Serotonin via 5-HT(1B) and 5-HT(2B) Receptors Stimulates Anion Secretion in the Rat Epididymal Epithelium

1. The short-circuit current (I(sc)) technique was used to study the role of 5-hydroxytryptamine (5-HT) in the regulation of anion secretion in cultured rat cauda epididymal epithelia. 2. 5-HT, the 5-HT(1B)-selective agonist 5-nonyloxytryptamine (5-NOT) and the 5-HT(2B)-selective agonist α-methyl-5-hydroxytryptamine (α-methyl-5-HT) added basolaterally stimulated I(sc) in a dose-dependent manner with EC50 values of 0.4, 20 and 0.3 μM, respectively. No other agonists for 5-HT receptors had any effect. 3. The pattern of responses to 5-HT was biphasic. Pretreating the tissues with 5-HT(1B)-selective antagonist isamoltane (200 μM) and the 5-HT(2B)-selective antagonist rauwolscine (200 μM) inhibited the rapid transient phase by 55 and 45%, whereas the sustained phase could only be blocked by rauwolscine. 4. Removal of chloride or bicarbonate or both from the normal Krebs-Henseleit solution reduced the response to 5-HT, 5-NOT and α-methyl-5-HT to varying degrees. The results suggest that 5-HT(1B)- and 5-HT(2B)-mediated responses were mainly due to chloride and bicarbonate secretion, respectively. 5. Manipulation of the cAMP and Ca2+ signal transduction pathways with chemical agents provided evidence that the responses to 5-HT were mediated through cAMP. Piroxicam pretreatment abolished the I(sc) response to α-methyl-5-HT but not to 5-NOT, indicating that the 5-HT(2B)-mediated response, but not the 5-HT(1B)-mediated response, is dependent on prostaglandin synthesis. 7. Immunohistochemical studies showed that 5-HT-like immunoreactivity was detected in nerve fibres and in small granular cells surrounding the epididymal tubules. 8. It is suggested that the 5-HT released from serotonergic nerve endings and/or from mast cells regulates electrolyte and fluid secretion in the epididymis