| Popis: |
Serotonin at 10−6M concentration induces an average 12-fold increase in cyclic AMP levels in dorsal abdominal epidermis of fifth-instar larval Rhodnius prolixus. The epidermal serotonin receptor is inhibited by a number of mammalian 5-HT2 receptor antagonists but only α-methyl 5-HT among the 5-HT2 receptor agonists tested caused any increase in cyclic AMP levels. Isolated anterior midgut from adult male Rhodnius also shows dose-dependent cyclic AMP elevation in response to serotonin (threshold approx. 10−7M, maximum 5 × 10−6M) with receptor characteristics similar to the hypothesized 5-HT2-like serotonin receptor in larval epidermis. HPLC analysis showed a rapid rise in serotonin concentration in the haemolymph of adult male Rhodnius during feeding (peak 91 nM at 3 min after the onset of gorging) similar to, although less pronounced than, that previously reported for fifth-instar larvae. These findings are consistent with the hypothesis that serotonin released into the haemolymph and onto target tissues during feeding plays an important natural role in the integration of epidermal cell responses, fluid transport across the anterior midgut, diuresis, and other feeding-related functions in Rhodnius. |
