Potentiation of serotonin-induced contractility of gastric fundus strips in lactating rats.
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. Pretreatment of non-lactating rats with haloperidol (which increases plasma prolactin levels) enhanced 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 microM) had no effect. Incubation of fundus strips in physiological solution containing prolactin (10 micrograms 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.
Deshpande
S B
SB
Department of Physiology, Banaras Hindu University, Varanasi, India.
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001971:Bromocriptine / Q000494:pharmacology; D004298:Dopamine / Q000502:physiology; D018492:Dopamine Antagonists; D005260:Female; D005748:Gastric Fundus / Q000187:drug effects*; D006220:Haloperidol / Q000494:pharmacology; D006632:Histamine / Q000494:pharmacology; D066298:In Vitro Techniques; D007774:Lactation / Q000502:physiology*; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects*; D011247:Pregnancy; D011388:Prolactin / Q000494:pharmacology / Q000502:physiology; D051381:Rats; D012701:Serotonin / Q000494:pharmacology*
D018492:Dopamine Antagonists; D012701:Serotonin; D001971:Bromocriptine; D006632:Histamine; D011388:Prolactin; D006220:Haloperidol; D000109:Acetylcholine; D004298:Dopamine