emptying or gastrointestinal transit. These results suggest that estradiol and a mixture of estradiol and progesterone inhibit, whereas progesterone enhances, gastric emptying. Testosterone did not play a role in gastrointestinal motility.

1 The effect of amphetamine on the secretion of testosterone and the production of testicular adenosine 3':5'-cyclic monophosphate (cyclic AMP) in rats was studied. 2 A single intravenous injection of amphetamine decreased the basal and human chorionic gonadotropin (hCG)-stimulated levels of plasma testosterone. Plasma LH levels were not altered by the injection of amphetamine. 3 Administration of amphetamine in vitro resulted in a dose-dependent inhibition of both basal and hCG-stimulated release of testosterone. 4 Amphetamine enhanced the basal and hCG-increased levels of cyclic AMP accumulation in vitro in rat testes. 5 These results suggest that amphetamine inhibits the spontaneous and hCG-stimulated secretion of testosterone from the testes through a mechanism involving an increase in cyclic AMP production.

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1 The e ect of amphetamine on gastrointestinal (GI) transit and the plasma levels of cholecystokinin (CCK) were studied in male rats. 2 Gastric emptying was inhibited both acutely and chronically by the administration of amphetamine. GI transit was decreased by the acute administration of amphetamine but not a ected by the chronic administration of amphetamine. 3 Plasma CCK levels were increased dose-dependently by amphetamine. 4 Proglumide, a CCK receptor antagonist, prevented amphetamine-induced inhibition of gastric emptying and the decrease in GI transit in male rats. 5 The selective CCK A receptor antagonist, lorglumide, dose-dependently attenuated the amphetamineinduced inhibition of gastric emptying in male rats. In contrast, the selective CCK B receptor antagonist, PD 135,158, did not reverse the e ect of amphetamine on gastric emptying. 6 Both lorglumide and PD 135,158 reversed the inhibitory e ect of amphetamine on GI transit in male rats. 7 These results suggest that amphetamine-induced inhibition of gastric emptying and intestinal transit is due in part to a mechanism associated with the hypersecretion of endogenous CCK.