| Abstract: | Gastric fundus strips isolated from lactating, non-lactating and pregnant rats were used to obtain agonist-induced contractions in vitro and the mechanism of alteration in gastric contractility to serotonin during lactation was investigated. The gastric contractile responses to 5-HT expressed as area per unit mass of muscle (cm2 g-1 muscle) were 60–65 % greater in lactating rats compared with non-lactating rats. However, responses evoked by acetylcholine (ACh) or histamine were not different. The EC50 values for 5-HT were not different in either group indicating that there was no alteration in the 5-HT affinity for its receptors in lactating rats. In pregnant rats, 5-HT-induced gastric responses were significantly (P < 0.05) lower than those of non-lactating rats. Pre-treatment of non-lactating rats with haloperidol (which increases plasma prolactin levels) enchanced the gastric contractile response to 5-HT (P < 0.05). On the other hand bromocriptine administration (which lowers plasma prolactin levels) in lactating or immature rats, decreased the contractile response to 5-HT significantly, while bath application of bromocriptine (0.1 μM) had no effect. Incubation of fundus strips in physiological solution containing prolactin (10 μg ml-1) for 24 h decreased the 5-HT evoked contractions, but not the ACh evoked responses. The results in this study indicate that prolactin modulates the intrinsic contractile activity of the gastric smooth muscles to 5-HT. |
